Electromagnetic switching transients in transmission line cooperating with the local subsystem

The article investigates the overvoltage occurring during switching states in the line cooperating with the local subsystem. It discusses the possibilities of determining extreme values of overvoltage of all kinds by means of simulation tests. In particular, special attention was paid to the need to faithfully representation of components in power system i.e. transmission line, voltage transformer and surge arrester for correct reproduce electromagnetic waveforms on the primary as well as secondary side of voltage transformers. Overvoltages appearing in the line connected to the local subsystem during switching operations are forced by the change of network operating conditions. Electromagnetic transients in the unloaded line were tested after its sudden disconnection from the power supply. In the research, particular attention was paid to the conditions of switching off the line (moment and disconnection unity), the influence of surge protection devices, the type of the voltage transformer and the short-circuit power of the power subsystems. Simulation tests have shown that under certain conditions overvoltages with dangerously high values (e.g. 2.25x400 kV) may occur.