A winning combination

2015-01-12 - The Skagerrak 4 transmission link not only strengthens the connection between Norway's and Denmark’s grids, but is also the first to combine HVDC Classic and HVDC Light technology.

Expansion of Skagerrak has been driven by the customers’ aim to add more renewable energy to their energy mix, and to use electricity more efficiently.
They say all good things come in threes, but in this case it is all about a winning combination of two.

It all started in 1976-1977 when a 50-year-old dream came true: ABB engineers commissioned the Skagerrak high-voltage direct current (HVDC) link, connecting Norway's hydropower and Denmark's thermal and wind power systems under the 600-meter deep waters south of Norway.

As the first subsea or overhead transmission link to be built entirely with thyristor valve technology, it was a revolution in HVDC technology. In fact, the dream worked so well it kept getting bigger. The 240-kilometer land and sea link’s capacity was nearly doubled from 500 megawatts (MW) to 940 MW when ABB added a third HVDC monopolar cable link to the two original cables in 1993.

This development was driven by the customers’ aim to add more renewable energy to their energy mix, and to use electricity more efficiently.

Then in 2011, ABB received an order for a fourth link, increasing Skagerrak’s total power capacity to 1,640 MW. This 700 MW, 500 kilovolt (kV) HVDC Light transmission line operates in bipole mode with the 1993 Skagerrak HVDC Classic link, having been completed in late 2014.

Securing future transmission

Through this installation, the interconnected networks will also enjoy the technology’s black-start capability, which is another major benefit. It allows for a fast restoration using power from the other end of the link in the event of a power disruption. These factors were essential in the selection of the HVDC Light technology for the fourth Skagerrak HVDC link.

In addition to a record high 500 kV HVDC Light transmission voltage, the link is revolutionary in yet another way. It is the first time an HVDC Classic and HVDC Light link will be tied together in such a bipole configuration. It is truly a winning combination enabled by ABB’s advanced MACH control system, also used in 2007 to update the 30-year-old control system of the first Skagerrak link. Such modernization is needed to secure future transmission and increase the controllability.

High-performance MACH is specifically designed for converters in power applications. It is the most-used control and protection system for HVDC and FACTS (Flexible Alternating Current Transmission Systems), with more than 1,100 installations worldwide.

The higher voltage level in the Skagerrak interconnections will help minimize transmission losses. The new link will also help reduce the impact of power system disturbances and contribute to the stability and reliability of both grids, enabling them to use electricity more efficiently and ensuring robust performance and power quality. This winning combination of HVDC Light and HVDC Classic may be a world’s first, but seeing how efficiently they work together predicts that there are more of the same kind to come.

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