On July 30, parts of North India came to a standstill, crippled with power failure that affected the states of Delhi, Punjab, Haryana, Himachal Pradesh, Uttar Pradesh, Rajasthan and Jammu and Kashmir. This power failure was attributed to overdrawing of power by some states. However, that has not been confirmed yet. While authorities were working round-the-clock to restore the Northern Grid, and were successful in partially restoring power in many parts after 15 hours, the northern grid collapsed again on the next day, July 31. This time, a cascading effect saw the collapse of the Eastern and North Eastern power grids as well. This affected the states of West Bengal, Odisha, Jharkhand, Bihar, Sikkim, Assam, Mizoram, Manipur, Nagaland, Meghalaya and Arunanchal Pradesh. In what’s being termed as the biggest ever power failure in Indian history, three inter-state transmission networks collapsed together, plunging most of north India into darkness and disrupting the daily lives of over 600 million people. (The states affected by grid failure are highlighted in the infographic).

Infographic - Power System in India (Illustration - Jagdish Limbachiya)

Infographic – Power System in India (Illustration – Jagdish Limbachiya)

The cause of the failure? Certain states in the northern region overdrew power, which led to the tripping and ultimate collapse of the Northern Grid. A blame game ensued with states accusing each other for the mayhem caused. It is being speculated that Uttar Pradesh, Haryana and Punjab overdrew power, but they have refuted these claims. One of the possible reasons for overdrawing power is the deficient rainfall, which meant increased use of electric pumps to withdraw water for farming in these agricultural states. But how did this snowball into a major power crisis that affected over 20 states?

To understand this, you will need to know how the electric grids work in India. The Power Grid Corporation of India oversees the distribution of power via its transmission network spread across the country. It has 95,009 circuit-km of transmission network, 1,36,358 MVA  transformation capacity and approximately 28,000 MW inter-regional power transfer capacity. India is divided into five electrical regions, namely, Northern (NR), Eastern (ER), Western (WR), Southern (SR) and North-Eastern (NER). Of these, the four zones NR, ER, WR and NER are inter-connected, and form what is known as the New Grid. The Southern zone is synchronously interconnected to the New Grid. (The further division of states is shown in the infographic). Every zone is then responsible for the power needs of the states that fall under it. There is a load dispatch centre in every zone that oversees the transfer of power from the generating plant to the states and further. Depending on the need, every state then buys power and has to adhere to the withdrawal limit.

Owing to the size of our country, and the fact that the power generating plants are scattered across the terrain, we have a very complex power transmission network in place. But its functioning, from power generation to power distribution is more or less the same across all regional zones. In each zone, power from various power plants is subjected to inter-state transmission, wherein the regional load dispatch centres monitor and control its distribution to the various states in each zone as scheduled. The next step is intra-state transmission, wherein the state load dispatch centre allocates power to various areas within the state, and then at local level. (View diagram in the infographic). The power is generated at very high voltage, but stepped down at each substation.

What happened on Monday is the classic example of what happens when limits are not adhered to. The generation plants, the power grids and the sub-stations have to work in tandem. An overload results in system failure. In spite of the warning issued, several states continued to overdraw power from the already overstretched generation system. The overdrawing of power caused a slight escalation in the grid frequency range, the permissible limit of which as defined by the Indian Electricity Grid Code is 49.5 Hz to 50.2 Hz. The escalation in the frequency ultimately caused the colossal power failure in north India on Monday. As there is free flow of power in the four zones that comprise the New Grid, Tuesday’s tripping of the Northern Grid had a cascading effect on the North Eastern and Eastern power grids.

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