Monitoring of rotor bar faults in induction generators with full-size inverter

Monitoring of generators is an essential part when operating a plant in remote areas. Nowadays demands on system reliability are very high and thus maintenance at regular intervals is necessary. Standard fault detection methods are usually based on several additional sensors. Such monitoring systems increase system costs and afford an additional source of fault. To avoid this disadvantage an alternative technique based only on the usage of sensors already available in the power inverter will be shown. The method is based on machine's response due to voltage pulses generated by inverter switching. Measurement of the current response and subsequent signal processing leads to very detailed information about the machine state. Identification and separation of machine asymmetries obtained from two subsequent Fast Fourier Transformations offer a high sensitive fault indicator. The generation of the excitation pulses, current sampling and the signal processing chain as well will be described. Measurements for several levels of rotor bar fault severity are presented and the fault detection sensitivity and efficiency is proven.