The Siemens Power Transmission and Distribution Group (PTD) has received an order from the Power Grid Corporation of India Ltd. (PGCIL; New Delhi, India) to set up four compensation systems featuring state-of-the-art thyristor technology. The purpose of this new equipment is to improve the transmission performance and the reliability of the 400-kV overhead line between Purnea in eastern India and Gorakhpur in the north of the country. The order includes the construction and installation work involved in the systems, along with supply and engineering of all the high-voltage components, the control and protection devices, and the thyristor valves. The order is worth around euro 25 million, and the systems are scheduled to commence operation in 2006.

PGCIL is constructing a 475-km-long overhead line from Purnea in the state of Bihar via Muzafarpur to Gorakhpur in the state of Uttar Pradesh. This project transmits surplus energy from eastern India to the conurbations around Delhi, where the existing generation capacity can no longer meet demand.

For the systems in Purnea and Gorakhpur, respectively, Siemens is supplying two thyristor-controlled series compensation systems and two fixed compensation systems. Series compensation systems enhance the transmission capacity of the overhead line and ensure stability in the grid.

The light-triggered thyristors used are notable for their very high current carrying capacity and blocking voltage. Direct light-fired thyristors make it possible to reduce the number of electronic components in the converter valves by about 80%. A further advantage of this modern thyristor design is that all the firing and monitoring electronics are at earth potential; consequently, the equipment is accessible during operation.
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