The Power System Operation Corporation (Posoco) which operates the national load dispatch centre expects the load to fall by 12,879 MW across the five regions during the nine-minute light switch-off event this evening, according to its advisory to state load dispatch centres. The Posoco has advised load managers to go for a graded reduction in generation to prepare the grid for the nine-minute event which will begin at 9 pm.
Indian grid system is designed to operate at a frequency of 50 Hz (or cycles per second). A sharp drop below this level or a sharp rise above this level will hamper the grid stability. If the fall or rise is too sharp, it can set off a series of tripping of transmission lines resulting in outage of generating stations.
Sharp fall in frequency used to be a general occurrence in the summer months in the 1990s with one state or the other within a region overdrawing from the grid causing the frequency to fall to precarious levels. It is another matter that such rogue states had to pay a fine. The trend, however, became a thing of the past after the power sector moved to merit-order dispatch or availability based tariff. In other words, tariffs payable by utilities is linked to the frequency.
As the load curve for March last week shows, India’s load hovers between 112551 MW and 101207 MW between 6 pm and 9 pm. The lighting load starts picking up after 6 pm.