There has been what can be called a paradoxical difference in the power restrictions imposed by Kerala State Electricity Board Limited (KSEB) on September 18 (Friday) and other days in September.

September 18 recorded the highest power consumption in the month of September, nearly 100 million units. Yet, on the day there was unheard-of power usage during this monsoon month, there was virtually no power shedding. Restriction was imposed, but only for a narrow five-minute window between 10.39 and 10.44 pm, and that too only in limited parts of Kerala.

However, on other days in September, when the consumption was 95 MU or below, the usual September power restrictions - bouts of 25-30 minute power cuts spread over a seven-hour stretch from 6 pm to 1 am next day morning - were in place. A day after the high of 100 MU, consumption came down marginally to 98 MU on September 19, the second highest this month. The power cuts returned.

How did the KSEB manage to do without restrictions on a day when daily usage touched 100 MU? On most days this September, when the average daily consumption was just 94 MU, heavy restrictions were in place.

On September 18, though the consumption was high, the power shortage at the point when the requirement was highest on the day, was a pleasantly meagre 21 MW. Usually during this month, the shortage during the point of highest requirement on a day would range from 500-900 MW. The next day (September 19), there was a slight drop in power usage but the shortage at the point of maximum requirement shot up to a humongous 752 MW. Interestingly, there were more rains on September 19.

There were two reasons why power shortage nearly vanished on September 18.

Reason 1: The grid frequency was generally healthy during the day.

On September 18, the operational frequency in the national grid was maintained within the Indian Electricity Grid Code (IEGC) band of 49.90 to 50.50 Hertz. When there is optimum grid frequency, power utilities can draw more power from the grid than what is originally scheduled. The national grid would be tolerant.

On September 18, therefore, KSEB drew an additional five million units from the grid. On that day, the Southern Regional Load Despatch Centre had scheduled only 74 MU from outside sources: central generating stations, medium- and short-term contracts, and daily purchases. However, KSEB went ahead and drained 5 MU more from the national grid and got away with it.

During most of September, the grid frequency was either below or above the IEGC band most of the time preventing power utilities from draining extra power. If in such instances, a power utility like KSEB attempts to draw more power than what is originally scheduled, the national power mechanism will automatically shut down certain feeders. This was how certain feeders in Kerala had tripped on September 16 causing more blackouts that day than the usual ones.

On September 19, too, the grid frequency was favourable. On that day, too, KSEB pulled in an additional 5 MU from the grid.

Reason 2: Still, if restrictions were kept to the barest minimum only on September 18, it can be attributed to the availability of power in the energy exchanges. For a change, there was power available in the exchanges during peak hours.

On September 18, as a result, KSEB could purchase over 16 MU from the Real Time and Day Ahead markets. In other days this month, the average purchase from these power exchanges was less than 5 MU.

The availability dropped the next day itself. On September 19, KSEBL could purchase only 12 MU. Though it was better than during the other days in September, it was not enough to compensate for the peak hour shortage that day.

Meantime, top KSEB sources said that attempts to contract additional power for September had failed till now. Even then, if rains pick up, daily power use will plummet. In such a situation, KSEB can lift at least a part of the restrictions it has planned for September.