Vizag I - Back-to-Back Converter Station

The Vizag 1 HVDC project, also known as Vizag I, is a back-to-back HVDC converter station located near Visakhapatnam (Vizag) in Andhra Pradesh, India. It was commissioned in 1999 as part of the Vizag back-to-back HVDC converter station complex, which facilitates power exchange between the Eastern and Southern regional grids of India.

Technical Specifications

Vizag 1 has a power transmission rating of 500 MW. It operates at a nominal DC voltage of 205 kV and has a current rating of 2,475 Amperes. The station utilizes air-insulated, water-cooled thyristor valves for AC/DC conversion. Its design is very similar to that of the Chandrapur back-to-back HVDC converter station.

Purpose and Functionality

The primary function of Vizag 1 is to enable asynchronous interconnection between the Eastern and Southern power grids of India. It allows for controlled power exchange between these two grids, which may operate at different frequencies or phases. The back-to-back configuration means that both the rectifier (AC to DC conversion) and inverter (DC to AC conversion) are located at the same site, without any long-distance DC transmission line between them.

Construction and Technology

Vizag 1 was built by Alstom between 1996 and 1999. It employs Line Commutated Converter (LCC) technology based on thyristor valves. This technology is well-suited for high-power applications and offers high efficiency in power transmission.

System Components

The station consists of converter transformers, thyristor valves, smoothing reactors, AC and DC filters, and control and protection systems. The thyristor valves are the core components, responsible for the actual conversion between AC and DC power.

Grid Integration

Vizag 1 is connected to the 400 kV AC systems on both the Eastern and Southern sides. It plays an important role in stabilizing the AC grids by providing voltage and frequency support during power disturbances.

Operational Flexibility

The back-to-back configuration of Vizag 1 allows for precise control of power flow between the two grids. It can rapidly adjust the amount and direction of power transfer, which is particularly useful for managing grid stability and responding to changing load conditions.

Environmental Considerations

By enabling efficient power transfer between regions, Vizag 1 helps in optimizing the use of generation resources across a wider area, potentially reducing the need for additional power plants and associated emissions.

Expansion and Upgrades

Vizag 1 was later complemented by Vizag 2, commissioned in 2005, which added another 500 MW of transmission capacity to the complex. Together, they form a 1000 MW back-to-back HVDC link, significantly enhancing the power exchange capabilities between the Eastern and Southern grids of India.

Current Status

While Vizag 1 continues to operate, its role has evolved since the synchronization of the Indian regional grids in 2013. It now functions more as an embedded power flow device within the national grid, helping to control power flow and maintain system stability.