Electrical power lines hang from a transmission pylons alongside a road in Mumbai, on October 12, 2020. India’s financial capital saw its biggest power outage in decades on the day. (File photo)
Electrical power lines hang from a transmission pylons alongside a road in Mumbai, on October 12, 2020. India’s financial capital saw its biggest power outage in decades on the day. (File photo)

Mumbai power outage: Electricity regulator had raised questions on islanding system

Mumbai’s electricity provider has acknowledged the October 12 power failure in the city could have been avoided had the system survived outside grid disturbance after operationalisation of the islanding scheme
By Anisha Dutta
UPDATED ON MAR 03, 2021 03:12 PM IST

Mumbai: Mumbai’s electricity regulator questioned the failure of the city’s decades’ old islanding system at its hearing held last year on the October 12 grid failure. It also pointed to a delay bringing the generating units on the bar during the outage.

The regulator, in an order, said that the failure of the system, the delay, possible inadvertent tripping by the station operator at Kharghar substation, delay in load management/load disconnections, inadequate load trimming, etc., are some of the reasons for the outage stated by the stakeholders.

“However, verification of individual submissions and root cause analysis by independent experts would be necessary to find out the exact reason for the incident. This analysis would also help to take appropriate (immediate and medium-term) remedial measures for ensuring that such an incident do not recur in future,” it said.

The stakeholders called to the hearing on October 20 also questioned the grid failure and the delay in restoration of power supply by Tata Power.

In its submission to the regulator on October 20, Brihanmumbai Electricity Supply and Transport (BEST) noted: “ Delayed restoration of power supply in Mumbai has caused immense hardship to BEST’s consumers in the critical Covid pandemic scenario. The prolonged power failure could have been avoided, had Mumbai system survived from outside grid disturbance after operationalisation of Mumbai Islanding scheme and if TPC (Tata Power Company Ltd) was able to bring its hydro/ thermal generation into service without delay. Hence, further review of Mumbai Islanding scheme considering load/generation balance is necessary.”

“Mumbai Generating Companies, Transmission Licensees and MSLDC [Maharashtra State Load Despatch Centre] were aware of critical situation arising due to failure of 400 kV lines in the early morning of 12 October, 2020. Accordingly, a contingency plan should have been initiated to avoid any further grid disturbance,” it added. The BEST said the strengthening of Mumbai transmission is essential to remove the congestion in the system.

“The occurrence severely affected the power supply to a large section of population of MMR [Mumbai Metropolitan Region]. Hence, occurrence was required to be taken cognisance of for ascertaining actions pertaining to dereliction of actions, if any, in operation and maintenance of lines, system security, failure of protection and to achieve intended islanding of critical load-generation balance for areas.”

The regulator said it was appropriate to initiate a suo motu proceeding to find the primary reasons for the partial grid failure, response, and performance of licensees/generators and for identifying preventive measures. It issued a notice on October 17 asking MSLDC to submit a detailed report on the partial grid failure.

Islanding system refers to the condition in which a generator provides electricity to a location even though electrical grid power is no longer available. Tata Power introduced the system in 1981. It is unique to the region and the only such system in the country.

At the hearing, executives of Tata Power too suggested that the islanding system needs to “be relooked”.

“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 and distribution, Tata Power, said in his representation to the regulator.

The islanding system has an embedded power generation of 1,877 megawatts. Banga said earlier this was enough to meet the electricity demand of Mumbai. It also 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.

According to the regulator’s order, Tata Power said that its hydro units were picked up but the same could not be synchronised with the grid. The company added the rate of frequency decline was so high that before the breaker operation could complete, the frequency dropped significantly.

Tata Power also noted that since 1997, there was no failure of the islanding system.

“ Initial analysis of TPC suggests that islanding system works effectively in generation rich system. In past islanding events, the embedded generation was around 80 to 90% of the load. However, in the present event, almost 60% of power was from outside Mumbai and also almost 1000 MW availability was dropped at Kalwa Substation. TPC-G generation was picking up, but the system changes were so rapid in its transient state that Islanding System could not operate successfully,” it said.

“Considering the fact that embedded generation capacity is reducing over time, Mumbai demand is increasing, and more and more power being received from outside Mumbai, review of existing Islanding System and review of frequency setting needs to be undertaken.” It added that the company has formed an internal committee to analyse the event and look into the technical issues in detail.

The regulator also ordered that a high-level expert committee be formed to analyse the root cause of the tripping that led to the grid failure. It added the committee will have to submit its report within three months of the formation. “The high level committee had in January asked for the extension in submitting its final report,” a power ministry official said.

According to MSLDC, there was inadvertent tripping by a station operator at the Kharghar substation, which resulted in the outage. “There was considerable delay in bringing TPC-G Unit 5 and Unit 7 on bar. Also, Hydro Generating Units that are expected to come on bar in short time, but same were also synchronised with the grid with considerable delay.”

The regulator noted: “It is necessary to find out as to what happened at individual stakeholder level and what needs to be done in future at individual stakeholder level and collectively at systems level to avoid recurrence of such event.”

It added in the past when similar incidents occurred, studies were undertaken through expert committees to find out the primary reason for the grid disturbances. Based on their recommendations, glaring difficulties were rectified. “However, the long-term plans for infrastructure augmentation/development seem not to have materialised in toto as was expected. Accordingly, it is necessary to examine as to whether the delay in implementation of recommendations/suggestions of the Committees had any bearing on the partial grid failure of MMR that occurred on 12 October, 2020.”

The outage was back in the spotlight after American cyber intelligence company Recorded Future said it had uncovered a suspected China-linked cyber operation that was focussed on India’s electricity grid and other critical infrastructure. While the company did not link the Mumbai incident to the operation it discovered, it did not rule it out either.

According to Recorded Future, RedEcho deployed malware known as ShadowPad, which has been previously linked to Chinese cyber soldiers. ShadowPad has the ability to hand over systems controls to malicious hackers, who can then make potentially catastrophic to sensitive industrial systems.

Chinese government-linked attackers possibly gained access to computer networks part of India’s power infrastructure, the American firm said, citing technical clues that federal power ministry officials separately said had been on their radar, fuelling speculation that a blackout in Mumbai last year may have been the result of sabotage.

Hours after the disclosure, the Union power ministry said it had received inputs from Indian agencies—first in November and then again in February this year—about the threat of infection from ShadowPad, prompting remedial measures to be taken.

On Tuesday, Union power minister RK Singh said the power outage in Mumbai in October was caused by “human error”, not a cyber-attack.

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