Interturn Faults

•Interturn faults occurs in machines i.e, Transformers, Motors and Generators. An Interturn fault occurs due to the insulation breakdown between the turns of the same phase or between the parallel windings belonging to the same phase of the machine. The cause of the interturn fault is usually an overvoltage or mechanical damage of the insulation.

•Interturn Faults are more severe on large alternators (generators), High voltage motors and power transformers. Interturn fault is most often experienced in rotating machines where multiple windings are present in the same groove. For large generators generally single winding rod per groove is designed in such cases interturn fault can occur only in the winding head region.

•Interturn Fault can occur at both stator and rotor for rotating machines like generators and motors.

•Interturn faults can occur on power transformers

•Interturn Faults in Stator: When an interturn fault occurs on stator of a rotating machine, there is a high probability that such fault can lead in to the ground fault.

•Interturn Faults in Rotor: When Interturn faults occur on the rotor winding following symptoms are observed:

–- When such fault occur high excitation current is required and this is compensated by the voltage regulator.

–- Machine runs less smoothly, because of the asymmetry of the excitation curve

–- magnetization of the shaft due to asymmetrical flux

–- Bearing damage due to current flowing in the bearings

•Interturn Faults in Transformer: Interturn faults on power transformers may occur due to the overvoltages accompnying ground faults or deterioration of the insulation due to chemical influence of the transformer oil.

•Interturn fault current depends on the number of the turns shorted and fault currents will be several times higher than the rated current of the windings and thus damages the windings.