The Power Grid Corporation of India Ltd. (Powergrid) ordered a second 500 MW back-to-back HVDC project in southern India to enable increased power interchanges between eastern and southern parts of the country.
The back-to-back HVDC station Vizag I came into service in 1999. Powergrid signed a contract with ABB for Vizag II in September 2002, and the station began operating commercially in February 2005. The Vizag II back-to-back HVDC station has nominal DC voltage and current ratings of 176 kV, 2,841 Ampere.
A back-to-back HVDC converter can be used when two asynchronous AC systems need to be interconnected for bulk power transmission or for AC system stabilization reasons. In such installations there are no overhead lines or cables separating the rectifier and the inverter, hence the DC current can be kept high and DC voltage low. The low DC voltage means that the air clearance requirement is low, which favors a compact valve hall design.
Vizag II is installed at Gazuwaka, located near the city of Vishakhapatnam on India's southeast coast. Sited beside an existing HVDC station, it increases the capacity for high-voltage power exchanges by 500 MW. In addition, the system provides voltage and frequency support for both eastern and southern grids during power disturbances.
Vizag I and Vizag II consist of two independent poles, each with a nominal power transmission rating of 500 MW. Both installations use air-insulated, water-cooled thyristor valves.