In my next few blogs, I will provide an overview of Voltage Source Converter (VSC) HVDC technology and its suitability for Smart Grids operation and control discussed.
VSC HVDC is based upon transistor technology and was developed in the 1990′s. The switching element is the Insulated Gate Bipolar Thyristor (IGBT), which can be switched on and off by applying a suitable voltage to the gate (steering electrode). Because of the more switching operations, and the nature of the semiconductor devices itself, the converter losses are generally higher than those of HVDC classic converters.
VSC HVDC is commonly used with underground or submarine cables with a transfer capacity in the range of 10 – 1000 MW, and is suitable to serve as a connection to a wind farm or supply a remote load. VSC HVDC technology has very fast steer and control functionality and is suitable for meshed networks. It is characterised by compactness of the converter stations, due to the reduced need for AC harmonic filters and reactive power compensation. Power flow reversal in VSC systems is achieved by reversal of the current, whereas in HVDC classic systems the voltage polarity has to change. An important consequence of this voltage source behavior is the ability to use cheaper and easier to install XLPE cables, instead of the mass-impregnated cables that are needed for HVDC classic.
Currently, only twelve VSC HVDC projects are in service. A few examples include: Estlink, which connects Estonia to Finland (350 MW), and BorWin1, connecting an offshore wind farm to Northern Germany (400 MW). Both are equipped with ±150 kV submarine cables, and the Trans Bay project in California (400 MW) that consists of 90 km ±200 kV submarine cable.
Most projects have submarine cable, but some projects include long lengths of underground cable, such as Murraylink (220 MW, 177 km underground cable), and Nord E.On 1 (400 MW, 75km underground cable).
The 500 MW East-West interconnector between Ireland and Great Britain, operating at ±200 kV, is scheduled to go into service in 2012. A 2000 MW 65 km cable interconnector ±320kV as part of the Trans European Network—between Spain and France—is scheduled for commissioning in 2013, and will represent the highest power rating for a VSC HVDC system installed at this time.
Make sure to check back next Tuesday for my next blog on the comparison between HVDC classic and VSC HVDC.
By: Peter Vaessen