After Mumbai's power outage, Tata power to upgrade city's islanding system

Following the power outage in Mumbai earlier this month, Tata Power has suggested that the unique ‘islanding power system’ of the city needs to “be relooked”. The review is also required because the power generation mix is changing due to increased renewable generation and rising power demand.

Executives from Tata Power were speaking at the suo-motu hearing conducted by Maharashtra Electricity Regulatory Commission (MERC) on the power breakdown that gripped Mumbai and adjoining areas on October 12. 

“We have all been historically dependent on the islanding scheme, but since the generation and incoming power ratio is changing, a change is required in the islanding scheme itself. With the central coordination and Western Regional Power Committee (WRPC), we have to completely relook at the islanding scheme in view of less embedded generation and more import of power,” Sanjay Banga, president, transmission & distribution, Tata Power, said during his representation to the MERC.

Introduced in 1981, the ‘islanding system’ developed and executed by Tata Power is unique and the only such power system in the country. Due to the system, Mumbai has the advantage of assured uninterrupted reliable supply of power. 

In the case of grid failure, the islanding system ensures uninterrupted power supply within city limits. In the case of breakdown in the Western Regional Power Grid, Tata Power’s system is automatically isolated from the rest of the grid. It ensures that generating units continue to function. All essential services are assured continuity of power supply, according to the Tata Power website. Electricity customers in Mumbai pay extra for the islanding system.

The islanding system has an embedded power generation of 1,877 megawatt (Mw). Banga said earlier this was enough to meet the electricity demand of Mumbai. Now, it accounts for less than half the peak demand of Mumbai and adjoining areas. To meet the balance demand, power is imported from outside the islanding system. 

Tata Power will engage the Indian Institute of Technology-Mumbai to study the islanding system and how it can be changed along with the WRPC. The WRPC is the responsible body for any changes to the islanding system.

“We will try to see what new changes need to be inducted due to increased supply of renewable power and the latest power outage incident, where the frequency drop was 3x more than normal. It will be difficult to maintain the islanding system unless we study what changes can be done,” said a senior Tata Power executive. 

He also said power distributors in the city are choosing cheaper options and renewable sources more lately, which also impacts the frequency of the island grid. Mumbai islanding has the participation of Adani Mumbai Electricity (AMEL) — the largest power distributor for the city.

After it took over operations from BSES in 2018, AMEL changed its power procurement mix. Vidarbha Industries Power, a subsidiary of Reliance Power, was to supply 600 Mw to Mumbai operations. The two units of Vidarbha, however, have been shut since the start of 2019, following which AMEL served a termination notice to the company. This development, and AMEL’s renewable power obligations, has led to the company changing its procurement mix.

In 2019, AMEL was relying on short-term power purchases from various alternative sources to make up for this deficit, which the management said has proved to be cheaper. “In order for it to be replaced on a long-term basis, we have already gone ahead and announced the requirement of hybrid power which will take care of the load profile of Mumbai and will help us further reduce the cost of input power to the distribution area,” said Anil Sardana, chief executive officer for Adani Transmission, in a call with analysts.

Tata Power executives during their representation also said all stakeholders should work towards making the islanding system successful and not completely abandon the embedded generation.

MERC heard representations from Tata Power, AMEL, Maharashtra’s transmission company, electricity distribution company, and the state’s load despatch centre. The regulator will decide on further action based on the submissions.