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White Paper Harmonics 2014 Six tough topics about harmonic distortion and Power Quality indices in electric power systems A white paper of the Schaffner Group Written by Alexander Kamenka All rights reserved. Copyright © 2014 by the Schaffner Group. No part of this publication may be changed in any form or by any means for any purpose without written permission from the Schaffner Group. This document may contain errors or inaccuracies, and it may be revised without advance notice. The Schaffner Group welcomes any recommendations or criticism regarding this paper. Customer feedback is always welcome as it helps us to continuously improve upon the quality of our products. If you have any comments or advice, please feel free to contact the Schaffner Group. Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. Distribution of the work or derivative of the work in any standard (paper) book form for commercial purposes are prohibited unless prior permission is obtained from the copyright holder. Copyright: Alexander Kamenka, The Schaffner Group Schaffner Group Nordstrasse 11 4542 Luterbach / Switzerland Phone +41 (0)32 681 66 26 • Fax +41 (0)32 681 66 41 Corporate website: http://www.schaffner.com Corporate email: [email protected] Six tough topics about harmonic distortion and power quality indices in electric power systems A white paper of the Schaffner Group Written by Alexander Kamenka Six tough topics about harmonic distortion and power quality indices in electric power systems 3 Contents Basics of the harmonic theory 7 Introduction 8 Basics 9 Composition and Decomposition of distorted waveforms 11 Classification of harmonics 13 Harmonic currents, voltage and impedance 15 Power quality indices under harmonic distortion 16 Power factor and reactive power 18 Linear and non-linear loads 20 Sources of harmonic distortion 22 Introduction 23 Harmonic Sources with Magnetic Iron Core 24 Transformers 24 Generators and Motors 25 Arc furnaces and Arc Welders 26 Power electronic and electronic equipment 27 Switched mode power supplies (SMPS) 27 Variable Frequency Drives 27 Commercial and residential facilities 29 Effects of harmonics 30 Introduction 31 Power Factor 31 Phase and Neutral conductors 32 Transformer 32 Motors and Generators 32 Electric and electronic equipment 33 PFC 33 Circuit breakers 33 Norms and Standards for harmonics 35 Overview 36 Standards governing equipment 37 Standard IEC 61000-3-2 for low-voltage equipment with rated current under or equal to 16 A 37 Standard IEC 61000-3-12 for low-voltage equipment with rated current higher than 16 A and lower than 75 A 39 Standards governing the quality of distribution networks 43 Standard EN 50160 43 Standard IEEE 519 44 All rights reserved. Copyright © 2014 by the Schaffner Group. 4 Six tough topics about harmonic distortion and power quality indices in electric power systems Standard G5/4 46 Standard D.A.CH.CZ 47 Standards governing compatibility between distribution networks and products 50 Standard IEC 61000-2-2 for public low-voltage power supply systems 50 Standard IEC 61000-2-4 for LV and MV industrial installations 50 Harmonic Filtering Techniques 52 Overview 53 Preventive solutions 54 AC line reactor 54 DC link choke 55 Multi-pulse converter systems 56 Corrective solutions 58 Passive harmonic filter 58 Active harmonic filter 60 Costs of Harmonics and Power Losses in Harmonic Distorted Networks 62 Introduction 63 Additional losses due to harmonic distortion 64 Premature aging of equipment 64 All rights reserved. Copyright © 2014 by the Schaffner Group. Six tough topics about harmonic distortion and power quality indices in electric power systems 5 Figures Figure 1 – Harmonic frequencies 10 Figure 2 – Distorted waveform 11 Figure 3 – Decomposition of a distorted waveform 11 Figure 4 – Spectrum of a distorted waveform 12 Figure 5 – Triplen harmonics on the neutral 14 Figure 6 – Power under harmonic conditions 19 Figure 7 – transformer magnetization curve 24 Figure 8 – harmonic current spectrum arc furnace 26 Figure 9 – waveform and harmonic spectrum of a SMPS 27 Figure 10 – waveform and harmonic spectrum of a B6-VSD 28 Figure 11 – D.A.CH.CZ. harmonic assessment scheme 49 Figure 12 – AC line reactor applied 54 Figure 13 – DC link choke applied 55 Figure 14 – 12-pulse setup 56 Figure 15 – 18-pulse setup 57 Figure 16 – Passive harmonic filter a.) not applied b.) applied 59 Figure 17 – performance curve passive harmonic filter 59 Figure 18 – function of an active harmonic filter 60 All rights reserved. Copyright © 2014 by the Schaffner Group. 6 Six tough topics about harmonic distortion and power quality indices in electric power systems Tables Table 1 - harmonic frequencies 9 Table 2 - harmonic orders 13 Table 3 - symmetrical components 13 Table 4 - Linear loads 20 Table 5 - Non-linear loads 21 Table 6 – pulses and harmonic spectra 28 Table 7 – 61000-3-2 Limits for class A equipment 38 Table 8 – 61000-3-2 Limits for class C equipment 38 Table 9 – 61000-3-2 Limits for class D equipment 39 Table 10 – 61000-3-12 Current emission limits for equipment other than balanced three-phase equipment 40 Table 11 – 61000-3-12 Current emission limits for balanced three-phase equipment 41 Table 12 – 61000-3-12 Current emission limits for balanced three-phase equipment under specified conditions (a,b,c) 41 Table 13 – 61000-3-12 Current emission limits for balanced three-phase equipment under specified conditions (d,e,f) 42 Table 14 – Values of individual harmonic voltages at the supply terminals given in percent of the fundamental voltage 44 Table 15 – Basis for harmonic current limits 45 Table 16 –current distortion limits for general distribution systems (120V through 69000V) 45 Table 17 –voltage distortion limits 46 Table 18 – Summary of THD planning levels 46 Table 19 – Planning levels for harmonic voltages in 400V systems 47 Table 20 – max permissible harmonic current emissions in amperes RMS for aggregate loads and equipment rated >16A per phase 47 Table 21 – AC Line reactors – Harmonic number / Input impedance vs. remaining harmonics [%] 55 Table 22-harmonics vs. pulse-numbers 56 All rights reserved. Copyright © 2014 by the Schaffner Group. Six tough topics about harmonic distortion and power quality indices in electric power systems 7 CHAPTER 1 Basics of the harmonic theory All rights reserved. Copyright © 2014 by the Schaffner Group. 8 Six tough topics about harmonic distortion and power quality indices in electric power systems Introduction The electricity supply would, ideally, show a perfect sinusoidal voltage at every point of the power network. In reality it is almost impossible to accomplish such desirable conditions. Voltage and current waveforms deviate massively from a sinusoidal. These waveform deviations are described by the use of waveform distortion and usually called harmonic distortion. Even if harmonic distortion is a quite old phenomenon it today presents one of the main concerns for public utilities, distribution system operators as well as their end customers. Already in the first years of operation of power distribution networks, there were first disturbances. In the beginning they came from mercury vapor rectifiers that were used in industrial environments. The major concern at this time was the effect that harmonic distortion had for the electric machines itself. Another well-known issue was interference in the telephone lines. But in general it can be said that harmonic distortion in former times did not have the same dangerous potential like it has today. Especially machines have been designed much more conservative and the distribution networks have not been on their limit loads. Starting a few years ago there is a clear and strong worldwide tendency towards energy efficiency realized by the increasing use of power electronics. This equipment along with power networks on the edge increases the voltage distortion and will continue rising. As this creates a lot of issues and problems the topics in this white paper are most important to know. All rights reserved. Copyright © 2014 by the Schaffner Group. Six tough topics about harmonic distortion and power quality indices in electric power systems 9 Basics The term "harmonics" originated in physical eigenvalue problems, meaning waves whose frequencies are integer multiples of one another. One example for such waves is the frequencies of the harmonics on stringed musical instruments. The notion of harmonics in the electrical meaning became known in the second half of the 20th century. Like surfers, most electrical devices are looking for the perfect wave. For alternating current, perfection is defined by a sinusoidal wave in which electrical voltage changes smoothly from positive polarity to negative and back again 50 (50Hz) or 60 (60Hz) times per second. Anyway to use the notion of wave though in connection with harmonics is not completely correct. A wave extends in time and space, whereas the oscillations observed here, do only expand in time. Thus a harmonic component in an AC power system is defined as a sinusoidal component of a periodic waveform that has a frequency equal to an integer multiple (the so called order of harmonic) of the fundamental frequency of the system: ..harmonic order, n..integer, fundamental frequency is either 50 or 60 Hz Harmonic order Freq. (Hz) in 50Hz networks Freq. (Hz) in 60Hz networks 1 50 60 3 150 180 5 250 300 7 350 420 11 550 660 13 650 780 n 50*n 60*n Table 1 - harmonic frequencies Figure 1 shows an ideal 50-Hz waveform with frequencies three (3rd harmonic), five (5th harmonic), seven (7th harmonic) and eleven (11th harmonic) times the fundamental frequency. 3rd harmonic (n=3) 5th harmonic (n=5) All rights reserved. Copyright © 2014 by the Schaffner Group. 10 Six tough topics about harmonic distortion and power quality indices in electric power systems 7th harmonic (n=7) 11th harmonic (n=11) Figure 1 – Harmonic frequencies All rights reserved.
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