DESIGN NEW LOAD SHEDDING SCHEME CONSIDERING POSSIBLE ISLANDING OPERATIONS IN SRI LANKAN NETWORK H.P.G.R.N.Chamikara 09/8653 Degree of Master of Science Department of Electrical Engineering University of Moratuwa Sri Lanka September 2012 DESIGN NEW LOAD SHEDDING SCHEME CONSIDERING POSSIBLE ISLANDING OPERATIONS IN SRI LANKAN NETWORK Henpita Polwatthe Gamarallage Nadun Chamikara 09/8653 Dissertation submitted in partial fulfillment of the requirements for the Degree Master of Science in Electrical Engineering Supervised by: Dr.K.T.M.Udayanga Hemapala Department of Electrical Engineering University of Moratuwa Sri Lanka September 2012 i DECLARATION “I declare that this is my own work and this dissertation does not incorporate without acknowledgement any material previously submitted for a Degree or Diploma in any other University or institute of higher learning and to the best of my knowledge and belief it does not contain any material previously published or written by another person except where the acknowledgement is made in the text. Also, I hereby grant to University of Moratuwa the non-exclusive right to reproduce and distribute my dissertation, in whole or in part in print, electronic or other medium. I retain the right to use this content in whole or part in future works (such as articles or books)”. ………………………. Signature of the candidate Date: (H.P.G.R.N.Chamikara) The above candidate has carried out research for the Masters Dissertation under my supervision. ……………………………. Signature of the supervisor Date: (Dr. K.T.M. Udayanga Hemapala) ii ABSTRACT Under frequency load shedding has been widely used to restore the power system frequency following a severe generation demand unbalance due to a disturbance. If system frequency is not counteracted properly system will be led to major blackouts. This frequency decline may be corrected by shedding certain amount of load so that system is back to stable state. This dissertation discusses on designing of new under frequency load shedding scheme align with the development of Sri Lankan power system. Further, due to present network configuration after certain power System failures some part of the system isolates from the main system and operates in islanding mode. This islanding operation fails at all the times due to unbalance of the generation and load. This dissertation also discusses in what way to overcome above situation by rearranging 33 kV Load Shedding Feeders in the Sri Lankan network. Whole Sri Lankan power system has been modeled using the PSS®E (Power System Simulator for Engineers) software. PSS®E dynamic model was validated considering an actual generator tripping occurred in the system. The Existing Load Shedding scheme was simulated using this model and identified its drawbacks. Proposed a new Load Shedding scheme and discussed the system improvements with simulations. The observations and results obtained from the simulations comprise frequency plots before and after applying the proposed new load shedding scheme. Further, identified possible islanding operations and analyzed the stability of them with proposed load shedding scheme. Finally rearrange the 33 kV load shedding feeders in the Sri Lankan network to facilitate islanding operation by analyzing the stability of the islands using simulation. This new load shedding schemes with rearranged 33 kV load shedding feeders will improve the Power System reliability and have a definite positive effect on customers which in turn improve the wellbeing of the people and economy of the country. Key words: Load Shedding, Islanding Operations, Simulations, Scheme, Feeders. iii ACKNOWLEDGEMENT First, I pay my sincere gratitude to Dr. K.T.M. Udayanga Hemapala who encouraged and guided me to conduct this investigation and on preparation of final dissertation. I extend my sincere gratitude to Prof. J.P. Karunadasa, Head of the Department of Electrical Engineering and all the lectures and visiting lectures of the Department of Electrical Engineering for the support extended during the study period. I would like to thank Mr. N.S.Wettasinghe, Chief Engineer, Protection Development Branch, Ceylon Electricity Board who gave me the initiative to do the Islanding Operation study for the Sri Lankan Network. I also thank to Eng. Eranga Kudahewa who gave me extreme support and valuable instructions during the simulations and preparation of final dissertation. I would like to take this opportunity to extend my sincere thanks to Mr.D.D.K. Karunarathne, Deputy General Manager (TD & E), Mr.T.D.Handagama, Deputy General Manager (System Control), Mr.D.S.R.Alahakoon, Chief Engineer (System Operations), Mr. J.Nanthakumar Chief Engineer (Operation Planning), Mr. G.R.H.U.Somapriya, Electrical Engineer (Protection Development Branch), Mr. R.G. Jayendra, Electrical Engineer (AGSAREP Project), Mr. L.A.A.N.Perera, Electrical Engineer (Transmission O&Ms Branch – Colombo Region) and all the Office Staff of Protection Development Branch of Ceylon Electricity Board who gave their co-operation to conduct my investigation work successfully. It is a great pleasure to remember the kind co-operation extended by the colleagues in the post graduate program, friends, my mother, father, sister Chathurika Ruchirani, brother-in law Sameera Manusanka and specially my wife Nirmani Rajapakshe who helped me to continue the studies from start to end. iv TABLE OF CONTENTS Declaration of the candidate & Supervisor i Abstract ii Acknowledgements iii Table of content iv List of Figures vi List of Tables vii List of Appendices viii 1. Introduction 1 1.1 Background 1 1.2 Importance of the Load Shedding Scheme 1 1.3 Identification of the Problem 2 1.4 Motivation 3 1.5 Objective of the Study 3 1.6 Methodology 4 2. Existing Load Shedding Scheme 5 2.1 Load Shedding Scheme 5 2.2 Existing Load Shedding Scheme 7 2.3 System Response to the System Disturbances 8 2.3.1 Tripping of Norochcholai coal Power Plant 8 2.3.2 Tripping of Kerawalapitiya Power Plant 8 2.4 Analyze of Existing Load Shedding Scheme 9 3. Power System Simulation 10 3.1 The Power System Simulator, PSS®E 10 3.2 Planning Criteria 10 3.2.1 Voltage criteria 10 3.2.2 Thermal criteria 10 3.2.3 Security criteria 11 3.2.4 Stability criteria 11 3.3 Validation of PSS®E simulation with actual system disturbance 12 3.4 Selecting initial System condition for Load Shedding Studies 13 3.4.1 HMDP (Hydro Maximum Day Peak) 14 v 3.4.2 TMDP (Thermal Maximum Day Peak) 15 3.4.3 HMNP (Hydro Maximum Night Peak) 16 3.4.4 TMNP (Thermal Maximum Night Peak) 16 3.4.5 HMOP (Hydro Maximum Off Peak) 17 3.4.6 TMOP (Thermal Maximum Off Peak) 18 4. Proposed Load Shedding Scheme 19 4.1 Formulating a Load Shedding Scheme 19 4.2 Maximum anticipated overload 19 4.3 Number of load-shedding steps 20 4.4 Time Delay 20 4.4.1 Simulation 1 21 4.4.2 Simulation 2 22 4.4.3 Simulation 3 25 4.5 Size of the load shed at each step 26 4.5.1 Simulation 4 27 4.5.2 Simulation 5 28 4.5.3 Simulation 6 29 4.5.4 Simulation 7 30 4.5.5 Simulation 8 31 4.6 Frequency settings 32 4.7 Proposed Load Shedding Scheme 32 5. Islanding Operation 34 5.1 Possible Islanding Operation 34 5.2 Tripping of 132 kV New Laxapana – Balangoda Line 1 and 2 34 5.3 Tripping of 132 kV Pannipitiya – Matugama Line and 45 Pannipitiya – Horana Line 6. Conclusion and Recommendation 52 Reference List 55 Appendix A: Load Flow Network Diagram of HMOP condition 57 Appendix B: Dispatch Scenario during HMOP Condition 58 Appendix C: Technical Details of Load Shedding relay 59 Appendix D: 33 kV Circuit Breaker Timing Test Results 60 vi LIST OF FIGURES Page Figure 2.1 System Frequency variation with the Load Shedding operation 6 Figure 2.2 System Frequency variation on 07th of June 2011 at 12.17 PM 8 Figure 2.3 System Frequency variation on 27th of July 2011 at 09.17 AM 9 Figure 3.1 Simulated frequency response due to tripping of AES 163 MW 12 Figure 3.2 Actual frequency response due to tripping of AES 163 MW 12 Figure 3.3 Frequency response of the System at HMDP condition 15 Figure 3.4 Frequency response of the System at TMDP condition 15 Figure 3.5 Frequency response of the System at HMNP condition 16 Figure 3.6 Frequency response of the System at TMNP condition 17 Figure 3.7 Frequency response of the System at HMOP condition 17 Figure 3.8 Frequency response of the System at TMOP condition 18 Figure 4.1 Frequency response of the System for Simulation 1 21 Figure 4.2 Frequency response of the System for Simulation 2 22 Figure 4.3 Pickup and operated time of each stage of existing scheme 24 Figure 4.4 Pickup and operated time of each stage of new scheme 25 Figure 4.5 Frequency response of the System for Simulation 3 25 Figure 4.6 Frequency response of the System for Simulation 4 27 Figure 4.7 Frequency response of the System for Simulation 5 28 Figure 4.8 Frequency response of the System for Simulation 6 29 Figure 4.9 Frequency response of the System for Simulation 7 30 Figure 4.10 Frequency response of the System for Simulation 8 31 Figure 5.1 Network Configuration of the Island 34 Figure 5.2 Load Flow diagram of Balangoda 132 kV Busbar 40 Figure 5.3 Frequency response of the System 41 Figure 5.4 Frequency response of the System after modification of Load Shedding Feeders. 43 Figure 5.5 Voltage response of the Busbars 43 Figure 5.6 Network Configuration of the Island 45 Figure 5.7 Frequency response of the System 49 Figure 5.8 Frequency response of the System after modification of Load Shedding Feeders. 50 vii LIST OF TABLES Page Table 2.1 Existing Load Shedding Scheme 7 Table 2.2 MW Rejection from Existing Load Shedding Scheme 7 Table 3.1 Allowable voltage variation in 220 kV and 132 kV systems 10 Table 3.2 Rate of Change of Frequency for different system conditions 18 Table 4.1 Proposed Load Shedding Scheme with new delay time settings. 26 Table 4.2 Proposed Load Shedding Scheme with new step size. 32 Table 4.3 Proposed New Load Shedding Scheme 33 Table 5.1 Night Peak load analysis of Balangoda GSS 35 Table 5.2 Night Peak load analysis of Deniyaya GSS 36 Table 5.3 Night Peak load analysis of Embilipitiya GSS 36 Table 5.4 Night Peak load analysis of Galle GSS 37 Table 5.5 Night Peak load analysis of Hambantota GSS 37 Table 5.6 Night Peak load analysis of Matara GSS 38 Table 5.7 Night Peak load analysis of Ratnapura GSS 38 Table 5.8 Generation Capacity of the Island 39 Table 5.9 Load Demand of the Island 39 Table 5.10 Load Shedded capacity of each GSS 40 Table 5.11 Under Frequency Trip Settings 41 Table 5.12 Load Shedded capacity of each GSS after modification 42 Table 5.13 Proposed Load Shedded capacity of each GSS in the island 44 Table 5.14 Night Peak load analysis of Ambalangoda GSS 46 Table 5.15 Night Peak load analysis of Horana GSS 47 Table 5.16 Night Peak load analysis of Mathugama GSS 47 Table 5.17 Generation Capacity of the Island 48 Table 5.18 Load Demand of the Island 48 Table 5.19 Load Shedded capacity of each GSS 48 Table 5.20 Load Shedded capacity of each GSS after modification 49 Table 5.21 Proposed Load Shedded capacity of each GSS in the island 51 Table 6.1 Proposed New Load Shedding Scheme 52 Table 6.2 Saved Load from Proposed New Load Shedding Scheme 53 Table 6.3 Saved Load from proposed feeder arrangement in each island 53 Table 6.4 Proposed Load Shedded capacity of each GSS in the islands 54 viii LIST OF APPENDICIES Page Appendix A Load Flow Network Diagram of HMOP condition 57 Appendix B Dispatch Scenario during HMOP Condition 58 Appendix C Technical Details of Load Shedding relay 59 Appendix D 33 kV Circuit Breaker Timing Test Results 60