HIGH VOLTAGE DIRECT CURRENT TRANSMISSION SYSTEMS

High Voltage Direct Current Transmission Systems



High Voltage Direct Current Transmission Systems

Beginning with a brief historical perspective on the development of High Voltage Direct Current (HVDC) transmission systems, this paper presents an overview of the status of HVDC systems in the world today. It then reviews the underlying technology of HVDC systems, and discusses the HVDC systems from a design, construction, operation and maintenance points of view. The paper then discusses the recent developments in HVDC technologies. The paper also presents an economic and financial comparison of HVDC system with those of an AC system; and provides a brief review of reference installations of HVDC systems. The paper concludes with a brief set of guidelines for choosing HVDC systems in today's electricity system development. A high-voltage, direct current (HVDC) electric power transmission system uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses. For underwater power cables, HVDC avoids the heavy currents required by the cable capacitance. For shorter distances, the higher cost of DC conversion equipment compared to an AC system may still be warranted, due to other benefits of direct current links. HVDC allows power transmission between unsynchronized AC distribution systems, and can increase system stability by preventing cascading failures from propagating from one part of a wider power transmission grid to another. (Grigsby, 2001, 45-99)

The modern form of HVDC transmission uses technology developed extensively in the 1930s in Sweden at ASEA. Early commercial installations included one in the Soviet Union in 1951 between Moscow and Kashira, and a 10-20 MW system between Gotland and mainland Sweden in 1954. The longest HVDC link in the world is currently the Xiangjiaba-Shanghai 2,071 km (1,287 mi) 6400 MW link connecting the Xiangjiaba Dam to Shanghai, in the People's Republic of China. In 2012, the longest HVDC link will be the Rio Madeira link connecting the Amazonas to the São Paulo area where the length of the DC line is over 2,500 km (1,600 mi).

In today electricity industry, in view of the liberalisation and increased effects to conserve the environment, HVDC solutions have become more desirable for the following reasons:

Environmental advantages

Economical (cheapest solution)

Asynchronous interconnections

Power flow control

Added benefits to the transmission (stability, power quality etc.)

Historical Perspective on HVDC Transmission

It has been widely documented in the history of the electricity industry, that the first commercial electricity

Generated (by Thomas Alva Edison) was direct current (DC) electrical power. The first electricity

Transmission systems were also direct current systems. However, DC power at low voltage could not be

Transmitted over long distances, thus giving rise to high voltage alternating current (AC) electrical systems.

Nevertheless, with the development of high voltage valves, it was possible to once again transmit DC (Thomas , 2009, 2)

Power at high voltages and over long distances, giving rise to HVDC transmission systems.

High voltage (in either AC or DC electrical power transmission applications) is used for electric ...