In his address to the nation, our PM has urged people across to turn off the lights in their homes for 9 minutes on April 5, starting at 9 pm. In response to this appeal, grid managers across states have flagged some risks.

Why is the 9-minute exercise a problem?

• India is one of the largest synchronous interconnected grids in the world, with an installed capacity of about 370 GW (3,70,000 MW), and a normal baseload power demand of roughly 150 GW.
• The big worry is that just before 9 pm there may be unprecedented load reduction, followed by a sudden increase in load post at 9.09 pm.
• The concern is that grid frequency should not swing beyond permissible limits and that all generators across the country must give frequency response as per the Grid Code.
• During this 9-minute lights out exercise, up to 10,000-15,000 MW of power demand could to drop suddenly and then come on stream a few minutes later.

How does grid function normally?

• Power System Operation Corporation Ltd (POSOCO), the national electricity grid operator, projects daily demand for power and regulates supply from power generators based on these projections.
• Frequency reflects the load generation balance in the grid at a particular instant and is one of the most important parameters for assessment of the security of the country’s power system.
• The nominal frequency is 50 hertz and POSOCO endeavours to maintain frequency within a permissible band (49.9- 50.5 hertz), primarily by balancing the demand-supply equation.

Impacts of light-out

• The frequency needs to be maintained within this range as all the electrical equipment and appliances at our homes are designed to perform safely and efficiently in a certain power supply band.
• An increase in frequency results in an increase in the voltage and a decrease in frequency results in a decrease in voltage.
• Exigency does occur during an outage at a power plant or the tripping of a transmission line or a sudden change in electrical demand.
• The grid operator needs to ensure that there is an automatic corrective response manually by curtailing demand or ramping generation from another source within a really short period of time.
• Handling imbalances are the most crucial function of the grid operator.

What are the key areas of concern?

While the possibility of the grid tripping on account of this is highly unlikely, operators expect a “jerk”. While the system is generally planned for an outage of the single largest unit outage, there are two riders:

1) Lockdown has severed domestic consumption

• One, the grid load is primarily on account of the domestic load now, especially since the lockdown implemented.
• The normal baseload power demand of roughly 150 gigawatts has already dropped by 20 per cent since the lockdown announcement as most of the industry and commercial establishments are not operational.
• With hotels and factories, malls, railway stations, airports closed, the domestic load is the predominant load.
• So the lighting load as a percentage of total loads is much higher now and the impact of a sudden drop in lighting load could be more accentuated than during regular times.

2) Fear of complete power-offs

• The second concern is if housing clusters and societies switch off mains, or if overzealous discoms switch off street lighting or even feeders to show compliance.
• During this part of the year, domestic load peaks at about 9 pm.
• This load could then be impacted much more than what’s being anticipated in the normal course, a concern that grid operators are flagging.

Why is this demand of significance in such a big grid?

• The domestic load is about 30-32 per cent of total load during normal times.
• Of India’s total electricity demand load pattern, industrial and agricultural consumption accounts for 40 per cent and 20 per cent load, while commercial electricity consumption accounts for 8 per cent of demand.
• So, theoretically, if only lighting load goes off, it should not have a major impact on grid frequency during normal times.

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