ISLAMABAD: The National Electric Power Regulatory Authority (NEPRA) has released inquiry report on major power breakdown in the country.
According to the report, on 09th 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.
This bolted fault was not cleared due to malfunctioning of the relevant Circuit Breaker and the subsequent breaker failure scheme. The above persistent fault reflected on 220kV and 500kV transmission lines which tripped on Distance Relays in zone 2 and Unstable Power Swing respectively.
The restoration process was initiated quickly by the power plants and NTDC, the System Operator. 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 Gul Ahmed power plants as its own machines of BAPS-II were not available in island mode, Since KCCPP was under shutdown due to low gas pressures, therefore, and its island facility could not be utilized.
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 20 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 report suggests 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.
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.