Cascade Tripping at Substation of MSETCL Line Tripping Led to Grid Failure: Tata Power

Praveer Sinha-led utility giant Tata Power said that the power failure was attributed to cascade tripping at state-run transmission company MSETCL’s sub-stations and transmission lines leading to grid failure at Mumbai that resulted in power outages on October 12, 2020.

The company said in a statement that, the inconvenience caused to the Mumbai consumers was due to the MSETCL transmission system failure which led to cascading impact on all the downstream suppliers of electricity including Tata Power and BEST.

However, to study the power breakdown which halted the Mumbai city, the Power Ministry sent the team of central officers led by the Central Electricity Authority (CEA) to Mumbai.

The company said that it is supporting the central team by providing information and data related to the chain of events which transpired on the day of the outage.

On the day of the power outage, the company in its statement said that as per its preliminary assessment of the situation, many parts of Mumbai experienced an unforeseen electricity failure in the morning due to tripping of MSETCL’s 400 KV transmission system at Kalwa, which supplies power to Mumbai and adjoining areas. There are 4 incoming Ckt /lines to MSETCL Kalwa receiving stations for further transmission of power to Mumbai . Out of these 4 lines , MSETCL’s 400kV Pune-Kalwa line was under forced shutdown since October 10, 2020.

On October 12, 2020, early in the morning MSETCL had taken emergency shutdown on another 400 KV Kalwa- Padghe line -1 to attend to fault and was expected to be revived by 09:30hr, but MSETCL could not revive it.

As per the chain of events, with 2 lines out of service, the 3rd line tripped at 09:58 hrs 400kV Kalwa-Padghe-2 carrying 644 MW power to the city tripped. This led to over loading of 4th ckt and subsequent tripping at 10:05 which led to sudden load drop and power outage in Mumbai system.

Mumbai’s islanding system that saves the city from major power outages was successfully separated at 9.58 am, however it could not hold sudden 1000 MW load drop at 10:05hrs. The company clarified that it rapidly initiated restoration by bringing in power from its 3 Hydro Units and activating its Trombay gas and coal units as soon as the MSETCL transmission lines were connected. Simultaneously, the company started restoring supply to its consumers progressively from 12 noon onwards and throughout the course of the day.