Sasaram - Back-to-Back Converter Station

The Sasaram HVDC project is a back-to-back HVDC connection located near Sasaram, Bihar, India. It was commissioned in 2002 to link the eastern and northern regional grids of India. The project was built by Alstom (now part of GE) for the Power Grid Corporation of India.

Technical Specifications

The Sasaram HVDC station consists of one pole with a power rating of 500 MW. It operates at a DC voltage of 205 kV and a current of 2,475 A. The converter station uses thyristor valve technology for AC/DC conversion. The thyristor valves are arranged in a quadrivalve configuration, with 50 thyristors forming a valve and four valves stacked vertically to create a quadrivalve tower.

The thyristors used are 100 mm diameter silicon wafers, clamped in pairs between water-cooled heatsinks. As is typical with all HVDC projects, the valve hall is designed to provide a controlled environment for temperature and humidity, with screened walls to contain radio frequency interference generated by the valves.

Key Components

The Sasaram HVDC station includes several important components. The converter transformers consist of 6 single-phase, 3-winding units rated at 234 MVA each. There are 3 banks of AC filters on each side, rated at 110 MVAR each, using HP12/24 configuration. The station has 2 air-insulated smoothing reactors, each rated at 30 mH, and shunt reactors of 80 MVAR on each side. The thyristor valves comprise 864 thyristors in total, with 36 thyristors per single valve.

Performance Characteristics

The Sasaram HVDC link has an overload capability of 10% for 2 hours and 33% for 5 seconds. It can operate with a maximum increase in firing angle of 63 degrees. The station occupies an area of approximately 450 x 150 meters.

System Integration

The Sasaram project was part of a larger initiative to interconnect India's regional grids. It completes the loop between the hydroelectric-rich north and south regions and the thermal-powered east and west regions. This integration allows for more efficient power transfer and helps balance supply with varying regional demands.

Current Status

In 2006, the Eastern and Northern regions became part of the combined NEW (North-East-West) grid. As a result, the Sasaram HVDC station is no longer required for its original purpose of asynchronously linking these grids. However, it can still function as an embedded power flow device to help control power flow within the AC system.