So here is all that you need to know about mumbai/report-battigul-in-mumbai-power-to-be-fully-restored-by-late-night-2015589">today’s power failure.
A 500 Mw unit by Tata Power tripped around 9.45 am, which resulted in the power cuts in island city. Tata Power is the sole supplier of power for Brihanmumbai Electricity Supply and Transport undertaking that distributes power in city, while Reliance Energy distributes power in suburbs. Two power generation units of Tata Power were already scheduled for maintenance so the overall deficit in the system was 1250 Mw.
What happens then?
Mumbai consumes about 3200 Mw during peak hours. Normally these peak hours are 7.00 am to 11.00 am and 5.00 pm to 8.00 pm. This is the time when industries, offices start functioning and the demand surges. Similarly, as the sun goes down, lights are switched on driving the demand up. So, when 1250 Mw generation is not available to cater to demand of 3200 Mw, it puts the system into a crisis. Tata Power supplies about 1000 Mw to BEST, the primary distributor in city. As a result, most BEST consumers were affected.
Why did suburbs suffer?
Suburbs are mainly catered by Reliance Energy, the distribution company in Mumbai suburbs, though post amendment in the Electricity Act, Tata Power is also supplying to a few customers in suburbs. Reliance Energy produces 500 Mw of its own demand and has power purchase agreements in place with other power producers as well. However, as the Reliance Energy also buys power from Tata Power, their feeders were affected too. If they were not switched off and if the rotational power cuts were not resorted to, there was a danger that the entire city would have plunged into darkness. It is called ‘the cascading effect’. To avoid total darkness, companies resort forced reduction in demand by resorting to power cuts.
Why could they simply not buy power from elsewhere?
As per the statement released by Tata Power, additional power was available in the neighboring states, the distribution network was already overloaded and the power could not have been imported. The company did use its hydro stations to pump in a little bit of power, it still requires to fire its boilers for a long time before power generation in a thermal power unit is restarted.
Could this not have been avoided?
Unfortunately, no. It is an accident and while you may provide for small shortfalls, you cannot create backup for the entire system. The crisis occurred as two units generating 750 Mw were already shut and another unit that generated 500 Mw suddenly tripped.