Flexible medium voltage stator coil insulation system for on-site winding

The dielectric performance of a fully cured non-VPI flexible stator coil insulation system was investigated by performing winding trials and series of dielectric tests. Different dielectric tests performed were voltage endurance (VE), surge test and thermal cycling. VE and thermal cycling tests are well understood and industry recognized test methods to qualify new or improved insulation systems. These are reliable test methods for comparing new insulation systems with service proven insulation systems. To develop a life curve, VE testing was performed at four different voltage levels and the acquired data was reduced using Weibull analysis. To demonstrate the impact of frequent starts and stops and to determine the effects of temperature rise, a thermal cycling test was performed following IEEE Std. 1310. Diagnostic, AC hipot withstand and VE testing after completion of 500 thermal cycles showed positive results. Stable partial discharge (PD), dissipation factor (DF), and tip-up results were recorded through the thermal cycling testing, which indicated no change in the insulation performance due to thermal cycling. In addition, VE testing after completion of thermal cycles showed promising results and met the requirements as outlined in the IEEE Std. 1553.