Un-impregnated vpi tape testing and effects on dielectric performance of VPI insulation systems

This paper studies electrical testing of dry (un-impregnated) vacuum pressure impregnation (VPI) ground wall insulating materials and the effect of pre-VPI electrical testing on the dielectric performance of VPI insulation systems. Rotating machines manufacturers need to identify insulation system defects after coil taping, coil insertion and / or connection of stator coils prior to VPI. The test method and levels must be selected carefully to avoid initiating defect during the tests. The correlation of the number of insulation layers and the breakdown voltage (AC and DC voltage) was investigated for un-impregnated (green) samples. This gave an indication of what level of test voltage might be severe as well as which level of test voltage would be sufficient to identify insulation defects such as missing or broken mica.