342 / 2018-12-15 18:39:40

Study of Correlation between Voltage Endurance and Dielectric Properties for Stator Coils of High Voltage Motors

high voltage motors, stator coils, voltage endurance, dissipation factor, 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 the good performance in mechanical, thermal and electrical aspects. The voltage endurance, dissipation factor and partial discharge are most common and effective means to assess the electrical properties of full size stator coils of different materials and manufacturing processes. The voltage endurance test is a destructive method to give direct estimation of lifetime for HV coils. The dielectric dissipation factor and partial discharge are non-destructive diagnostic methods to identify the insulation quality in the integral or local way. Therefore, it is meaningful to i the destructive voltage endurance test and non-destructive diagnostic measurements of dielectric dissipation factor and partial discharge, allowing systematic and comprehensive means of insulation assessment for HV coils. In this paper, the relationship between voltage endurance and dissipation factor as well as partial discharge was investigated for stator coils with the rated voltage 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 activity was measured to obtain PD inception voltage (PDIV), PD extinction voltage (PDEV) and QIEC value in operating voltage (Un/√3) and rated voltage (Un). It has been found that the group of coils with longer voltage endurance tends to show lower loss tangent and tip-up, higher inception and extinction voltages and smaller apparent partial charges. It manifests that both the destructive voltage endurance test and non-destructive diagnostic measurements of dielectric dissipation factor and partial discharge can be available means of insulation assessment for HV coils. Moreover, the calculation of correlation coefficients between voltage endurance life and dissipation factor or partial discharge parameters shows that the tanδ and partial discharge magnitude at the operating voltage (line-to-ground, 0.6Un) can be more effective in evaluate the quality and estimate the lifetime of insulation system for coils, compared with such parameters measured at the rated voltage.