Grid-locked into darkness

In New York, demand at the time of the blackout was about 28,500 megawatts as compared to the record high of more than 31,000 megawatts. So, overloading in New York cannot be the reason. When demand exceeds supply its frequency drops below 60 cycles (in the US). Usually, reduction in frequency is so small there that it is measured in hundredths or tenths of a cycle. But that day generation and consumption probably went out of balance. The frequency dropped to 57 cycles — that is, by 5 per cent. Why this happened is not yet explained. (In India, rules permit up to a 3 per cent drop in frequency which here is 50 cycles. Often our systems operate at that permissible limit of 48.5 cycles and sometimes even lower, like 48 cycles. Thermal power stations, however, automatically shut down if the frequency drops below 47.5 cycles. Thus we work many times on a very fine margin of 0.5 to 1 cycle only. That is why we have more frequent grid failures in India.)

Officials in the US were warning a decade ago of weaknesses in their grid and saying that challenges had grown with deregulation. Under the old system, a local utility monopoly built and owned both the power plants and the wires in a region. Under deregulation, the plants have been sold to other companies that often sell their power to utilities hundreds of miles away on a daily auction basis, increasing traffic on the grid. This allows a lot more power on the transmission lines than can be handled. No wonder the largest blackout in American history was waiting to happen!

It was five years ago that a federal task force of prominent experts warned the department of energy that the reliability of the electrical system was based on a mishmash of voluntary standards, and that Washington needed to impose mandatory rules on the electricity sector. Pleas of experts to improve the system were ignored, due to political and regional disputes, or caught up in debates about regulating private industry. It has been pointed out that in the US even today there are digital and analog controllers with a large difference in their response times for controlling generators and switch gear in the same grid. This leads to unpredictable transients on the grid and appears to be the root cause of cascade trippings both in the US and in India.

Now some measures are being suggested in the US and they may be worth considering in India too. The simplest one is to make the grid simpler by dividing it back into smaller regional grids to avoid any cascading effect. Texas’s grid is cited as an example. Another suggestion is to use silicon switches in place of electromechanical switchgear. Yet another suggestion is to use DC grid instead AC grid.

In India the electricity bill was drafted in 2000 and was passed with several changes in 2003. The Electricity Act 2003 incorporates a deregulation policy similar to America’s and provides an open access system which depends heavily upon smooth functioning of grids.

While the state-level grids are under the control of individual state governments, the regional grids comprising of all the states in a region (the western grid, for instance, consists of Maharashtra, Goa, Gujarat and Madhya Pradesh) which may be under the control of different political parties caused headaches a few years ago. Being a grid of regional grids, the national grid is correspondingly more complex. And yet there are grid enthusiasts who talk of a Saarc grid!

(The writer is a former assistant professor in IIT, Delhi)