Winding Insulation Stressing During the Switching of Electrical Machines.

The winding insulation of electrical machines is often subjected to high electrical stresses when the machines are switched off. This applies especially to high-voltage induction motors of low rating. A distinction must be made between medium-frequency switching voltages produced by the chipping effect of the current shortly before the current zero and high-frequency surge voltages caused, for example, by restriking in the breaker.