The lights-off event planned for Sunday can lead to disruptions in power supply when everyone switches off their lights from 9pm and switches on after nine minutes. Electricity authorities have studied power consumption patterns across India and the share of lighting in it to come up with a plan to handle the expected dip and surge in consumption that day.
When everyone switches off their lights, the power plants will be impacted. The situation can be compared to a bicycle climbing upward. When the lights go off all at once, it is akin to the cyclist suddenly reaching the peak and continuing to pedal as before during the climb down. The bicycle speed will then ramp up and could lead to the cyclist losing his balance. The voltage in the grid and the frequency will surge. The frequency can be understood as the electrical equivalent of the bicycle’s speed. The bicyclist losing his balance is like our power plants stopping operation as a result of these sudden changes. If the bicyclist anticipates the steepness of the terrain and the cliff, then he can pedal as required.
Electricity authorities have observed consumption patterns across States and concluded that the dip and surge is likely to be of the order of 12 to 14 gigawatts, which is roughly 10% of electricity consumed (load, actually) at any given point in time in India. And the dip and the surge will each happen in 2-4 minutes.
Different types of power plants have different abilities to handle sudden increase or decrease in load. The control we have on these plants varies. In hydro plants, the water can be stored in dams to the brim and then let down. In coal-fired plants, it would be harder to suddenly reduce or increase their power generation. They take a while. In gas-fired plants, load changes can be much quicker. In nuclear plants, this ability is quite limited. It would be difficult to switch off or load these plants suddenly or quickly. In solar and wind, there is little or no control. The sun and the wind do not obey us at all.
Based on these, the Power System Operation Corporation Limited has come up with a strategy.
In India, power consumption hits a low at around 6:10 p.m.. This is when everyone’s left their offices. Lights are off in offices and not yet on at homes. The sun hasn’t set yet. Fans are probably off, too. After the low, power consumption rises and hits a peak at around 7:20 p.m. It then starts reducing.
During the evening when power consumption starts rising after the 6:10 p.m. low, the hydro plants will be powered down by decreasing the water flowing to the turbines and instead storing the water in the reservoirs during the evening (after 6pm) when power demand hits a peak. The load will be taken up by other units.
Before lights-out on Sunday, by 8:55 p.m., the thermal generating units such as coal and gas will be powered down to 60% of their capacity. And hydro plants will be powered up to take the shortfall from thermal plants.
After 8:57, both types of plants will be powered down as people switch off their lights. Power managers will keep a watch over the frequency. If they reduce the power but the demand is still there and not enough people are switching off their lights, then the frequency will dip too much. The Indian power system has codes specifying how low or high these frequencies can go. The frequency of power supply will in turn have an impact on all motors running — our fans, pumps, fridge and A/C compressors.
As the lights-out picks up, hydro units will be brought down to less than 10% of the maximum power they can produce. Gas units will be brought down to minimum power.
From 9:05 p.m., the thermal units will start ramping up, and from 9:09 p.m. hydro units will start powering up. After stabilisation, the operation of all types of power plants will be brought to normal.
Solar plants don’t produce power in the night. Power tapped from wind plants will be stopped if the frequency were to go above a certain level, which, as explained above, is a consequence of sudden loss of load.
Measures to control voltage will also be in place.
Operationally, the Power System Operation Corporation has asked all senior personnel to be on duty. And shift timings should be adjusted so more personnel are present.
Contingency plans include black start — starting power plants during a black-out.
(The writer is an independent journalist.)
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