An applied laboratory characterisation approach for electric machine insulation

Insulation is a fundamental part of electric machines as it provides suitable electrical isolation between the different parts and sub-components. Developing techniques for analysing properties of insulation is extremely useful for the assessment of operating conditions, insulation quality and degradation (state of health). This paper investigates a novel non-invasive experimental approach to characterise phase-to-phase and phase-to-ground insulation by measuring electrical impedance and derived parameters (capacitance, dissipation factor) over a wide frequency range (100 to 2 MHz) at various different temperatures. Due to its simplicity the method lends itself better to an electrostatics interpretation compared with the typical twisted pair approach. Analysis is presented for the method which show its effectiveness under different operating conditions. This work has important applications in the area of condition monitoring of insulation using impedance based measurements.