Even the 'island city' is not an island, to extrapolate the John Donne quote. Mumbai's much-debated 'islanding' system failed to hold up, after an additional 900MW load dropped at 10.05am. In the event of a grid blackout, the islanding scheme is supposed to isolate or insulate Mumbai from the grid so that it can draw power directly from a generating station. This system was seen in action in the July 2012 outage in which states in north India were affected, but Mumbai was cut off from the grid, thus isolating it from the effect.
Developed in 1981, the system had successfully saved Mumbai from blackouts 27 times, during major grid disturbances. But it miserably failed on Sunday. The scheme has been revised several times by the Western Region Power Centre (WRPC), in line with the development of the Mumbai power supply network.
State energy department sources told The Free Press Journal, ‘‘Mumbai’s islanding, that saves the city from major power outages by Tata Power was separated. However, it could not hold an additional load of 900MW. Although Adani Electricity operated islanding and continued power supply to major installations, it was not enough.’’
At 10.10am, there was simultaneous substation tripping in the MSETCL's Kalwa and 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 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. Power supply to the 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 that at the moment of the disruption, Mumbai’s demand was 2,400MW, comprising Dahanu’s 500MW, Tata Power’s 1,100MW, while 800MW was from outside Mumbai. ‘‘Even if Tata Power’s islanding had worked, still one-third of Mumbai (800MW demand), would have been in darkness. Because of Covid, the demand for power is not as much but generally, it is in the range of 3,200MW in Mumbai,’’ he noted.
Pendse said this means Tata Power and Dahanu together can meet only 40% of city’s demand. ‘’However, for the balance 60 per cent of Mumbai’s demand we need 400kV substations and to 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 a similar grid disturbance had occurred,’’ he noted.
The officer recalled that the WRPC had, in March 2018, said total embedded generation in Mumbai is around 1,877MW, which is 50 per cent of the peak demand of almost 3,825MW. In case of grid disturbance, generation will not be able to meet the demand. Therefore, the 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 loadshedding 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 Mumbai city would be without power,’’ the WRPC had said in its report. However, these suggestions have not been implemented in letter and spirit, preventing Mumbai’s islanding scheme from being at play today.