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Mumbai blackout puts a question mark on the city’s ‘islanding’ system

For long Mumbai has been the envy of most of the other metros in India. Even if the rest of India went dark after a grid collapse, like the one in 2012, the country’s financial capital had an ‘islanding system’ that allowed it to isolate itself and ensure continued power supply.

Though the 2012 blackout didn’t spread to Maharashtra, Mumbaikkars would proudly say that they would have been unaffected even if it did.

In the morning of October 12, however, the opposite seemed to have happened. Just as Mumbai was gearing up for the first day of the week, large parts of it went out of power.

“At 10.10 am there were simultaneous substation tripping in MSETCL’s Kalwa, Kharghar causing a huge dip in frequency in the Mumbai transmission system which led to tripping of Mumbai power supply,” Tata Power said in a statement.

“Restoration work in is in progress to bring supply from the 3 Hydro units and Trombay units once the MSETCL transmission lines are connected. Inconvenience is regretted,” added Tata Power, which supplies much of the Mumbai with its energy requirement.

By 2pm, industry officials said half of the supply has been restored. “We need more power to restore supply for the rest of the customers. At present, power availability is low,” said an official from the power utility.

Another official from the industry added that power will be completely restored after knowing the reason behind the mismatch between supply and demand. The Maharashtra Chief Minister has formed a committee to look into the matter.

On the other hand, Adani Electricity Mumbai Ltd, or AEML, said its “distribution system operated Islanding facility successfully and continued to successfully supply power to vital installations with the help of Dahanu Thermal Power Station (DTPS).” Along with Tata Power, AEML also supplies power to Mumbai. State-owned Brihanmumbai Electricity Supply and Transport, or BEST, is the other supplier.

“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 Mahatransco”, said AEML Spokesman

Irrespective of the outcome of the inquiry, the power outage brings back the focus on the demand-supply mismatch in Mumbai. Experts have previously said that the city needs to further add capacity for the ‘islanding’ to remain effective.

A 2018 report of Western Region Power Committee says that “due to reduction in embedded generation and growth in Mumbai demand, there is increased power flow from outside to Mumbai through tie-lines to meet the demand of the island.” The report added that the total embedded generation in Mumbai system is 1877 MW, which is approximately 50 percent of the peak demand.”

With the city becoming more dependent on outside source for power, how effective will be islanding?
The islanding system in Mumbai was developed by Tata Power in 1981. It has worked efficiently in the past.

The 2018 report quoted above says that the system has helped Mumbai stay immune to major grid disturbances – which otherwise affected other parts of the state and country – 27 times, since 1981.

How does an islanding work? A Mint story, quoting Tata Power officials explains. In case of a blackout because of a tripping in a major grid, a micro-grid goes in to an ‘intentional islanding,’ mode. Under this, the micro-grid disconnects the local circuit from the bigger grid, and the entire power demand is met locally. Apart from Mumbai, Kolkata is also said to have an islanding mechanism.

In Mumbai, the islanding depends on Tata Power’s supply network that comes from its thermal plant in Trombay, and its hydro units in Khopoli, Bhira and Bhivpuri, all in Pune district. Adani’s supply comes from its unit in Dahanu.

For both the power companies, the Kalwa sub-station is an important part of their networks. It is unclear yet what led to the sudden surge in demand that caused the tripping. But the islanding system may not work as efficiently if the city’s dependence on outside sources grow.

While AMEL’s lines were not affected, its customers in Mumbai also were affected. “That is because the company’s capacity in Dahanu alone is not enough to meet the demand of its customers. So it buys power from the grid, which uses the Kalwa lines,” said an industry official.

It is not the first time though the sub-station at Kalwa has seen problems. In 2018 too, a snag in the sub-station had led to outages in Thane and Navi Mumbai.

But none in the industry expected a repeat that would impact nearly all of the island city. -Money Control

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