The much-debated Mumbai’s islanding system failed to cope with the situation as it could not hold after an additional 900 mw load dropped at 10.05 am. Under the 'islanding scheme', Mumbai can be isolated and insulated from the grid so that it can draw power directly from a generating station in case of a collapse. The islanding scheme proposes that in the event of a grid blackout, as was seen in the July 2012 outage which cut power to states in north India, Mumbai can be cut off from the grid, thus isolating it from the effects of a large outage.
The islanding system, developed in 1981, had successfully saved Mumbai from several blackouts – on 27 occasions -- during major grid disturbances. But the islanding system miserably failed to save the city from power failure on Monday. The scheme has been revised several times by the Western Region Power Centre (WRPC) in line with the development of Mumbai power supply network.
State energy department sources told Free Press Journal, ``Mumbai’s islanding by Tata Power that saves the city from major power outages was separated. However, it could not hold an additional load of 900 mw which dropped. Although Adani Electricity distribution operated islanding and continued power supply to major installations but that was not enough.’’
At 10.10 am there was 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," said Tata Power.
On its part, Adani Electricity Mumbai ( AEML) said: ''Its distribution system operated the islanding facility successfully and continued to successfully supply power 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 Mahatransco.
Power sector expert Ashok Pendse said at the moment of disruption, Mumbai’s demand was 2,400 mw comprising Dahanu’s 500 mw and Tata Power’s 1100 mw, while 800 mw was coming from outside Mumbai. ‘’Even if Tata Power’s islanding had worked, still one third of Mumbai demand worth 800 mw would have been in darkness. Because of Covid the demand for power is less but generally it is in the range of 3,200 mw in Mumbai,’’ he noted.
Pendse said this means Tata Power and Dahanu put together can meet only 40% of city’s demand. ''‘However, for the balance 60% of Mumbai’s demand we need 400 kv sub stations and strengthen the transmission link. This has been well documented by a committee constituted by the then MahaVitaran MD Ajoy Mehta comprising IIT Professor SA Khaparde when similar grid disturbance had occurred,’’ he noted.
The officer recalled that the WRPC in March 2018 had said total embedded generation in Mumbai is around 1877 mw which is 50% of the peak demand of almost 3,825 mw. In case of grid disturbance, generation will not be able to meet the demand. Therefore, WRPC had emphasised the urgent need to review the existing Mumbai islanding scheme. '‘ In order to ensure successful operation of separation of Mumbai island in the event of grid disturbance and to ensure survival of the formed island, it is utmost important to identify some additional loads for load shedding in Mumbai. It was also suggested that generation within Mumbai should be given preference to supply within Mumbai, so that adequate generation is available within Mumbai. Further, it was also stated that public life and safety would be seriously affected, if the Mumbai city is without power supply,’’ said WRPC in its report. However, the suggestions have not been implemented in letter and spirit which led to Mumbai’s islanding scheme to be at play today.