Study on the effect of humidity on dielectric response and partial discharges activity of machine insulation materials

Operational and environmental conditions can affect the dielectric response of the insulation system of large rotating machines. Humidity is one of the well-known environmental parameters which could affect dielectric parameters such as insulation resistance, polarization index and dissipation factor up to a certain degree. It also could affect partial discharges occurring in rotating electrical machines with open ventilated cooling system. In order to investigate the effect of humidity on the characteristics of different insulation systems, one asphalt coil and one epoxy bar were subjected to high humidity for a certain period of time and the humidity effect on time and frequency domain dielectric responses were studied. Also partial discharge measurements were conducted on two samples to study the possible correlation between partial discharges and changes in other parameters such as insulation resistance and polarization index due to exposure to high humidity.