The Use of Dielectric Spectroscopy for Detection of Insulation Defects in End Turns of Medium Voltage Motors

Artificial defects were introduced inside the insulation of the end turns of a medium-voltage motor. Low-frequency dielectric analysis was conducted at 30 °C in the range 10^-2-10³ Hz. The missing electrode which is required for the measure was provided by immersion of the end turns in water during the 10-min testing. The seven end turns that were considered had each a specific defect. Dielectric analysis enabled the detection and identification of six among the seven defects under consideration. The capacitance at 1 kHz proved to be a reliable marker for identification. The differences between the models with defects and the reference model are qualitatively justified in terms of dielectric properties.