Design and Testing of Three Earthing Systems for Micro-Grid Protection During the Islanding Mode

Smart Grid and Renewable Energy, 2010, 1, 132-142 doi:10.4236/sgre.2010.13018 Published Online November 2010 (http://www.SciRP.org/journal/sgre)

Design and Testing of Three Earthing Systems for Micro-Grid Protection during the Islanding Mode

Rashad M. Kamel, Aymen Chaouachi, Ken Nagasaka

Environmental Energy Engineering, Department of Electronics & Information Engineering, Tokyo University of Agriculture and Technology, Nakamachi, Koganei-shi, Tokyo, Japan. Email: [email protected], [email protected], [email protected]

Received October 26th, 2010; revised November 19th, 2010; accepted November 21st, 2010

ABSTRACT This paper presents and tests three earthing systems (TT, TN and IT) for Micro-Grid (MG) protection against various fault types when the MG transferred to the islanding mode. The main contribution of this work is including the models of all micro sources which interfaced to the MG by power electronic inverters. Inverters in turns are provided with current limiters and this also included with the inverter models to exactly simulate the real situation in the MG during fault times. Results proved that the most suitable earthing system for MG protection during the islanding mode is the TN earthing system. That system leads to a suitable amount of fault current sufficient to activate over current protection relays. With using TN earthing system, touch voltages at the faulted bus and all other consumer’s buses are less than the safety limited values during islanding mode. For the two others earthing systems (TT and IT), fault currents are small and nearly equal to the over load currents which make over current protection relay can not differentiate between fault currents and overload currents. All models of micro sources, earthing systems, inverters and control schemes are built using Matlab®/Simulink® environment.

Keywords: Micro Grid Protection, Earthing Systems, Fault Current, Touch Voltage, Micro Sources and Inverters

1. Introduction nologies, e.g. micro gas turbine, fuel cell, photovoltaic system and several kinds of wind turbines. The energy The earthing of an electricity supply network requires its storage system often is a flywheel system. The micro network plant and customer electrical equipment to be sources and flywheel are not suitable for supplying en- connected to the earth in order to promote safety and ergy to the grid directly [11]. They have to be interfaced reduce the possibilities of damage to equipment. Effec- with the grid through an inverter stage. The use of power tive earthing prevents long term over voltages and mini- electronic interfacing in the MG thus leads to a series of mizes risk of electric shock hazards. Earthing also pro- challenges in the design and operation of the MG. One of vides a predetermined path for earth leakage currents, the major challenges is protection design of the MG to which are used to disconnect the faulty plant or circuit by comply with the relevant national Distribution Codes and operating the protective devices. Micro-Grid (MG) is a to maintain the safety and stability of the MG during unique example of a distribution system and needs care- both grid-connected mode and islanded mode. ful assessment before deciding on its earthing system. However, the inverter based MG can not normally A MG consists of a cluster of micro sources, energy provide the required levels of short circuit current. In storage systems (e.g. flywheel, battery, ultra capacitor, …) extreme cases, the fault current contribution from the and loads, operating as a single controllable system. The micro sources may only be twice load current or less voltage level of the MG is 400 Volt or less. The archi- [12,13]. Some over current sensing devices will not even tecture of the MG is formed to be radial with a number of respond to this level of over current. In addition, the feeders. The MG often provides both electricity and heat over/under voltage and frequency protection may fail in to the local area. The MG can be operated in both grid- detecting faults on the MG due to the voltage and fre- connected mode and islanded mode as described in de- quency control of the MG. That unique nature of the MG tails on our previous research [1-10]. requires a fresh look into the design and operation of the The micro sources are usually made of many new tech- protection. This is the task of this manuscript.

This manuscript presents three earthing systems for that of property (fire, damage to electrical equipment) is MG protection during the islanding mode. The two main less so. The three sub-systems in TN earthing system are contributions of this manuscript are: 1) consider the models described below with their key characteristics. of all micro sources (and their inverters) installed in the 2.2.1. TN-C Earthing System MG and 2) Included current limiter with each inverter As shown in Figure 2(a), TN-C system has the following inside the MG to simulate exactly the real situation dur- features: ing fault time. 1) Neutral and protective functions are combined in a Three earthing systems are implemented and tested for single conductor throughout the system. (PEN—Protec- MG protection. Comparison between the performance of tive Earthed Neutral). the three systems is highlighted. The most suitable earthing 2) The supply source is directly connected to earth and system is deduced from the comparison. all exposed conductive parts of an installation are con- To conduct the proposed study, this manuscript is or- ganized as follow: Section 2 describes the three designed   3 earthing systems. Section 3 presents the fault behavior in 3 Ph HV LV each earthing system plus advantages and disadvantages N of each one. MG network included all micro sources, inverters and earthing system is presented in Sction 4. Sec- tion 5 shows the results obtained with applying the three earthing systems and the sequence of the events occur with each one. Conclusions are indicated in Sction 6. Figure 1. TT earthing system configuration. (Ph is the phase 2. Types of Earthing Systems wire, N is the neutral wire). A low voltage (LV) distribution system may be identified  according to its earthing system. These are defined using  the five letters T (direct connection to earth), N (neutral), C (combined), S (separate) and I (isolated from earth). The first letter denotes how the transformer neutral (supply source) is earthed while the second letter denotes how the metalwork of an installation (frame) is earthed. The third and fourth letters indicate the functions of neutral (a) and protective conductors respectively. There are three   possible configurations [14]: 1) TT: transformer neutral earthed and frame earthed. 2) TN: transformer neutral earthed, frame connected to neutral. 3) IT: unearthed transformer neutral, earthed frame. The TN system includes three sub-systems: TN-C, TN (b) -S and TN-C-S, as discussed in the following sub-sections.   2.1. TT Earthing System In this system, the supply source has a direct connection to earth. All exposed conductive parts of an installation also are connected to an earth electrode that is electri- cally independent of the source earth. The structure of (c) TT system is shown in Figure 1 [15]. Figure 2. (a) TN-C earthing system configuration. (Ph is 2.2. TN Earthing System phase symbol; PEN is the protective earthed and neutral wire); (b) TN-S earthing system configuration. (Ph is phase In TN earthing system, the supply source (transformer symbol, N is the neutral wire and PE is the protective neutral) is directly connected to the earth and all exposed earthed wire); (c) TN-C-S earthing system. (Ph is phase conductive parts of an installation are connected to the symbol, N is the neutral wire and PE is the protective neutral conductor. Safety of personnel is guaranteed, but earthed wire).

nected to the PEN conductor. present, the fault current Id is only limited by the impedance of the fault loop cables. Short circuit protection de- 2.2.2. TN-S Earthing System vices (circuit breaker or fuses) generally provide protec- The TN-S earthing system architecture is shown in Fig- tion against insulation faults, with automatic tripping ure 2(b) and has the following features: according to a specified maximum breaking time (de- 1) The TN-S earthing system has separate neutral and pending on phase-to-neutral voltage U ). Typical break- protective conductors throughout the system. o ing times in the TN earthing system are tabulated in Ta- 2) The supply source is directly connected to earth. All ble 1 according to IEC 60364 (U is the limited safety exposed conductive parts of an installation are connected L voltage). to a protective conductor (PE) via the main earthing terminal of the installation. 3.1.1. Advantages of the TN Earthing System 1) The TN earthing system always provides a return path 2.2.3. TN-C-S Earthing System for faults in the LV grid. The grounding conductors at the TN-C-S earthing system configuration is shown in Fig- transformer and at all customers are interconnected. This ure 2(c) and has the following features: ensures a distributed grounding and reduces the risk of a 1) Neutral and protective functions are combined in a single conductor in a part of the TN-C-S system. The sup-   ply is TN-C and the arrangement in the installation is TN S. 2) Use of a TN-S downstream from a TN-C. 3) All exposed conductive parts of an installation are connected to the PEN conductor via the main earthing terminal and the neutral terminal, these terminals being linked together.

2.3. IT Earthing System Figure 3. IT earthing system. In this system, the supply source is either connected to   I earth through deliberately introduced high earthing im- d pedance (Impedance earthed IT system) or is isolated from earth as shown in Figure 3. All exposed conductive parts of an installation are connected to an earth electrode. Every exposed-conductive part shall be earthed to sat- isfy the following condition for each circuit [16]:

Rd RIbd50 V (1) Where: U d Rb: Resistance of the earth electrode for exposed conductive-parts. Id: Fault current which takes account of leakage currents and the total earthing impedance of the electrical Figure 4. A fault behavior in the TN-S earthing system. (Id installation. is the fault current; Rd is the conducting parts resistance, Ud is the touch voltage). 3. Fault Behavior and Characteristics of Different Earthing Systems Table 1. Braking time in TN system (taken from IEC 60364 tables 41 and 48 A). An insulation failure in an electrical installation presents hazards to humans and equipments. At the same time it Uo (Volts) Braking time Braking time Phase/neutral (seconds) (seconds) may cause unavailability of electrical power. The fault voltage UL = 50 Volt UL = 25 Volt currents and voltages differ from one earthing system to 127 0.8 0.35 another as described in the following sub sections. 230 0.4 0.2 3.1. Fault Behavior in the TN Earthing System 400 0.2 0.05 Figure 4 shows fault behavior in the TN earthing system and the path of fault current. When an insulation fault is >400 0.1 0.02

customer not having a safe grounding.   I d 2) Lower earthing resistance of the PEN conductor. A Ph A 3 HV LV Ph B 3) TN earthing system has the advantage that in case Ph C N of an insulation fault, the fault voltages (touch voltages) D are generally smaller than in TT earthing systems. This is PE due to the voltage drop in the phase conductor and the lower impedance of the PEN conductor compared with the consumer earthing electrodes in TT systems. C B R 4) No overvoltage stress on equipment insulation. R d a R 5) TN-S system has the best Electromagnetic Com- b patibility (EMC) properties for 50 Hz and high frequency U d currents, certainly when LV cables with a grounded sheath I d is applied. 6) TN earthing system could work with simple over current protection. Figure 5. The fault behavior in the TT earthing system. (Id 7) High reliability of disconnection of a fault by over is the fault current; Rd is the conducting parts resistance, Ud current devices (i.e. fault current is large enough to acti- is the touch voltage, Ra and Rb are the resistances of the vate the over current protection devices). earthing electrodes at main supply and consumers).

3.1.2. Disadvantages of the TN Earthing System 4) Simple earthing of the installation and the easiest to 1) Faults in the electrical network at a higher voltage implement. level may migrate into the LV grid grounding causing 5) No influence of extending the network. touch voltages at LV customers. 2) A fault in the LV network may cause touch voltages 3.2.2. Disadvantages of the TT Earthing System at other LV customers. 1) Each customer needs to install and maintain its own 3) Potential rise of exposed conductive parts with the ground electrode. Safety and protection depends on the neutral conductor in the event of a break of the neutral customer, thus complete reliability is not assured. network conductor as well as for LV network phase to 2) High over voltages may occur between all live parts neutral and phase to ground faults and MV to LV faults. and between live parts and PE conductor. 4) The utility is not only responsible for a proper 3) Possible overvoltage stress on equipment insulation grounding but also for the safety of customers during of the installation. disturbances in the power grid 3.3. Fault Behavior in the IT Earthing System 5) Protection to be fitted in case of network modifica- tion (increase of fault loop impedance). 3.3.1. First Fault in the IT Earthing System 6) TN-C system is less effective for Electromagnetic Figure 6 shows the occurrence of the first fault in the IT Compatibility (EMC) problems. earthing system. The fault voltage is low and not dangerous. Therefore it is not necessary to disconnect an 3.2. Fault Behavior in the TT Earthing System installation in the event of a single fault. However it is Figure 5 explains fault behavior in the TT earthing sys- essential to know that there is a fault and need to track tem. When an insulation fault occurs, the fault current Id and eliminate it promptly, before a second fault occurs. is mainly limited by the earth resistances (Ra and Rb). At To meet this need the fault information is provided by an least one residual current device (RCD) must be fitted at Insulation Monitoring Device (IMD) monitoring all live the supply end of the installation. In order to increase conductors, including the neutral [16]. When the neutral availability of electrical power, use of several RCDs en- is not distributed (three-phase three-wire distribution), the sures time and current discrimination on tripping [16]. following condition must be satisfied [16]:

3.2.1. Advantages of the TT Earthing System 0.866Uo ZS  (6.2) 1) The most commonly found earthing system. I f 2) Faults in the LV and MV grid do not migrate to other customers in the LV grid. Where: 3) Good security condition, as the potential rise of the ZS = Earth fault loop impedance comprising the phase grounded conductive part must be limited at 50 V for a conductor and the protective conductor. fault inside the installation and at 0 V for a fault on the If = fault current. network. Uo = the supply phase to neutral voltage.

1 When the neutral is distributed (three-phase four-wire ZS = Earth fault loop impedance comprising the neu- distribution and single phase distribution), the following tral conductor and the protective conductor. condition must be satisfied [16]: 3.3.2. Second Fault in the IT Earthing System 0.5U Figure 7 shows the occurrence of the second fault in the Z1  o (6.3) S IT earthing system. Maximum disconnection times for I f the IT earthing system are given in Table 2 (as in IEC Where: 60364 tables 41 B and 8 A) [16].

  I f Ph A 3 HV LV Ph B Ph C N

PE Insulation Surge Monitoring limiter I f device I f I f

B C C C f f C f C f

ICN ICC ICB U d

I f

Figure 6. First insulation fault current in the IT earthing system. (If is the fault current, Rd is the conducting part resistance, Cf is the charging capacitance, IC is the charging current).

0.8U 0   I d Ph A 3 HV LV Ph B Ph C N

PE Insulation Surge R Ph I Monitoring limiter d RPh I d device I d

RPE RPE

U d U d

Figure 7. Second insulation fault current in IT system (distributed neutral).

Table 2. Maximum disconnection time in the IT earthing system (second fault)

UL = 50 volt Braking time (sec.) UL = 25 volt Braking time (sec.) Uo/U (Volt) Neutral not distributed Neutral distributed Neutral not distributed Neutral distributed

127/220 0.8 5 0.4 1.0

230/400 0.4 0.8 0.2 0.5

400/690 0.2 0.4 0.06 0.2

580/1000 0.1 0.2 0.02 0.08

Uo phase to neutral voltage, U phase to phase voltage

Table 3 [17-21]. 3.3.2.1. Advantages of the IT Earthing System Complete Matlab®/Simulink® model which built for 1) The IT earthing system used when safety of persons testing the three earthing systems is shown at the end of and property, and continuity of service are essentials. this paper (Figure 17). 2) Fault current is zero or very small value. 3.3.2.2. Disadvantages of the IT Earthing System 5. Performance of the Three Earthing 1) Insulation Monitoring Device (IMD) is required for Systems in MG Protection during monitoring all live conductors to can discover the first the Islanding Mode fault occurrence. During this case, MG operates in the islanding mode. 2) High voltage stress on the equipments after the first Flywheel interfaced by the voltage source inverter (VSI) fault occurrence (phase voltage will multiply by 1.71 and at bus # 1 represents the slack (reference) bus for the MG. became equal to line voltage). The studied disturbance is a short circuit (single phase to 3) Overvoltage protection should be used to protect ground fault) occurs at the consumer feeds at bus # 2. sensitive voltage equipment against the high voltage Fault current, touch voltages at all consumers, voltage of stress after the first fault occurrence. healthy phases and voltage of the main transformer neu- 4. Architecture of the Studied Micro Grid tral point are shown in the following figures (Figure 9 to Figure 16) when the three earthing systems (TN-S, TT Figure 8 shows single line diagram of the studied MG. It and IT) are employed in the MG. consists of 7 buses. Flywheel (storage device) with rating From the results which are presented in the previous 30 kW/0.5 kWh is connected at bus 1. Fixed speed wind figures, the following points can be concluded: generation system (10 kW) is connected to bus 2. Two 1) Figure 9 shows the fault current. When TN-S earthing photovoltaic panels with rating 10 kW and 3 kW are con- system is used, the fault current (maximum value) in- nected to buses 4 and 5, respectively. Single Shaft Micro creases to about 400 A. On the other hand, with using TT Turbine (SSMT) with rating 25 kW is connected to bus 6. and IT earthing systems, the fault current not different Bus 7 is provided with Solid Oxide Fuel Cell (SOFC) more than the steady state value and the over current with rating 20 kW. All MG’s components (micro sources, protection devices can not differentiate between the fault inverters with different control schemes, loads, …) are modeled in details in our previous research [1-10]. current and the overload current inside the MG. This fact The developed model is general and can be used to make TN-S earthing system is more suitable than TT and investigate the behavior of the MG under all fault types. IT earthing system in MG protection. The fault presented in this study is single phase to ground 2) Figure 10 shows the touch voltage at the faulted fault, which is the most common fault in the consumer bus. As shown, with TN-S earthing system, touch voltage premises. In the simulation model, micro sources are (maximum value) about 30 Volt, while with using TT taken into account. It is assumed that all power electronic system, touch voltage (maximum value) reach to 300 inverters which used to interface micro sources are Volt (higher than the safety value) and it is dangerous for equipped with current limiters to limit the fault current to persons. This is another advantage makes TN-S earthing about 150% of the inverter’s full load current. This cur- system is the more suitable earthing system for MG. rent limiter is included in each inverter circuit to protect When IT earthing system is used, touch voltage at the inverter semiconductor switches from damages and rep- faulted bus not increase than zero. Also as shown in Fig- resent the real situation accurately. In Figure 8, the stud- ure 11 to Figure 14, touch voltages at all buses and con- ied MG is illustrated. Line parameters are tabulated in sumers with TN-S earthing system not increase than 15

Volt, which prove that TN-S is still suitable. When using voltages of the healthy phases has small drop than the TT and IT earthing systems, the touch voltages at all un- steady state value. When TN-S system is used, those faulted buses not increase than zero value which proves voltages dropped to a small value. that with using TT and IT earthing system, fault not 4) Figure 16 shows the voltage of the neutral point of transfer from the consumer to another consumer. the main transformer. As shown, with TN-S and TT 3) Figure 15 shows the voltage of unfaulted (healthy) earthing systems, the neutral point voltage increases to a phases (at bus #2). With using IT earthing system, volt- small value. On the other hand, with using IT earthing ages of the unfaulted phases increase to the line value system, the neutral point voltage equal to the phase volt- (220 V increase to 380 V) which causes high voltage age and this is the reasons of voltage rising of unfaulted stress on the equipments connected to the two healthy phases shown in Figure 15. phases. On the other hand, with using TT earthing system, 5) In conclusions, TN-S system represents the most



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1 3, I s  40 A

6  1 , I s  40 A

S max  47 kVA 80 S 0  25kVA

Figure 8. Single line diagram of the studied MG.

10 400 TN-S TN-S TT 8 300 TT TN-S 6 TN-S IT 200 IT 4 100 2 0 0 -100 -2 Fault current (A) -200 -4 -300 TT, IT -6 TT, IT -400 Touchvoltage at load of bus # 5 (Volt) -8 -500

-10 2.96 2.98 3 3.02 3.04 3.06 3.08 3.1 3.12 3.14 2.95 3 3.05 3.1 Time (sec.) Time (sec.)

Figure 9. Fault current with the three earthing systems during islanding mode. Figure 12. Touch voltage at consumer of bus # 5.

300 TN-S TT 10 TT TN-S 200 IT

5 IT 100

0 0

-100 -5 TN-S

Touch voltage atfault position(Volt) -200 TT

Touch volatge at load of bus 6 (volt)# TT , IT TN-S IT -10 -300

2.98 3 3.02 3.04 3.06 3.08 3.1 2.96 2.98 3 3.02 3.04 3.06 3.08 Time (sec.) Time (sec.)

Figure 10. Touch voltage at consumer of bus # 2 (faulted bus). Figure 13. Touch voltage at consumer of bus # 6.

10 15 TT TN-S TN-S 8 TN-S TT IT TN-S 6 10 IT 4 5 2

0 0 -2

-4 -5

-6

Touch voltage at loadof bus (Volt) #4 TT, IT Toutch voltage at load of bus # 7(Volt) -10 -8 TT, IT

-10

2.95 3 3.05 3.1 2.95 3 3.05 3.1 Time (sec.) Time (sec.)

Figure 11. Touch voltage at consumer of bus # 4. Figure 14. Touch voltage at consumer of bus # 7.

Table 3. MG line parameters.

Line Type R (Ω/km) X (Ω/km) Rn (Ω/km)

Overhead-Twisted cable 4 × 120 mm2 Al 0.284 0.083 0.284

Overhead-Twisted cable 3 × 70 mm2 Al + 54.6 mm2 AAAC 0.497 0.100 0.63

Overhead-Conductor 4 × 50 mm2 Al 0.397 0.279

Overhead-Conductor 4 × 35 mm2 Al 0.574 0.294

Overhead-Conductor 4 × 16 mm2 Al 1.218 0.318

Underground-XLPE cable 3 × 150 mm2 Al + 50 mm2 Cu 0.264 0.071 0.387

Connection-Cable 4 × 6 mm2 Cu 3.41 0.094

Connection-Cable 4 × 16 mm2 Cu 1.38 0.085

Connection-Cable 4 × 25 mm2 Cu 0.87 0.083

Connection-Cable 3 × 50 mm2 + 35mm2 Cu 0.462 0.077 0.526

Connection-Cable 3 × 95 mm2 + 35 mm2 Cu 0.41 0.071 0.524

500 TT IT 300 IT TN-S TT 400 IT TN-S TT 200 IT 300 TT 200 100 TN-S 100 TN-S

0 0

-100 -100 -200 Voltage of unfaulted phase (Volt) -300 -200

-400 Voltage of main transformer neutral point (Volt) -300 -500 2.95 3 3.05 3.1 2.96 2.98 3 3.02 3.04 3.06 3.08 3.1 Time (sec.) Time (sec.)

Figure 15. Voltage of healthy phases (at bus # 2). Figure 16. Main transformer neutral point’s voltage. suitable earthing system for MG during the islanding for the other two earthing systems (TT and IT), protec- mode. With that system, simple over current protection tion relay can not differentiate between the fault current devices are suitable to clear the fault in MG. However, and overload current. Also, touch voltages at all con- with the other two earthing systems (TT and IT), over sumers with using TN system are small and less than the current protection devices can not differentiae between safety limit value. While, with TT earthing system, touch the fault current and overload current inside the MG. voltage at the faulted bus is very high and higher than the 6. Conclusions safety limit value. With using IT earthing system, voltages of the healthy phases will nearly doubled (220 V In this paper, three earthing systems are applied to pro- became 380 V) and causes voltage stress for all equip- tect the MG against different faults during the islanding ments which are feed from the healthy phases. In conclu- mode. It is observed from the results that the most suit- sions, the TN earthing system is the most superior system able system is the TN earthing system. This is because for MG protection from the point of view of fault current fault current with TN earthing system is sufficient and touch voltages. From this paper results, TN earthing enough to activate the protection relay. On the other hand, system is the most recommended system for MG protect-

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Goto6

CVS2 1 To f1 + s 3 filter 0.0001s+1 Product2 3 [M] -K- Goto4 v4 To v 4 CVS1 Product1 1 Sine2 filter 6 filter sin(2*pi*u) 0.0001s+1 1 f0 -K- Sine1 f1 sin(2*pi*u) 2 Product -K- Saturation4 Sine [M] Saturation1 From6 sin(2*pi*u) [wt1] Goto7 1 1 filter 1 filter 0.2s+1 filter 2 0.2s+1 [w t] 1/3 Goto5 delta v 1 PQ Vabc Iabc 3phasePQ t 50 To t -C- 50 delta v 2 From2 [I_abc] From1 [e_abc] From5 delta_V] Clock [ Figure 17. Matlab®/Simulink® Developed model for MG with the erathing system.

tion during the islanding mode. Author’s next step re- ing and Electrical Engineering, Vol. 16, No. 6, 2009, pp. search is applying and testing the performance of those 137-144. three earthing systems in MG protection during the con- [9] R. M. Kamel, A. Chaouachi and K. Nagasaka, “Carbon nected mode. Emissions Reduction and Power Losses Saving besides Voltage Profiles Improvement Using Micro Grids,” Low REFERENCES Carbon Economy (Journal), Vol. 1, No. 1, 2010, pp. 1-7. [10] R. M. Kamel, A. Chaouachi and K. Nagasaka, “Effect of [1] R. M. Kamel and B. Kermanshahi, “Design and Imple- Wind Generation System Rating on Transient Dynamic mentation of Models for Analyzing the Dynamic Per- Performance of the Micro-Grid during Islanding Mode,” formance of Distributed Generators in the Micro Grid Low Carbon Economy (Journal), Vol. 1, No. 1, 2010, pp. Part I: Micro Turbine and Solid Oxide Fuel Cell,” Scien- 29-38. tia Iranica, Transactions D, Computer Science & Engi- [11] S. Barsali, et al., “Control Techniques of Dispersed Gen- neering and Electrical Engineering, Vol. 17, No. 1, June erators to Improve the Continuity of Electricity Supply,” 2010, pp. 47-58. Power Engineering Society Winter Meeting, Vol. 2, 27-37 [2] R. M. Kamel, A. Chaouachi and K. Nagasaka, “Micro- January 2002, pp. 789-794. Grid Dynamic Response Enhancement Using New Pro- [12] S. R. Wall, “Performance of Inverter Interfaced Distrib- portional Integral Wind Turbine Pitch Controller and uted Generation,” Transmission and Distribution Con- Neuro-fuzzy Photovoltaic Maximum Power Point Track- ference and Exposition, Vol. 2, 28 October-2 November ing Controller,” Electric Power Components and Systems, 2001, pp. 945-950. Vol. 38, No. 2, 2010, pp. 212-239. [3] R. M. Kamel, A. Chaouachi and K. Nagasaka, “Wind [13] N. Jayawarna, et al., “Task TE2—Fault Current Contri- Power Smoothing Using Fuzzy Logic Pitch Controller bution from Converters,” Micro Grids Draft Report for and Energy Capacitor System for Improvement Micro- Task TE2. Grid Performance in Islanding Mode,” Energy, Vol. 35, [14] C. Prévé, “Protection of Electrical Networks,” by ISTE No. 4, March 2010, pp. 2119-2129. Ltd, book, 2006 [4] R. M. Kamel, A. Chaouachi and K. Nagasaka, “Micro [15] B. Lacroix and R. Calvas, “Earthing Systems in LV,” Grid Transient Dynamic Response Enhancement during Schneider Electric’s Cahier’s Technique, Vol. 172, March and Subsequent to Huge and Multiple Disturbances by 2002, pp. 1-30. Connecting It with Nearby Micro Grids,” International [16] N. Jayawarna, M. Lorentzou and S. Papathanassiou, “Re- Journal of Sustainable Energy, Vol. 30, No. 4, August view of Earthing in a Micro Grid,” MICROGRIDS Large 2010, pp. 223-245. Scale Integration of Micro-Generation to Low Voltage [5] R. M. Kamel, A. Chaouachi and K. Nagasaka, “Effect of Grids Project, WORK PACKAGE E, April 2004. Micro Sources Failure on Dynamic Performance of the [17] S. Papathanassiou, N. Hatziargyriou and K. Strunz, “A Micro-Grid during and Subsequent to Islanding Process,” Benchmark Low Voltage Microgrid Network,” Proceed- ISESCO Science and Technology Vision, Vol. 6, No. 9, ings of CIGRE Symposium Power Systems with Dis- May 2010, pp. 2-10. persed Generation,” Athens, April 2005, pp. 1-8. [6] R. M. Kamel, A. Chaouachi and K. Nagasaka, “Im- [18] W. Xueguang, N. Jayawarna, Y. Zhang, N. Jenkins, J. P. provement of Transient Dynamic Response of Micro- Lopes, C. Moreira, A. Madureira and J. P. da Silva, “Pro- Grid Subsequent Islanding and Failure of Micro Sources tection Guidelines for a Micro-Grid,” Deliverable DE2 by Connected Two Nearby Micro-Grids,” ISESCO Sci- for EU MicroGrids Project, June 2005. ence and Technology Vision, Vol. 5, No. 8, 2009, pp. 46-55 [19] “IEEE Guide for Safety in AC Substation Grounding,” IEEE Standard 80-2000 (Revision of IEEE Standard 80- [7] R. M. Kamel, A. Chaouachi and K. Nagasaka, “A Novel 1986), 2000. Pi Pitch Controller and Energy Capacitor System for Re- ducing Wind Power Fluctuations and Keeping Micro- [20] “Urban Area Substation Analysis,” Safe Engineering Ser- Grid Stable Subsequent Islanding Occurrence,” Interna- vices & Technologies Ltd., Version 8, Montreal, Canada, tional Journal of Power & Energy Systems, Vol. 30, No. January 2000. 2, April 2010, pp. 131-138. [21] C. Marnay, F. J. Robjo and A. S. Siddiqui, “Shape of the [8] R. M. Kamel and B. Kermanshahi, “Optimal Size and Micro Grid,” IEEE PES Winter meeting, Columbus, January Location of Distributed Generations for Minimizing Power 2001, pp. 150-153. Losses in a Primary Distribution Network,” Scientia Iranica, Transactions D, Computer Science & Engineer-