Intentional Islanding Operation to Improve the Service Reliability of Thailand Electric Power System Pradit Fuangfoo Wei-Jen Lee Energy Systems Research Center University of Texas at Arlington Arlington, TX 76019 Khaled A. Nigim Department of Electrical & Computer Engineering University of Waterloo Waterloo, Ontario, Canada, N2L 3G1
Agenda! What is Islanding Operation?! Pros and Cons of Islanding Operation! Methodology! Case Study! Conclusion
What is Islanding Operation?! Inadvertent islanding operation! Intentional islanding operation
Forming of Islanding! Islanding caused by Fault Normally unsuitable operation due to large disturbances during forming. Generator protection will disconnect DG from the system. While repairing the system, the islanding part could be supplied by DG as islanding operation caused by maintenance.! Islanding caused by Maintenance Before forming islanding operation for a purpose of maintenance, the total remaining loads have to be nearly and less than the capacity of DG.
Inadvertent Islanding Operation Subtransmission System 230kV 115kV Fault B 1 B 6 B 7 Substation CB 1 opened CB 2 opened B 2 B5 B 3 B 4 Islanding System DG
Intentional Islanding Operation Subtransmission System 230kV 115kV Maintenance on Up-Stream B 1 B 6 B 7 Substation CB 1 opened CB 2 opened B 2 B5 B 3 B 4 Islanding System DG
Pros and Cons of Islanding Operation! Advantages of Islanding operation! Disadvantages of Islanding operation
Advantages of Islanding Operation! Improve Reliability! Reduce Outage Cost! Increase Revenue
Disadvantages of Islanding Operation! Utility Side Safety of line crew Equipment/Devices may fail due to unsuitable power quality Complicated operation! DG Side DG may be damaged in the case of inappropriate operation
Issues Related to Islanding Operation! Load Following During changing of loads, DG must continue to supply loads as well as system frequency and voltage are adjusted to appropriate levels.! Large Load Rejection When large loads disconnected from the main grid, DG must adjusted system frequency and voltage to the appropriate levels quickly.! Fault during Islanding Operation When faults occur in the power system during islanding, faults must be eliminated before the power system is unstable.
Resynchronization! To resynchronize the islanding part to the main grid, DG has to be disconnected from the system before the islanding part is connected the main grid.! If these islanding loads are critical loads, the remote resynchronization of DG at a substation is required. 8
Case Study! Forming of islanding! Dynamic performances! Effect of DG control modes
Thailand s EPS structure (As of Nov 2004)
PEA Key Information (As of Nov 2005)! Peak Demand: 14,741 MW! Number of Customers: 13,423,051! Transmission Lines (115 kv): 7,588 cct-km! MV Distribution lines (22kV and 33 kv): 270,079 cct-km! LV Distribution lines (400/230 V): 407,601 cct-km! Number of Electrified Villages: 72,301! % of Electrified Villages: 99.66! % of Load Growth: 6.3
PEA s Service Areas
Case Study Procedure Set up base case Max load Min load Fault Maintenance of up stream system - Load following - Large load rejection - Large motor starting - Fault Load Sheding Adjust protection scheme - Set up regulation - Set up operation
Study of a Sample Subtransmission System External Electric Power System Fault or Maintenance 30 MW 15 MVAR L1 Bus # 5082 1 km 0.5 km 13.9 km Bus # 5081 Bus # 508 115 kv and 6,000 MVAsc Out of service 11 km 10 MW 5 MVAR L4 1.6 km 0.1 km 10.4 km Bus # 5083 Bus # 5084 Bus # 5085 Bus # 5086 V3 L2 20 MW 10 MVAR L3 90 MW 44 MVAR L5 20 MW 10 MVAR DG 1 DG 2
Quasi-Steady State Performance of Islanding Operation Large Motor Starting Frequency Voltage
Dynamic Performance Load following/rejection during islanding Frequency Dev Voltage
Dynamic Performance Fault during islanding 5 cycles 10 cycles
Effect of DG control modes Synchronous Generator with Control mode Frequency Voltage Islanding Operation w/o AVR + Gov Uncontrollable Uncontrollable Not suitable w/ AVR Uncontrollable Controllable Not suitable w/ GOV Controllable Uncontrollable Not suitable w/ AVR + GOV Controllable Controllable Possible
Effect of DG control modes (con.) Power Frequency Dev Voltage
Normal system operation Estimate total system load in the part of intentional islanding operation Operational practice Total DGs capacity > Total system load Yes Reduce power outputs of DGs close to total system load Synchronize DG to the main grid No Increase DGs capacity? Yes Change protection scheme from normal operation mode to islanding mode No Load shedding until Total DGs capacity > Total system load Open switching device to perform intentional islanding operation Decrease power output of DGs close to total system load (Automatically performing by governor control) No Total DGs capacity < Total system load (Max DGs capacity < Total peak load) Yes A B C
Operational practice (conti conti.) A B C Yes Close switching device to reconnect the islanding part to the main grid Load shedding until regain system frequency Disconnect DGs out of the islanding system Yes Re-synchronize back to the main grid? No Still operating in islanding mode
Conclusion! During transition to islanding operation, system will have a small oscillation if the difference between total generation and total load is small.! If total load is greater than total generation, the load shedding scheme is required.! Dynamic impact study is required to analyze performances of the DGs under islanding operations.! The study results show that SG with governor and exciters control can be operated in islanding mode, including doubly-fed induction generator.! Most cases show that protection settings need to be changed during islanding operation.
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