Carl-Axel Roseen, Area Marketing Executive, has already made many of the comparatively short trips from the central offices of ABB Power Systems to the nearby Hellsjön Station. He indicates that this particular HVDC Light installation has a 10 kV connection to a breaker inside the station. The voltage is filtered by a harmonic filter of broad band type and the current is subsequently transferred to phase reactors and then directly to the converter bridge. A cooling system has been installed to remove heat from the losses of the converter valves.
A control room located within a container at the site monitors the entire operation. Roseen observes that, in principle, this control equipment could be much smaller than its current size and the man-machine interface could even be situated at a remote site. In such a case, he notes that the cooling system could well be situated at the other side of the same container as the control equipment.
Among the key elements of the new converter technology utilized in the HVDC Light concept are insulated gate bipolar transistors (IGBTs) which are fired by the optical signal which has been converted from an incoming electrical signal at the interface. “One of the basic lessons we had to learn” says Roseen “is how to connect several of these IGBTs and to operate them.” He goes on to indicate that ABB has filed some 25 different patents in this specific area. “It took us three to four years to learn all these lessons” he states “and, at the moment, from the articles published within our industry we do not yet see any of our traditional competitors in this business.”
Roseen observes that the Hellsjön site is ideal from the perspective of being close-at-hand and therefore quite easy to demonstrate to visitors coming to the company’s head office. “The utility did not need this installation as such” admits Roseen, “but by giving us the space to make our tests and to put up this first installation, they are benefiting from the voltage control that the system offers.” Roseen anticipates that one large potential market sector for HVDC Light would
be providing additional power to city centers where existing AC cables are already operating at or close to full power. “If these cables could also operate at DC and if there is sufficient space to locate the two converter stations, this would be one good opportunity to increase the capacity of the cables.”
Aside from the initial installation at Hellsjön, ABB Power Systems has now obtained a second order for an HVDC Light system to be installed on the island of Gotland, off the eastern Swedish coast. Valued at about US $ 15 million, this 60 MW project will cover a distance of about 70 kilometers between the two converter stations. Eriksson remarks that the distance between these stations is generally determined by economic rather than physical constraints. Up to now, Gotland has been supplied by an HVDC cable to the mainland first installed in 1954 and extended by about 50 per cent in 1970 by adding the world’s first thyristor converter. The original cable was then replaced in 1983.
