LAHORE: The National Transmission & Despatch Company (NTDC) has admitted that much-hyped system protection mechanism in place failed to avert the cascading effect of tripping, plunging the whole country into darkness following the January 23 power breakdown.
In a report titled ‘Complete Power System Collapse on January 23’ dated January 24, 2023, the National Power Control Centre (NPCC) of NTDC admits: “Cross trip schemes and Rate of Change of Frequency (Rocof) Schemes operated but system could not survive and led to complete blackout in NTDC and K-Electric.”
Commenting on the acknowledgement of NTDC, sources said, had this system protection mechanism worked efficiently, the scale of power failure could have been limited to a fairly small area. Hence, recovery time also could have been far less, they added.
With non-functioning of system protection equipment, waning resilience of national grid against large-scale power outages become evident. It stems from faltering mechanism put in place by the NTDC to isolate such faults to limited area, claimed sources. The significance of ROCOF Relays at different levels helps in making islanding in which parts of national grid is electrically isolated from other parts of the system, restricting fault to a limited area while avoiding cascading effect, explained sources.
In its report, the NTDC also noted that on Jan 23, 2023, at 07:34:15 hrs, system frequency had gone up to 50.75 Hz and severe hunting was observed on 500 kV system in south that caused load and voltage variation on 500 kV transmission lines. As a result, 500 kV transmission lines tripped, which resulted in isolation of North and South system, followed by blocking of HVDC system. These include 500 kV Muzaffargarh-DG Khan, 500 kV Guddu-Muzaffargarh circuit, 500 kV Guddu-DG Khan circuit, 500 kV Rahim Yar Khan-Guddu 747 circuit and 500 kV Guddu Old-Guddu 747 circuit.
Though under frequency, cross trip schemes and ROCOF Schemes operated, the system could not survive and led to complete blackout in NTDC and K-Electric, it observed.
Before the incident, total system generation was 11,356 MW including Hydropower of 1,280 MW, GENCOs + IPPs input of 10,202 MW. The system frequency was 50.31 Hz, while K-Electric withdrawal from national grid was 450 MW. Due to adverse effects of breakdown, following power plants tripped and as result of tripping: KANUPP-II: 1,040 MW, KANUPP-III: 900 MW, Port Qasim: 621 MW, Lucky Coal: 606 MW, Thar Energy Limited: 150 MW, Engro Thar: 150 MW, SECL 1,230 MW, CHASHNUPP-I 304 MW; CHASHNUPP-II 317 MW; CHASHNUPP-III 318 MW, UCH-I 372 MW, UCH-II 188 MW, Foundation 178 MW, Guddu Old 145 MW, Sahiwal Coal 621 MW; Atlas 40 MW; AGL 100 MW, Nishat Power 40 MW, Liberty Tech 100 MW, HBS 1,190 MW, Balloki 1,183 MW, Total Wind 3 MW, Total bagasse 136 MW. Resultantly, around 11,356 MW generation went out of the system.
As far as sequence and time of restoration is concerned, restoration process was started immediately after the blackout as per standard operating procedure from Tarbela, Mangla and Warsak in North and from UCH-I in south simultaneously. The generating units at Tarbela and Mangla could not maintain stability and tripped a number of times during the restoration process. On the other hand, the system extended by using UCH-I power plant equipped with back start facility up to 220 kV Grid Stations DM Jamali, Sibbi, Shikarpur, Rohri, Daharki, Quetta Industrial, Guddu, Jamshoro and UCH-II, Engro, Foundation Power Plants. Finally, at 1700 Hrs, Mangla generation was extended to Tarbela and Tarbela started to synchronise their units in synchronism with Mangla and restoration of system started by maintaining system parameters by both the power stations, especially Mangla.