Cascade tripping at MSETCL sub-stations led to power outage in Mumbai on October 12: Tata Power

Mumbai (Maharashtra) [India], October 16 (ANI): The power outage of October 12 in Mumbai was because of cascade tripping at the sub-stations and transmission lines of Maharashtra State Electricity Transmission Company (MSETCL), said Tata Power, assisting a central team in a probe into the matter, on Friday.
Tata Power is supporting the team, comprising of the officials from Central Electricity Authority, by providing information and data related to the chain of events in the city on Monday.
On the day of the power outage, Tata Power said that as per its preliminary assessment of the situation, many parts of Mumbai experienced an unforeseen electricity failure in the morning due to the tripping of MSETCL's 400-KV transmission system at Kalwa. There are four incoming lines to MSETCL Kalwa receiving stations for further transmission of power to Mumbai. Out of these four lines, MSETCL's 400-KV Pune-Kalwa line was under forced shutdown since October 10, 2020.
Early on Monday morning, the MSETCL went for an emergency shutdown of another 400-KV Kalwa-Padghe line-1 to attend to a fault and expected to revive it by 9.30 am, but could not, Tata Power said in a release.
"As per the chain of events, with two lines out of service, the third line tripped at 9.58 am. The 400-KV Kalwa-Padghe-2, carrying 644 MW power to the city, tripped. This led to the overloading of the fourth and subsequent tripping at 10.05 am, which led to a sudden load drop and power outage in Mumbai," it added.
Tata Power further said Mumbai's islanding system that saves the city from major power outages was successfully separated at 9.58 am. "However it could not hold a sudden 1,000-MW load drop at 10.05 am. Tata Power rapidly initiated restoration by bringing in power from its three hydro units and activating its Trombay gas and coal units as soon as the MSETCL transmission lines were connected. Simultaneously, Tata Power started restoring supply to its consumers progressively from noon onwards and throughout the course of the day." (ANI)