Biswanath - Agra

The Biswanath-Agra HVDC project, also known as the North-East Agra transmission link, is a groundbreaking ultra-high voltage direct current (UHVDC) transmission system in India. It is the world's first multi-terminal UHVDC project, operating at ±800 kV with a power transfer capacity of 6,000 MW.

The project connects the hydropower-rich northeastern region of India to major load centers in the north and west. It spans a distance of 1,728 km, traversing through the states of Assam, West Bengal, Bihar, and Uttar Pradesh. The link originates from two converter stations in the northeast - one at Biswanath Chariali in Assam and another at Alipurduar in West Bengal - and terminates at a converter station in Agra, Uttar Pradesh.

Technical Specifications

The system comprises four terminals across three converter stations. The Biswanath Chariali and Alipurduar stations each have one rectifier terminal with a capacity of 3,000 MW, while the Agra station has two inverter terminals in parallel configuration, capable of handling the full 6,000 MW. A unique feature of this project is its 33% continuous overload capability, allowing it to reach a maximum conversion capacity of 8,000 MW, making it one of the most powerful HVDC transmission systems ever built.

The project uses a total of 60 single-phase, two-winding, oil-immersed transformers.

The transmission line uses ±800 kV UHVDC technology, which minimizes transmission losses over long distances and improves overall grid efficiency. The project employs 12-pulse converters, with each converter pole having a nominal rating of 1,500 MW. The system is designed to operate in bipolar, monopolar (ground return/metallic return), and hybrid modes, providing flexibility in case of outages in different HVDC line sections or converters.

Innovative Design Features

A notable technical aspect of the project is the indoor DC hall at the Agra terminal, measuring 75x75x35 meters, which houses DC yard equipment such as smoothing reactors, DC filters, and DC disconnectors. This is the first time an 800 kV project has featured an indoor DC hall of this scale.

The project incorporates advanced control and protection systems. It includes a master control facility to coordinate power flow, and if one converter trips during operation, the other pole can automatically compensate for the power lost. The system also has black-start emergency assistance capability.

Earth Electrodes

The earth electrodes for this project is designed for 5,000 amperes direct current continuous current, which is a technical achievement in itself.

Importance and Impact

The Biswanath-Agra HVDC link plays an important role in India's power transmission infrastructure. At full capacity, it can supply enough electricity to serve approximately 90 million people, based on average national consumption. The project not only facilitates the transfer of clean hydroelectric power from the northeast to major load centers but also acts as a stabilizing force for the national grid.

Project Execution and Timeline

The project was jointly executed by Power Grid Corporation of India Limited (PGCIL), Hitachi Energy, and Bharat Heavy Electricals Limited (BHEL). Construction began in 2015, with the first pole commissioned in November 2015, enabling bidirectional flow of up to 1,500 MW of power. The second 1,500 MW pole was commissioned in 2016, and the full project was completed in 2017.

This UHVDC multi-terminal project showcases India's capability in implementing complex, large-scale electrical infrastructure projects.