Search coil systems for early fault detection in wind turbine generators

The important types of faults and damages in electrical machines directly lead to characteristic changes in the magnetic air-gap field. These changes can be used to detect a fault by search coils placed in the stator slots based on the voltage induced in them to identify the type of fault in dependence of the frequency. Search coil systems are especially suitable for the detection of interturn faults and eccentricities, since these faults have no or little influence on the quantities at the terminals of a machine and are therefore not easy to be detected from the outside. This paper describes two different search coil systems for early fault detection of wind turbine generators. Therefore the design criteria of search coils systems for synchronous generators are presented and based on this the special challenges of search coil systems for multi-pole synchronous generators are deduced. As alternative to search coils systems to be placed in stator slots a rotor-fixed search coil system is designed.