Nepra Holds NTDC Responsible for Power Blackout
The National Electric Power Regulatory Authority (Nepra) has held the National Transmission Dispatch Company (NTDC) responsible for the partial blackout in the country on October 13, 2022.
In its inquiry report, it stated that the receiving of a false DTT signal at the 500kV Gatti G/Station from the Ghazi Barotha end initiated the tripping of the 500kV Gatti Ghazi Barotha Circuit-11.
The blackout was caused by the failure to complete the dedicated transmission line for the evacuation of power from the K2 and K3 power plants.
The power regulator further stated that the tripping of the 500kV K2/K3-NKI T/Line and the 500kV K2/K3-Jamshoro T/Line was due to mechanical failure of the hardware/conductor.Check KE Duplicate Bill |K-Electric Duplicate Bill 2023
This was a result of improper interim arrangements with non-standard/non-specific hardware material and a lack of periodic maintenance of transmission lines as per standard operating procedures (SOP).Check IESCO Bill Online| Download IESCO Duplicate Bill April 2023
Power Blackout
On October 13, 2022, at 09:33 Hrs., a breakdown of the power supply system occurred, plunging a significant region of the country into darkness.
NEPRA took notice of the incident and decided to conduct an inquiry. An Inquiry Committee was formed to investigate the matter.
According to the findings of the power regulator, the initial cause of the tripping was overheating and subsequent damage of T-clamps and conductor at the temporary diversion between location number 26A and 27 of the 500KV K2/K3-NKI circuit for the evacuation of power from the K2/K3 plants.
Since the construction of the dedicated transmission line for the evacuation of power from K2/K3 could not be completed by NTDC, an interim arrangement was made, which is still in place indefinitely as the dedicated transmission line remains incomplete.
This interim arrangement involves a number of joints with different types of clamps, such as T-clamps and L-clamps, based on availability at the time of execution.
The conductor of the transmission lines being used for the interim arrangement is approximately 26 years old and installed in a heavily coastal polluted area, resulting in deterioration.
Initially, a fault developed on the 500kV NKI-K2/K3 circuit due to overheating and breakage of T-clamps of the jumper, which resulted in tripping from both ends.
This caused a shift in the load, approximately 2700 MW of CPHCL and K2/K3, to the remaining two circuits between K2/K3 and Jamshoro, as the CPHGCL-Jamshoro circuit was already under scheduled outage since 08:48 hrs.
The additional load affected the 500kV K2/K3-Jamshoro circuit, which is an older circuit, where a subconductor of the Red phase heated up at the dead-end body at location number 26A and consequently detached and fell to the ground.
The tripping should have occurred instantaneously through the tele-protection scheme instead of zone-2.
The relay indications and fault recorder data at the Jamshoro end show that the tele-protection signal (permissive) was not received at Jamshoro from the K2/K3 end.
This needs to be checked and addressed. Regarding the failure of hardware within three years of commissioning, it is due to the improper interim arrangement with non-standard, non-specified hardware material and a lack of periodic maintenance of transmission lines as per SOP.
The tripping of circuit breakers on the 500kV HUBCO-K2/K3 circuit at K2/K3 upon receipt of the DIT signal, which isolated CPHGCL, was due to a false signal, as verified through the telecom log during a visit to HUBCO, where no signal was transmitted. This false telecom signal needs to be checked and addressed.
The Lucky Power Plant tripped due to “Over Excitation Protection” caused by overfrequency. However, its Power System Stabilizer (PSS) is yet to be brought into service to stabilize the system. In the South region, the system could not sustain due to insufficient generation compared to the load demand.
Some load was shed automatically through under-frequency schemes.
However, the region was subsequently restored through KE power plants and NTDC supply, and the NTDC-KE system synchronized at 17:25 hrs.
Although the system was restored within a reasonable time, the restoration of the KE system was slightly delayed as about 60% of their restored network tripped through cross-trip schemes.
This could have been minimized if KE, who was well aware of the situation, had blocked the cross-trip scheme before initiating the restoration process.
During the visit to the breakdown/interim arrangement site, the Inquiry Committee observed that even after rehabilitation, the condition is still risky, especially that of the conductor, which is bulged at some points. It needs to be addressed as soon as possible to avoid any unforeseen events.
The status of previous inquiry report findings and recommendations regarding the total power collapse on January 09, 2021, and the NTDC Inquiry Report dated October 13, 2022, regarding the partial shutdown, are still under implementation.
Nepra provided the following remedial measures and recommendations in its report:
The power regulator said that the existing interim arrangement should be immediately reinforced with standard hardware.
The aging factor of the conductor and the quality of material and proper workmanship during the execution of the interim arrangement must be ensured.
Periodic maintenance and monitoring activities, especially for the interim arrangement designed for K2/K3 circuits, must be ensured as per SOP.
The pending work on dedicated transmission lines for the evacuation of power from K2 and K3 plants should be completed with top priority.
A fully functional SCADA facility for the complete system related to NTDC, GENCOS, lPPs, and DISCOs is essential for the system operator to ensure online monitoring of system parameters, security, stability, and analysis of events through GPS-synchronized time event recorders.
Installation of modern technology devices such as Wide Area Management (WAM), including Phasor Management Units (PMU), to detect oscillation instability, which can be mitigated by Remedial Action Scheme (RAS).
Availability of required professionals and staff as per approved yardstick, along with required tools and equipment, including thermovision cameras, especially in the southern region, must be arranged urgently to ensure timely maintenance of the existing network for system stability, reliability, and security.
Nepra emphasized that all approved transmission line projects must be completed on schedule. Work on delayed projects should be accelerated on a priority basis to ensure stable evacuation of power generation.
The deficiencies in the NTOC Telecom department must be addressed to ensure proper communication of intergrid signals and avoid the transmission of false signals.
Protocols and SOPs should be developed to streamline operational coordination between KE and NPCC.
The quantum of load to be shed through under-frequency and Rate of Change of Frequency (ROCOF) schemes in the South region needs to be increased to ensure the survival of the region during under-frequency situations.
The practice of switching off transmission lines to control overvoltage on the system, which is not prudent or recommended, should be studied to install additional Shunt Reactors at appropriate locations, such as Grid Station Busbars.
