The impact of non-linear permeability on electromagnetic stator core tests

Routine electromagnetic testing is used to detect developing faults in the stator cores of large electrical machines. However the non-linear permeability and hysteresis of electrical steel cause the development of harmonics in the magnetic field, potentially affecting fault interpretation. A method to determine the Rayleigh hysteresis from specification data is developed. Since the use of sinusoidal test flux is shown to prevent an analytic solution of the magnetic field, a numeric integration is required to compute the resultant harmonics. The impact of these on the electromagnetic test is analysed and shown to be minor depending on the class of instrument.