NEPRA makes public inquiry report into country’s wide power outage

ISLAMABAD: The National Electric Regulatory Authority (NEPRA) on Tuesday made public inquiry report into country’s wide power breakdown on January 9 and declared that persistent bolted fault at Guddu switchyard and Unstable Power Swing in the power system were causes of the outage.

The authority recommended that in order to address Unstable Power Swing Phenomenon, a comprehensive study should be arrange from a reputable international firm to avoid such incidents in future, said the report.

“On 09 January, 2021 at 23:40 hours, on closing of a 220kV Circuit Breaker at Guddu switchyard, bolted fault occurred as the earth switch of related Isolator was left closed. The bolted fault was not cleared due to malfunctioning of the relevant Circuit Breaker and the subsequent breaker failure scheme. The said persistent fault reflected on 220kV and 500kV transmission lines which tripped on Distance Relays in zone 2 and Unstable Power Swing respectively,” it further said.

The report said that in winter season, the power flows from the power plants located in South towards North to meet the load requirement of that zone. The separation of North and South zones created an unbalance of generation v/s connected load in both the zones. In south, the generation was higher as compared to the connected load whereas, in North, the power plants experienced excessive connected load. This unbalancing of generation and connected load contributed towards complete breakdown.

Regarding the restoration, the report said that System Operation National Transmission and Despatch Company (NTDC) and power plants initiated the restoration process quickly. Some of the power plants did not respond to the notice to synchronize (NTS) by the system operator and took more time than the specified.

Similarly, KE also acted quickly by getting supply from Tapal and GulAhmed power plants as its own machines of BAPS-II were not available in island mode.

Most of the thermal power plants were synchronized with NTDC within 27 hours. The WAPDA Hydel power plants were synchronized with the National Grid within two hours. In case of K-Electric, the power plants were synchronized with its system in 17 hours. Overall, NTDC's power supply was restored in 20 hours, whereas KE took about 22 hours for the restoration. NTDC, KE and concerned power plants do not have contingency plans and SOPs for system recovery under total and/or partial shutdown of power supply.

The Regulatory recommended that the black start facility shall be made available at power plants to be identified by NTDC, Moreover, a function should be developed at the Power House of 200MW and above that at least one machine shall remain available in island mode during under frequency situation to facilitate early restoration. For sequential tripping instead of simultaneous outage of machines on over frequency, settings shall be managed accordingly.

The quantum of load to be rejected through under frequency relays along with time and setting coordination between those of transmission lines and machines needs to be reviewed for making those efficient and effective.

The regulator said a number of deficiencies were noted in 220kV switchyard and control room at TPS Guddu which needed to be addressed on top priority.

The bolted fault 'which consequently resulted in the black out was created due to the negligence of the staff of Guddu Power Plant. Technical trainings be arranged for skills improvement and capacity building for staff and engineers at Guddu Power Plant.

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.