Guddu plant staff committed gross negligence

An inquiry report of the National Electric Power Regulatory Authority (Nepra) has found officials of the Guddu Thermal Power Plant in “gross negligence” that resulted in the countrywide blackout on January 9, this year. The regulator recommended the management of the Guddu Power plant to initiate the departmental action against the delinquent staff regarding the instant breakdown and management reforms for systematic working. Nepra had conducted the inquiry into the nationwide power blackout. The regulator had constituted a three-member inquiry committee, which submitted it report on February 8, 2021, and made public on Tuesday. According to the report, the 3-phase to earth bolted fault was caused because of gross negligence of Guddu Power Plant staff, who operated the 220kV Circuit Breaker D12Q1 (CB) without opening the earth switch of the 220kV Isolator D12Q31 and that too without the permission – of NPCC. Unfortunately, not only the CB failed to trip but CBF scheme also did not operate. As a result, cascade tripping occurred due to the bolted fault which divided the power system in South and North zones -- consequently, there was sufficient unbalance between the generation and the load. In the South Zone, including K-E, there was more generation as compared to load, which at first experienced tripping due to over voltage /over speed/over frequency and consequently on under frequency, the report said. “The power system of North Zone tripped on under frequency condition where the generation was too less against the load, it said, adding that it took about 22 hours for complete restoration of the power supply in their respective jurisdictions. “No doubt, under such circumstances, the complete restoration of the power system takes considerable time, however, the companies could have taken lesser time for restoration, had their power plants responded appropriately,” the report noted. According to the report, lapses were observed on the part of power plants, which despite prior notice by NPCC to synchronise, failed to restart and synchronise their all units with the system in specified time. “It is the obligation of System Operators of both NTDC and K-E to establish contingency plans and SOPs for system recovery following the total and/or partial shutdown, however, no such document was placed in this regard before the IC,” the report said. “Hence, NTDC, K-E together with concerned power plants are responsible for delay in complete restoration of power system,” it added. According to the report, the physical inspection of 220kV Isolator D12Q31 revealed that this equipment was in open condition, whereas, it’s earthing switch was in closed position before closing of 220kV Circuit Breaker D12Q1. There were sparks and carbonisation on contacts of the earth switch of 220kV Isolator D12Q31 and the grounding wire found damaged on its yellow phase. Further, the indication of Circuit Breaker Failure (CBF) of the breaker D12Q1 indicates that it did not operate on the operation of relevant protection due to bolted fault caused by the closed position of earthing switch of 220kV Isolator D12Q31. It was further noticed that the operation of CBF protection failed to trip the circuit breakers of relevant 220kV Bus Bar. Further, the comparison of log sheet and operation/indication record provided by TI’S Guddu shows several contradictions. The report further said that since 2013, nine complete or partial power outages occurred and each time an inquiry was conducted, which had made several recommendations. The review of the previous reports revealed that the recommendations made therein have been either partially complied with or still in progress or pending. Further, there are some recommendations given in previous reports, which need to be carried out and monitored regularly. It was recommended that certain number of 220kV Cl3s installed it Guddu Power House was reported last year by the NTDC as very old, which have completed their life time and need to be replaced, however, no action was taken. Similarly delay in the system restoration has also been caused due to non-availability of Black Start Facility in Power Plants located in central region. The Power Purchase Agreement for the future plants needs to include the black start facility for quick restoration, the report recommended. It was also recommended by the previous reports that during the canal closure and foggy seasons ie Dec 15-to Feb 15, hydel generation is recommended to be maintained at 1,500MW (minimum) at all times and at 2,000MW during peak hours, however it was not implemented. The inquiry report recommended that in order to avoid the recurrence of such events in the future; as regard to Power Swing phenomenon, a comprehensive study should be arranged from a reputed international firm to suggest Out-Of-Step (OOS) protection (Power Swing Blocking (PSIS) and Out-of-Step Tripping (OST)) in order to avoid major power breakdowns and blackouts. The NTDC, the K-E and the power plants should prepare contingency plans and establish procedures for restoration of supply in case of emergency, partial and complete power failure, the report further recommended. The report also recommended a centralised event recorder, no operation of power houses and grid stations be carried out without the knowledge and directions of the NPCC – a function should be developed at the power houses with capacity of 200MW and above so that instead of tripping of all machines, at least one of that shall remain available in Island Mode during under frequency, and shall be in a position to energise the bus bar to facilitate the startup of other machines and speedy restoration of the network. The black start facility shall be made available at the power plants suggested/selected by the NPCC, especially for those located in South and Central zones; In case of under frequency situation, at least one machine in power plants shall be made available in Island Mode in order to facilitate for early restoration of supply, the report said. In this regard, the report proposes that necessary amendments to any applicable document ie PPS, Tariff Determination, Licence or Grid Code etc be made, if required. The feeders which were supposed to, but did not, trip on under frequency shall be checked and kept healthy; the power plants which were not available for synchronisation despite the notice of the NPCC shall be dealt with under PPA; Grid Station Equipment and Protection/Control System of 220kV Switchyard, Guddu, shall be maintained in accordance with SOPs issued by TSG NTDC/manufacturer of the equipment. The report called for updating Single Line Diagram of 220kV switchyard Guddu and Mimic diagram of its 220kV control room and made available at site as well as with the NTDC. It said that routine testing of the HIV equipment at Guddu switchyard, including protective relays, shall be carried out regularly; technical trainings be arranged for the staff and engineers at the TPS Guddu for their skills improvement and capacity-building The report called for the departmental inquiry by the Guddu Power Plant management against the delinquent staff regarding the instant breakdown and management reforms at the TI’S Guddu for systematic working.

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