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The massive grid failure in India last week affected over 600 million people. With so much speculation buzzing about the reasons for the failure, we decided to talk to engineers working at the local load-dispatch centers to get a firsthand understanding of what really happened. The following are some observations.

Demand/supply mismatch ultimately led to the grid failure, and this scenario is not new in India. The country has always struggled with power shortages, and in this instance, the fragile safety mechanisms (relays) seemed to have failed under pressure from having to meet rising demand from the agricultural sector due to weak monsoons and mismanagement by regional dispatch centers.

This year, the monsoons have been weak and delayed in India, and the lack of precipitation is felt especially acutely in some northern states that have economies dependent on agriculture. The sowing of sugarcane has started in some states, and there is high demand for power for irrigation.

Also, the state of affairs is politically very sensitive, and there have been instances where the farming community has become extremely agitated during times of power shutdown. Moreover, no elected officials want to displease the farmers because of their political clout.

There are five major grids in India connecting namesake regions - Northern, Southern, Eastern, Western and Northeastern. There is also a grid - known as NEW - that interconnects the Northern, Eastern, Northeastern and Western grids. It was this NEW grid that failed, and through a cascading effect, the Northern, Northeastern and Eastern grids also failed.

The Western grid isolated automatically and avoided the failure, whereas the Southern grid was unaffected because of the existing asynchronous system. (The Southern grid is connected via direct-current transmission by means of three high-voltage DC links).

As a rule, all states in India are given a government allocation from central generating stations (National Thermal Power Corp., National Hydroelectric Power Corp. and Nuclear Power Corp. of India Ltd.) to draw power from the national grid, which consists of the five sub-grids. The allocation of bulk power is handled by the regional load dispatch centers, which are responsible for managing power demand and supply in their respective regions in coordination with state load dispatch centers.

In India, the power frequency of the grid is 50 cycles. If demand exceeds supply, the frequency drops. When there is a drop in frequency, adjustments have to be made by varying generation or shedding load. (There is automated generation control in case of surplus generation). States receive a first warning when the frequency of the grid falls below 49.7 cycles, and a second warning goes out at 49.5 cycles.

It is important to note that the frequency in the NEW grid is different from the frequency of the Southern grid, as there are many more states connected to the NEW grid, resulting in heavy demands placed on that system. Frequency fluctuations can be very high at any given time.

So, what happened last week? Two states allegedly overdrew power beyond their allocation while grid frequency was falling to dangerous levels. The NEW grid tripped and cascaded to the Northern and Eastern grids. The Western grid managed to survive by rapidly reducing demand and managing its existing supply and islanding from the NEW grid.

And why did it take so long to restore power? During this failure, the generation tripped and had to be restored in phases and matched with the system. Also, the Northern grid is highly dependent on thermal power supply (coal). Hydropower generates a small percentage of power for the Northern grid, but the below-average precipitation from the monsoon season has pushed hydropower generation to even lower levels.

Once thermal power stations are shut off due to this kind of tripping, it normally takes at least six to eight hours to come back online because they have to be cooled and stabilized, whereas hydropower plants can come back online immediately. Because the Northern grid is largely dependent on coal and nuclear power plants, it takes much longer to restore when tripped.

Could this historic blackout have been avoided? Yes. This was a clear case of mismanagement by the regional load dispatch centers, which were negligent or did not see the warning signals. There should have been a safety mechanism that automatically shuts off load when frequencies drop down to dangerous levels, due to the overdrawing of power.

For example, the Southern grid has deployed an under-frequency (UF) load mechanism that prevents states from drawing more power from the grid when the frequency dips below 49.5 cycles. There is also a system protection scheme in the Southern grid, whereby the load feeder in the grid systems trip when there is a problem but the main grid remains safe and stable. Hence, such catastrophic grid failures are very rare in the Southern grid.

In fact, the Northern grid also has such systems in place but are generally not implemented due to non-technical and political issues. Per the Indian Electricity Grid Code, responsibility for maintaining the grid is clearly defined via regional load-dispatch instructions to be followed by state load dispatch centers.

Supervisory control and data acquisition systems help in providing facts and detecting problems online and in real time. However, grip operators still need to act upon those data points, creating potential for human errors.

In India, increasing power supply and transmission capacity are critically important issues. But this blackout has made it abundantly clear that there is also a critical need to put automated safety mechanisms in place across the country to avoid such catastrophes in the future.

Raj Prabhu is managing Partner at Mercom Capital Group LLC, a consulting and communications firm focused on the smart grid, wind power and solar energy sectors. The firm's consulting division advises cleantech companies on new market entry, custom market intelligence and overall strategic decision-making, and Mercom also produces comprehensive market-intelligence reports for the industries it serves. For more information about Mercom, click HERE.

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