High Precision Loss Measurement at HVDC Converter

In energy transmission, high power converters are widely used because they offer advanced opportunities for controlling power flow at very high efficiency. Although electrical losses of these converters are rather low yet they add over the lifetime of equipment (e.g. 30 years) and reach the range of the investment cost of a plant. Therefore, every decision on a certain manufacturer to deliver the plant includes a careful evaluation of the calculated losses and a strict comparison to the actual losses which must be measured correctly. Measurement error margins are to be kept small as they are subtracted from the indicated values. While units with two blocks allow a back-to-back operation a special measurement procedure has to be defined for precise loss measurements at single block units. Usually, the power flow direction at converters can be changed easily by circuit capabilities and control. A special selection of power flow forward and backward is used for internal compensation of measurement system errors to a high extent. The loss measurement procedure at a single block yielding very small error margins is described and the hardware used is evaluated.