Maharashtra State Load Dispatch Centre (MSLDC), in a preliminary analysis, attributed the power grid failure that took place on October 12 to the tripping of the 400kV Padghe-Kalwa circuit II and the subsequent hand tripping of 400kV Talegaon-Kkharghar that resulted in the complete failure of the power supply to 400 kV Kalwa and Kharghar substations. This non availability of 400 kV sources resulted in the shifting of the complete load of the lower 200 kV network to other sources, including Padghe, Uran, Boisar and Koyna circuits and the Mumbai generators.
MSLDC has submitted its analysis to the Maharashtra Electricity Regulatory Commission (MERC), which has suo moto convened e-hearing on October 21. Before the grid collapsed, Maharashtra’s power demand was 17664 MW and Mumbai’s demand was 2590 MW.
The tripping of other sources on overload, subsequent fall in grid frequency and reverse power flow from Mumbai Metropolitan Region (MMR) to the Maharashtra State Electricity Transmission Corporation (MahaTransco) network initiated the operation of the Mumbai islanding scheme and separation of Mumbai network.
The Adani Electricity-Transmission network got islanded from Tata Power network and 250x2 Adani Electricity-Generation units continued to supply critical load at 385 mw in Mumbai in the islanded mode of operation. “The load generation imbalance persisted in the Tata Power network (demand 1033 mw, generation 864 mw). With this, there was a large dip in frequency in the isolated Tata Power network. Thus, the Trombay units 5 and 7 tripped on under frequency, resulting in the total blackout in the Tata Power and BrihanMumbai Electric Supply and Transport (BEST) network,” said MSLDC.
As reported by Free Press Journal, MSLDC clearly stated that the Mumbai islanding, which was launched way back in 1981, miserably failed last Monday. “Though the islanding scheme is operated as envisaged, it was partially successful. The Mumbai network got separated from the MahaTransco network, but the Tata Power island was unable to sustain due to the continuous drop in frequency and tripping of its generators (Unit-5: 500 MW & Unit-7: 180 MW). The Adani Electricity Transmission island was able to sustain with its generators (Dahanu plant: 2 x 250 MW) and critical load,” noted MSLDC.
The islanding scheme to the island Mumbai network in case there is disturbance in the grid is in service. When the grid frequency dropped to the under frequency relay (UFR) setting of 47.9 Hz with reverse power from MMR to the MahaTransco network, the Mumbai islanding scheme operated and resulted in the opening of all MahaTransco-MMR inter-connections. This separated the Mumbai system from the MahaTransco network.
“With the operation of the Mumbai islanding scheme, the total load relief obtained was 600 MW from Tata Power & BEST networks and 550 MW from Adani Electricity network. Further drop in frequency due to the load generation imbalance in MMR resulted in the separation of Tata Power and Adani Electricity network. The Adani Electricity Transmission network got islanded and 250x2 Adani Electricity Generation units continued to supply critical load at 385 MW in Mumbai in the islanded mode of operation,” said MSLDC. However, due to this continuous dip in frequency in the isolated Tata Power network, the Trombay Unit-5 & Unit-7 tripped on under frequency, resulting in the total blackout in the Tata Power & BEST networks.