ISLAMABAD: National Electric Power Regulatory Authority (Nepra) said that deficiencies in the transmission system, bolted fault at Guddu, unbalanced generation and connected load contributed to the complete breakdown across the country on January 9, 2021 which took over 20 hours to restore power.
A three-member Inquiry Committee (C) comprised of Nadir Ali Khoso Director General, Nepra (convener), Manu Ram Manager (Retd.) 500/220kV GSO, NTDC Private Sector (Member) and Khalid Mehmood Chief Engineer (retd) System Protection, NTDC.
Private Sector (Member) visited Guddu Power Plant to find out the reasons for the country-wide blackout.
According to the IC, the bolted fault resulted in the blackout due to the negligence of the staff of Guddu Power Plant. A departmental inquiry against the delinquents initiated by management of Guddu Power Plant needs to be concluded.
The reports of Power Division and its attached organizations/committees are ready but yet to be made public.
According to the Nepra IC, on January 9, 2021 at 23:40 hours, the whole country was suddenly plunged into darkness. From the initial reports appearing in media and the information obtained from NTDC, it was revealed that “some severe fault” in the system had caused the collapse of the entire power system of the country.
Nepra, being the regulator of the power sector, took serious notice of the incident and constituted an Inquiry Committee (IC) to investigate the matter in detail and submit a report to the Authority.
As per the Terms of Reference (ToRs), the IC was required to determine the nature of the fault, it’s causes and recommend the way forward for avoidance of such breakdown in future.
The IC in the process of its proceedings visited a number of power houses, grid stations, offices of NTDC, Member (Power) and K-Electric. IC was briefed by the concerned offices. Some relevant record was provided to them and the incident was also discussed in detail.
Some of the findings and recommendations based on its 24-page inquiry report are as follows: (i) On January 9, 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. This persistent fault reflected on 220kV and 500kV transmission lines which tripped on distance relays in zone 2 and unstable power swing respectively;(ii) 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 imbalance 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; (iii) 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 BQPS-II were not available in island mode.
Since KCCPP was under shutdown due to low gas pressure, therefore, its island facility could not be utilized;(iv) 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 most of the thermal power plants were synchronized with NTDC within 27 hours. 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;(v) the causes of blackout are the persistent bolted fault at Guddu switchyard and resultant unstable power swing in the power system. In order to address unstable power swing phenomenon, a comprehensive study should be arranged from a reputable international firm to avoid such incidents in future; (vi) 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 houses of 200MW and above that at least one machine shall remain available in island mode under frequency situation to facilitate early restoration; (vii) for sequential tripping instead of simultaneous outage of machines on over frequency, settings shall be managed accordingly;(viii) 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;(ix) a number of deficiencies were noted in 220kV switchyard and control room at TPS Guddu which need to be addressed on top priority.
The bolted fault which consequently resulted in the blackout was created due to the negligence of the staff of Guddu Power Plant. The departmental inquiry against the delinquents initiated by management of Guddu Power Plant need to be concluded.
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 Technical Services Group (TSG) NTDC/manufacturer of the equipment.
According to the IC, there is no centralized event recorder available with NPCC. So the sequence of tripping of transmission lines and machines in the power system cannot be ascertained precisely. It is observed that the distance relays in the system have operated randomly which the committee believes is undesirable.
It is noted that none of the machines in power plants which were operational at the occurrence of event went into the islanding mode under frequency situation which could have helped in early restoration of supply.
There are no contingency plans and agreed procedures between the System Operator-NPCC, NTDC and power plants for restoration of supply during total and partial shutdowns.
Copyright Business Recorder, 2021