Measurement of short-circuit capacity

The short-circuit capacity in the electric transmission and distribution system is important when connecting equipment to the network. In the transmission system, this could for example be connection of HVDC lines or very big consumers, and at lower voltage levels it could be minor power stations or other consumers. The short-circuit impedance is dependent on the actual configuration of the network, and of the consumption. This investigation concerns establishing methods for measuring the short-circuit impedance from naturally occurring variations in voltage and current. In particular two cases, where the measurements are presently requested are investigated. The first case is about the 400 kV bus in Bjæverskov, where the short-circuit capacity should be known before start of the HVDC line to Germany. The second case is a measurement on the 132 kV bus in Hove, where a pronounced consumer is connected, and the problem is voltage fluctuations, for which reason the impedance measurement is combined with a flicker measurement.
In the project, two pc-based measurement systems are developed. The first one with the sampling rate locked to the power frequency, and the second one with constant sampling rate. In the frequency locked system, the naturally occurring variations in voltage and current are collected and used as basis for a statistical analysis and an estimation of the short-circuit impedance. In the system with constant frequency data acquisition, the method includes an algorithm for detection of significant events in the variation of voltage and current.