Comparison between Measurement and Calculation of Line Switching with Inductive and Complex Source-Modeling Requirements

Knowledge of the switching overvoltages during energizing of unloaded lines is required for an optimal insulation coordination. These overvoltages can be calculated with analog or digital models provided that the correct models for the switched line and the feeding network are used. The decision which models are correct and should be selected, is made using measurements for the verification of the calculations. Fig. 1a shows one of the measured voltage waveforms (sending end) in a network with an inductive source, while in Fig. 1b the results of the calculation with correct models for both the switched line and the feeding network are plotted. The measured and calculated voltage waveforms (receiving end) for a complex source are given in Fig. 2 and Fig. 3 respectively. It can be seen that there is a good resemblance as a result of the correct modelling. The main requirements for correct modelling can be summarized as follows: In the case of an inductive source: The lines connected to the primary side of the feeding transformers should not be neglected. - The capacitances at the feeder should be taken into account. In the case of a complex source: - If a terminal station is one node behind the node the switched line is connected with, the lines of lower rated voltage connected to the terminal station should be taken into account. - The feeding network in situations as discussed should be simulated up to two nodes behind the node the switched line is connected with.