Nepra finally releases inquiry report on January’s power breakdown

ISLAMABAD-NEPRA has finally released the inquiry report on January’s countrywide power breakdown, after a delay of two months, holding NTDC, KE, Port Qasim Company Limited and Central Power Generation Limited Company (CPGCL) responsible for the incident. The NEPRA Inquiry Committee report on total power breakdown on January 23, 2023 in the country released here Friday said that the contributing factors for cascaded tripping were the injection of wind power generation in South and curtailment of hydel power generation in Ghazi Barotha Power Station at North by NPCC. Running back of Port Qasim Power Plant instead of shutdown at set over-frequency setting was another contributing factor. 
National grid system and KE system were completely restored at 03:22 05:08 am, respectively, on January 24, said the report. The factors for delayed restoration were frequent tripping of Tarbela units while energization/loading of circuits, delayed synchronization of Mangla Power Station with bus bar due to internal fault, late synchronization of Tarbela and Mangla Power Stations by system operator, delayed availability of following power plants despite Notice to Sync (NTS) by System Operator: Nandipur, Sahiwal Coal, Guddu, China Hub, HUBCO, Halmore. 
Causes and faults which resulted in cascade tripping and system collapse included, the induction of power generation at south and reduction of generation at north caused oscillations in the system which gave rise to power swing. Power swing could not be controlled due to nonoperation of out of step protection devices. Hence in the south initially over frequency and later under frequency whereas only under frequency occurrence in the north caused in the cascaded trippings of lines and power houses which resulted in total power blackout/breakdown in the country. 
While fixing the responsibility, the report held NTDC, Central Power Generation Limited Company (CPGCL), Port Qasim Company Limited and KE jointly responsible for the incident. 
Delay in restoration of the NTDC system was mainly due to failed attempts of black start facilities at WAPDA Hydel Power Stations and KAPCO. Other factors include delay in synchronization of various power plants and non-availability of SCADA system in NPCC. Whereas, KE system was also delayed due to repeated failed attempts on their black start facilities. 
The report recommended that VAR compensations study shall be carried out and required measures in light of study shall be taken to avoid power swing. The stability of HVDC system needs to be ensured through proper study to avoid frequent signals of ‘Commutation Failure’. NTDC staff needs to be trained for thorough understanding of HVDC transmission system. 
Fully functional SCADA facility for complete system related to NTDC, GENCOS, IPPs and DISCOs is essentially required for system operator in order to ensure the online monitoring of system parameters in all respect for sake of system security, stability and analysis of events. Implementation of protection settings issued by NTDC for power plants, mutually agreed, shall be ensured under witness of NTDC through CPPA-G.  NTDC shall ensure the healthiness and operation of recently installed out of step devices, as the same did not operate during the event. 
Quantum of load to be rejected through under frequency schemes need to be increased, especially in South region, where it is considerably less. 
Simultaneous tripping of K2/K3 Units on over frequency shall be made stage wise.  SECL, Thal Nova and Thar Energy Power Plants are not included in the over frequency tripping scheme, hence shall be considered. 
SOP to be developed between all stakeholders to maintain required water indent for relevant hydel power station under acute emergency situations. 
KE shall set right the cause of undesired tripping of Unit # 10 at BQPS-III. 
KE shall also set right their Black Start facilities as multiple attempts were made during restoration and as such not satisfactory.  Periodical testing of Black Start facilities shall be carried out to ensure their satisfactory performance at the time of need. 
Black start facilities are required at some additional locations, better study based near Lahore and Hyderabad to help early restoration during Black Out. 
Repeated tripping of machines at Tarbela and Mangla during Black Start need to be checked and set right, as successful restorations have been carried out through these stations in the past.

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