Explained: Only 30% of power is used for house lights, so switching them off shouldn’t trip the grid… we hope During this 9-minute lights out exercise on Sunday night, up to 10,000-15,000 MW of power demand could to drop suddenly and then come on stream a few minutes later.

Anil Sasi |IE| New Delhi | April 4, 2020 :  Explained: Why is there concern that the 9 pm lights-out could impact India's electricity grid?

In his address to the nation on Friday, Prime Minister Narendra Modi asked people across the country 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 such as Punjab, Uttar Pradesh, Gujarat and Tamil Nadu, though their respective state load despatch centres (SLDCs), are learnt to have flagged the risks and are preparing for the worst case scenario as a contingency measure, with the assumption being that all lighting load in the country could simultaneously go off for 9 minutes on Sunday evening and then come back on.

9 pm 9 minutes: How can the switching off of lights impact the functioning of the grid?

India is one of the largest synchronous interconnected grids in the world, with an installed capacity of about 370 gigawatts (3,70,000 mega watts), and a normal baseload power demand of roughly 150 gigawatts.

Power System Operation Corporation Ltd (POSOCO), the national electricity grid operator, projects daily demand of power and regulates supply from power generators based on these projections to maintain frequency (demand-supply balance) round the clock to prevent the grid from tripping.

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.

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 decrease in voltage.

When an exigency occurs, like an outage at a power plant or the tripping of a transmission line or a sudden change in electrical demand, the operator needs to ensure that there is automatic corrective response, failing which it needs to manually intervene to avert a crisis by curtailing demand or ramping generation from another source within a really short period of time.

Handling imbalances is the most crucial function of the grid operator.

PM Modi’s appeal: Why is the 9-minute exercise a problem?

The big worry is that just before 9 pm there may be unprecedented load reduction, followed by sudden increase in load post 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.

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

Domestic load is about 30-32 per cent of total load during the 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.

What then are the key areas of concern?

While the possibility of the grid tripping on account of this in highly unlikely, operators expect a “jerk”.

While the system is generally planned for outage of single largest unit outage, there are two riders:

One, the grid load is primarily on account of domestic load now, especially since the lockdown implemented from March 26. The normal baseload power demand of roughly 150 gigawatts has already dropped by 20 per cent since the lockdown announcement as most of industry and commercial establishments are not operational.

With hotels and factories, malls, railway stations, airports closed, domestic load is the predominant load. So the lighting load as a percentage of total load is much higher now and the impact of a sudden drop in lighting load could be more accentuated than during regular times.

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.

There is, however, hope that the airconditioning load, which is still to kick in in the northern region, would act as a counterbalance. In the western and southern regions, the airconditioning load is already up, which could ensure that the switching off of the light could place a lesser stress on the grid.