On-line rotor cage monitoring of inverter-fed induction machines by means of an improved method

This paper suggests a fault-detection technique to monitor defects such as cracked rotor bars in induction machines. It has been introduced as the Vienna monitoring method [1], [2]. Rotor bar faults cause an asymmetric magnetic flux pattern in the air gap, Thus, the current phasor (or voltage phasor at current-controlled machines), flux phasor, and air-gap torque differ from those of an ideal symmetric machine. The Vienna monitoring method compares the outputs of a reference model, which represents an ideal machine, to a measurement model. Observing the deviations of these two models makes it possible to detect and even locate rotor faults. It can be applied to inverter-fed machines as no frequency analysis is used. The method is verified by on-line experimental results from a digital signal processor (DSP)-controlled insulated gate bipolar transistor (IGBT) inverter drive. The findings match the outcomes of a detailed machine simulation. Air-gap flux density evaluation by a measurement coil system proves both the excellent sensitivity and fault location ability of the proposed scheme.