Friday, August 03, 2012: The Northern region of India including the states of Delhi, Punjab, Haryana, Himachal Pradesh, Uttar Pradesh, Rajasthan and Jammu and Kashmir was fast asleep when the disaster occurred at around 2 am on the night of 29 July that seemed to look like a mere power failure. Everyone woke up to the news of the collapse of the Northern Grid due to overdrawing of power by some states. The authorities were successful in restoring power by Monday evening but again the nightmare re-appeared on 31 July. This time including West Bengal, Odisha, Jharkhand, Bihar, Sikkim, Assam, Mizoram, Manipur, Nagaland, Meghalaya and Arunanchal Pradesh.
Three inter-state transmission networks collapsed together and more than half of India was thrown out of gear because certain states in the northern region overdrew power due to low rainfall in the region, which led to the tripping and ultimate collapse of the Northern Grid. Uttar Pradesh, Haryana and Punjab are suspected but all of them have denied it.

So, how is rainfall to be blamed for the disaster? Deficient rainfall causes increased use of electric pumps by farmers to withdraw water for farming in agricultural states. But can farmers of three states make 20 states in India to go powerless?

Let's look at the structure of electricity grids in India. India is divided into:

Northern (NR)
Eastern(ER)
Western (WR)
Southern (SR)
North-Eastern (NER)

The NR, ER, WR and NER are inter-connected, and are called the New Grid. The Southern zone is synchronously interconnected to the New Grid. Each of the zones takes care and monitors the power need of the states that fall under it. A load dispatch centre in every zone monitors the power transmission from the generating plant to the states. Every state has to calculate its power demand and accordingly buy power. The states have to stick to the maximum consumption limit.

The Power Grid Corporation of India has a 95,009 circuit-km of transmission network, 1,36,358 MVA transformation capacity and around 28,000 MW inter-regional power transfer capacity. The main problem is that the power generating plants are scattered across the county and the functioning, from power generation to power distribution is pretty complex.

There are two terms in the distribution of power. Inter-state transmission and Intra-state transmission. In each of these five zones, power is generated from the concerned power plant and plants are subjected to inter-state transmission. The regional load dispatch centres monitor and control its distribution to the member states that fall in its zone.

After that, the intra-state transmission takes over, in which each of the states’ load dispatch centre distributes power to various region as per the demand and then the process is further divided at the local level by stepping down the power (wattage) at each substation because different zone require different voltage like Metro, railway service require current at a high potential difference compared to local housing which needs just 220V.

The disaster was simply caused by excessive demand. Certain states did not adhere to the power limit which tripped the entire grid. Excess demand caused the grid frequency to cross the permissible limit of 49.5 Hz to 50.2 Hz, as defined by the Indian Electricity Grid Code. For those who are unaware of this, check the rating of any of your household device. You will notice it’s stated as 220V 50Hz AC.

The power is supplied by large rotating AC generators turning in sync with the frequency of the grid. The frequency of all these generators will be identical and is tied directly to the RPM of the generators themselves. If there is sufficient power in the generators then the frequency can be maintained at the desired rate i.e. 49.5 Hz to 50.2 Hz.

A slight increase in grid frequency can throw the entire system out of sync. The entire grid collapses and it takes at least 6 hours to restart the process. The North and Eastern grids are connected under the New Grid. The damage caused by the failure of the Northern Grid was collaterally transferred to the North Eastern and Eastern power grids on 31 July. Thus, the entire disaster recipe was cooked in this fashion.