POWER QUALITY ASSESSMENT

BY

HUSSEIN MOHAMED EL-EISSAWI FATHI

A Thesis Submitted to the Faculty of Engineering at Al-Azhar University In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy IN ELECTRICAL POWER AND MACHINES

Under the Supervision of

Prof. M. Zaher Prof. N. Ayad Dr. G. Abdel Salam Al-Azhar University Atomic Energy Authority Ministry of Electricity

FACULTY OF ENGINEERING AL-AZHAR UNIVERSITY CAIRO, EGYPT 2012

POWER QUALITY ASSESSMENT

BY

HUSSEIN MOHAMED ELEISSAWI FATHI

A Thesis Submitted to the Faculty of Engineering at Al-Azhar University In Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy IN ELECTRICAL POWER AND MACHINES

Approved by the Examining comm ittee

Prof. Dr. Fahmy Metwally Ahmed Bendary (Member) ------Benha University Prof. Dr. Mohamed Mohamed Ibrahim Al-Gazar (Member) ------Al-Azhar University Prof. Dr. Mohamed Abdel-Moety Ragheb Zaher (Advisor) ------Al-Azhar University Prof. Dr. Nabil Mohamed Abdel-Fatah Ayad (Advisor) ------Atomic Energy Authority

FACULTY OF ENGINEERING AL-AZHAR UNIVERSITY CAIRO, EGYPT 2012

I I

TABLE OF CONTENTS

Page CONTENTS II LIST OF FIGURES V LIST OF TABLES VII LIST OF SYMBLOS VIII ACKNOWLEDGMENT IX ABSTRACT X LIST OF PUBLICATIONS XII

CHAPTER (1) INTRODUCTION 1 1.1 Background 1 1.2 Objectives – Scope of the thesis 2 1.3 Overview of the thesis 3

CHAPTER (2) LITERATURE REVIEW 4 2.1 Power quality definition 4 2.2 Power disturbances 4

2.3 Types of electrical power disturbances 4 2.4 Power quality monitoring 14 2.5 Power quality standards 15 2.6 Power quality solutions 19 2.7 Power quality assessment procedure (PQAP) 22 2.8 Related studies done by other researchers 27

CHAPTER (3) DESCRIPTION OF CASE STUDY AND MEASURING PROCESS 37 3.1 Description of the case study (ETRR-2) 37 3.2 Electrical system of ETRR-2 38

II II

3.3 Electrical defects of ETRR-2 40 3.4 Measuring process 40

CHAPTER (4) MONITORING IN ETRR-2 44 4.1 Introduction 44 4.2 Measurement results 44 4.3 Measurement results of the first feeder (source1) 44 4.4 Site appraisal of incoming feeder from substation1 (source 1) 53 4.5 Measurement results of the second feeder (source2) 54 4.6 Site appraisal of incoming feeder 2 (Source 2) 66 4.7 Invesigation results and mitigation techniques 67

CHAPTER (5) MITIGATION APPLICATIONS 68 5.1 Introduction 68 5.2 Harmonic Filters 68 5.3 Dynamic Voltage Restorer (DVR) 76 5.4 Uninterruptible Power Supplies (UPS) 84

CHAPTER (6) CONCLUSIONS AND RECOMMENDATIONS 87 6.1 Conclusions and recommendations 87 6.2 The most important points that have been reached 87 6.3 Future work 88

REFERENCES 89

APPENDIX A 95 Power quality standards

III

APPENDIX B 98 Trend graphs b.1 The trend graphs of incoming feeder 1 (Source 1) 99 b.2 The trend graphs of incoming feeder 2 (Source 2) 123

IV IV

LIST OF FIGURES Page Figure (2-1) : The voltage sag scenario 5 Figure (2-2) : The voltage swell scenario 6 Figure (2-3) : The under voltage scenario 6 Figure (2-4) : The over voltage scenario 7 Figure (2-5) : Typical instantaneous flicker signal recorded Close 9 to an electric arc furnace Figure (2-6) : Waveforms with harmonic and interharmonic 11 components Figure (2-7) : Voltage notching due to power electronic devices 11 Figure (2-8) : Voltage noises 12 Figure (2-9) : power system with nonlinear load 13 Figure (2-10) : power quality assessment procedure (PQAP) 26

Figure (3-1) : ETRR-2 general view 37 Figure (3-2) : Single line diagram of the electrical system of ETRR-2 39 Figure (3-3) : The Unipower 900F front panel 42 Figure (3-4): Single line diagram of PCC and measuring points 43

Figure (4-1): VTHD of incoming feeder of Source 1 45 Figure (4-2): ITHD of incoming feeder of Source 1 45 Figure (4-3) : ITHD variations of source 1 at 2nd day 46 Figure (4-4) : power variations of source 1 at 2nd day 46 Figure (4-5) : Voltage swell on phase 3 49 Figure (4-6) : Overvoltage on phase 1 50 Figure (4-7) : Overvoltage on phase 2 50 Figure (4-8): Overvoltage on phase 3 51 Figure (4-9): Short time voltage flicker of Source 1 52 Figure (4-10) : Long time voltage flicker of source 1 52 Figure (4-11) : VTHD of incoming feeder of source 2 54

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Figure (4-12) : VTHD variations of source 2 at 2nd day 55 Figure (4-13): Power variations of source 2 at 2nd day 55 Figure (4-14): ITHD of incoming feeder of source 2 56 Figure (4-15): ITHD variations of source 2 at 2nd day 57 Figure (4-16): Power variations of source 2 at 2nd day 57 Figure (4-17): ITHD variations of source 2 at 3rd day 58 Figure (4-18): Power variations of source 2 at 3rd day 58 Figure (4-19) : Voltage sag on phase 1 61 Figure (4-20) : Voltage sag on phase3 61 Figure (4-21) : Voltage swell on phase 3 62 Figure (4-22) : Voltage transient on the three phases 63 Figure (4-23) : Voltage transient on the three phases 63 Figure (4-24) : Voltage Outage 64 Figure (4-25) : Short time voltage flicker of source 2 65 Figure (4-26) : Long time voltage flicker of source 2 65

Figure (5-1) : Single tuned filter 70 Figure (5-2) : Typical schematic of a power system compensated by the 77 DVR. Figure (5-3) : Basic Configuration of DVR 79 Figure (5-4): Effective transformer connection in stand-by and boost 79 modes Figure (5-5) : General control system block diagram 81 Figure (5-6 ) : Schematic of double conversion on-line UPS 85

VI

LIST OF TABLES

Page Table (2-1) : Summary of IEEE standard 1100-1992 21

Table (4-1) : VTHD and ITHD at max. and min.loads of source1 47 Table (4-2) : Voltage deviation at max. and min. loads of source1 47 Table (4-3) : Voltage unbalance at max. and min. loads of source1 48 Table (4-4) : VTHD and ITHD at max. and min. loads of source2 59 Table (4-5) : Voltage deviation at max. and min. loads of source2 59 Table (4-6) : Voltage unbalance at max.and min. loads of source2 60

Table (5-1): calculations for 5th harmonic filter 75 Table (5-2): IEEE Std 18-2002 75 Table (5-3) : The situation of developing and researching for DVR 77

VII

LIST OF SYMBOLES

Pst Short time flicker severity

Plt Long time flicker severity THD Total harmonic distortion V Voltage I Current D Distortion power Pf disp Displacement power factor

Pf distortion Distortion power factor

Wth Thermal power

Pav Average power

Pf total Total power factor

.h r. Harmonic order of resonant frequency

XC Capacitor reactance

XR Reactor reactance STF Single tuned filter DVR Dynamic voltage restorer PCC Point of common coupling VPCC Voltage at point of common coupling S Apparent power

CDVR Cost of dynamic voltage restorer

CVS Cost of voltage sag

NVS Number of voltage sag per year

Tpayback Payback time

XF Filter reactance

IFF Filter fundamental current

QF Filter reactive power

XT Transformer reactance

IP Peak harmonic current

VIII

ACKNOWLEDGMENT

The author wishes to express his sincere gratitude and appreciation first of all for his parents, Prof. Dr. Mohamed Zaher; Al-Azhar University, Prof. Dr. Nabil Ayad; Atomic Energy Authority and Dr. Gamal Abdel-Salam; Ministry of Electricity. For their supervision and active guidance during the preparation of this thesis. Thanks are also extended to Prof. Dr. Mohamed Al-Gazar; Al-Azhar University and Prof. Dr. El-Metwally EL-Sherbiny; Atomic Energy Authority. For their great assistance to complete this work. And greeting to the spirit of the late Prof. Dr. Mohamed Askora; Al-Azhar University. For his help and guidance during the work of this thesis.

IX IX

ABSTRACT

The electrical power systems are exposed to different types of power quality disturbances problems. Assessment of power quality is necessary for maintaining accurate operation of sensitive equipments especially for nuclear installations, it also ensures that unnecessary energy losses in a power system are kept at a minimum which lead to more profits. With advanced in technology growing of industrial / commercial facilities in many region. Power quality problems have been a major concern among engineers; particularly in an industrial environment, where there are many large-scale type of equipment. Thus, it would be useful to investigate and mitigate the power quality problems. Assessment of Power quality requires the identification of any anomalous behavior on a power system, which adversely affects the normal operation of electrical or electronic equipment. The choice of monitoring equipment in a survey is also important to ascertain a solution to these power quality problems. A power quality assessment involves gathering data resources; analyzing the data (with reference to power quality standards); then, if problems exist, recommendation of mitigation techniques must be considered. The main objective of the present work is to investigate and mitigate of power quality problems in nuclear installations. Normally electrical power is supplied to the installations via two sources to keep good reliability. Each source is designed to carry the full load. The Assessment of power quality was performed at the nuclear installations for both sources at different operation conditions. The thesis begins with a discussion of power quality definitions and the results of previous studies in power quality monitoring. The assessment determines that one source of electricity was deemed to have relatively good power quality; there were several disturbances, which exceeded the thresholds. Among of them are fifth harmonic, voltage swell, overvoltage and flicker. While the second source has bad power quality. There are several and regular disturbances, which exceeded the thresholds. They were voltage sag, voltage swell, under-voltage, temporary outage, voltage transient and flicker. Mitigation techniques were suggested to install passive harmonic filter to mitigate harmonic distortion, install a dynamic voltage restorer

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(DVR) to mitigate voltage disturbances and isolate all the sensitive and critical loads of nuclear installations and feed them via uninterruptible power supplies (UPS). The thesis ends with the conclusion and recommendation of the effective/economic mitigation techniques and the need for further studies in the discipline.

XI

LIST OF PUBLICATIONS

This thesis is based on the work reported in the following papers:

Paper 1: M. Zaher, M. Askora, N. Ayad, G. Abdel Salam, H. Eleissawi, "Power Quality and Voltage Interruptions in Nuclear Research Reactors", Journal of Al-Azhar University Engineering Sector, JAUES, 2012.

Paper 2: M. Zaher, N. Ayad, E. Elsherbiny , G. Abdel Salam, H. Eleissawi, " Investigation and Mitigation Techniques of Power Quality Problems in Nuclear Installations", Arab Journal of Nuclear Sciences and Applications, 2012.

XII

CHAPTER (1) INTRODUCTION

1.1- Background The concept of power quality has often been misunderstood and oversimplified. But in this day and age of sophisticated electronics, assessment of power quality has become too important. The widespread use of hightech devices has complicated all aspect of electrical power. Not only are these devices more sensitive to the effects of power quality, but they can also impact it negatively. Poor power quality can result in less productivity, lost and corrupt data, damaged equipment and poor power efficiency. “Power Quality” is a broad term used to describe the electrical power performance. The causes and solutions of power quality problems is site dependent, so the power quality assessment is important for sensitive projects. Under normal (ideal sinusoidal, balanced, and symmetric) conditions power quality is basically a loading problem. But with the growth in the power electronics and control systems industry, the once majority linear customer loads, are now being dominated by a majority of nonlinear customer loads. Such loads like: switch mode power supplies used in both industrial and commercial computers / microprocessors; variable speed drives used in process control; arcing device like welders and arc furnaces; silicon controlled rectifiers used in airconditioners; and basically any electronic device which draws current in pulses are termed to be nonlinear. So the power quality of a system is equally the customers’ concern as much it is the supply authorities’ concern. Power quality assessment has become a critical concern for virtually all electric utilities through the world. It is primarily due to the fact that customer equipment has become more sensitive and is now interconnected in extensive networks and processes. The result is that variations in the power quality that were never a concern can now be very expensive in terms of process shutdowns and equipments malfunctions. The objectives of distribution system power quality assessment work were to:

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1 Design a statistically valid power quality measurement program that would enable assessment of power quality levels. 2 Perform measurements of power quality delivered to customers sufficient to describe the transient, harmonics, shortand long duration voltage variation, and momentary interruption characteristics of present distribution supply system. 3 Perform analytical, modeling and simulation studies to verify and /or improve analytical models by using the measured data. 4 Assess the limitations of a typical electric utility distribution system to supply loads that degrade power quality. 5 Perform studies to identify measures to improve power quality from the supply system perspective. 6 Determine the cumulative effect as the number of small (sensitive and /or polluting) loads is increased. 7 Provide a rational basis for the development of a recommended practice for providing solutions to power quality problems and improving system power quality levels.

1.2- Objectives – Scope of the thesis : The purpose of power quality investigation is to generate a data resource about a power system where, following the analysis of that data resource, an appropriate solution to the problem will be found. Due to the infancy of this technology and the diversity of power systems, there is no set method for power quality surveys and analysis. However there is one common goal of power quality assessment to find a solution. This analysis of the power system data was in accordance with the standards. However, before proceeding directly to perform a site survey, some background knowledge of the power quality area is essential. An understanding of the characteristics of various faults, along with typical causes and prevention techniques are suggested. The aim of this thesis therefore is to firstly introduce the reader to common power quality problems, their causes, and techniques or devices used to reduce their impact on systems. An analysis of the results from the two incoming sources of nuclear installation power quality studies is then presented. The investigation of the site generated a data resource. If the data gathered from the site indicate deviations, which ٢

exceeds the limitation of the power quality standards, then logical explanations for the disturbances should be suggested. Once this explanation is proposed, the next stage of solving the problem can be initiated.

1.3- Overview of the thesis This thesis discusses power quality assessment conducted with in a nuclear installation. These surveys present a modular format for the analysis and classification of power quality and power system problems. This thesis consists of six chapters: Chapter one presents the introduction, the objective and the overview of the thesis. Chapter two contains all the terms and definitions of power quality, it describes the different types of power disturbances, power quality monitoring, power quality standards, solutions of power quality problems and power quality assessment procedure. It contains also a review of studies conducted by other researchers. Chapter three presents a general description of electrical system of nuclear installation, electrical defects and measuring process.

Chapter four discusses the results, analysis and discussion of the power quality investigation conducted at the case study.

Chapter five contains the mitigation techniques. The thesis document concludes with chapter six, which presents conclusions, recommendations and future work in this area.

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CHAPTER (2) LITERATURE REVIEW

2.1 - power quality definition [1] Power quality problem is any power problems manifested in voltage, current, or frequency deviations that result in failure or missed operation of utility or end user equipment.

2.2 Power disturbances [2], [3] and [4] The electrical power system is exposed to different types of disturbances leading to power quality problems. These problems such as; voltage, current or frequency deviation may result in failure or misoperation of customer equipment.

2.2.1 Sources of disturbances

Electrical power quality is mainly affected by disturbances in feeding systems.

The sources of these disturbances are:

1 Disturbances originating from utility feeding system due to faults which disturb the source voltage waves and can be isolated within two seconds to one minute by protection systems, or supply interruption will occur.

2 Disturbances originating from consumers’ networks and devices is mainly due to threephase loads, connection unbalance, absence of appropriate neutral wire, absence of earthing system or low circuit breaker rating.

3 Nonlinear characteristics of loads and devices or unsuitable line sites are other sources of disturbances.

2.3- Types of electrical power disturbances : 2.3.1- Voltage spikes and surges

It is a short duration from microsecond to millisecond voltage increase; it occurs due to lightning, switching of heavy loads and power system faults. It leads to equipment failure, system lockup, data corruption and data loss. Solutions to voltage spikes and ٤

surges problems include equipment such as surge arresters, filters and isolation transformer.

2.3.2-Voltage sag (dip)

It is a reduction in voltage outside the normal tolerance for a short time less than few seconds. The magnitude of the reduction is between 10 percent and 90 percent of the normal (rms) voltage. It occurs due to starting of heavy loads and power system faults. It reduces the energy being delivered to the end user and causes computers to fail, adjustablespeed drive to shut down and motors to stall and over heat.

Figure (21) shows the voltage sag scenario. Solutions to voltage sag problems include equipment such as ferroresonant transformer, energy storage technologies, uninterruptible power supply (UPS) and dynamic voltage restorer (DVR).

Figure (2 1) the voltage sag scenario

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2.3.3-Voltage swell

It is a momentary increase in voltage outside the normal tolerance. The (rms.) voltage variations that exceed 110 percent. Faults and turning off heavy electrical equipment cause voltage swell. The increased energy from a voltage swell often overheats equipment and reduces its life. Figure (22) shows the voltage swell scenario. Voltage regulator, motorgenerator set and uninterruptible power supply can mitigate the voltage swell effects.

Figure (22) the voltage swell scenario.

2.3.4Under voltage

As shown in figure (23) it is a decrease in the rms ac voltage to less than 90% at the power frequency. A load switching on or a capacitor bank switching off can cause an under voltage until the voltage regulation equipment in the system can bring the voltage back within tolerances. Overloaded circuits and the loss of major transmission support can also result in under voltages. It can cause sensitive computer equipment to read data incorrectly and motor to stall and operate inefficiently. Utility can prevent under voltage by building more generation and transmission lines.

Figure (23) the under voltage scenario.

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2.3.5 Over voltage

As shown in figure (24) it is an increase in the rms ac voltage greater than 110% at the power frequency. Overvoltage is usually the result of the switchingoff of a large load, or the energizing of a capacitor bank. Overvoltages occur either because the system is too weak for the desired voltage regulation or the voltage controls are inadequate. An incorrect tap setting in transformers is one example.

Figure (24) the over voltage scenario

2.3.6 Voltage modulation

It is a periodic increase and decrease of amplitude. Periodic loads cause it. It leads to poor power quality.

2.3.7- Voltage imbalance (IEEE Std. 1159) or unbalance

It can be defined as the maximum deviation from the average of the threephase voltages, divided by the average of the threephase voltages and expressed in percentage points. Imbalance can also be defined using symmetrical components. The ratio of either the negative or zero sequence components to the positive sequence component can be used to specify the percent imbalance. The primary source of voltage imbalance (typically less than 2%) is the unequal distribution of singlephase loads in a threephase circuit. Voltage imbalance can also be the result of blown fuses in one phase of a threephase capacitor bank. Severe voltage imbalance (greater than 5%) can result from singlephasing conditions. Voltage imbalance causes motors and transformers to overheat. This is because the current imbalance in an induction device.

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2.3.8 Phase angle imbalance

It is the deviation from the normal 120 or 240 degree between threephase voltages. Phase angle imbalance can be caused by the uneven distribution of loads among the phases.

2.3.9-Voltage fluctuations (flicker)

As shown in figure (25) they are cyclical variations in the voltage rms values or a series of random voltage changes, whose magnitude does not normally exceed voltage ranges of 0.9 p.u. to 1.1 p.u. A common phenomenon of voltage fluctuations is the voltage flicker. Loads, which can exhibit continuous, rapid variations in the load current magnitude, can cause voltage fluctuations or flickers. The present industry practice is to characterize the severity of a voltage flicker with respect to the sensitivity of the human visual perception. Typically, magnitudes as low as 0.5% can result in a perceptible lamp flicker. Arc furnace and welders are the most common causes of voltage fluctuations in utility transmission and distribution systems. Other sources of voltage fluctuation include lumber mills, draglines, and rock crushing machines. Voltage fluctuations can be considered as repetitive random voltage sags and swells. Therefore, voltage fluctuations have propagation characteristics similar to those of sags. They can be assessed using steadystate power system models. A strong supply system can greatly reduce severity of voltage fluctuation. Voltage fluctuations can cause incandescent and fluorescent lights to blink rapidly. It can also cause sensitive equipment to malfunction. Static VAR system can mitigate the flicker effects [2]. As the annoyance created by flicker is a function of both the intensity of perception and the duration of exposure, according to IEC the severity of the disturbance is described by two parameters: the short term severity (Pst ) measured over a period of ten minutes. And the long term severity (P lt) calculated from a sequence of 12 Pst values over a two hours interval, according to the following expression:

3 12 p sti 3 plt = ∑ i=1 12 (21)

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Figure (25) typical instantaneous flicker signal recorded

Close to an electric arc furnace .

2.3.10 Outage

It is a complete loss of power, it is caused by faults and accidents. Solutions to outage problems including equipment such as standby engine generator.

2.3.11- Power frequency variations

They are the deviations in the power system fundamental frequency from its normal value. The power system frequency is directly related to the rotational speed of the generators supplying the system. Slight variations in frequency occur as the dynamic balance between load and generation changes. The size of the frequency shift and its duration depend on the load characteristics and the response of the generation control system to load changes. In modern interconnected power systems, significant frequency variations are rare. Frequency variations of consequence are much more likely to occur for loads that are supplied by generators isolated from the utility system. In such cases, the generator response to abrupt loads changes may not be adequate to regulate the frequency within the narrow bandwidth required by frequency sensitive equipment. [1]

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2.3.12 Waveform distortion [1], [5] and [6]

It is defined as a steadystate deviation from an ideal sinusoidal wave of power frequency. It is characterized by the spectral content of the deviation. Primary types of waveform distortion are harmonics, notching, interharmonics, DC offset and noise. Figure (2 –6) indicates waveforms with harmonic and interharmonic components.

- Harmonics are sinusoidal voltages or currents having frequencies that are integer multiples of the fundamental frequency. Distorted waveforms can be decomposed into the sum of the fundamental frequency and the harmonic components. Harmonic distortion levels are described by the complete harmonic spectrum with magnitudes and phase angles for each individual harmonic component. It is also common to use a single quantity, the Total Harmonic Distortion (THD) , as a measure of the effective value of harmonic distortion. Harmonic distortion originates in the nonlinear characteristics of devices and loads in the power system. Typical harmonic sources are variable speed drives and other power electronics based equipment. One of the major problems related to harmonic disturbances is harmonic resonance. The resonance can magnify harmonic distortions to a level that can damage the equipment or cause equipment malfunction. Power factor correction capacitors in distribution system are the main cause of harmonic resonance. Other effects of harmonics are equipment overloading, increased losses and sometimes equipment malfunction.

The most commonly used harmonics index is:

∞ ∞ 2 2 ∑Vh ∑ I h h=2 h=2 THD V = * 100 % and THD I = * 100 % (22) V1 I1

This is defined as the ratio of the rms value of the harmonic components to the rms value of the fundamental component and usually expressed in percent. This index is used to measure the deviation of a periodic waveform containing harmonics from a perfect sine wave. For a perfect sine wave at fundamental frequency , the THD is zero. Similarly, the measures of individual harmonic distortion for voltage and current at h th order are defined as Vh/V 1 and I h/I 1, respectively.

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-Interharmonics are voltages or currents having frequency components that are not integer multiples of the fundamental frequency. They can appear as discrete frequencies or as a wideband spectrum. Cycloconverters are one of the sources of interharmonics. It must be noted that due to the limitations of power quality instruments timevarying harmonics can be recorded as interharmonics. Technically sound methods for the accurate recording of the interharmonics have yet to be developed. The effects of interharmonics are not known well. They have been shown to affect power line carrier signaling.

Figure (2 –6) waveforms with Harmonic and Interharmonic Components

Notching, as shown in figure (27). It is a periodic voltage disturbance caused by the normal operation of power electronics devices when current is commutated from one phase to another. Notching can be characterized through the harmonic spectrum of the affected voltage. Although notching is a special case of voltage harmonics, it is generally treated as an independent disturbance. The frequency components associated with notching can be quite high and may not be readily measured with equipment normally used for harmonic analysis.

Figure (2 –7) voltage notching due to power electronic devices .

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Noise, as shown in figure (28). It is defined as unwanted electrical signals with broadband spectral content lower than 200 kHz, superimposed upon the power system voltage or current in phase conductors, or found in neutral conductors or signal lines. Power electronic devices can cause noise in power systems, control circuits, and arcing equipment. Improper grounding that fails to conduct noise away from the power system often exacerbates noise problems. Basically, noise consists of any unwanted distortion of the power signal that cannot be classified as harmonic distortion or a transient. Noise disturbs electronic devices such as microcomputers and programmable controllers.

Figure (2 –8) voltage noises

-DC Offset refers to the presence of a dc voltage or current in an ac power system. This phenomenon can occur as the result of a geomagnetic disturbance or due to the effect of halfwave rectification. Direct current in alternatingcurrent networks can have a detrimental effect by biasing transformer core fluxes. Transformers can become saturated even in normal operation. This causes additional heating, loss of transformer life, and the production of harmonics. DC offset may also cause the electrolytic erosion of grounding electrodes and other connectors.

2.3.13- Distortion power factor [7] Example for the nonsinusoidal situations is shown in figure (29). An expression for distortion power factor can be arrived from current and voltage harmonic distortion factors. From [7] and the definition of these factors, rms harmonic voltages and currents can be written as

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Figure (29): power system with nonlinear load

2 Vrms(h) = Vrms 1+ (THDV 100 ) (23)

2 I rms(h) = I rms 1+ (THDI 100 ) (24)

Therefore, the total power factor is

P P P pftotal = = = (25) S V I 2 2 total rms(h) rms(h) Vrms I rms 1+ (THDV 100 ) 1+ (THDI 100 )

2 2 2 Where, Stotal = P + Q + D , D is the distortion power , (26)

Neglecting the power contributed by harmonics and also voltage distortion, as it is generally small

1 pftotal = cos(δ 1 −θ1 ) = pf displacment • pf distortion (27) 2 1+ (THDI 100 )

Because displacement power factor ( pf disp) can never be greater than unity, then the true power factor in nonsinusoidal situations has the upper bound

pf total ≤ pf distortion . (28)

It is important to point out that it cannot be, in general, compensate for poor distortion power factor by adding shunt capacitors. Only the displacement power factor can be improved with capacitors. This fact is especially important in load areas that are dominated by singlephase power electronic loads, which tend to have high displacement power factors but low distortion power factors. In these instances, the ١٣

addition of shunt capacitors will likely worsen the power factor by inducing resonance and higher harmonic levels. A better solution is to add passive or active filters to remove the harmonics produced by the nonlinear loads, or to utilize low distortion power electronic loads.

2.4- Power quality monitoring : [8] and [9] Power quality monitoring is needed to determine what type of power quality disturbance is present, as disturbances are not always obvious. Many types of power quality monitors are available. It measures and records all energy data such as voltage, current, average power factor, instantaneous power factor, active power, reactive power, frequency and all the disturbances. Monitoring power quality instruments are connected to the network through transducers and transducers should be selected according to the system. This will require current transformers for current measurement on low voltage. Higher voltages require correctly installed current and voltage transformers for connection of monitoring equipment. Transducers should be selected based on the frequency response required. There are some basic instruments specifications such as the following: Appropriate variable threshold for all required power quality disturbances. Range of disturbance types recorded. High crest value needed to avoid clipping and modifying over voltage in the monitored waveform. Can ride through disturbances. Type and amount of data stored – raw data or parameters, sufficient for the desired logging period. Number of channels, sampling rate and accuracy: 7 channels are necessary for the recording of three phase voltage, current and neutral current as is desirable for investigation of plant problems. Another channel for measuring neutralearth voltage can also be useful. Good reporting software. Associated large database capabilities. Easy to use.

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2.5- Power quality standards : [10], [11] and [12]

The purpose of power quality standards is to protect utility and enduser equipment from failing or misoperation when the voltage, current or frequency deviates from normal values. Power quality standards provide this protection by setting measurable limits as to how for the voltage, current or frequency can deviate from normal values, by setting these limits.

Power quality standards help utilities and customers to gain agreement to what are acceptable and unacceptable levels of service. The customer should have level of service corresponding to their devices, it is impossible to obtain a pure voltage wave with fixed amplitude at each customer terminals. So, acceptable and allowed disturbance levels should be specified in networks at different levels. There are many standard organizations provide the acceptable levels. Such as Institute of Electrical and Electronics Engineers (IEEE), European Union Standards organization (CENELEC), International Electrotechnical Commission (IEC), American National Standard Institute (ANSI), National Electrical Manufactures Association (NEMA), Underwriters Laboratories (UL), National Fire Protection Association (NFPA) and Semiconductor Equipment and Material International (SEMI).

2.5.1 Standard levels in power quality: [13] and [14]

- IEEE Standard 141-1993 , Recommended Practice for Electric Power Distribution for Industrial Plants. A thorough analysis of the basic electricalsystem considerations are presented. Guidance is provided in design, construction, and continuity of an overall system to achieve safety of life and preservation of property; reliability; simplicity of operation; voltage regulation in the utilization of equipment within the tolerance limits under all load conditions; care and maintenance; and flexibility to permit development and expansion. - IEEE Standard 142-1991, Recommended Practice for Grounding of Industrial and Commercial Power Systems. Presents a thorough investigation of the problems of grounding and the methods for solving these problems .

- IEEE Standard 242-2001 , Recommended Practice for Protection and Coordination of Industrial and Commercial Power Systems. Deals with the proper election

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application and coordination of the components which constitute system protection for industrial plants and commercial buildings.

- IEEE Standard 446-1995 , Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications. Recommended engineering practices for the selection and application of emergency and standby power systems. It provides facility designers, operators and owners with guidelines for assuring uninterrupted power, virtually free of frequency excursions and voltage dips, surges, and transients.

- IEEE Standard 493-1995, Recommended Practice for Design of Reliable Industrial and Commercial Power Systems, the fundamentals of reliability analysis as it applies to the planning and design of industrial and commercial electric power distribution systems are presented. Included are basic concepts of reliability analysis by probability methods, fundamentals of power system reliability evaluation, economic evaluation of reliability, cost of power outage data, equipment reliability data, and examples of reliability analysis. Emergency and standby power, electrical preventive maintenance, and evaluating and improving reliability of the existing plant are also addressed.

- IEEE Standard 519-1992, Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems .This guide applies to all types of static power converters used in industrial and commercial power systems. The problems involved in the harmonic control and reactive compensation of such converters are addressed, and an application guide is provided. Limits of disturbances to the AC power distribution system that affect other equipment and communications are recommended. This guide is not intended to cover the effect of radio frequency interference.

IEEE Standard 929-2000, Recommended Practice for Utility Interface of Photovoltaic (PV) Systems.

- IEEE Standard 1100-2005 , Recommended Practice for Powering and Grounding Sensitive Electronic Equipment. Recommended design, installation, and maintenance practices for electrical power and grounding (including both powerrelated and signal

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related noise control) of sensitive electronic processing equipment used in commercial and industrial applications.

- IEEE Standard 1159.3-2003, Recommended practice for the transfer of power quality data.

- IEEE Standard 1250-1995 , Guide for Service to Equipment Sensitive to Momentary Voltage Disturbances. Computers, computerlike products, and equipment using solidstate power conversion have created entirely new areas of power quality considerations. There is an increasing awareness that much of this new user equipment is not designed to withstand the surges, faults, and reclosing duty present on typical distribution systems. Momentary voltage disturbances occurring in AC power distribution and utilization systems, their potential effects on this new sensitive, user equipment and guidance toward mitigation of these effects are described. Harmonic distortion limits are also discussed.

- IEEE Standard 1346-1998, Recommended Practice for Evaluating Electric Power System Compatibility with Electronic Process Equipment. A standard methodology for the technical and financial analysis of voltage sag compatibility between process equipment and electric power systems is recommended. The methodology presented is intended to be used as a planning tool to quantify the voltage sag environment and process sensitivity. It shows how technical and financial alternatives can be evaluated. Performance limits for utility systems, power distribution systems, or electronic process equipment is not included.

- IEEE Standard 18-2002, Standard for Shunt Power Capacitor.

- IEEE Standard 1453-2004 , Recommended Practice for Measurement and Limits of Voltage Fluctuations and Associated Light Flicker on AC Power System.

- IEEE Standard 1159-2009 , Recommended Practice for Monitoring Electric Power Quality. Monitoring of electric power quality of AC power systems, definitions of power quality terminology, impact of poor power quality on utility and customer equipment, and the measurements of electromagnetic phenomena are covered.

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- SEMI E-10-1999 , Standard for Definition and Measurement of Equipment Reliability, Availability, and Maintainability, it defines the sag ride through capability.

SEMI F-42-1999 ،Test Method for Semiconductor Processing Equipment Voltage - Sag Immunity, it defines the test methodology to confirm compliance to the standard.

UL 1449 Second Edition, 1998 . Standard 1449 is a Safety, Construction, and Performance Standard for Transient Voltage Surge Suppressors. The second edition revision includes withstand for loss of neutral condition without damage to the suppressor.

- ANSI C84.1-1995 , Electric Power Systems and Equipment Voltage Ratings. Published by NEMA, National Electrical Manufacturers Association, This voluntary standard was first approved in 1954 as a joint effort by the Edison Electric Institute and the NEMA to recommend voltage ratings for both electric systems and equipment to promote compatibility. ANSI standard establishes the steady state voltage delivery window of +/ 5% at the point of delivery. It also recommends a tolerance window of +6% and 13% for end use equipment. The standard also establishes a tolerance window for voltage unbalance of +/3%.

EMA MG 1- 1998 , Motors and Generators National Electrical Manufacturers Association. This standard gives technical specifications used by manufacturers. Power quality concerns that can be referenced include voltage and current unbalance tolerance, over and under voltage tolerance, electrical starting characteristics, and insulation values.

- NEMA Standards Publication No. LS1-1992 , Low Voltage Surge Protective Devices. This is a good standard for quality construction of the device.

-EN50160 indicates Voltage Characteristics of Electricity Supplied by Public Distribution Systems. [11] - IEC61000-4-15 , Flicker meter Functional and Design Specifications. [12]

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2.6 Power quality solutions: [1]

There are four ways to solve power quality problems:

1 Design equipment and electrical systems to prevent electrical disturbances from causing equipment or systems to malfunction. Where, manufactures of sensitive equipment can reduce or eliminate the effect of power quality problems by designing their equipment to be less sensitive to disturbances. They can add some devices to their equipment according to situation, for instance a capacitor to provide temporary energy storage when the voltage sags are too low. They can also alter their equipment to desensitize it to power quality problem for example; they can design special K factor transformers that tolerate harmonics.

2 Analyze the symptoms of power quality problems to determine its cause and solution. It is important to determine source and type of power quality problems, the type of power quality problem and its cause often determine the solution.

3Identify the medium that is transmitting the electrical disturbances and reduce or eliminate the effect of that medium.

4 Treat the symptoms of the power quality problems by use of power conditioning equipment. It provides essential protection against disturbances. Power conditioning equipment include devices that reduce or eliminate the effect of a power quality disturbance. It can be used to condition the source, the transmitter, or the receiver of the power quality problems. The equipment can be divided into ten categories, surge suppressors, noise filter, isolation transformer, lowvoltage line reactors, various line voltage regulators, motorgenerator sets, dual feeders with static transfer, uninterruptible power supplies, harmonic filters and Dynamic voltage restorer (DVR).

2.6.1-Selection of appropriate power conditioning equipment:

End user should implement the following steps before selecting the appropriate power conditioning equipment to mitigate their problem: Determine the power quality problem. Correct wiring and grounding and faulty equipment problems before purchasing power conditioning equipment. Recent surveys by ERRI and others indicate that improper grounding and wiring ١٩

cause 80 to 90 percent of the power quality problems. However, many end users overlook improper grounding and wiring in their facilities. They should always investigate the wiring and grounding in their facilities before purchasing and installing expensive power conditioning equipment.

Evaluate alternative power conditioning solutions. Develop a powerconditioning plane. Determine if the utility source is compatible with the load. Select and install power conditioning equipment. Operate and maintain powerconditioning equipment

Table (21) from IEEE standard 11001992. Indicates how to select the appropriate power conditioning technology to match the power quality problem.

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Table (21) Summary of IEEE std.11001992

The condition should be corrected by the indicated powerconditioning technology.

There is a significant variation in product performance.

The condition may or may not be fully correctable by the technology.

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2.7- Power quality assessment procedure (PQAP): [6] and [15]

Power quality assessment procedure is based on a variety of different power quality concerns that can exist and focuses on a combination of monitoring and analysis to characterize these concerns. Once the power quality concerns are characterized, the analysis procedures developed can be used to evaluate possible solutions to the power quality problems. These solutions must then be evaluated from both a technical and an economic perspective.

There are a number of important areas that must be addressed in the power quality assessment procedure. These include:

Data collection requirements.

Important power quality concerns as a function of the type of customer.

Equipment sensitivity.

Important parameters of the power quality concerns.

Roles of measurements and simulations in evaluating the concerns.

Implementation of possible solutions to solve the problem.

Power quality assessment procedure provides a general framework that contains all the possible elements that may be needed for power quality study. The following sections summarize the general steps involved in the procedure.

2.7.1Identify power quality concerns

The specific power quality concerns that need to be evaluated will be different from customer to customer. A review of the types of equipment used by the customer, process requirements and economic impacts of problems will lead to a list of concerns that need to be studied. They can include possible problems with both the utility distribution system and the customer facilities. Possible power quality problem categories to be evaluated include the following:

Voltage transients caused by circuit switching and load switching within the customer facility.

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Harmonic distortion from nonlinear loads.

Transformer heating caused by harmonic current levels.

Transient magnification at low voltage capacitor banks.

Transients and notching associated with power electronics equipment operation.

Neutral conductor overloading due to harmonic producing loads.

Voltage flicker from arc furnace loads and arc welding loads.

Voltage sags due to faults on parallel circuits on the same distribution system or faults on the transmission system.

Momentary interruptions at industrial and commercial installations due to recloser operations on feeder circuit breakers.

Coupled voltage at customer facilities due to lightning transients on the primary distribution system.

Identification of particular concerns involved for an installation provides a focus for the study. Development of a model for analysis of the problem is dependent on the frequency range of the power quality variations that need to be studied. The model can be for computer simulations, hand calculations, or application of simple rules.

2.7.2-Collect data A representation of the customer system and important parts of the utility system should be developed for preliminary analysis. In cooperation with the customer, the data is collected and compiled into a database for convenient reference during the analysis. Important information includes:

load characteristics

motors

power electronics

process control

computers ٢٣

adjustable speed drives

lighting

Transformer sizes/ ratings

Conductor lengths, characteristics

Customer capacitor sizes, location and switching procedures

Customer equipment and circuit switching

Power conditioning equipment

surge suppressors

isolation transformers

constant voltage transformers

U.P.S system

harmonic filters

Distribution system characteristics

primary voltage

underground / overhead

protection practices and switching procedures

capacitor applications (locations, sizes and switching)

2.7.3-Develop measurement program and perform monitoring The utility and customer systems being evaluated should be monitored to characterize the power quality variations. The measurement program should be designed based on the particular sensitive loads existing at the customer facilities. Monitoring will typically be performed at the customer service entrance and close to particular sensitive loads in order to characterize disturbances coming from the utility system and disturbances which are localized at the sensitive loads. A measurement program plan should be developed which specifies the following: ٢٤

Quantities to monitor.

Monitoring durations.

Threshold levels which will trigger recording of disturbances.

Waveform sampling and data storage requirements.

Analysis procedure and data presentation formats.

The monitoring process requires close cooperation between the customer and utility personnel. Monitoring sites and instrumentation should be selected based on the particular concerns being characterized. The duration of monitoring will depend on the parameters which can affect the power quality concerns.

2.7.4-Evaluate measurement results and develop solutions The measurement results are analyzed. The initial measurements and the site survey are used to identify the phenomena involved and the important parameters. This information is used for possible solutions to the power quality problem.

Once the range of technical solutions is identified, economic analysis need to be performed to evaluate the possible alternatives for solving customer power quality problems. These alternatives will generally include the following options:

Power conditioning and / or filtering at the sensitive loads.

Central power conditioning and /or filtering at the customer service entrance.

Changing operating procedures or system design on the utility distribution system.

Modification to the design of sensitive loads to make them less sensitive to power quality variations.

The requirements for each of these options will be developed and the analysis of measurements results will be performed.

Figure (210) indicates a summary of power quality assessment procedure (PQAP)

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Identify Power Quality Concerns Voltage Sags Momentary Interruptions Capacitor Switching Transients Lightning Harmonic Distortion Neutral Conductor Overloading Transformer Heating Voltage Flicker Voltage Notching Circuit/Load Switching Transients

Collect Data Utility System Data Customer System Data Equipment Characteristics

Evaluate Measurement Results/Develop Solutions Develop Measurement Program/ Identification of Cause of Problem Perform Monitoring Evaluate Solutions Location(s) to Monitor Economic Analysis of Solutions Quantities to Monitor Power Conditioning Instrumentation Requirements Utility System Modification Thresholds Equipment Design Modifications Analysis Requirementst Customer Participation

Implement Solution

Figure (210) power quality assessment procedure (PQAP)

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2.8- Related studies done by other researchers: This part presents preliminary results from different researchers in the power quality assessment on electric distribution system. These researches were done in various locations around the world.

- Barker P. P [16], this work done in mid 1989, the Niagara Mohawk Power Corporation’s Research and Development Department sponsored a major power quality study of two distribution feeders in the Buffalo, New York region. The aims of this twoyear study were: i) Assist Niagara Mohawk in identifying and correcting abnormal conditions resulting from possible poor power quality in a residential area, served by the Shawnee Substation, and referred to as Wurlitzer Park. ii) Create a database of power quality measurements, which could be used for system wide comparison and analysis. The results of the study proved that majority of the problems were actually caused by the customer’s owned equipment.

– Dabbs W. et al [17], in 1990, the Electric Power Research Institute (EPRI) has decided to corporate with Electrotek Concepts to conduct a study of the state of power on the various power distribution systems in the United State. The purpose of this survey is to develop a statistical representation of the power system, the disturbances being measured, the protective relaying devices and other site characteristics. The distribution power quality project was planned which involves the monitoring and simulation of power quality phenomena on the distribution systems.

The project was starting in June 1992, over a period of two years, quite a large number of PQ nodes were places on a total of about 300 monitoring points. The results of these studies have shown that the most common type of faults found in the power disturbances were voltage sag, transients, harmonic distortions and momentary interruptions.

Dorr D. S. et al . [18], in 1991, the Canadian Electrical Association (CEA) started a three year long power quality survey. With twentytwo utilities involved on a total 550 site, the monitored activities went on for 25 days per site. The data collected were

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from different groups, such as industrial, commercial and residential. The main objective was to obtain an indication of power quality on the utility’s distribution system in Canada. In order to avoid getting readings influenced by individual loads or wiring error in the utilities, the sites being monitored were at the customer's service entrance panel. The gathered results were then served as a baseline for further comparisons of newly founded results in the near future.

- M. McGranahan [15], in 1991, the Electric Power Research Institute (EPRI) published procedure for assessment the power quality. This report presents the results of an effort sponsored by the Electric Power Research Institute (EPRI) and Pacific Gas and Electric Company (PG E) to develop a standardized approach for dealing with power quality problems. The approach taken here is to develop an understanding for the full range of possible power quality concerns. A set of definitions for different power quality categories is presented. Under each category, important characteristics of the concern are identified, possible causes of the power quality variations are presented, and possible solutions are outlined. After developing an understanding for the various phenomena, a standard procedure for evaluating power quality problems is presented. This Power Quality Assessment Procedure (PQAP) involves a combination of measurements and simulations and emphasizes on the required cooperation between all the parties involved. A power quality survey was also performed to assist in identifying the most important concerns reported by customers on the PG E system.

- D. D. Sabin et al [19], this work done in 1996, the Electric Power Research Institute (EPRI) published a technical report "An assessment of distribution system power quality”, this report provides a comprehensive statistical database of power quality measurements collected during the EPRI distribution power quality projects as well as guidelines for monitoring and modeling power quality phenomena on distribution system. Presented are triggering methods, characterization algorithms, and statistical analysis for voltage disturbances.

Chan, V.K.K [20], this work presents power quality survey at University of Queensland, St. Lucica campus was done during a thesis study. The monitoring was carried out in three different locations within the University of Queensland. Two transformers that were monitored one with a 1000kVA rating and the other one with ٢٨

750kVA rating. The result of this case study has concluded that, the most of the transients occurred between 5:00 – 7:00AM. These disturbances were probably caused by the switching of the controlled capacitor banks. - Tapan Saha et al [21], this paper presents an investigation of power quality problems in a remote gold mine site in Papua New Guinea and was done during thesis work at the University of Queensland. The results has concluded that, the common voltage sag phenomena was observed and a dynamic voltage restorer (DVR) was used as a solution of this problem.

- Eloi Ngandui [22], this work discusses power quality monitoring and analysis of a university distribution system. The analysis of the recorded data at the point of common coupling of the University of Quebec at TroisRivieres yield the following results: the voltage THD is below the 5 % limit set by the IEEE 5191992 the current injected has a TDD below the 5 % limit set by the IEEE 5191992. 99% of the time the TDD is below 2.04 %. The information provided in this analysis gives a reference level for future study and extension of the electrical installation of the University of Quebec at TroisRivieres.

- M. Izhar et al [23], In 2003, an investigation on power quality at electrical and electronic engineering department building in the University of science Malaysia for three phase fourwire system was done. The survey was conducted through out a day during peak and off peak hours. The harmonic level, total harmonic distortion, neutral current and power associated such as power consumption, true power factor, etc. for each line were measured and analyzed. The analysis of data from the measured distribution system showed that the harmonic level was highest at odd harmonic compared to even harmonic. The results also reveal that power consumption and instantaneous power increased during peak hours. The power factor correction mechanism too was functioning well and approaching unity. One very interesting factor is that the neutral currents and total harmonic distortion were excessive in the line neutral distribution system and would affect the distribution system performance. Ideally, it should be zero.

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Wes Sunderman et al [24], this paper presents the findings of a followon project, referred to as DPQ 11, which was conducted in 2001 and 2002 in U.S. This project resulted in characterizing power quality in terms of shortduration variations such as voltage sags, voltage swells, and voltage interruptions. The characterization was based on analysis of data from 480 power quality monitors at different locations in a power system spanning a date range from August 30, 1993, through December 12, 2002. The results of the analysis that are presented in this paper provide a unique opportunity to understand the electrical environment in terms of shortduration variations and further validate the findings of DPQ 1.

- Jose C.C. Costa et al [25], this work presents an example of power quality assessment study in an electrical panel that supplies investigation laboratories, office rooms and an electronics workshop, using a developed power quality monitor. The results of this study are analyzed using international standards as reference in order to determine the quality of the supplied energy.

A.M. El-Zonkoly [26], the paper presents an intelligent system for power quality assessment application. This system is used for power system model validation. A genetic algorithm (GA) based system for validating the power system model in capacitor switching studies has been developed. The problem formulation and the proposed solution are illustrated. The feasibility of the developed system for practical applications is demonstrated by evaluation studies.

- M.H.J. Bo1 ten et al [27], the work presents model has been incorporated in the method for reliability/power quality analysis of industrial power systems, Simulations are presented to show the influence of the postfault voltage sag due to motor re acceleration on the reliability/power quality of the supply. The simulations result in a table with the expected number of interruptions of plant operation for different load sensitivities.

-Surya Santoso et al [28], the paper presents an approach to detect, localize, and investigate the feasibility of classifying various types of power quality disturbances. The approach is based on wavelet transform analysis, particddy the dyadic

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orthonormal wavelet transform. The key idea underlying the approach is to decompose a given disturbance signal into other signals which represent a smoothed version and a detailed version of the original signal. The decomposition is performed using multiresolution signal decomposition techniques. They demonstrate and test their proposed technique to detect and localize disturbances with actual power line disturbances. In order to enhance the detection outcomes, they utilize the squared wavelet transform coefficients of the analyzed power line signal. Based on the results of the detection and localization, they carryout an initial investigation of the ability to uniquely characterize various types of power quality disturbances. This investigation is based on characterizing the uniqueness of the squared wavelet transform coefficients for each power quality disturbance.

- G. T. Heydt et al [29], the paper discusses the application of the Windowed Fast Fourier Transform to electric power quality assessment. The WFFT is a time windowed version of the Discrete Time Fourier Transform. The window width may be adjusted and shifted to scan through large volumes of power quality data. Narrow window widths are used for detailed analyses, and wide window widths are used to move rapidly across archived power quality data measurements. The mathematics of the method is discussed and applications are illustrated.

A. P. Salas Meliopoulos et al [30], the work represents a statistical method to power quality assessment. The method is based on Monte Carlo simulation of the integrated utility system/customer system. The proposed integrated model is based on the physical design parameters of the system. This approach makes it possible to relate the design parameters of a system to the statistical power quality level of the system at the customer site. Thus the proposed model is very fusel for meaningful improvements of the system to maximize power quality.

- E.F. EL-SaadanyY et al [31], the paper focuses on capacitor switching events, capacitor switching transient depending on capacitor location, load type, load level, voltage level and instant of switching. The effect of these factors on capacitor transient was examined by using Wavelet and Fast Fourier Transforms.

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T. K. Abdel-Galil et al [32], the paper discusses a new monitoring strategy for power quality events. This new strategy will be implemented using a distributed power quality monitoring nodes, which will be connected via Ethernet connection to a central diagnosis unit.

Mihaela Albu et al [33], the paper presents using the root mean square, a mathematical operation in power quality assessment. The root mean square mathematical operation is widely used in power engineering. The process has a frequency response characteristic and an associated time constant which is important especially for short term signals. Potential problem areas in using RMS values in power quality assessment are identified and discussed .

- Abd-Elmoneim Moussa et al [34], the paper discusses a proposed work to introduce a new concept of advanced power quality assessment. The introduced system is implemented using applications of a set of powerful software algorithms and a digital signal processor based hardware data acquisition system. The suggested scheme is mainly to construct a system for real time detection and identification of different types of power quality disturbances that produce a sudden change in the power quality levels. A new mitigation technique through generating feedback correction signals for disturbance compensation is addressed. The performance of the suggested system is tested and verified through real test examples. The obtained results reveal that, the introduced system detects fast and accurately most of the power quality disturbance events and introduce new indicative factors estimating the performance of any supply system subjected to a set number of disturbance events.

- Lucian Mandache et al [35], the paper discusses a new and accurate method of harmonic analysis that permits to mitigate most of power quality related problems. The principle is to estimate intermediate points between the initial samples given by the available data acquisition system; therefore, the Fourier coefficients are estimated more precisely using the Fast Fourier Transform. As interpolation technique they chose the reconstruction of the analog signal using an ideal low pass filter. The excellent results are validated on a pair of synthesized signals having known harmonic spectrum.

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- Ivan J. Rivera et al [36], the paper represents a work to develop a time frequency signal analysis system to detect and recognize different kinds of power quality events or disturbances. To achieve their goal, design of computational signal processing methods is addressed using developing timefrequency tools based on signal algebra operators. The use of signal algebra operators permits the formulation of time frequency algorithms in a computational framework setting, allowing the search for efficient hardware implementations. Timefrequency formulations are implemented for embedded system applications using Digital Signal Processing (DSP) and Field Programmable Gate Array (FPGA) units. Voltage disturbances are responsible for many disruptions in industrial, commercial and residential power supply systems, causing time and monetary losses. It is necessary to identify fast methods of determining when these disturbances are occurring in order to make correct power quality decisions. Automated information processing systems are needed to assess existing problems. Although a lot of work has been done on power line disturbance assessment, new techniques are desired to address new challenging power quality issues, especially in the area of physical security. Timefrequency signal analysis is a well known tool used in fields such as speech, sonar, and radar processing and is now finding its being in power quality assessment. A time frequency representation is a twodimensional representation that shows how the spectral content of a given signal changes with time. There is a genuine interest in this kind of representations for the field of power quality signal analysis systems since they provide more information than the typical one dimensional analysis. To achieve the goals of this work an environment is created using MATLAB to simulate power line signal disturbances such as swells, sags, harmonic distortions, and outages. This environment computes desired timefrequency representations of selected signals to produce twodimensional time frequency characterizations of the disturbances. Timefrequency tools such as the Discrete Short Time Fourier Transform (DSFT), the Discrete Ambiguity Function (DAF), and the Discrete Wigner Distribution (DWD) are being used in the MATLAB environment. These tools are characterizing the voltage disturbances, since the time frequency representations reveal patterns or properties that are not readily perceptible in one dimension.

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A. K. Al-Othman et al [37], the paper discusses a new digital approach for the measurements of voltage flicker and its frequency using Particle Swarm Optimization technique (PSO). The problem is formulated as a dynamic estimation problem. The goal is to minimize the error of the estimated coefficients via a deigned fitness function. The method is tested using simulated case study. The algorithm is tested using simulated data. Effects of number of samples, sampling frequency and the sample window size are studied. Results are reported and discussed.

- Cheng-Ting Hsu et al [38], the work presents the power quality assessment of large synchronous motor starting and loading in the integrated steelmaking cogeneration facility. To execute the transient stability analysis, the proper mathematical models, and the accurate parameters of the cogeneration units, excitation systems, governor systems, load, and Static Var Compensators (SVCs) are investigated in detail. Four case studies with or without considering the connection of the power grid, the installation of autotransformer (AT) starter, and SVC are performed to demonstrate the dynamic responses of the system frequency, voltage, and cogeneration units due to motor starting and loading. Also, the voltage sag ride through curve of sensitivity load has been included, and a Power Quality Index (PQI) due to voltage variation in the assessment period has been proposed to find the impact of motor starting and loading on the power quality of the cogeneration system. It is concluded that the system dynamic responses and PQI values have better performance if the AT starter is applied with either the regulation of the SVC system or connection to the bulk power grid.

- Surajit Chattopadhyay et al [39], the paper discusses an approach for assessment of power quality parameters using analysis of fundamental and harmonic voltage and current waveforms. Park transformation technique has been utilized for the analysis in threephase system, which has reduced the computational effort to a great extent. Contributions of fundamental and harmonic components in power system voltage and current signals have been assessed separately. An algorithm has been developed to calculate the power quality parameters from online signals. This algorithm has been simulated for a radial system, and the results have been compared with that obtained

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from a standard FFTbased system. The results are seen to be in good agreement with that of the standard system.

- Sudipta Nath [40], this paper presents the application of continuous wavelet transform to detect power quality disturbances. A power system network revealing power quality disturbances has been simulated using Electromagnetic Transient Program. Then continuous wavelet transform has been applied for feature extraction.

- Sutherland, P. E et al [41], the paper discusses a project to assess the specific transformer grounding and connection methods that are used at the subject utility for distributed generators (DGs) and provide a risk assessment in terms of potential impact, ways to minimize the impact, and site specific screening criteria for additional protection that may be required for DG interconnection. The utility has standardized on a grounded wyegrounded wye transformer connection for customers connected to their distribution system. When a backup generator exists in the customer's facility that could be paralleled with the utility system, a contactor is installed on the neutral to ground connection on the generator. This contactor is opened at any time the generator is paralleled. The utility is considering remotely dispatching, these distributed generation assets in times of peak load in the future. This will require the generators to run paralleled for extended periods of time. Grounding practices for auxiliary generators were evaluated, and simulations of both steadystate and fault conditions were conducted. The most critical factors were found to be assuring that the generator ground switch was closed during islanding and that the overvoltage protection operates correctly to isolate the generator during fault conditions. Recommendations for overvoltage protection and testing were developed based upon the results.

- Legarreta, Andres E. et al [42], the work describes some of the constrictions and requirements assumed for the design of the high performance power quality data logger PQ1000, taking into account the international standards IEC 61000430 Class A and the IEC 61000415 published in August 2010. Trough it, the most important demands of the IEC 61000430 class A instruments are exposed. Details of the hardware components are also shown, and the most important points of the signal

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processing path are explained. The performance in the RMS values determination is given, also the frequency response for harmonics measurement are shown, and a detailed analysis of fulfillment of the tests given in the IEC 61000415 are given in the final section .

-Souza, L.F.W. et al [43], this paper discusses methods and criteria for the assessment of the Low Voltage RideThrough (LVRT) needs of the power grid. Simulation techniques are used to investigate both how voltage dips caused by short circuits spread over the grid and what impact do they cause in the operation performance of power systems with wind generation. The analysis is performed for Wind Trbines (WT) with different LVRT characteristics. It is shown that, depending on system's topology characteristics and the voltage level of WT's point of connection; ridethrough needs may be different throughout power systems, especially those of continental countries as Brazil. As a conclusion, it is possible to have less severe LVRT requirements without risking system operation security.

Su, H.J. et al [44], This paper presents simulations for numerical models of two wind turbine schemes, fixed and variable speed types, by using Matlab/Simulink, where simplified analytical model of wind turbines for voltage spectral analysis are illustrated for the power quality assessment.

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CHAPTER (3) DESCRIPTION OF THE CASE STUDY AND MEASURING PROCESS

3.1- Description of the case study [45]:

The case study is the Egypt 2nd Testing Research Reactor ( ETRR-2), also known as the Multipurpose Nuclear Reactor ( MPR ), it is an open pool type reactor, 22 MW thermal power purchased from INVAP Argentina. The reactor is a powerful tool for various researchs and applications. Several experimental and production facilities are installed to meet the requirements of various utilization groups including universities, research institutes, industry, and medical organizations. Figure (31) shows ETRR2 general view.

Figure (31) ETRR2 general view

The Egyptian 2nd Testing Research Reactor ( ETRR-2) has the following benefits:

Economic Benefits:

• Production of radioisotopes to be used in different fields (such as, medicine, agriculture, industry...etc.).

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• Production of radioactive cobalt60 radiation sources with applications in food preservation, oil logging and medicine. • Production of silicon ingots, doped using Neutron Transmutation Doping (NTD) techniques. • Gem stones irradiation. • Neutron radiography for industrial utilization.

Using Neutron activation analysis for environmental studies, geological mapping and medical applications.

-Technical Benefits:

• Material testing research. • Reactors physics research. • Reactors and thermal engineering research. • The reactor will serve as a training school to qualify staff on reactor operation and maintenance.

-National Benefits:

• Development of highly qualified and skilled personnel in the field of research reactor design and operation. • Increasing the role of Egypt in the field of nuclear industries.

3.2- Electrical system of ETRR-2 [46]

The electrical loads of the reactors have been classified according to the following categories: Class ‘A’ loads: are those loads essential from a safety point of view, they required uninterruptible AC power. The capacity of UPS is 15 KVA. This capacity meets all class ‘A’ required load demands and conditions ( including duty cycles , electrical transients ) with autonomy of 30 minutes. Class ‘B’ loads: are loads whose reconnection to the system is convenient in order to increase their availability after interruption of electrical supply from the external lines. Class ‘B’ loads are fed by two sources, the normal power supply and the power plant. The power plant has two diesel generators design to furnish AC power

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adequate for supplying class ‘B’ and the uninterruptible power system in case the external lines are unavilable. The capacity of plant is two generators with 300 KVA for each. Class ‘C’ loads: they admit interruption the supply for definite time. They fed from the normal power supply. Power is brought to the ETRR2 substation by two independent sources at 11kV line. Source1 feeds transformer T1 , and Source 2 feeds transformer T2 . Transformer T1 feeds the left busbars and transformer T2 feeds the right busbars , both the busbars class ‘C’ loads left and right have redundant full capacity. The load categories and the single line diagram are shown in figure (32). The normal power supply is capable of starting and operating all required loads and the transformers are identical, each of them (primary voltage 11kV, 50Hz, secondary voltage 0.4/0.231kV, connected group Dy 11) has 100 % of the total sum of individual maximum demands. Each transformer has a capacity of 2000 kVA, which is the power required for the ETRR2.

Source 1 ( 11 Kv) Source 2 ( 11 Kv)

T2 Power Transformer T1 Power Transformer 2000 KVA 2000 KVA

CB1 CB2

CB3

Class " C" Loads Class " C" Loads

G G

CB 8 CB 6 CB 7 CB 9

CB 4 CB 5

UPS Class B Loads Class B Loads Class A Loads

Figure (32) single line diagram of the electrical system of ETRR2

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3.3- Electrical defects of ETRR-2 Because of a lot of electrical power disturbances, The ETRR2 is affected by electrical defects such as:

Failure of some component such as electronic cards, capacitors, etc. Phantom tripping of breakers, noisy bus ducts and distribution equipment. Overheating at low loads, noisy and failures of transformers. Overheating, excessive vibration, noise and winding burning out of motors. A lot of lamps and ballasts failing at abnormal rate. Erratic operation of sensitive equipment. Loss of power and hence shutdown the reactor. Malfunction and error signals lead to shut down the reactor. Bad performance of the electrical system. All the problems described above, reflect poor power quality of electrical system of ETRR2. These problems lead to increase of operating costs and decrease the useful life of the system component. Where, any disturbance leads to shut down the reactor and then loss of money. The amount of money loss is depending on the cost and the state of the reactor fuel. Normally the reactor needs about one hour to restart after scram, but need about 50 hours to restart if it was at the end of fuel cycle due to the reactivity. From experience the disturbance cost of ETRR2 is approximately (5000 $) at normal state.

3.4- Measuring process:

A general rule, it is necessary to test each location for at least one week, unless results definity indicate power quality issues at location that could causing problems. In such case the interval could be shorted [10]. The electrical power of the nuclear research reactor is supplied to the installation via two incoming feeders from two different substations to keep good reliability. Each feeder is designed to carry the full load. The monitoring investigations were performed at the nuclear research reactor for both feeders at different operation conditions. Measurements were carried out with power analyzer instrument on the medium voltage side for each source separately.

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3.4.1- power quality analyzer (UNIPOWER 900F) [47] Network optimization and preventive measures increase in actuality when the demands from power quality are increased. Long term measurements are required in order to demonstrate that delivered electric energy maintains a promised quality. The network analyzer Unipower 900F from Unipower is an excellent aid to this type of weekly or monthly measurements. So, it is chosen as a power quality analyzer instrument. - Main functions of Unipower 900F: Automatic transducer identification General purpose transmitters 020 and 420mA -Measures Quantities:

All units measured simultaneously and the Unipower 900F has the following measurements:

Quantities and units like V, A, W, VA, VAr, kWh, kVArh, PF, CosΦ, Hz, °C,

IFL , P ST , P LT

Transients

Voltage sag (dips) and swell.

Flicker (one and three phase)

Harmonics. Odd, even, inter harmonics and power harmonics

Threephase voltage unbalance

Frequency deviations

InRush current

Temperature

٤١

-Performance of Unipower 900F:

Unipower 900F is an eightchannel network analyzer with its own hard disc and battery operation for up to fifteen minutes of standby operation. The unit can store multiple files in sequences without previous dumping. Useful if it is necessary to measure on several points in the same facility and collect an amount of measuring files. Figure (33) shows the front panel of the Analyzer (Unipower 900F).

Figure (33) the Unipower 900F front panel

- Real-time measurements:

The network analyzer Unipower 900F allows measurements to take place in realtime for all units simultaneously. The oscilloscope waveforms for currents and voltages can be studied as well as the vector diagram phase positions. The realtime window allows studying of waveforms, diagram for harmonics, flicker, etc. With the disturbance analyzer it is easy to capture transients, sags and swells, and also voltage and current levels. Simply adjust nominal voltage level with permitted discrepancy and instruct Unipower 900F to monitor the waveforms for all the phases. If and when a disturbance appears it will be captured by the analyzer. The waveforms are stored on the hard disc and the disturbances can then be shown on a viewing screen.

-Evaluation of Unipower 900F

Power Profile shows data and waveforms in a graphic mode, easy to print and to copy.

Unipower Report for power quality assurance in relation to engineering standard and standard specifications e.g. EN 50160 including automatic report generation.

٤٢

Possibility to export data and measured files to other software, for instance spread sheets. The Unipower 900F complies with the international standard specifications.

3.4.2-Measuring Points: Measurments were carried out on the medium voltage side of the following: 1 Incoming feeder from substation1 (source1) for one week. 2 Incoming feeder from substation2 (source2) for one week . As shown in figure (34) When the measurments are carried out of source1 from substation1 , the distribution center (PCC) feeds through panel (Pn2) and panels no. (1,3,4) were switched off. And when the measurments are carried out of source2 from substation2 , the distribution center feeds through panel (Pn3) and panels no. (4,1,2) were switched off.

Measurments were carried out under different operation conditions of Egypt 2nd Testing Research Reactor (ETRR2) as indicated in the following chapter.

Source 1 Source 2 11 KV 11 KV

Pn1 Pn2 Pn3 Pn4

PCC 11 KV

Pn5,6

Pn7 8 9 10 11 12 13 14

Senstive Senstive Other Loads Other Loads load1 load2 2 MVA 2 MVA

Points of Measurment

Figure (34) Single line diagram of distribution center and measuring points

٤٣

CHAPTER (4)

MONITORING IN ETRR-2

4.1- Introduction : This chapter illustrates the analysis and discussion of the results collected by power analyzer and evaluating the power quality in accordance with the international standard specifications . The monitoring process was carried out in the Egypt 2nd Testing Research Reactor (ETRR2) at two ponits as the following:

Incoming feeder from substation1 (source1) for a period of one week. Incoming feeder from substation2 (source2) for a period of one week.

4.2- Measurement results:

The block diagram in figure (34) shows the single line diagram of distribution center and measuring points.

After gathering data, an analysis using MS Excel was done. And all the daily trend graphs are shown in appendex B. The discussion of the results and analysis are shown at the following:

4.3-Measurement results of the first feeder (source1):

4.3.1- Harmonics:

During the measurements period, it is observed that all the three phases are combined into one single plot for comparisons. As shown in figure (41) the Voltage Total Harmonics Distortion (VTHD) levels do not exceed the acceptable tolerance of 5 % set by the IEEE standard, but from the recorded measurements data the 5th harmonic exceeds the acceptable tolerance of 3 %. And as shown in figure (42) the Current Total Harmonics Distortion (ITHD) levels are not exceeding the acceptable tolerance of 15 % set by the IEEE standard. However there is an immense increase in the ITHD levels at one point and referring to figures (43) and (44). This point is light load, wherever the power at this point is approximately 180 kVA. ٤٤

Figure (41) VTHD of incoming feeder of Source 1

Figure (42) ITHD of incoming feeder of Source 1

٤٥

Figure (43) ITHD variations of source 1 at 2nd day

Figure (44) power variations of source 1 at 2nd day

٤٦

From the analysis of measured data, the values of VTHD and ITHD at maximum and minimum loads are indicated in table (41). It is obvious that the THD at minimum load is greater than at maximum load.

Table(41) VTHD and ITHD at max. and min.loads of source1

VTHD(%) ITHD(%)

IEEE IEEE

R S T limit R S T limit

1.45 1.63 1.64 5 1.7 2.1 1.91 15 Max. load

2.6 2.95 2.8 5 6.44 5.45 7.64 15 Min. load

4.3.2- Voltage Deviation

As shown in table (42) the percentage of voltage deviation does not exceed the IEEE limit which is 5%.

Table (42) Voltage deviation at max. and min. loads of source1

Percentage of Voltage deviation

At max.load At min.load Accepted limit

1.65 1.72 4.1 4.45 5

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4.3.3- Voltage Unbalance The percentage of voltage unbalance does not exceed the accepted IEEE limit of 2 %, which most equipment can tolerate. The percentage of voltage unbalances values at maximum and minimum loads are indicated in table (43).

Table(43) Voltage unbalance at max. and min. loads of source1

Percentage of voltage unbalance

At max.load At min.load Accepted limit

0.062 0.06 2

4.3.4- Voltage swell:

Occurrence of voltage swell on phase3 is being observed; it was occurred on fourth day at (10:00:22 AM). As shown in figure (45). Percentage voltage increasing is 25% and lasted for 150 ms. Referring to the trend graphs, the system is stable and the power is about 200 kW and there was no capacitor switched on. The disturbance is occurred at phase 3 only due to network transient. This indicated that this disturbance is imported from the substation.

٤٨

Voltage

Time

Figure (45) Voltage swell on phase 3

4.3.5- Overvoltage:

During the monitoring priod, an overvoltage of about 10% of the nominal value was occurred on 6th day at (06:09:03 AM); and it was lasted for 1 minute. This disturbance was occurred on three phases as shown in figures (46), (47) and (48) respectively. Reffering to the measured data and the trend graphs, the power is constant at 400 kW and there is no capacitor bank switching on. This disturbance was probably caused by the switching of large loads.

٤٩

Voltage

Time

Figure (46) Overvoltage on phase 1

Voltage

Time

Figure (47) Overvoltage that occur on phase 2

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Voltage

Time

Figure (48) Overvoltage that occur on phase 3

4.3.6- Short Time Flicker

During the measurements period, and as shown in figure (49) it is observed that, the short time flicker (P st ) exceeds the acceptable limits. The short term severity (Pst ) is measured over a period of ten minutes. Short time flicker (P st ) is indicated daily. It is imported from the substation because it is feeding industrial loads and these loads are considered sources of voltage flicker.

4.3.7- Long time flicker

The long time flicker (P lt ) exceeds the limit as shown in figure (410). It is indicated daily. The long term severity (P lt) is calculated from a sequence of 12 Pst values over a two hours interval, according to the following expression:

3 12 p sti 3 plt = ∑ i=1 12

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Fig. (49) Short time voltage flicker of Source 1

Fig (410) Long time voltage flicker of source 1

٥٢

4.3.8- Power frequency variations

Throughout the whole survey, the power frequency variations do not exceed the IEEE limit, which is ±1%.

4.4- Site appraisal of incoming feeder from substation1 (source 1):

Generally, the analysis of all the data attained during the survey compared with the power system disturbance suggests that the power quality is relatively good at source 1, with the exception of a few irregular occurrences. The results of monitoring are:

THD does not exceed the IEEE limits, but the fifth harmonic exceeds 3%.

Voltage deviation does not exceed the IEEE limits.

Voltage imbalance does not exceed the IEEE limits.

Power frequency variations don not exceed the IEEE limits.

Flicker exceeds the IEEE limits.

Occurrence of few irregular disturbances (voltage swell, overvoltage and flicker). The power disturbance encountered during the period of the investigation were due to the natural causes of the disturbances.

٥٣

4.5- Measurement results of the second feeder (source2):

4.5.1- Harmonics:

During the monitoring period, it is observed that all three phases are combined into one single plot for comparisons. As shown in figure (411) generally the Voltage Total Harmonics Distortion (VTHD) levels do not exceed the acceptable tolerance of 5% set by the IEEE standard. However, there is an immense increase in the VTHD levels at one point. And referring to figures (412) and (413) the power is approximately 150 kVA, so, this point is considered light load.

Voltage Total Harmonic Distortion variation

40

35

30

25

20

VTHD 15

10

5

0 14:05 21:17 04:29 11:41 18:53 02:05 09:17 16:29 23:41 06:53 14:05 21:17 04:29 11:41 Time VTHD1 VTHD2 VTHD3

Figure (411) VTHD of incoming feeder of source 2

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Figure (412) VTHD variations of source 2 at 2nd day

Figure (413) power variations of source 2 at 2nd day

٥٥

And as shown in figure (414) the Current Total Harmonics Distortion (ITHD) levels are close to the acceptable tolerance of 15% set by the IEEE standard. But there are increasing in the ITHD levels at three points. Referring to figures (415), (416), (4 17) and (418), the power is very low at these points, hence these points are considered light load.

Current Total Harmonic Distortion Variation

100

90

80

70

60

50

ITHD 40

30 20 IEEE Limit 10

0 14:05 21:17 04:29 11:41 18:53 02:05 09:17 16:29 23:41 06:53 14:05 21:17 04:29 11:41 Time ITHD1 ITHD2 ITHD3

Figure (414) ITHD of incoming feeder of source 2

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Figure (415) ITHD variations of source 2 at 2nd day

Figure (416) power variations of source 2 at 2nd day

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Figure (417) ITHD variations of source 2 at 3rd day

Figure (418) power variations of source 2 at 3rd day

٥٨

And the values of VTHD and ITHD at maximum and minimum loads are indicated in table (44). It is obvious that the THD at minimum load is greater than at maximum load.

Table (44) VTHD and ITHD at max. and min. loads of source2

VTHD(%) ITHD(%)

IEEE IEEE

R S T limit R S T limit

1.18 1.26 1.22 5 1.92 1.93 2.02 15 Max. load

1.43 1.45 1.41 5 9.91 10.44 9.98 15 Min. load

4.5.2- Voltage deviation

As shown in table (45) that the percentage of voltage deviation does not exceed the limit of IEEE standard which is 5%.

Table (45). Voltage deviation at max. and min. loads of source2

Percentage of Voltage deviation

At max.load At min.load Accepted limit

3.31 – 3.42 .096 .099 5

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4.5.3- Voltage Unbalance

The percentage of voltage unbalance does not exceed the IEEE accepted limit of 2%, which the most equipment can tolerate. The percentage of voltage unbalance values at maximum and minimum loads are indicated in table (46).

Table(46) Voltage unbalance at max.and min. loads of source2

Percentage of voltage unbalance

At max.load At min.load Accepted limit

0.083 0.28 2

4.5.4- Undervoltage

An undervoltage of about 20% of the nominal value was occurred on 3rd day at (10:15 AM); and it was lasted for 1.1 min, and from the recorded measurments data the power is 450 kW and there is no capacitor bank switching off. And the disturbance has a long time. So this disturbance is imported from the utility.

4.5.5- voltage sag

It’s observed the occurrence of voltage sag on phase 1. As shown in figure (419), percentage voltage reduction is 35%, for duration of 250 ms. And also, on phase 3 as shown in figure (420) that percentage voltage reduction is 30%, for duration of 250 ms. This disturbance occurred on 4th day at (17:48:40 PM). Referring to the trend graphs, the power is about 250 kW and there is no starting or short circuit at the electrical system of ETRR2. So, this disturbance is imported from the substation.

٦٠

Voltage

Time

Figure (419) Voltage sag on phase 1

V oltage

Time Figure (420) Voltage sag on phase3

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4.5.6- Voltage swell

It’s observed the occurrence of voltage swell on phase 3. As shown in figure (421), the percentage voltage increasing is 25%, for duration of 200 ms. This disturbance was occurred on 4th day at (17:49:10 PM). Referring to the trend graph, the system is stable and the power is about 250 kW and there is no capacitor switched on. The disturbance is occurred at phase 3 only due to transient network. This disturbance is imported from the substation.

Voltage

Time Figure ( 421) Voltage swell on phase 3

4.5.7- Voltage Transient

There was a transient voltage observed during the period of monitoring, it’s observed the occurrence of voltage transient on the three phases as shown in figures (422) and (423). These disturbances were occurred on 4th day at (08:07:39 AM) and (16:25:03 PM) respectively. Referring to the power trend graphs and the recorded data the ETRR2 load is stable; there is no starting or any variation. So, this disturbance is imported from the substation also. This disturbance was probably caused by switching or short circuit.

٦٢

Voltage

Time Figure (422) Voltage transient on the three phases

Voltage

Time Figure (423) Voltage transient on the three phases

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4.5.8- Outage

Throughout the whole survey, there was one outage occurred and lasted for 500 ms; It was occurred on 4th day at (09:03:02 AM). As shown in fig. (424). There is no faults or accidents in the electrical system of ETRR2, so this outage occurred from the substaion.

0 Voltage

Time Figure (424) Voltage Outage.

4.5.9- Short Time Flicker

During the period of monitoring the short time flicker (P st ) exceeds the limit as shown in figure (425). It is indicated daily. Because of the substation is feeding industrial loads and these loads including arc furnace and welders. These loads are considered sources of voltage flicker, so this disturbance is imported from the substation.

4.5.10- Long Time Flicker

The long time flicker (P lt ) exceeds the IEEE limit as shown in figure (426). It is indicated daily. The long time flicker is calculated from a sequence 12 P st – values over a two hours interval.

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Figure ( 425) Short time voltage flicker of source 2

Figure ( 426) Long time voltage flicker

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4.5.11- Power frequency variations

Throughout the whole survey, the power frequency variations did not exceed the IEEE limit, which is ±1%.

4.6 - Site appraisal of incoming feeder 2 (Source 2):

Generally, the analysis of all the data attained during the survey compared with the power system disturbance suggests that the power quality is bad at the incoming feedre of substation2 (Source 2), there are many irregular occurrences, like (undrevoltage, voltage sag, voltage swell, voltage transients, temporary outage, and flicker ). The results are:

THD does not exceed the IEEE limits.

Voltage deviation does not exceed the IEEE limits.

Voltage imbalance does not exceed the IEEE limits.

Power frequency variations does not exceed the IEEE limits

Flicker exceeds the IEEE limits.

Occurrence of many irregular disturbances (undervoltage, voltage sag, voltage swell, voltage transients and flicker).

From experience, most of the electrical defects of ETRR2 occurred when ETRR2 was fed through the incoming feeder of substation 2. This substation is pollutant because it is feeding industrial and nonlinear loads which are considered as source of power disturbances.

٦٦

4.7- Invesigation results and mitigation techniques:

Generally, the analysis on all the information gathered during the investigation period done in ETRR2, there are many irregular disturbamces such as : Fifth harmonic. Voltage flicker. Voltage sags/swells. Under/over voltage. Transients. Temporary outage (500 ms). Referring to the results of power quality monitoring of the electrical system of ETRR2, and according to the power quality solutions, mitigation techniques are suggested as the following: Install Passive Filters at low voltage side. Install Dynamic Voltage Restorer (DVR) at medium voltage side. All sensitive and critical loads should be isolated and fed through Uninterruptible Power Supply (UPS).

The following chapter will indicate the mitigation applications required for elimination of the power disturbances of the electical system of ETRR2.

٦٧

CHAPTER (5)

MITIGATION APPLICATIONS

5.1- Introduction Disturbance mitigation can be done through changes in the power system configuration, increasing equipment immunity or the use of mitigation devices. It is well known that the delta connection of transformer prevents the flow of triplen harmonics. Other changes in the system configuration that play a role in the mitigation of power quality problems, especially voltage sags are in the reduction of the number of faults, reducing faultclearing time or designing parallel feeders. [21]. Referring to the results of monitoring of power quality of the electrical system of ETRR2 and according to the power quality solutions, mitigation techniques are suggested as the following: Install Passive Filters at low voltage side. Install Dynamic Voltage Restorer (DVR) at medium voltage side. All sensitive and critical loads should be fed through Uninterruptible Power Supply (UPS). Passive filters are the most common method used to control the flow of harmonic currents. The most common design is a singletuned filter. DVR is used to protect voltage sags on lines feeding sensitive / critical equipment, the DVR is specifically designed for large loads served at distribution voltage. [48] Normally, UPS are used to interface critical loads such as computers and communication systems to the utility systems. The most common design of UPS is The double conversion mode.

5.2- Harmonic filters:

Passive filters at suitable locations, preferably close to the source of harmonic generation can be provided so that, the harmonic currents are trapped at the source and the currents propagated in the system are reduced. The active filtering techniques, generally incorporated with the harmonic producing equipment itself can reduce the ٦٨

harmonic generation at the source. Hybrid combinations of active and passive filters are also a possibility .

5.2.1- Shunt filters [49] and [50]:

Shunt filters are the most common method used to control the flow of harmonic currents. They are designed as a combination series of reactors and capacitors. They are referred to as “tuned filters” or “traps” because they absorb the harmonic current to which they are tuned. The most common design of shunt filter is a Single Tuned Filter (STF). As shown in figure (51) it is connected as shunt element in parallel with the source of a certain harmonic considered. This harmonic current is shorted to ground with the filter and prevented from entering the system. The filter may have a series resistance either added to it or found inherently in its inductance. The resonance frequency is given by the following expression:

1 X C f r = = f 0 (51) 2π LC X L

Where: fr : Resonance frequency.

L : The inductance of the filter.

C : the capacitance of the filter.

f0 : the fundamental frequency.

XL : Inductive reactance at fundamental frequency = 2Лf0L.

XC : Capacitive reactance at fundamental frequency =1/(2Лf0C).

Also the following parameters are defined to filter:

R : Series resistance.

Q : Quality factor of the filter , it is equal to the ratio of the inductive or capacitive reactance at resonance, to the resistance. It ranges from 15 to 80 for the filters used in

٦٩

low voltages in industrial and commercial applications. It determines the sharpness of tuning and, it determines the fundamental frequency losses.

Figure (51) single tuned filter

-Steps of filter design [51] and [52]:

1 Determine the capacitance needed to improve the power factor to eliminate any penalty. This usually is about 0.95 2 Select the reactor to series tune the capacitor to the desired harmonic order. The tuned frequency is taken slightly less than the filter harmonic order (310 %) to reduce the stresses on the filter and to avoid parallel resonance at less harmonic order. 3 Calculate the voltage and current stresses on the capacitors and inductors of the filter. i Capacitor duties 1. rms current. 2. Harmonic voltage. 3. Fundamental voltage. 4. Maximum peak voltage. 5. Maximum peak current. 6. Maximum reactive power. ii Inductor duties

1 Fundamental current. 2 Filter rms current.

٧٠

3 Harmonic current. 4 Choose standard components to the duty that is placed upon them.

5-2-2- Design of fifth harmonic passive filter: [53]

Referring to the results of monitoring in ETRR2, the Total Harmonic Distortion (THD) does not exceed the IEEE limits, but the fifth harmonic level increases 3%. It is considered a common feature in the ETRR2 system, and must be mitigated. According to the power quality solutions, mitigation techniques are suggested installing passive filter at low voltage side. The most costeffective filter is generally a single tuned passive filter and this will be applicable for the majority of the cases. Filters must be carefully designed to avoid unexpected interactions with the system.

Referring to the electrical system of ETRR2,

Harmonic order = 5

Threephase capacitor bank rating = 500 kVAr

Capacity rating = 500 kVAr, 400 V

Nominal bus voltage = 400 V

Transformer rating = 2000 kVA, 6%

5th harmonic current = 40% of fundamental current (assumed)

Filter tuning harmonic = 4.7

Utility harmonic voltage source = 1%

The design steps as the following:

Capacitor F.L current

IF.L = Q / ( 3 *V) = 500 / ( 3 *0.4) = 721.68 A (52)

Capacitor reactance

2 2 Q = V / X C, hence, XC = (0.4) / 0.5 = 0.32 (53)

٧١

Reactor reactance

2 2 XR = X C / h = 0.32 / (4.7) = 0.01448 (54)

Filter reactance at fundamental frequency

XF = X C –XR = 0.32 + 0.01448 = 0.305 (55)

Filter fundamental current

IFF = V / (X F* 3 ) = 400 / (0.305* 3 ) = 757.18 A (56)

Filter reactive power

QF = 3 * V* I F = 3 * 0.4*757.18 = 524.59 kVAr (57)

Transformer reactance at 5th harmonic

2 2 XT5 = 5*0.06*V / S = 5*0.06*(0.4) / 2 = 0.024 (58)

Filter reactance at 5th harmonic

XF5 = (h*X R)(X C/h) = (5*0.01448)(0.32/5) = 0.0084 (59)

Total harmonic reactance

XTOTAL = X T5+X F5 = 0.024+0.0084 = 0.0324 (510)

Filter utility harmonic current

IF5 = (0.01*V) / ( 3 *X TOTAL ) = (0.01*400) / ( 3 *0.0324) = 71.277 A (511)

Peak harmonic current

IP5 = (IFL *0.4) + IF5 = (721.68*0.4) + 71.277 = 359.9 A (512)

٧٢

Max r.m.s current

2 2 2 2 Irms = (I FF ) + (I P5 ) = (757 18. ) + (359 )9. = 838.38 A (513)

Fifth harmonic voltage (line voltage)

VC5 = I P5*(X C/5)* 3 = 359.9*(0.32/5)* 3 =39.89 V (514)

Fundamental capacitor voltage (line voltage)

VCF = I CF *X C* 3 = 757.18*0.32* 3 = 419.67 V (515)

Max capacitor voltage

Vcmax = V CF + V C5 = 419.67 + 39.89 = 459.56 V (516)

Max filter current

IFmax = I FL + I P5 = 757.18 + 359.9 = 1117.08 A (517)

Capacitor r.m.s voltage

2 2 2 2 VCrms = (VCF ) + (VC5 ) = (419 67. ) + 39( 89. ) = 421.56 V (518)

Max capacitor reactive power

Qmax = 3 * V crms *I rms (519)

Qmax =0.001* 3 * 421.56 * 838.38 = 612.15 kVAr

-Capacitor limits ( IEEE Std 18-2002) [54]

Peak voltage: Vcmax / 400 = 459.56 / 400 = 114.8 % < 120 %

Maximum r.m.s current: I rms / I cfl = 838.38 / 757.18 = 110.72 % < 135 %

Capacitor r.m.s voltage: V Crms / 400 = 421.56 /400 = 105.39 % < 110 %

٧٣

Maximum reactive power: Q max. / 500 = 612.15 /500= 122.43 % < 135%

Hence, all the values are accepted and the design is correct.

5.2.3- Cost of Filter:

The cost of fully automatic system is 60 $/ kVAr [55]

For 500 kVAr, this is required for the case study, then,

Cost = 500 * 60 = 30000 $.

And it is very low compared with its benefits; it can protect the electrical system equipment from the harmonics effects.

5.2.4- Harmonic Filter Calculation Spreadsheet:

The harmonic filter calculations spreadsheet provides a convenient method for determining low voltage filter component values and duties. A computer program designs it for uses with Microsoft excel.

The design of this spreadsheet is depend on the previous equations, which used to design the 5th harmonic passive filter.

This spreadsheet provides the user with a convenient method for entering the required data. The entered specified data includes:

filter tuning specification capacitor bank rating, voltage and frequency nominal bus rating transformer name plate rating and impedance total harmonic load utility background harmonic voltage distortion Table (51) shows design example of the calculations for the 5th harmonic filter. Calculations including capacitor derating, filter component values and capacitor duty with respect to standard. And table (52) shows IEEE Std 182002.

٧٤

Table (51) calculations for 5th harmonic filter

Table (52) IEEE Std 182002

CAPACITOR LIMITS:(IEEE Std 182002)

Limits Actual value %

Peak Voltage 120% 458.8600254 114.7150064

RMS Current 135% 837.2054316 110.7550444 KVAR 135% 523.7079184 122.0567296

RMS Voltage 110% 420.8613741 105.2153435

٧٥

5.3- Dynamic Voltage Restorer (DVR) [56] The proliferation of voltage sensitive equipment in industrial sector has made industrial processes more vulnerable to supply voltage deviations. Such voltage deviations in the form of voltage sag, swell or temporary outage cause severe process disruptions resulting in millions of dollars of loss of revenue. Therefore, power supply authorities as well as customers have been desperately looking for a costeffective solution currently to ride through momentary power supply disturbances. As such, the proposition of a novel custom power device called Dynamic Voltage Restorer (DVR) for compensating voltage disturbances in distribution systems has generated a great deal of interest recently. Apart from the DVR, some researchers have proposed several other devices to mitigate momentary disturbances. Among those, static voltage booster and unified voltage controller have been noteworthy. The DVR is the most economic and effective means in improving the voltage relative power quality problems. The DVR is power electronics based solution that employs series voltage boost technology for compensating voltage sags / swells. The DVR usually consists of an injection transformer, which is connected in series with the distribution line, a voltage sourced PWM inverter bridge which is connected to the secondary of the injection transformer and an energy storage device (batteries, capacitors…etc.) connected at the dclink of the inverter bridge. A typical schematic of the DVR is shown in Fig. (52). The inverter bridge output is filtered before being fed to the injection transformer in order to nullify switching frequency harmonics. The series injected voltage with a variable amplitude, phase and frequency of the DVR is synthesized by modulating pulse widths of the inverter bridge switches. The injection of an appropriate series voltage component in the face of a voltage disturbance requires a certain amount of real and reactive power supply by the DVR. The real and reactive power supplied by the DVR however depend on the type of voltage disturbance experienced, as well as the direction of the DVR injected voltage component with reference to presag voltage. The idea of advancing the injected voltage in order to minimize the real power supplied by the DVR has generated a great deal of research interest recently.

٧٦

Many companies have begun to customize the special monographic study of the electric power technology, and have introduced commercialization DVR devices. Table (53) shows the developing and demonstration projects situation of the ABB, Siemens, and American Superconductor for the DVR installations. [57]

Fig. (52): Typical schematic of a power system compensated by the DVR

Table (53): The situation of developing and researching for DVR

٧٧

5.3.1-- Operating principle of DVR: [58] and [61]

When we talk about maintaining a certain voltage level on a bus, usually we think first of capacitors and Static Var Compensators (SVC). However, they only control of the voltage indirectly is through altering the system’s effective impedance. To cope with voltage sags caused by faults in the transmission or distribution system, the injection of voltage combined with the supply of active power is necessary, which is the distinguishing feature of a DVR as outlined in the following. As shown in figure (53) the basic idea of the DVR is to inject a dynamically control1ed voltage VG (t) generated by a forcedcommutated converter in series to the bus voltage by means of a booster transformer. The momentary amplitudes of the three injected phase voltages are controlled such as to eliminate any detrimental effects of a bus fault to the load voltage VL(t) . This means that, any differential voltages caused by transient disturbances in the AC feeder will be compensated by an equivalent voltage generated by the converter and injected on the medium voltage level through the booster transformer T1. This principle works independently of the type of the AC fault provided that the whole system remains connected to the supply grid, i.e.; the line breaker does not trip. For most practical cases, a more economical design can be achieved by only compensating the positive and negative sequence components of the voltage disturbance seen at the input of the DVR. This option is reasonable because for a typical distribution bus configuration, the zero sequence part of a disturbance will not pass through the step down transformers because of infinite impedance for this component. This zero sequence blocking function is achieved by the delta winding of the loadside step down transformer TL. The DC capacitor between the charger and the converter serves as the energy buffer to the DVR, generating and absorbing power during voltage sags and voltage swells, respectively. For most of the time, the DVR has virtually “nothing to do” except monitoring the bus voltage, that means it does not inject any voltage ( VG = 0) independently of the load current. Therefore, it is suggested to particularly focus on the losses of a DVR during regular hot standby operation. Two specific features addressing this loss issue have been implemented in this concept, which are the transformer design with low impedance, and the semiconductor devices employed.

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Figure (53): Basic Configuration of DVR

The booster transformer's low voltage winding is shorted through the converter in the DVR's standby mode (left side in Figure (54). No switching of semiconductors occurs in this mode of operation, because the individual converter legs are triggered such as to establish a shortcircuit path for the transformer connection. Therefore, only the comparatively low conduction losses of the semiconductors in this current loop contribute to the losses.

Figure (54): Effective transformer connection in standby and boost modes

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As shown in Figure (54), the DVR transformer in short circuit mode (SCO) resembles a shorted current transformer. In this mode the booster transformer works like a secondary shorted current transformer that means the injected voltage and the magnetic flux are virtually zero. It should be noted that the converter does not switch during SCOmode. Only the semiconductors' conduction losses appear, which are very low due to the advanced IGCT (Integrated Gate Commutated Thyristor) technology. Since the DVR will be most of the time in this particular standby mode, conduction losses will account for the bulk of converter losses during operation.

5.3.2- Control and Protection of DVR

The basic functions of a controller in a DVR are the following: Detection of voltage sag/swell events in the system. Computation of the correcting voltage. Generating of trigger pulses to the sinusoidal PWM based DCAC inverter. Correction of any anomalous in the series voltage injection. Termination of the trigger pulses when the system has passed. The controller may also be used to shift the DCAC inverter into rectifier mode to charge the capacitors in the DC energy link in the absence of voltage sag. Figure (55) shows a general control block diagram of DVR. To maximize dynamic performance, a direct feedforwardtype control architecture should be applied in the control concept of the DVR. With this concept a fast response time (approximately 1ms) can be achieved to compensate voltage sags.

All protective functions of the DVR should be implemented in the software. Differential current protection of the transformer, or short circuit current on the customer load side are only two examples of many protection functions possibility. Depending on the particular fault condition, the fast control and protection may switch the DVR into bypass if it becomes inoperable, thus secure an uninterrupted energy flow to the customer’s plant. A modified industrial PC could serve as an event recorder to log and display the various steps during operation of the DVR.

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Figure (55) General control system block diagram

Pulse logic shall establish the interface between the electrical switching orders supplied by the modulator, and the input / outputs of the Gate Units (GU) of the converters. In particular they can have the following basic: Signal conversion electrical ↔ optical Maintaining of timing constraints (min. Ontime ; min. Offtime ; Overcurrent delay) required by the Voltage Source Converter ( VSC) Control of Short Circuit Operation (SCO) Supervision and signaling of correct operation of the IGCT’s.

5.3.3- Losses of DVR: As the DVR most of the time is in standby operation, the standby losses must be very small. Any switching of semiconductors or other operations of the DVR should be avoided during the standby time. A concept that does not require the DVR converter to maintain and control the DCvoltage is preferred, in order to avoid switching and the theretorelated losses. The function of the DVR should be insensitive to minor variations in the DC voltage. The evaluation and specification of the losses should be related to the operation and during standby also, considering all auxiliaries, which are in operation. This means the transformer losses, converter losses, DClink losses and auxiliaries' losses. Another loss cut results from the IGCT technology (Integrated

٨١

Gate Commutated Thyristor) utilized in this converter. These novel semiconductor devices combine the low conducting losses of a GTO (Gate Turn Off) thyristor with a switching performance similar to a transistor. With turnoff times in the range of a few microseconds, highpower IGCT type converters show approximately 30 percent lower losses than conventional GTOtype systems. The efficiency should be related to the definition of the DVR, which is the load to be protected (for example 2MVA) and the standby losses. This definition will give a possibility to compare different DVR solutions. Typically an efficiency of >98.5% can be achieved.

5.3.4-- Harmonics of DVR: In standby mode, the DVR should not actively generate any harmonics, the valves have to be in SCO mode, i.e., establishing only the shortcircuit path for the booster transformer's secondary winding. Under boost mode, the DVR will generate harmonics, which are almost negligible with a 3level 12pulse converter configuration.

5.3.5- Availability of DVR:

The reliability and the availability are very important items in the design of a DVR. Usually, the DVR operates in a standby mode and is waiting for sag; therefore it is very crucial that the equipment has a high reliability and availability. A high availability can be achieved by reducing the number of components, which are used in the DVR. The design of the parts itself should have enough safety so that, for example a short overcurrent (e.g. motor startup) does not bring the DVR in a bypass mode. Today, an availability of >98.5% can be achieved with the use of IGCT’s. As there is the capability of operating in direct coupling to the energy storage, with only one energy conversion, which does increase the availability of the equipment.

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5.3.6- DVR capacity and specification: [57] and [58]

Referring to the electrical system of ETRR2: - Vpcc = 11 kV

S = 2000 kVA , PF = 0.9 Response time = ¼ cycle Max three phase voltage sag = 60 % Duration of sag to protect = 500 ms Rated of DVR (kVA) =? Energy (kJ) =?

PCC (11 kV)

DVR Sensitive load (ETRR2)

It is recommended to adopt DVR technology to compensate the bus voltage sag and restore to 100 % of the rated value.

When the sag depth is lower than 60 %

Therefore, the compensating voltage of DVR = 0.7 p.u. By taking into consideration of peak load (2000 kVA) with power factor 0.9

The compensating power = 0.7*2000 = 1400 kVA

Energy = power * time (520)

For duration time 0.5 sec.

The required energy = (kVA * PF) * time = (1400*0.9)*0.5 = 630 kJ. (521)

For more reliability and availability, DVR with (2 MVA, 900 kJ) is selected. And it should be installed in the 11 kV side of the system.

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5.3.7- Cost and Payback Time: [55] and [59]

Assume, Cost of DVR: C DVR

Cost of sag: C VS

Number of sags: N VS , (number per year)

Payback time: T, (year)

Then, C DVR = C VS * NVS * T (522)

The Cost of DVR = 300$/KVA + 5% (maintenance and running)

The Cost of DVR= 2000*300*1.05 = 630000 $

According to disturbance cost of ETRR2 at normal mode, the cost of voltage sag is (5000 $), and assume the number of voltage sag occurrence is 52/ year (one sag every week)

Then, T = 630000/ (5000*52) = 2.42

T payback= 2.5 year

Hint: this solution is economic because the life time of DVR is about 15 years.

5.4- Uninterruptible Power Supplies (UPS):

Uninterruptible power supplies in nuclear reactors are designed to provide a stable, and uninterruptible vital AC power to the safety related, nonsafety related instrumentation, and control systems. Uninterruptible power supplies are used to provide a reliable uninterruptible source of voltage and frequency regulated AC power to the vital loads required to shutdown the reactor and maintain in a safe condition after an anticipated operational occurrence or a postulated design basis accident. There are many types of UPSs, but the on-line double conversion technology offers highest security. Only this design offers absolutely uninterruptible power supply and equalizes all power disturbances such as voltage fluctuations, distorted voltage waveform, frequency fluctuations, voltage transients, short ٨٤

interruptions and long power outage. Critical loads will be supplied with a high quality voltage waveform, even in the case of heavy nonlinear loads drawing a non sinusoidal high crest factor current.

5.4.1- The Operational Principle of on-line double conversion UPS: [60]

This is the most common type of UPS above 10 kVA. The block diagram of the Double Conversion OnLine UPS is shown in Figure (56), it is the same as the Standby, except that the primary power path is the inverter instead of the AC main.

Figure (56): Schematic of Double Conversion OnLine UPS

It is the ultimate in UPS protection because the utility supply power does not flow directly to the load like the offline UPS. Instead, the power flows continuously through a charger/rectifier that feeds both a storage battery and an inverter. The inverter generates AC power to the load being protected. In the event of a power failure, the battery feeds the inverter. Since the power flows through the rectifier and inverter before reaching the load, most power disturbances are eliminated through constant filtering. Therefore, an online UPS is a good idea for any system which is sensitive to transients, noise, and/or cannot tolerate any power interruption.

5.4.2- UPS capacity and specification:

All the critical and sensitive loads of ETRR2 = 45 kVA

The grand load of UPS = total loads * 1.2 (523)

Wherever: (The factor 1.2, may be dynamic load at the system)

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The grand load of UPS = 45 * 1.2 = 54 kVA

Hence, UPS with 60 kVA rated power was selected.

5.4.3- Cost of UPS:

According to [55] the cost of UPS is (500$ / kVA)

The cost of UPS = (rated kVA) * 500 + 5% (running and maintenance)

The cost of UPS = (60 * 500) * 1.05 = 31500 $.

And it is very low compared with its benefits; however, it is related to the safety of nuclear research reactor.

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CHAPTER (6) CONCLUSIONS AND RECOMENDATIONS

6.1- Conclusion and recommendations

This work presents the assessment of power quality problems on the behavior of the electrical system of nuclear installations. The analysis of the recorded data at the point of common coupling yields that, fifth harmonics, flickers, voltage sags/swells, under/over voltage, transients and temporary outage (500 ms) are the most severe events and should be taken in consideration for any evaluation. It is recommended that, mitigation techniques should be done to keep good performance of the electrical system and then avoid operation problems of the nuclear installations. The Passive Filters, Dynamic Voltage Restorer (DVR) and Uninterruptible Power Supply (UPS) are most economic and effective solutions to mitigate the power quality problems.

6-2- The most important points that have been reached

1Power quality of supply has a direct impact on the electrical equipments and various systems because the disturbances lead to damage of equipments and bad performance of the system.

2In any project – especially projects with high sensitivity equipments, power quality assessment should be done regularly to keep good performance.

3The thesis considers a guide of power quality assessment study by using data recorded, analysis according to standards specifications and developing solutions to improve the power quality.

4In the projects that contain high level sources of harmonics, it is not preferred adding capacitors to improve power factor, but the best solution is using filters to eliminate harmonics and also improve the power factor.

5Power quality assessment should be considered as one of the important steps in determining the site for sensitive projects to avoid the bad impact of power disturbances.

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6.3-Future work

Power quality assessment should be continued regularly at the sensitive projects. And it is strongly recommended that for future work on this topic, the time allocated for monitoring should be longer, it should be more than seven days, and this to ensure that, more detailed and complete data could be obtained. Thus, the analysis of the data would be more precise. It is also suggested that, more monitoring points to be allocated in the site, so that more data could be gathered on the distribution system. This would allow a more detailed analysis on the affected areas and other locations on the same distribution system. It is strongly recommended that, for important and sensitive projects, the assessment of power quality should be done as part of the site selection procedure. It is strongly recommended that, for future work, solutions of power quality problems can done by load reconfiguration. And also for future works, power quality aspects of smart grids should be involved.

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Monitor”, IEEE , international conference on electrical engineering, Coimbra, Portugal, 2005.

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[37] A. K. AlOthman and ElNagger K.M, "Voltage Flicker Measurement Using Particle Swarm Optimization Technique for Power Quality Assessment", IEEE MELECON, 2006.

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[48] K.M.nor and Hasamaini M. , “Digital Simulation of Uninterruptible power supply (UPS) and Dynamic Voltage Restorer (DVR) for Voltage Sag Mitigation”, AUPEC 2001, Australia, 2001.

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APPENDIX (A)

POWER QUALITY STANDARDS

Power quality standards set voltage and current limits that sensitive electronic equipment can tolerate from electrical disturbances. Utilities need standards that set limits on the amount of voltage distortion their power systems can tolerate from disturbances produced by their customers with nonlinear loads. End users need standards that set limits not only for electrical disturbances produced by utilities but also for disturbances generated by other end users. Several national and international organizations have developed power quality standards. There is a confusing number of different organizations that set power quality standards. The following tables show some international standards.

Table (A1) IEEE11591995 standards.

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Table (A2) Voltage distorsion limites

Note – High voltage systems can have up to 2.0 % THD where the cause is an HVDC terminal that will attenuate by the time it is tapped for user.

Table (A3) Current distortion limits for general distribution systems (120 V through 69000 V)

All power generation equipment is limited to these values of current distortion, regardless of actual ISC /I L.

Note: Even harmonics are limited to 25 % of the odd harmonic limits above. Current distortions that result in a direct current offset, e.g., halfwave converters are not allowed.

Where ISC is the maximum shortcircuit current at PCC, IL is the maximum demand load current (fundamental frequency component) at PCC .

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It is recommended that the load current IL be calculated as the average current flow during the maximum demand for the preceding twelve months.

Table (A4) Power system disturbance classification to EN 50160

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APPENDIX (B)

TREND GRAPHS

This appendex illustrates the the trend graphs of the analysis. The monitoring was carried out in the case study at two ponits as the following:

Incoming feeder 1 (source1) for a period of one week. Incoming feeder 2 (source 2) for a period of one week. The trend graphs show the analysis of voltage variations, current variations, power factor variations, power variations , voltage total harmonics distortion, current total harmonics distortions, short time flicker and long time flicker.

All the daily trend graphs of the monitoring are illustrated as the following: Part (B1) shows the Trend graphs of incoming feeder1 (source1) Part (B2) shows the trend graphs of incoming feeder 2 (source 2)

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B.1- The Trend graphs of incoming feeder1 (source1)

B.1.1- The Trend graph of 1st day

Figure (b1) voltage variations of source 1 at 1st day

Figure (b2) current variations of source 1 at 1st day

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Figure (b3) power factor variations of source 1 at 1st day

Figure (b4) power variations of source 1 at 1st day

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Figure (b5) VTHD variations of source 1 at 1st day

Figure (b6) ITHD variations of source 1 at 1st day

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Figure (b7) short time voltage flicker of source 1 at 1st day

Figure (b8) long time voltage flicker of source 1 at 1st day

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B.1.2- The trend graphs of 2nd day

Figure (b9) voltage variations of source 1 at 2nd day

Figure (b10) current variations of source 1 at 2nd day

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Figure (b11) power factor variations of source 1 at 2nd day

Figure (b12) power variations of source 1 at 2nd day

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Figure (b13) VTHD variations of source 1 at 2nd day

Figure (b14) ITHD variations of source 1 at 2nd day

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Figure (b15) short time voltage flicker of source 1 at 2nd day

Figure (b16) long time voltage flicker of source 1 at 2nd day

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B.1.3- The trend graphs of 3rd day

Figure (b17) voltage variations of source 1 at 3rd day

Figure (b18) current variations of source 1 at 3rd day

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Figure (b19) power factor variations of source 1 at 3rd day

Figure (b20) power variations of source 1 at 3rd day

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Figure (b21) VTHD variations of source 1 at 3rd day

Figure (b22) ITHD variations of source 1 at 3rd day

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Figure (b23) short time voltage flicker of source 1 at 3rd day

Figure (b24) long time voltage flicker of source 1 at 3rd day

١١٠

B.1.4- The trend graphs of 4th day

Figure (b25) voltage variations of source 1 at 4th day

Figure (b26) current variations of source 1 at 4th day

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Figure (b27) power factor variations of source 1 at 4th day

Figure (b28) power variations of source 1 at 4th day

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Figure (b29) VTHD variations of source 1 at 4th day

Figure (b30) ITHD variations of source 1 at 4th day

١١٣

Figure (b31) short time voltage flicker of source 1 at 4th day

Figure (b32) long time voltage flicker of source 1 at 4th day

١١٤

B.1.5- The trend graphs of 5th day

Figure (b33) voltage variations of source 1 at 5th day

Figure (b34) current variations of source 1 at 5th day

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Figure (b35) power factor variations of source 1 at 5th day

Figure (b36) power variations of source 1 at 5th day

١١٦

Figure (b37) VTHD variations of source 1 at 5th day

Figure (b38) ITHD variations of source 1 at 5th day

١١٧

Figure (b39) short time voltage flicker of source 1 at 5th day

Figure (b40) long time voltage flicker of source 1 at 5th day

١١٨

B.1.6- The trend graphs of 6th day

Figure (b41) voltage variations of source 1 at 6th day

Figure (b42) current variations of source 1 at 6th day

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Figure (b43) power factor variations of source 1 at 6th day

Figure (b44) power variations of source 1 at 6th day

١٢٠

Figure (b45) VTHD variations of source 1 at 6th day

Figure (b46) ITHD variations of source 1 at 6th day

١٢١

Figure (b47) short time voltage flicker of source 1 at 6th day

Figure (b48) long time voltage flicker of source 1 at 6th day

١٢٢

B.2- The trend graphs of incoming feeder 2 (Source 2)

B.2.1- The trend graphs of 1st day

Figure (b49) voltage variations of source 2 at 1st day

Figure (b50) current variations of source 2 at 1st day

١٢٣

Figure (b51) power factor variations of source 2 at 1st day

Figure (b52) power variations of source 2 at 1st day

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Figure (b53) VTHD variations of source 2 at 1st day

Figure (b54) ITHD variations of source 2 at 1st day

١٢٥

Figure (b55) short time voltage flicker of source 2 at 1st day

Figure (b56) long time voltage flicker of source 2 at 1st day

١٢٦

B.2.2- The trend graphs of 2nd day

Figure (b57) voltage variations of source 2 at 2nd day

Figure (b58) current variations of source 2 at 2nd day

١٢٧

Figure (b59) power factor variations of source 2 at 2nd day

Figure (b60) power variations of source 2 at 2nd day

١٢٨

Figure (b61) VTHD variations of source 2 at 2nd day

Figure (b62) ITHD variations of source 2 at 2nd day

١٢٩

Figure (b63) short time voltage flicker of source 2 at 2nd day

Figure (b64) long time voltage flicker of source 2 at 2nd day

١٣٠

B.2.3- The trend graphs of 3rd day

Figure (b65) voltage variations of source 2 at 3rd day

Figure (b66) current variations of source 2 at 3rd day

١٣١

Figure (b67) power factor variations of source 2 at 3rd day

Figure (b68) power variations of source 2 at 3rd day

١٣٢

Figure (b69) VTHD variations of source 2 at 3rd day

Figure (b70) ITHD variations of source 2 at 3rd day

١٣٣

Figure (b71) short time voltage flicker of source 2 at 3rd day

Figure (b72) long time voltage flicker of source 2 at 3rd day

١٣٤

B.2.4- The trend graphs of 4th day

Figure (b73) voltage variations of source 2 at 4th day

Figure (b74) current variations of source 2 at 4th day

١٣٥

Figure (b75) power factor variations of source 2 at 4th day

Figure (b76) power variations of source 2 at 4th day

١٣٦

Figure (b77) VTHD variations of source 2 at 4th day

Figure (b78) ITHD variations of source 2 at 4th day

١٣٧

B.2.5- The trend graphs of 5th day

Figure (b79) voltage variations of source 2 at 5th day

Figure (b80) current variations of source 2 at 5th day

١٣٨

Figure (b81) power factor variations of source 2 at 5th day

Figure (b82) power variations of source 2 at 5th day

١٣٩

Figure (b83) VTHD variations of source 2 at 5th day

Figure (b84) ITHD variations of source 2 at 5th day

١٤٠

Figure (b85) short time voltage flicker of source 2 at 5th day

Figure (b86) long time voltage flicker of source 2 at 5th day

١٤١

B.2.6 – The trend graphs of 6th day

Figure (b87) voltage variations of source 2 at 6th day

Figure (b88) current variations of source 2 at 6th day

١٤٢

Figure (b89) power factor variations of source 2 at 6th day

Figure (b90) power variations of source 2 at 6th day

١٤٣

Figure (b91) VTHD variations of source 2 at 6th day

Figure (b92) ITHD variations of source 2 at 6th day

١٤٤

دة ا ا

إاد

اى

ر إ آ ا ازه ل در ا ( دآراة ) ) ه اى وات ا

إاف

د.ا . زاه د.ا / د د . ل ام ه ازه ه ا ار وزارة اء وا

آ ا ازه اهة ر ا ٢٠١٢ دة ا ا

إاد

اى

ر إ آ ا ازه آء ت ال در اآراة ه اى وات ا

ا

.ا د / ا ارى ( ) ه ا –

.ا د / ااه اار ( ) آ ا– ازه

.ا د / ا را زاه ( ف ) آ ا– ازه

ا . د / اح د ( ف ) ه ا ار

آ ا ازه اهة ر ا ٢٠١٢ ا

ا ا أه ر ا ادة ى ا . و ا م ا أه ا ا أى ة ا ور ا ا از . و ا ال ت ا و ار و ا اام اآء ا و ا ا ا ت ا و اوور إ آ ال ا ا دى إ ا ا ووث آ اات واات ا ا . و أدى ذ إ ض ام ا اات دة ا ا و ء اداء ات وا ا ا دى إ ا اوت ا وا و. ول ه او واة ارات ا ا ا وه درا " دة ا ا " . و داد أه ه ارا رة ت او ا أ . و ض ا اآ ا ا دة ا ا وآ ض و و اآ ات ا ا . و و ا أ ااح و ال ا هة اآ دة ا ا . آ إن ا م د إردي إاء درا دة ا ا ح ات ا ا . آ ا اط ا وات ا ا ا إ.

و ا ا ل و : :

ا اول : : ا . .

ا ا : : ول و ام ع دة ا ا ا و اات ا وق وس اات واات ا ادة اات ول آ دة ا ا وآ إا ء درا دة ا ا وى أ درا ا دة ا ا . .

ا ا : : ول و م ة و وو ام ا ودر ا ا ا ر ظ اار . وى أ اآ ا ا م ا و ى و ز ارة ام أء إاء هة ارا إ ط اس ااد دة ا ا ه . .

ا اا : : ض و و ا ا ا ز ارة ر در ا ا دا وآ د ا ا ا ار ات ا ا و أه اآ واات ا اة ام ا . .

ا ا : : وول ااح و ال ا اآ واات ا واه هة ال وات ه وآ ا اات و وآ د اات ا ا ال ا وا و ل ر رة . .

ا ادس : : ى ا ت ا وات واه اط ا ا ا إ ل ا هة ارا إ ا اح ا ار ا اع . . ا اول : ى اات ا ا دة ا ا . . ا ا : ى ات ا وات ا ض و ا ل إاء هة ارا . .