Tuesday’s power outage in Mumbai may not be a one-time occurrence if the city’s power requirement on any given day, especially in summer, exceeds 3400 MW.

Mumbai city has a peak demand of 3350 MW and off peak demand of about 2500 MW.

The city power system is islanded to some extent by local generation of 2500 MW. Import of power is 1400 MW.

The islanding was done years ago to make the city generation self-sufficient and ensure that even if outside power import fails, the locally generated power would sustain the network without power shedding.

Mumbai being surrounded by water on three sides also restricts transmission, as the lines have to come from the land locked side.

However, demand has been continuously rising each year and with no new generation capacity being added the islanding, which was once sustainable, now stands exposed to higher power.

The total local generation of 2500 MW, includes unit-6 of Trombay, which is on cold standby as the cost of generation is over ₹12 a unit.

Anil Sardana CEO and MD, Tata Power, while addressing the media on Wednesday, said the load when the tripping took place was 2950 MW. With Trombay unit-5 of 500 MW going offline and unit-6 also of 500 MW being on cold standby, the import of 1400 MW and local generation of 1500 MW totalling 2900 MW fell short of the demand, leading to load shedding.

Tata Power restarted unit -6 to restore normalcy in power supply. The restarting of unit -6 took about 12 hours as it was on cold standby. Unit-5 is expected to be online by late Wednesday evening.

Unit-6 supplies power to BEST and the latter had asked Tata Power to stop generation due to the high generation cost. (BEST is an electricity distribution utility like Tata Power and Reliance Energy.)

Sardana said fuel cost of unit-6 was pass-through and BEST had to bear the fuel cost. Tata Power’s revenue from the unit comes from the fixed charge component, which is about ₹0.60 a unit, he said.

Meanwhile, the Maharashtra Government has ordered a probe into the Tuesday’s power shedding. The Principal Secretary (Energy) will enquire into the incident.

Needless to say, the islanding will still serve its purpose provided BEST is willing to bear the fuel cost of generation. Or Tata Power may have to be allowed to convert the oil fired unit to a coal fired one, for which it has the environment clearance in place. This will bring down the generation cost to about ₹4 a unit.

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