ISLAMABAD - National Electric Power Regulatory Authority (NEPRA) inquiry report, regarding nationwide power breakdown in country, has hold the staff of Guddu Thermal Power Plant responsible for gross negligence which had resulted in the blackout.
The inquiry report recommended that the departmental enquiry initiated by Guddu Power Plant management against the delinquent staff regarding the instant breakdown be concluded and management reforms at Guddu for systematic working.
The inquiry set up by NEPRA, on nationwide power blackout occurred in January, has also hold the staff of Guddu Power Plant responsible for the gross negligence.
National Electric Power Regulatory Authority (NEPRA) had constituted a three member Inquiry Committee to investigate the power blackout which had plunged the entire country into darkness. The committee had submitted it report on February 8, 2021, which was released on Tuesday.
As per the report the 3 phase to earth bolted fault was caused by 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 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 KE, 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 power system of North zone tripped on under frequency condition where the generation was too less against the load.
The System Operator/NTDC together with the Power Plants took around 20 hours and IKE 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. Lapses are 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 KE 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. Hence, NTDC, KE together with concerned power plants are responsible for delay in complete restoration of power system.
The report noted that “Despite assurance by Member (Power), the office of Member (Power) failed to provide the copy of the Inquiry Report regarding black out which occurred in Feb, 2013”.
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 NTDC as very old which have completed their life time and need to be replaced however no action was taken. Similarly delay in 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. It was also recommended by the previous reports that during the canal closure and foggy seasons i.e. 15th Dec to 15th Feb, 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 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. NTDC, KE and Power Plants shall prepare contingency plans and establish procedures for restoration of supply in case of emergency, partial and complete power failure.
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 NPCC; a function should be developed at the power houses with capacity of 200 MW 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 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. In this regard, necessary amendments in any applicable document i.e. PPS, Tariff Determination, License 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 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.
Single Line Diagram of 220kV switchyard Guddu and Mimic diagram of its 220kV control room be updated and made available at site as well as with NTDC.
Routine testing of HIV equipment at Guddu switchyard including protective relays shall be carried out regularly; Technical trainings be arranged for staff and engineers at TPS Guddu for their skill improvement and capacity building; The departmental enquiry initiated by Guddu Power Plant management against the delinquent staff regarding the instant breakdown be concluded; Management reforms are required at TI’S Guddu for systematic working.