EFFECT OF ADDING DISTRIBUTED GENERATION TO DISTRIBUTION NETWORKS - CASE STUDY 1: Voltage regulation in 25kV weak system with wind and hydro

EFFECT OF ADDING DISTRIBUTED GENERATION TO DISTRIBUTION NETWORKS - CASE STUDY 1: Voltage regulation in 25kV weak system with wind and hydro generation interconnected

EFFECT OF ADDING DISTRIBUTED GENERATION TO DISTRIBUTION NETWORKS - CASE STUDY 1: Voltage regulation in 25kV weak system with wind and hydro generation interconnected Second edition prepared by: Guillermo Hernandez-Gonzalez and Chad Abbey Natural Resources Canada CanmetENERGY Energy Technology and Programs Sector 1615 Boul. Lionel Boulet CP4800 Varennes (Québec) J3X 1S6 May, 2009 Report 2009-025 (RP-TEC) 411-MODSIM February 2009

CITATION Hernandez-Gonzalez, G. and Abbey, C., Effect of Adding Distributed Generation to Distribution Networks Case Study 1, Second edition, report # 2009-025 (RP-TEC) 411-MODSIM, CanmetENERGY, Varennes Research Centre, Natural Resources Canada, May, 2009, 34 pp. DISCLAMER This report is distributed for informational purposes and does not necessarily reflect the views of the Government of Canada nor constitute and endorsement of any commercial product or person. Neither Canada nor its ministers, officers, employees or agents makes any warranty in respect to this report or assumes any liability arising out of this report. ACKNOWLEDGMENT Financial support for this research project was provided by Natural Resources Canada through the Program on Energy Research and Development. The first edition of this report was prepared by C. Kwok and A.S. Morched in April 2006 [1]. Report 2009-025 (RP-TEC) 411-MODSIM i May 2009

TABLE OF CONTENT 1 Introduction... 1 2 Description of Assignment... 2 2.1 Distributed Generation Technologies... 2 2.2 Distribution System Description... 2 3 Overview of Solution... 5 3.1 Study Procedure... 5 4 Peak Load Conditions... 6 4.1 No Distributed Generator connected... 6 4.2 Addition of a Distributed Generator...7 4.2.1 Synchronous Generator... 8 4.2.2 Induction Generator at a Power Factor of 80%... 10 4.2.3 Induction Generator at Unity Power Factor... 13 4.3 Addition of a Voltage Regulator...15 4.3.1 In the Absence of the Distributed Generator... 15 4.3.2 In the Presence of the Distributed Generator... 16 4.4 Summary of Peak Load Cases... 18 5 Light Load Conditions... 19 5.1 No Distributed Generator Connected... 19 5.2 Addition of a Distributed Generator... 20 5.2.1 Synchronous Generator... 21 5.2.2 Induction Generator at a Power Factor of 80%... 23 5.2.3 Induction Generator at Unity Power Factor... 26 5.3 Addition of a Voltage Regulator...28 5.3.1 In the Presence of the Distributed Generator with Unity Power Factor... 28 5.4 Summary of Light Load Cases... 30 6 Conclusions... 31 7 Bibliography... 32 Report 2009-025 (RP-TEC) 411-MODSIM ii May 2009

LIST OF FIGURES Figure 1 - Reduced 25 kv Rural Distribution Network... 3 Figure 2 - Voltage Profile, Reference network at peak load... 6 Figure 3 - Power flow, Reference network at Peak Load... 7 Figure 4 - Voltage Profile, Synchronous Generator under Voltage Control Mode... 8 Figure 5 - Power Flow, Synchronous Generator under Voltage Control Mode... 9 Figure 6 - Split of MW Supply between the Source and the DG, Synchronous Generator under Voltage Control Mode... 9 Figure 7 - Split of MVAR Supply between the Source and the DG, Synchronous Generator under Voltage Control Mode... 10 Figure 8 - Voltage Profile, Induction Generator at 0.8 Power Factor... 11 Figure 9 - Power Flow, Induction Generator at 0.8 Power Factor... 11 Figure 10 - Split of MW Supply between the Source and the DG, Induction Generator at 0.8 Power Factor... 12 Figure 11 - Split of MVAR Supply between the Source and the DG, Induction Generator at 0.8 Power Factor... 12 Figure 12 - Voltage Profile, Induction Generator at Unity Power Factor... 13 Figure 13 - Power Flow, Induction Generator at Unity Power Factor... 14 Figure 14 - Split of MW Supply between the Source and the DG, Induction Generator at Unity Power Factor... 14 Figure 15 - Split of MVAR Supply between the Source and the DG, Induction Generator at Unity Power Factor... 15 Figure 16 - Voltage Profile, Using a Regulator, No Regulator and no Generator... 16 Figure 17 - Voltage Profile, Induction Generator at 0.8 Power Factor with Added Voltage Regulator in Zone 2... 17 Figure 18 - Voltage Profile, Various Generator Types and Regulator, Peak Loading... 18 Figure 19 - Voltage Profile, Reference network at light load... 19 Figure 20 - Power flow, Reference network at Light Load... 20 Figure 21 - Voltage Profile, Synchronous Generator under Voltage Control Mode... 21 Figure 22 - Power Flow, Synchronous Generator under Voltage Control Mode... 22 Figure 23 - Split of MW Supply between the Source and the DG, Synchronous Generator under Voltage Control Mode... 22 Figure 24 - Split of MVAR Supply between the Source and the DG, Synchronous Generator under Voltage Control Mode... 23 Figure 25 - Voltage Profile, Induction Generator at 0.8 Power Factor... 24 Figure 26 - Power Flow, Induction Generator at 0.8 Power Factor... 24 Figure 27 - Split of MW Supply between the Source and the DG, Induction Generator at 0.8 Power Factor... 25 Figure 28 - Split of MVAR Supply between the Source and the DG, Induction Generator at 0.8 Power Factor... 25 Figure 29 - Voltage Profile, Induction Generator at Unity Power Factor... 26 Figure 30 - Power Flow, Induction Generator at Unity Power Factor... 27 Figure 31 - Split of MW Supply between the Source and the DG, Induction Generator at Unity Power Factor... 27 Figure 32 - Split of MVAR Supply between the Source and the DG, Induction Generator at Unity Power Factor... 28 Figure 33 - Voltage Profile, Induction Generator at 1.0 Power Factor with Added Voltage Regulator in Zone 2... 29 Figure 34 - Voltage Profile, Various Generator types and Regulator, light loading... 30 Report 2009-025 (RP-TEC) 411-MODSIM iii May 2009

LIST OF TABLES Table 1 - System Loads... 4 Report 2009-025 (RP-TEC) 411-MODSIM iv May 2009

SUMMARY This report details the first of a series of case studies which have the intent of disseminating knowledge about the impact of distributed generation on distribution planning and operation. This case study 1 is based on a voltage regulation impact study on a 25kV weak system with both wind and hydro generation interconnected. The second edition for this series of case studies is meant to update the information in the first edition and facilitate the study of the integration of DG. This case study is meant to be accompanied by the corresponding CYMDIST case study files; however, it also serves as a self-contained and informative report. SOMMAIRE Ce document est le premier d une série d études de cas qui ont comme but de diffuser la connaissance sur le sujet de l impact de l intégration de la production distribuée sur l opération et la planification des réseaux électriques. Cette étude de cas 1 est basée sur un problème de régulation de tension sur un système faible de 25kV avec production éolienne et hydro. Cette deuxième édition vise à mettre à jour les études de cas de la première édition, toujours avec l intention de faciliter l étude de la production décentralisée et son intégration. Ce document décrit l étude de cas, incluant les étapes suivies et les résultats. Il a été conçu pour accompagner les fichiers de simulation de CYMDIST mais peut aussi servir de référence utile et informative. Report 2009-025 (RP-TEC) 411-MODSIM v May 2009

1 Introduction The installation of distributed generation (DG) is becoming more common for utilities. In many cases, these sources support the distribution network and enhance its operation. While there are several positive aspects associated with the use of distributed generation, there are several pitfalls to their application in existing distribution systems. Therefore, if the addition of these sources is not well planned and studied, it could lead to deterioration of network reliability through voltage regulation, protection coordination and security problems. The interaction between distributed generation and the distribution system in which it is embedded involves several phenomena that are worth careful investigation. Hence it is necessary to conduct thorough analyses and careful studies of the impact of different DG technologies and their implementation in the distribution system. The impact of distributed generation on the distribution system voltage profile is one of the major problems that needs to be scrutinized carefully in order to select the proper distributed generation technologies and their mode of operation. As will be seen hereafter, and as may be intuitively obvious, the use of distributed generation capable of contributing to voltage regulation is less likely to result in voltage profile problems. On the other hand, the use of distributed generation at constant power factor can result in under voltage or over voltage problems for peak load and low load conditions, respectively. The use of voltage regulators, or the addition of capacitor banks to the distribution system, can help in alleviating voltage limit violation problems. Report 2009-025 (RP-TEC) 411-MODSIM 1 May 2009

2 Description of Assignment The objective of this assignment is to investigate the impact of implementing different distributed generation (DG) technologies on the voltage profile of the network in which they are embedded. For the purpose of this tutorial, the user should investigate the impact of DG on the voltage profile of the system for two extreme loading conditions of the network. These extreme conditions are the peak load and light load conditions (30% of the peak load). 2.1 Distributed Generation Technologies Two types of distributed generators are considered in this exercise: 1. Synchronous generators capable of controlling their terminal voltage, thus capable of delivering or absorbing reactive power as required. 2. Asynchronous generators (Induction Machines). Induction machines require an external source of reactive power to supply their field. The reactive power required for the excitation of the induction machine can be supplied either by the network or by external sources such as capacitor banks. Both modes of operation and their impact on the voltage profile of the system are analyzed in this tutorial. In the first scenario, the induction machine operates at a power factor which varies with loading, and is typically in the order of 0.8 at the nominal rating of the machine. In the second mode of operation, the addition of an external source of reactive power, such as a switched capacitor bank, could permit the operation of the induction machine at a predetermined power factor. In many cases, a power factor of 1, or close to 1, is selected. 2.2 Distribution System Description The distribution system selected for this tutorial is a 25 kv (nominal) multi-grounded distribution circuit with several (single-phase) laterals feeding multiple loads, which operates at 25.83 kv. The circuit had to be reduced to a representative equivalent circuit maintaining the main generation and load feeding points, for better observation of the impact of DG sources on the circuit. The equivalent circuit is shown in Figure 1. The equivalent circuit is divided into 3 zones to facilitate the portrayal of the results. Zone 1 includes 2 loads, and covers the sections from 0ft to 54790 ft (16700m) from the main source. Zone 2 includes 2 loads, and covers the section from 54790 ft to 104658 ft (31900m) away from the main source. Zone 3 includes 2 loads as well, and covers the sections from 104658 ft to Report 2009-025 (RP-TEC) 411-MODSIM 2 May 2009

189961 ft (57900m) away from the main source. The results of this tutorial are reported with respect to these Zones, as depicted in Figure 1. Figure 1 - Reduced 25 kv Rural Distribution Network The power capacity of the circuit of Figure 1 is limited to 6 MVA, which is the capacity of its feeding source transformer. The feeding source transformer has been omitted from the equivalent circuit for simplicity purposes. The loads are fed through overhead lines constructed of 3/0 all aluminum conductors. The total load in the circuit is concentrated at the locations L1 L6 of Figure 1. The total demand of the equivalent concentrated loads, in MVA, and their corresponding power factor, are given in Table 1. Report 2009-025 (RP-TEC) 411-MODSIM 3 May 2009

Table 1 - System Loads LOAD (in MVA) Peak (100%) Normal Light (30%) (60%) Zone 1 2.09 1.26 0.63 L1 0.50 (PF = 95) 0.30 0.15 L2 1.59 (PF = 94.6) 0.95 0.48 Zone 2 1.29 0.77 0.39 L3 0.58 (PF = 96.8) 0.34 0.17 L4 0.71 (PF = 96.6) 0.43 0.21 Zone 3 0.88 0.53 0.26 L5 0.32 (PF = 98.3) 0.19 0.09 L6 0.56 (PF = 97.5) 0.34 0.17 Total 4.27 2.56 1.28 Report 2009-025 (RP-TEC) 411-MODSIM 4 May 2009

3 Overview of Solution The simulations of the different case-studies of this tutorial are conducted in a pre-released version 5.0 of CYMDIST software. The voltage profile of the system and the load flow results for each case study are obtained from an unbalanced Voltage Drop Analysis. Every case study has been saved as a self-contained study file, as specified in Annex A. 3.1 Study Procedure The procedure followed in this study involved: 1. Selection of a representative distribution network with distributed generation already embedded. 2. Reduction of the detailed system to a manageable size, maintaining pre-specified load and generation points of interest, for speedy analysis and easy interpretation of results. 3. Conduction of a load flow simulation of the network for peak load conditions without the embedded generation in the circuit, and monitoring of the resulting voltage profile. 4. Conduction of load flow simulation of the network for peak load conditions including different types of embedded generation in the circuit under different operating modes, and monitoring of the resulting voltage profile in each case. 5. Investigation of potential solutions for cases where voltage violation conditions are observed. 6. Repetition of steps 3, 4 and 5 for low load conditions. Report 2009-025 (RP-TEC) 411-MODSIM 5 May 2009

4 Peak Load Conditions 4.1 No Distributed Generator Connected A base case-study for the system operation, at peak load and without the distributed generation included, is established as a reference for comparison with case-studies involving distributed generation. The resulting voltage profile of the base case-study is shown in Figure 2, whereas the load flow results are shown in Figure 3. Figure 2 shows that the system experiences a low voltage problem on phase B for Zone 3, i.e. for loads L5 and L6. Hence it would be prudent to examine different technologies available to solve this problem, such as the addition of distributed generation and/or the usage of a voltage regulator. Both alternatives are studied in the following sections. Figure 2 - Voltage Profile, Reference network at peak load Report 2009-025 (RP-TEC) 411-MODSIM 6 May 2009

Figure 3 - Power Flow, Reference Network at Peak Load 4.2 Addition of a Distributed Generator For this exercise, it is desired to examine the effect of installing a distributed generation source on the voltage profile of the system. The distributed generator is installed at Zone 2, as indicated in Figure 1. In this section, three types of distributed generators are considered: a) A synchronous generator with a capacity of 3.750 MVA. The synchronous generator supplies 3 MW of real power and operates under the voltage control mode. b) An induction generator capable of supplying 3 MW of real power. The induction generator consumes reactive power from the system to supply its own field at a power factor of 80%. c) An induction generator capable of supplying 3 MW of active power. The induction generator consumes the reactive power to maintain its field from an external source, such as a capacitor bank. Thus the induction generator operates at unity (1) power factor. Report 2009-025 (RP-TEC) 411-MODSIM 7 May 2009

4.2.1 Synchronous Generator Figure 4 shows the voltage profile of the system with the added synchronous generator controlling its terminal voltage to 1.03 pu. Figure 4 shows that the system does not experience any voltage problem. The voltage of all three phases falls within the voltage tolerance of ±5%. Hence, at peak load, the installation of a synchronous generator, operated under a voltage control mode, solves the initial low-voltage problem experienced by the network. Figure 5 shows the active and reactive power flow in the distribution feeder after the addition of the synchronous generator while operating in the voltage control mode, and holding its terminal voltage at 1.03 pu. Figures 6 and 7 show the split of the supplied active and reactive power to each load, between the system source and the added synchronous generator. Figure 4 - Voltage Profile, Synchronous Generator under Voltage Control Mode Report 2009-025 (RP-TEC) 411-MODSIM 8 May 2009

Figure 5 - Power Flow, Synchronous Generator under Voltage Control Mode Distribution of Supply of MW 3.5 MW 3.0 2.5 2.0 1.5 1.0 0.5 MW supplied by Main Source MW supplied by Generator 0.0-0.5-1.0-1.5-2.0 Main Source L1 L2 L3 Generator L4 L5 L6 59.1% 40.9% Loads and Sources Figure 6 - Split of MW Supply between the Source and the DG, Synchronous Generator under Voltage Control Mode Report 2009-025 (RP-TEC) 411-MODSIM 9 May 2009

D istribution of Supply of M Var 1.0 0.8 0.6 0.4 Mvar supplied by Main Source Mvar supplied by Generator MVar 0.2 13.8% 0.0-0.2 Main Source L1 L 2 L3 86.2 % Generator L4 L5 L6-0.4-0.6 Loads and Sources Figure 7 - Split of MVAR Supply between the Source and the DG, Synchronous Generator under Voltage Control Mode 4.2.2 Induction Generator at a Power Factor of 80% Figure 8 shows the voltage profile of the system with the added induction generator with a power factor of 80%. Figure 8 shows that the system experiences a low voltage violation in Zone 3. This voltage violation is caused by the additional reactive power that the system must deliver to supply the field of the installed induction generator. Hence, at peak load, the installation of the induction generator operating at a power factor of 80% does not solve the initial low-voltage problem of the network. Figure 9 shows the real and reactive power flow in the distribution feeder after the addition of the induction generator operating at power factor of 80%. Figures 10 and 11 show the split of the supplied active and reactive power to each load, between the system source and the added induction generator. Report 2009-025 (RP-TEC) 411-MODSIM 10 May 2009

Figure 8 - Voltage Profile, Induction Generator at 0.8 Power Factor Figure 9 - Power Flow, Induction Generator at 0.8 Power Factor Report 2009-025 (RP-TEC) 411-MODSIM 11 May 2009

Distribution of Supply of MW 3.5 3.0 2.5 2.0 1.5 MW supplied by Main Source MW 1.0 0.5 0.0-0.5-1.0 Main Source L1 L2 L3 Generator L4 L5 L6 59.1% MW supplied by Generator -1.5 40.9% -2.0 Loads and Sources Figure 10 - Split of MW Supply between the Source and the DG, Induction Generator at 0.8 Power Factor Distribution of Supply of MVar MVar 5.0 4.0 3.0 2.0 1.0 0.0-1.0-2.0-3.0 Main Source L1 L2 L3 Generat or L4 L5 L6 Loads and Sources Mvar supplied by Main Source Mvar supplied by Generator Figure 11 - Split of MVAR Supply between the Source and the DG, Induction Generator at 0.8 Power Factor Report 2009-025 (RP-TEC) 411-MODSIM 12 May 2009

4.2.3 Induction Generator at Unity Power Factor Figure 12 shows the voltage profile of the system with the added induction generator operating at unity power factor. Figure 12 shows that the system does not experience any voltage problem. The voltages of all three phases fall within the voltage tolerance of ±5%. Hence, at peak load, the installation of an induction generator, operated at unity power factor, solves the initial voltage problem of the network. Figure 13 shows the real and reactive power flow in the distribution feeder after the addition of the induction generator operating at unity power factor. Figures 14 and 15 show the split of the supplied active and reactive power to each load, between the system source and the added induction generator. Figure 12 - Voltage Profile, Induction Generator at Unity Power Factor Report 2009-025 (RP-TEC) 411-MODSIM 13 May 2009

Figure 13 - Power Flow, Induction Generator at Unity Power Factor Distribution of Supply of MW MW 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0-0.5-1.0-1.5-2.0 Main Source L1 L2 L3 Generator L4 L5 L6 59.1% 40.9% Loads and Sources MW supplied by Main Source MW supplied by Generator Figure 14 - Split of MW Supply between the Source and the DG, Induction Generator at Unity Power Factor Report 2009-025 (RP-TEC) 411-MODSIM 14 May 2009

Distribution of Supply of MVar 1.5 MVar 1.0 0.5 0.0-0.5 Main Source L1 L2 L3 Generator L4 L5 L6 Mvar supplied by Main Source Mvar supplied by Generator -1.0 Loads and Sources Figure 15 - Split of MVAR Supply between the Source and the DG, Induction Generator at Unity Power Factor 4.3 Addition of a Voltage Regulator The addition of a voltage regulator to the distribution circuit, in the presence or absence of the distributed generation, may provide a means to rectify the voltage decline problem. 4.3.1 In the Absence of the Distributed Generator The selected voltage regulator, in the absence of a distributed generation, is a no-reverse sensing mode voltage regulator that is set to regulate the voltage at its secondary terminal and is located in Zone 2, as indicated in Figure 1 (L3). The voltage profile for this case-study is reproduced in Figure 16. Figure 16 shows that the addition of the voltage regulator solves the initial low-voltage problem of the network. The results of Figure 16 correspond to the voltage of phase B in both cases. Report 2009-025 (RP-TEC) 411-MODSIM 15 May 2009

Figure 16 - Voltage Profile, Using a Regulator, No Regulator and no Generator 4.3.2 In the Presence of the Distributed Generator As shown in Figure 8, the installation of an induction generator at a power factor of 80% cannot solve the initial low-voltage problem in the network. It may be worthwhile considering whether adding a voltage regulator to the network, along with the induction generator operating at a power factor of 80%, can deal with the low-voltage problem. The selected voltage regulator in this case-study is a co-generation mode regulator and is located in Zone 2, as indicated in Figure 1 (L3). The voltage profile for this case is reproduced in Figure 17. Figure 17 shows that the addition of the voltage regulator results in solving the initial voltage decline problem. Report 2009-025 (RP-TEC) 411-MODSIM 16 May 2009

Figure 17 - Voltage Profile, Induction Generator at 0.8 Power Factor with Added Voltage Regulator in Zone 2 Report 2009-025 (RP-TEC) 411-MODSIM 17 May 2009

4.4 Summary of Peak Load Cases Figure 18 shows a summary of the impact of adding distributed generation of different types on the voltage profile of the network during peak load conditions. The results of Figure 18 correspond to the voltage of phase B for all cases. Without the addition of a distributed generator, the network experiences a low-voltage problem. The installation of a synchronous generator in Zone 2 (at L4) that controls its terminal voltage to 1.03 pu alleviates the low voltage situation. On the other hand, the addition of an induction generator operating at 0.8 power factor cannot solve the voltage problem. However, when the induction generator is provided with a means to supply its own field and therefore is operated at unity power factor, the low voltage problem disappeared. It can also be seen that the addition of a voltage regulator to the circuit at the indicated location can solve the low voltage problem without additional distributed generation. Such addition to the network with an induction generator operation at 0.8 power factor solves the low voltage problem as well. Therefore it may be convenient to install a voltage regulator in the circuit for use during special operating conditions. Figure 18 - Voltage Profile, Various Generator Types and Regulator, Peak Loading Report 2009-025 (RP-TEC) 411-MODSIM 18 May 2009

5 Light Load Conditions 5.1 No Distributed Generator Connected A base case-study for the system operation at light load, without the distributed generator, is established as a reference for comparison with cases involving distributed generation. The resulting voltage profile and power flow in the network for this case are shown in Figures 19 and 20, respectively. Figure 19 shows that the system does not experience any voltage problem during light load conditions. It is prudent to examine the impact of the addition of distributed generation and the usage of a regulator in the system to control the voltage under this operating condition. The impact of different types of distributed generation should also be considered. Figure 19 - Voltage Profile, Reference network at light load Report 2009-025 (RP-TEC) 411-MODSIM 19 May 2009

Figure 20 - Power flow, Reference network at Light Load 5.2 Addition of a Distributed Generator For this exercise, it is desired to examine the effect of installing a distributed generation source in Zone 2, at the location indicated in Figure 1, on the voltage profile and power flow in the study system. In this section, three types of distributed generators are considered: a) A synchronous generator with capacity of 3.750 MVA, which supplies 3 MW of real power. The synchronous generator operates under the voltage control mode. b) An induction generator capable of producing 3 MW of real power. The generator consumes reactive power from the system to supply its own field at a power factor of 80%. c) An induction generator capable of producing 3 MW of real power. The induction generator is supplied with reactive power from external source to maintain its own field. Therefore the generator operates at unity (1) power factor. Report 2009-025 (RP-TEC) 411-MODSIM 20 May 2009

5.2.1 Synchronous Generator Figure 21 shows the voltage profile of the system with the added synchronous generator controlling its terminal voltage to 1.0 pu. Figure 21 shows that the system does not experience any voltage problem. The voltages of all three phases fall within the voltage tolerance of ±5%. Hence, at light load, the installation of a synchronous generator, operated in a voltage control mode does not cause any initial voltage problem in the system. Figure 22 shows the real and reactive power flow in the distribution feeder after the addition of the synchronous generator under the voltage control mode and holding its terminal voltage at 1.0 pu. Figures 23 and 24 show the split of the supplied real and reactive power to each load, between the system source and the added synchronous generator. Figure 21 - Voltage Profile, Synchronous Generator under Voltage Control Mode Report 2009-025 (RP-TEC) 411-MODSIM 21 May 2009

Figure 22 - Power Flow, Synchronous Generator under Voltage Control Mode 4.0 Distribution of the supply of MW 3.0 2.0 MW supplied by Main Source MW 1.0 0.0 Main Source L1 L2 L3 Generator L4 L5 L6 MW supplied by Generator -1.0-2.0 Loads and Sources Figure 23 - Split of MW Supply between the Source and the DG, Synchronous Generator under Voltage Control Mode Report 2009-025 (RP-TEC) 411-MODSIM 22 May 2009

Distribution of supply of MVar 2.5 2.0 MVar 1.5 1.0 0.5 0.0-0.5 Main Source L1 L2 L3 Generator L4 L5 L6 Mvar supplied by main source Mvar supplied by Generator -1.0-1.5-2.0 Loads and Sources Figure 24 - Split of MVAR Supply between the Source and the DG, Synchronous Generator under Voltage Control Mode 5.2.2 Induction Generator at a Power Factor of 80% Figure 25 shows the voltage profile of the system with the added induction generator with a 0.8 power factor. Figure shows that the system experiences no voltage problem. Figure 26 shows the real and reactive power flow in the distribution feeder after the addition of the induction generator operating at a power factor of 0.8. Figures 27 and 28 show the split of the supplied active and reactive power to each load, between the system source and the added induction generator. Report 2009-025 (RP-TEC) 411-MODSIM 23 May 2009

Figure 25 - Voltage Profile, Induction Generator at 0.8 Power Factor Figure 26 - Power Flow, Induction Generator at 0.8 Power Factor Report 2009-025 (RP-TEC) 411-MODSIM 24 May 2009

4.0 Distribution of supply of MW 3.0 2.0 Mvar supplied by Main Source MW 1.0 Mvar supplied by Generator 0.0-1.0 Main Source L1 L2 L3 Generator L4 L5 L6-2.0 Loads and Sources Figure 27 - Split of MW Supply between the Source and the DG, Induction Generator at 0.8 Power Factor 4.0 Distribution of supply of MVar MVar 3.0 2.0 1.0 0.0-1.0 Main Source L1 L2 L3 Generator L4 L5 L6 Mvar supplied by Main Source Mvar supplied by Generator -2.0-3.0 Loads and Sources Figure 28 - Split of MVAR Supply between the Source and the DG, Induction Generator at 0.8 Power Factor Report 2009-025 (RP-TEC) 411-MODSIM 25 May 2009

5.2.3 Induction Generator at Unity Power Factor Figure 29 shows the voltage profile of the system with the added induction generator operating at unity power factor. Figure 29 shows that the system experiences a high voltage problem. This can be attributed to the fact that the additional generation relieves the circuit from voltage drop due to the decrease in current flowing in the lines. Meanwhile, it does not produce a voltage drop of its own since it does not draw any reactive current from the circuit. Figure 30 shows the real and reactive power flow in the distribution feeder after the addition of the induction generator operating at unity power factor. Figures 31 and 32 show the split of the supplied active and reactive power to each load, between the system source and the added induction generator. Figure 29 - Voltage Profile, Induction Generator at Unity Power Factor Report 2009-025 (RP-TEC) 411-MODSIM 26 May 2009

Figure 30 - Power Flow, Induction Generator at Unity Power Factor Distribution of supply of MW 4.0 3.0 2.0 MW supplied by Main Source MW 1.0 0.0-1.0 Main Source L1 L2 L3 Generator L4 L5 L6 MW suppled by Generator -2.0 Loads and Sources Figure 31 - Split of MW Supply between the Source and the DG, Induction Generator at Unity Power Factor Report 2009-025 (RP-TEC) 411-MODSIM 27 May 2009

Distribution of supply of MVar 0.400 MVar 0.300 0.200 0.100 0.000-0.100 Main Source L1 L2 L3 Generator L4 L5 L6 Mvar supplied by main source Mvar supplied by Generator -0.200 Loads and Sources Figure 32 - Split of MVAR Supply between the Source and the DG, Induction Generator at Unity Power Factor 5.3 Addition of a Voltage Regulator The addition of a voltage regulator to the distribution circuit, in the presence or absence of the distributed generation, is generally added to solve voltage decline problems which can be typically associated with peak-load conditions. However, its operation should also be investigated under light loading conditions. 5.3.1 In the Presence of the Distributed Generator with Unity Power Factor As shown in Figure 29, the installation of an induction generator at a power factor of 1.0 produces a high-voltage problem in the network under light load conditions. It may be worthwhile considering the use of a voltage regulator along with the induction generator to deal with this situation. The voltage regulator chosen in this case is a co-generation mode regulator and is located in Zone 2 as indicated in Figure 1. The voltage profile for this case is reproduced in Figure 33. Figure 33 shows that the addition of the voltage regulators results in solution of the high-voltage problem. Report 2009-025 (RP-TEC) 411-MODSIM 28 May 2009

Figure 33 - Voltage Profile, Induction Generator at 1.0 Power Factor with Added Voltage Regulator in Zone 2 Report 2009-025 (RP-TEC) 411-MODSIM 29 May 2009

5.4 Summary of Light Load Cases Figure 34 provides a summary of the impact of adding distributed generation of different types on the network voltage profile during low load conditions. The results of Figure 34 correspond to the voltage of phase B for all cases. Figure 34 shows that, without the addition of a distributed generator, the distribution circuit does not suffer any voltage problem. The installation of DG technologies such as a synchronous generator in Zone 2, controlling its terminal voltage to 1.0 pu, or an induction generator operating at a power factor of 0.8, has no ill effect on the voltage profile. On the other hand, the addition of an induction generator operating at unity power factor introduces a high voltage situation throughout most of the circuit. As in the case of peak load conditions, the addition of a voltage regulator to the circuit at the indicated location can solve the high voltage problem for the condition of an induction machine operating at unity power factor. Therefore, the need of installing a voltage regulator in the circuit for use during special operating conditions is emphasized. Alternatively, the reactive compensation device installed at the induction generator generally capacitor banks could be coordinated with feeder loading, as is typically done with capacitor banks installed on the system. Figure 34 - Voltage Profile, Various Generator types and Regulator, light loading Report 2009-025 (RP-TEC) 411-MODSIM 30 May 2009

6 Conclusions The addition of distributed generation sources to an existing distribution system can have a major impact on the system s voltage regulation. The addition of distributed generation relieves the distribution circuit from transmitting power to the load. Thus, it is reasonable to expect that the addition of DG to the system would, in general, result in an improvement in the voltage profile of the distribution circuit. This positive effect on voltage profile may not always be achievable. Depending on the type of distributed generation and operating conditions, the addition of distributed generation may have a degrading effect on the voltage profile of the circuit, either at the point of interconnection or at a distant location. The effect of the distributed generation types and operating conditions can be summarized as follows: 1. Distributed generation units with voltage control capability, such as synchronous generators or electronically coupled units with similar capability, will always help in maintaining voltage profile at set levels. 2. Induction generators directly coupled to the distribution network, from which they draw reactive power to supply their own field, will almost always result in aggravation of low voltage conditions, which are especially common at peak load. 3. Distributed generators forced to operate at or near unity power factor in order to avoid voltage decline problems during peak loads, may lead to over voltage problems during low load conditions. 4. Different solutions can be implemented to mitigate voltage limit violation problems including the use of distributed generators capable of voltage control, or the addition of switched capacitor banks. 5. Under some special conditions, the addition of voltage regulators to the distribution system may be necessary to solve voltage limit violation problems. When DG is involved the interaction with voltage regulators should be treated with care. Report 2009-025 (RP-TEC) 411-MODSIM 31 May 2009

7 Bibliography [1] Kwok, C and Morched, A.S., Effect of Adding Distributed Generation to Distribution Networks Case Study 1, report # CETC 2006-099 (TR), CANMET Energy Technology Centre Varennes, Natural Resources Canada, April 2006, 34 pp. [2] Katiraei, F., C. Abbey, and R. Bahry, Analysis of voltage regulation problem for a 25- kv distribution network with distributed generation, IEEE Power Engineering Society General Meeting 2006, Montréal, Canada, June 18-22, 2006. [3] http://canmetenergy-canmetenergie.nrcanrncan.gc.ca/eng/renewables/integration_der.html Report 2009-025 (RP-TEC) 411-MODSIM 32 May 2009

ANNEX A CYME file references Report 2009-025 (RP-TEC) 411-MODSIM 33 May 2009

ANNEX A CYME file references The CYMDIST software and the CYMDIST files corresponding to the case studies of this report can be obtained from CYME International (www.cyme.com). Interested users should contact CYME International directly. Section CYMDIST Files 4.1 No Distributed Generator connected Peak_no_generator.sxst 4.2.1 Synchronous Generator Peak_synchronous.sxst 4.2.2 Induction Generator at pf = 0.8 Peak_induction80_sxst 4.2.3 Induction Generator at unity pf Peak_induction100_sxst 4.3.1 Adding a voltage regulator in the absence of the distributed generator 4.3.2 Adding a voltage regulator in the presence of the distributed generator Peak_regulator_sxst Peak_induction80_regulator.sxst 5.1 No Distributed Generator connected Light_no_generator.sxst 5.2.1 Synchronous Generator Light_synchronous.sxst 5.2.2 Induction Generator at pf = 0.8 Light_induction80.sxst 5.2.3 Induction Generator at unity pf Light_induction100.sxst 5.3.1 Adding a voltage regulator in the presence of distributed generator with unity power factor Light_induction100_regulator.sxst Report 2009-025 (RP-TEC) 411-MODSIM 34 May 2009