343 / 2018-12-18 13:21:10

Correlation between Voltage Endurance and Dielectric Loss and Partial Discharge for Stator Coils of High Voltage Motors

high voltage motors, stator coils, voltage endurance, tanδ, partial discharge, correlation

Vacuum pressure impregnation (VPI) technique is now widely used in the insulation systems of high voltage (HV) motors and generators due to good mechanical, thermal and electrical performances. The voltage endurance, tanδ and partial discharge are most common and effective means to assess the electrical properties of full size stator coils. In this paper, the relationship between voltage endurance and tanδ as well as partial discharge was investigated for stator coils with the rated voltage (Un) of 10kV. The voltage endurance test was carried out at 3Un 50Hz. The tanδ measurement was performed over the voltage range of 0.2Un-1.2Un with intervals of 0.2Un. Partial discharge was measured to obtain the inception voltage, extinction voltage and QIEC values in the operating voltage (Un/√3) and the rated voltage (Un). It has been found that the coil group with longer voltage endurance tends to show lower tanδ and tip-up, higher inception and extinction voltages and smaller apparent partial charges. It manifests that the destructive voltage endurance test and non-destructive diagnostic measurements of tanδ and partial discharge have good consistency in assessing the insulation properties for HV coils. Moreover, calculations of correlation coefficients between voltage endurance and tanδ or partial discharge parameters show that the tanδ and partial discharge magnitude at the operating voltage can be more effective for evaluating the quality and estimating the lifetime of insulation system for HV coils, compared with such parameters measured at the rated voltage.