It has long been recognised that a more reliable and efficient power supply is required to support India’s rapid development. Recently, this growing demand for electricity, particularly in the country’s vast sprawling urban metropolises such as Mumbai and Calcutta, prompted the utility company Power Grid Corporation of India to launch a stringent transmission enhancement plan – the largest of its type yet – which includes strengthening its networks with a technology known as ‘flexible AC transmission system’, or FACTS.
At the heart of Power Grid’s transmission enhancement plan is an integrated national grid that services more than 10 million people who are demanding more and different uses of power. Today’s programme of 9,500MW inter-regional power transfer capacity is expected to be increased to 30,000MW by 2012.
An important development in the power supply in cities such as Mumbai is the relocation, for environmental reasons, of power generation from city centres out into the surrounding countryside, sometimes at a considerable distance. Even more significantly, sufficient power to cover increasing demand must be delivered from additional sources that are normally located far away from the load centres. This is why the transmission of large power blocks over long distances is becoming increasingly important. Furthermore, efficiency and reliability of supply play an important role in every planning process, particularly in the face of increasing energy prices and almost incalculable safety risks during power blackouts.
This is certainly the case in India. An increasing demand for electricity and a growing awareness of the need for reliable power supplies, for the fast developing mega-cities in particular, have prompted Power Grid not only to continue with its overall transmission plan, but also to strengthen it.
Power Grid has already made steps to enhance its east-to-west power transfer with the help of its 400kV series compensation system (SCS), which is the preferred FACTS solutions for substation projects in Purnea and Gorakhpur. The power generated in the Tala hydroelectric power plant, located in Bhutan, is transmitted via a newly built 400kV double-circuit transmission line to Gorakhpur substation. There the line is connected to the existing 400kV network, and feeds into the northern industrialised region around the capital New Delhi. Because of this interconnection the north-east of India can also profit from economic hydro power.
Series compensation has been recognised as a ‘low cost’ solution for bulk-power long distance AC transmission and it can also be applied very effectively in meshed systems for balancing the load flow by means of ‘load displacement’. The principle of series compensation consists of using a series capacitor which compensates the line reactance, so the line becomes virtually shorter. Because of this the transmission angle is reduced and system stability increased. This increases the transmission capacity of the existing line without having to install new conductors.
The simplest form of series compensation is known as fixed series compensation (FSC), the main benefit of which is to allow an increase in transmission capacity. The more sophisticated TCSC (thyristor controlled series compensation) is deployed if fast control of the line impedance is required, for load-flow control, and for damping power oscillations. It also has the benefit of allowing mitigation of subsynchronous resonances.
Siemens received the order for the FSC/TCSC from Power Grid at the end of May 2004, and a project team with members from India and Germany was assigned to the job. Reactors, capacitor banks, MOV, circuit breakers, spark gaps, thyristor valves and the control system for the project, which has been financed by the World Bank, were supplied by Siemens Germany. All other equipment and activities, which included platforms, civil works, installation and commissioning were provided by Siemens India.
The Purnea-Muzafarpur and Muzafarpur-Gorakhpur double-circuit transmission line has been constructed to carry power from the eastern to the northern part of the country. Power Grid Corporation of India with consultancy Government of India Enterprise established the 475km long, 420kV line in two sections 242km and 233km long. As a part of civil works, in the floodplain area between Purnea in Bihar State and Gorakhpur in the State of Uttar Pradesh (some 50km north of the Ganges) piling was necessary to stabilise the foundations.
Both transmission lines and the FACTS equipment were put into operation in 2006. Since then they have been providing a reliable transmission corridor for delivering power from the eastern part of India to the load centres in the north of the country.
Parts of this article first appeared on our sister website Modern Power Systems (http://www.modernpowersystems.com)