Light-Triggered Thyristors Modernize India’s Electrical Grid

A new 2500-MW ac power line from Siemens is improving the supply of power in northern India. The 475-km line between Purnea in the state of Bihar and Gorakhpur can carry five times more power from the east to the north than the previous direct current line. Light-triggered thyristors enhance the reliability of the line, which is scheduled to enter service in early 2006. The order has a volume of approximately euro 25 million. Delhi, a metropolitan region with 15 million residents, suffers from a shortage of power. The power plants do not meet the demand. For historical reasons, India’s electrical networks have not, to date, been linked together in any appreciable way, so power cannot be imported from regions that have a surplus of energy. The new line transporting 400-kV ac makes the supply of power far more flexible and responsive to demand. What's more, the construction costs are low in comparison with a dc connection.

In both Purnea and Gorakhpur, two series compensation systems with light-triggered thyristors are used. These semiconductor components control the compensation systems in the line when voltage fluctuations or load drops occur. That allows the line to retain its transmission capacity even when there are disruptions in the electrical grid. The technology of direct light-triggering developed by Siemens makes thyristors very compact and extremely responsive. They use about 80% fewer electrical components than conventional thyristors. Light-triggered thyristors are switched on by a light pulse 10 µs and a peak power of 40 mW. Conventional technology uses electrically triggered thyristors, which require a pulse with a peak power of several watts. This pulse is generated by complex electronic equipment.

For more information, visit www.siemens.com.