Separation of fundamental wave and transient components of the current signal for machine insulation state monitoring

In this work a method to detect insulation degradation of an adjustable speed drive (ASD) based on analyses of the transient current reaction caused by inverter switching is proposed. The drive system consists of an inverter fed three phase induction machine with 1.4MW. The standard current sensors are used to analyze the transient signal ringing to extract an insulation state indicator of the winding system and for the control of the machine as well. Using the inverter as a source of excitation, it is possible to perform an insulation test by evaluation of the resulting transient current sensor signals. The influences of the fundamental wave portion and transient component of the current signal on the insulation state indicator are analyzed. An effective separation of these components is investigated with an algorithm applicable for real time evaluation of the insulation state.