HVDC LightTM makes wind energy easier to transport and network-friendlier

In the Kyoto Protocol, the European Union undertook to reduce the emissions of greenhouse gases like CO2. Germany's resultant commitments include doubling its proportion of electricity from renewable energy sources by 2010. One important element in achieving this goal is the German federal government's strategy for progressing wind power utilisation at sea, targeting up to 20'000 megawatts of power from offshore installations in the long term.

Besides developing offshore-friendly wind turbines in the megawatt range, together with the associated foundation technologies (both of these advancing most promisingly), the main priority here is creating appropriate solutions for the transmission of the power to the mainland and feeding it into the existing high-voltage grid. Technical studies, plus the results of dena's network study, have shown that traditional three-phase current technology reaches its limits here. From certain distances upwards, for example, three-phase current network links using submarine cables are no longer technically feasible, nor can the stability of the networks concerned be assured in all control states by traditional means for the ratings involved.

In this situation, ABB is now spotlighting one of its new products developed in recent years: "HVDC LightTM" are the magic words involved. This is a design enhancement of the traditional HVDC technology (high-voltage direct-current transmission), originally premiered and field-proven in the mid-20th century, but now incorporating the present-day's semiconductor components and control technologies. Specifically, this means that instead of the traditional thyristors, IGBT components are now being used, and micro-processor-based / computerised control systems have replaced the old analog controls.

The result of this development process is an entirely new generation of HVDC transmission equipment, which has eliminated certain characteristics of traditional HVDC transmission systems and is branded as HVDC LightTM. The new technology scores in terms of the following characteristics: (relatively) small, compactly dimensioned installations, low harmonic loads, complete decoupling of the two networks connected in regard to malfunctions or failure of one network, no reactive-power problems etc.

HVDC LightTM can be supplied up to a unit output of currently 500 MW. This power can be transported over large distances with low losses using just one two-pole DC cable, likewise newly developed. ABB emphasises the ability of HVDC LightTM to decouple each of the two networks from a malfunction in the other grid, and to keep it running operating in this case too, as specified in the new grid connection rules drawn up by several transmission system operators.

Six of these installations are already in operation, two of them as prototype and demonstration systems, and four of them in full commercial use. The first of these installations was built in 1999, with the others coming on line during 2002 / 2003; another offshore installation is currently under construction. The performance spectrum for the operational systems ranges from 8 MVA to 200 and 330 MVA respectively for the two largest installations.