On-line protection of electrical machines stator windings against interturn insulation failures

Existing models to predict surge voltage distribution within stator windings have been modified to take into account the effect of all three phases of the winding simultaneously. Furthermore, a method has been proposed which is capable of predicting voltage distribution within the winding, when the machine is faced with a train of repetitive surges from the supply end. The advantage of the proposed method is that it does not require considerable computing power as compared to the case where the winding is subjected to a single surge and thereby enabling on-line calculations required for condition monitoring of the machine under load conditions. It has become evident that reducing the repetition rate further from a critical value has a strong influence on the resulting interturn voltage distribution within the winding. This could be used by both machine and switchgear manufacturers to ensure better coordination between breaker switching characteristics and machine winding insulation strength, and thereby reduce considerably the probability of insulation failures.