SMALL SCALE TRANSMISSION TO AC NETWORKS BY HVDC LIGHT

HVDC Light is a small scale around 3 150 MW transmission technology combining converters and cables. The converters are based on Voltage Source Converters (VSC) and Pulse Width Modulation (PWM). The use of series connection of power semiconductors with capability to turn off is fundamental to the development of the technology to high voltage applications. An HVDC Light transmission is in operation in a commercial network in Sweden since March 1997. A second transmission link is on order to be in operation first half of 1999. Complementary with the new converter technology is a newly developed HVDC Light cable based on modified triple extrusion technology and specially designed insulation material for operation with DC stresses. Such cables can be light and flexible even for fairly high ratings and can be installed in an easy manner by e.g. ploughing in ground, hanging overhead in air or for submarine transmissions. HVDC Light is excellent for transmitting power to distant loads and to feed power from distant generation into networks. Renewable generation is often small scale and local, such as wind, solar, tidal and also small hydro generation. In many cases such plants have been restricted in size or not been built because they have, for technical or economical reasons, not been possible to connect to an AC grid. By use of the combined system HVDC Light converters and cables, it is possible to overcome the technical difficulties to connect small scale generation to the AC grid and to make the connection economical and environmentally friendly.