Operating Experience Of Rihand - Dadri +- 500kv HVDC Transmission System

The first high voltage direct current transmission system in India was planned between Rihand Super Thermal Power Station and Dadri to transmit bulk power of 1500 MW at ±500 kV over a distance of 810 km. National Thermal Power Corporation (NTPC) specified the overall design and supervised the construction and commissioning. Operating in parallel with this HVDC line, are 400 kV AC lines. These are required to supply Delhi and part of the Northern Grid. Under a Government re-organization of the power industry, ownership was transferred to the National Power Transmission Corporation Limited, subsequently renamed as Powergrid Corporation of India Ltd (POWERGRID) in 1993. The first pole was commissioned in December 1990 and the second pole in September 1991. Since then the HVDC link has regularly transmitted between 1000 MW and 1100 MW continuously; at times reaching 1200 MW. The scheme has operated successfully and has established a high availability and reliability. Because this project was the first of its kind in India and since there was no previous experience of design, construction and operation available within the Indian utilities, the scheme is not entirely without problems. A few of the salient points which affect the performance of the link are discussed and modifications which have been carried out in order to improve availability and reliability are described.