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August 23, 2012

The grid locks

Implications of the blackout for grid security in India

In public discourse on electric power in India one finds a well-intentioned emphasis on generation scarcity. Unfortunately this way of thinking is somewhat misplaced when it comes to the power blackout of 2012. It really does not matter how much electricity one generates. Lacking grid security, there is simply no way that the electricity will get to the customers in a timely fashion. The responsibility of getting the electricity to the customers falls to the Power Grid Corporation of India (PGCIL) and it fulfills its responsibility via an extremely large distribution network spanning the length and breadth of India.

The electricity grid in India is divided into five regions – the northern, eastern, north-eastern, western and southern grids. Together these grids distribute some 170 GW of electricity. The grids are interconnected via high voltage transmission lines and it is very common for them to share resources and for grids with low demand to pump power to grids with higher demand. As the Indian economy expands, the number of people drawing electricity from the grid grows. To address this demand more generation (60 GW) is scheduled to come online soon. From the perspective of economic growth, it is absolutely vital that the electricity gets to the end users with as little disruption as possible. Expanding distribution on a grid while simultaneously increasing the amount of energy generated is extremely challenging. So far the Government of India has focused extensively on the generation side of things. A number of initiatives are under way to rapidly increase the number of power plants (nuclear, coal fired etc.). However a similar push on the distribution side is lacking. This is what came into sharp focus during the massive blackout of July 2012.

After the recent blackout the Power Minister, Sri. Sushil Kumar Shinde blamed Punjab, Haryana and UP for drawing too much power from the northern distribution grid. Most state power secretaries responded to this statement by denying that their states were overdrawing power from the grid. The Haryana Power Secretary Sri. Ajit Sharan substantiated his claim by saying that the grid frequency was higher than 50 Hz at the time of the blackout. The grid frequency tends to reduce if there is too much load on the grid. If the grid frequency was higher than normal prior to the collapse, then the load dispatch centre controlling the grid would have no reason to think there was a loading issue and no warnings would be issued to state electricity boards to reduce load. From the point of view of the state electricity boards, as the grid frequency was high, there was excess generation on the grid and drawing more power would not cause overload.

Photo: Jalal Hameed Bhatti

For a smoothly functioning grid, there has to be detailed balance between generation, distribution and consumption. If the generation and load (distribution and consumption) are not matched exactly, the principle of conservation of energy forces the grid frequency to shift. If the load increases, the rotational frequency of the generator falls causing the grid frequency to ‘droop’ (slowly reduce). The notion that there was a load mismatch on the grid and that grid surveillance did not detect a frequency droop is deeply disturbing.

The Indian Electricity Rules of 1956 set clear limits on the permissible frequency fluctuations on the grid. These limits have been progressively tightened by the Central Electricity Regulatory Commission. All electricity suppliers to the grid are allowed to deviate from these limits for short periods of time but any excursions are also regulated and discouraged. As the regulations on deviation are continuously tightened and the band of permissible frequencies is steadily narrowed, things have been getting better on the grid in India. At the present time in India, the grid frequency is permitted to oscillate between 49.5 Hz- 50.2 Hz, i.e. approximately 0.35 Hz band around the nominal frequency but excursions as low as 48.5 Hz and as high as 51 Hz are on record. By contrast to this, in developed countries, the frequency band is usually a factor of 10 smaller (closer to approximately 0.036 Hz around the nominal frequency). The regulatory authorities in developed countries keep a very close eye on the number of fluctuations in the grid frequency and put a great deal of effort into correlating the excursions with specific events on the generation or load side. This kind of monitoring results in a much tighter control over the grid frequency band and a very high quality of electric supply.

Against this backdrop of an unstable grid frequency it becomes easier to see how a frequency droop event might be missed in India. It is highly plausible that the anticipated droop on account of a rising load is simply masked by a simultaneous high frequency excursion on the generation side. It is possible to monitor high and low frequency excursions in the grid in India, and correlate them to specific loading or generation events. It should also be possible to electronically fingerprint each generator and carefully monitor shifts in its frequency spread. However only limited efforts have been made in this direction in India.

In the interests of a stable economic growth, it is necessary to immediately allocate more resources to studying higher order correlations in the frequency stability of the grid in India. If sources of instability are identified, then corrective measures can be taken to narrow the band and diminish the excursions. Unless this noise on the nominal frequency is eliminated it will be difficult to ensure that a reliable early warning system for rising load is available to the regulators. Absent such an early warning system of detecting load increases, cascading failures of the kind seen in late July 2012 will become a recurring feature in India. This has all the makings of very poor grid security.

Without enhanced grid security measures, there are likely to be more disruptions to the economic growth of India. Some commentators have suggested that the money be allocated to improving grid management in the 12th plan. That is a good idea, but as a hedge against immediate disruptions, it may even be advisable to set up a special task force to retrospectively examine grid frequency excursions in greater detail and to come up with ways to reposition the early warning metrics used by the load dispatch centres.


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