Power outage brings Mumbai to a standstill; probe ordered

Millions of people across the Mumbai Metropolitan Region (MMR) went without electricity for between three and 12 hours, owing to a rare grid failure triggered by

Millions of people across the Mumbai Metropolitan Region (MMR) went without electricity for between three and 12 hours, owing to a rare grid failure triggered by “multiple trips” during maintenance work on Monday morning. A power outage of this scale had last happened in November 2010, while in mid-2018, a fire on a transformer caused major electricity cuts in the city and its suburbs.

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Monday’s blackout from around 10.05am paralysed India’s financial capital, already strained by a pandemic, stranding thousands of train passengers; affecting hospitals, online exams and mobile telephone services; disrupting the new normal of work-from-home; trapping people in elevators and even causing the police control room to crash.

While the power supply was gradually restored starting 1pm, many parts of the city (especially in eastern suburbs), Thane and Navi Mumbai were without electricity for more than 12 hours. In some areas, supply was restored only to be cut again and it hadn’t been restored until late night.

According to a statement from the chief minister’s office (CMO), MMR gets its power supply via four main transmission lines. Of the four, on October 10, there were issues with the Kalwa-Talegaon line, on which repairs were undertaken as a conductor was broken. Later, the 400KV Kalwa-Padghe line-1 also tripped, owing to excess voltage around 4.33am and work of changing the insulator was undertaken by the Maharashtra State Electricity Transmission Company Limited (MSETCL). While Mumbai’s supply was on via the other two transmission lines, Kalwa-Padghe line-2 was hit by technical problems and tripped at 10.01am.

Thus, three of the four lines that supply power to Mumbai and surrounding areas were affected, officials said. This resulted in tripping of 500MW of Tata Power’s Trombay plant and 250MW of Adani Electricity’s Dahanu plant.

The power fiasco prompted Maharashtra chief minister Uddhav Thackeray to order a probe and convene a meeting with officials, including state energy minister Nitin Raut, on Monday evening. “The probe will look into reasons for the outage, find out whether it was unavoidable and caused because of negligence on part of the officials concerned. The committee will also recommend measures to be taken to avoid such an occurrence in the future,” Thackeray said.

He also asked officials to remain alert as there is a heavy rain forecast for the city. The CM meeting was also attended by minister of state for energy Prajakt Tanpure, senior officials from the government and representatives of Tata Power, Adani Electricity Mumbai Limited (AEML) and Brihanmumbai Electric Supply and Transport (BEST) agency. The government is expected to set up a committee under its technical advisor Uttam Zalte, with experts from IIT-Powai, and officials from the energy department. Raut said, “The probe committee will do a technical audit and root-cause analysis, which will help us avoid any such failure in future. It will also see whether the department followed all protocols required, while going for the maintenance of the transmission system, all precautions were taken among others. The probe will find out flaws if any, but the transmission company today [Monday] did a commendable job by restoring electricity in just three-and-a-half hours.”

The power outage in areas served by all four distribution companies —BEST, AEML, Tata Power Co Ltd and Maharashtra State Electricity Distribution Company Limited (MSEDCL)— virtually brought the city to a standstill, with traffic jams caused by around 700 disrupted traffic signals and also dysfunctional street lights across the eastern express highway late in the evening.

Meanwhile, Mumbai civic chief IS Chahal directed the administration to ensure diesel for generators for civic hospitals and Covid care centres.

According to MSETCL, the Kalwa-Padgha line-1 was affected owing to over-voltage around 4.33am. Post which, restoration work undertaken. The cascading effect of multiple tripping lines resulted in affecting a total of 1,700MW load in Mumbai. The city’s demand is anywhere between 1,600MW to 2,600MW. Around 6pm, MSETCL stated that 70% of the power restoration has been completed and power has been restored mainly for essential services like railways and hospitals.

While Mumbai has a well-known islanding system, which isolates itself during a state grid failure to continue supply to the city, Tata Power in its statement on Monday said that islanding could not hold owing to the additional drop of 900MW.

The company said, “Mumbai’s islanding system, which saves the city from major power outages, was separated, however, it could not hold as additional 900MW dropped at 10.05 hours.”

It further said, “Tata Power swiftly began restoration work to bring back supply from the 3 Hydro units and Trombay gas and coal units as soon as the MSETCL transmission lines were connected. Tata Power started restoring supply to its consumers progressively from 12 noon onwards. Tata Power regrets the inconvenience caused to its consumers due to this unforeseen event in power failure due to the transmission system failure leading to the cascading impact to all downstream suppliers of electricity including Tata Power, BEST and its consumers.”

The MSETCL, which handles the units, stated that there were sparks observed at the Kharghar unit, too, post which both the Kalwa and Kharghar unit came down to zero load, also affecting the Trombay power unit, which is a major supplier for Mumbai.

Dinesh Waghmare, managing director of MSEDCL, said, “Ideally, when there is a failure in the state grid, Mumbai could isolate itself owing to the Trombay and Dahanu power plants, however, on Monday, there was a cascading effect.”

MSETCL said that the technical fault resulted in tripping 570MW of Tata Power, 440MW of BEST and 700MW of AEML.

Tata Power caters to seven lakh consumers, while BEST and AEML cater to 10 lakh consumers in the island city and close to 30 lakh consumers in the suburbs respectively.

AEML in its statement said that it went into islanding for essential installations in the city, though residential units did face power outage.

AEML, in its statement said, “Due to transmission network failure outside of our system at around 10.05 this morning, power grid saw outages across utilities in Mumbai. However, AEML operated islanding facility successfully and continued successfully power supply to vital installations with the help of Dahanu Thermal Power Station (DTPS). We wish we had more power for which we are dependent on grid input. The power supplies to remaining consumers of AEML are being restored in phased manner as input power is being restored by Grid operations of Maha.”

On Monday, Mumbai’s power demand was close to 2,600MW. While DTPS has an installed capacity of 500MW, Trombay has a capacity of about 1,100MW, sources said.