#9baje9minute: PowerGrid Corp alerts voltage spurts on April 5 could lead to outage in places

The state run Power System Operation Corporation (POSOCO) in its advisory to all states on Saturday clearly said that the reduction in load of the order of 12,000 to 13,000 mw would kppen in 2-4 minutes and recover nine minutes later within 2-4 minutes on April 5 in the wake of switching off lights for nine minutes.

This sharp reduction in load and recovery, which is unprecedented, will need to be handled through hydro and gas resources. At the same time the PowerGrid Corporation, which is the Central Transmission Utility, has alerted that a sudden increase in system voltage at various stations leading to grid outage at places. Similarly, the Forum of Load Dispatchers also held a crucial meeting to ensure grid security.

POSOCO has asked that all clocks at generating stations may be synchronized to Indian standard time. During the evening peak hours i.e. from 18.10 to 20.00 hrs- hydro generation will be reduced and conserved for providing flexibility during 21.00 hrs event. During this time thermal and gas generation will be adjusted to manage the peak.

Subsequently, after the peak hour, thermal interstate generation stations generation would be gradually reduced to near technical minimum level of 60% by 20.55 hrs and simultaneously hydro generation should be increased to maintain the load generation balance.

Hydro generation and gas generation should be ramped down starting from 20.57 hrs keeping a watch on the system frequency. The hydro units should be kept rolling at 0-10 % of the rating and not to be disconnected during this period. Gas station should be ramped down to the minimum level.

After stabilization of system parameters hydro units may be withdrawn in consultation with regional load dispatch centres (RLDCs) and state load dispatch centres (SLDCs).

More importantly, all India grid frequency may be kept at lower side of the Indian Electricity Grid Code (IEGC) band (49.90 Hz) from 20.30 hrs onwards in view of anticipated frequency rise due to demand reduction at 21.0 hrs.

Since COVID-19 containment measures implemented from March 25, 2020 nearly 220-240 lines at 400 kV voltage level and above are kept in open condition for voltage control. System voltages have been kept within the Indian Electricity Grid Code (IEGC) band. The voltage levels would be within control keeping the generation scheduling.

Notwithstanding these measures, all switching operation of transmission lines, line reactors, and bus reactors should be completed by 20.00 hrs to keep voltage preferably around 760 kV/400 kV respectively on April 5.

Further, POSOCO has told regional and state entities to maintain their interchange with the grid as per schedule. All SLDCs have been asked to advise distribution companies to avoid any feeder switching operation from 20.00 hrs to 22.00 hrs.

All the RLDCs, SLDCs and National Load Dispatch Centre are advised to extend the evening shift timings till 22.00 hrs preferably and allow overlap with the incoming night shift.

PowerGrid Corporation Advisory

The PowerGrid Corporation of India has asked its regional centres to advise all station in charge and Regional Transmission Asset Management Centre (RTAMC) operation staff to be on high alert with required staff.

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