Detection of electromagnetic faults (air gap eccentricity, open rotor bars, connection issues) in induction rotating machines with off-line dual imbalance test through stator windings

Various faults can be detected with on-line methods, but with unsteady load the diagnosis might be inconclusive. Known off-line methods can be of limited sensitivity or requiring shaft rotation. DC resistive imbalance (DC R) test is prescribed by EASA AR100, but true DC R of an assembled motor is not measurable with ordinary short-time techniques. This new improved off-line method can be applied on assembled machine, to provide alternative detection of the total electromagnetic imbalance (through the parameter RE-M): air gap eccentricity, broken rotor bars, connection issues, etc. It utilises long decay time (>> 1 s) of the rotor RL circuit. The true resistive imbalance (Rtrue DC) is measured and used for decomposition of the electromagnetic trajectory, hence “dual imbalance”. Motors…