Comparison of Parameters for Characterization of Insulation Material Ageing During Lifetime Based on Voltage and Temperature

Abstract

The stator insulation of electrical machines used in industry is exposed to high frequencies and transient voltage stress. This stress is strengthened by the development of new technologies that offer high switching frequencies such as silicon carbide (SiC). Another significant factor influencing stress is high dv/dtdv / dt. All of these factors are considered damaging to the insulation. These factors favor and contribute to the formation of partial discharges (PDs). There is evidence that PDs are the main mechanism that contributes to the degradation of insulation and destroy it over its lifetime. In accordance with international standards, the repetitive partial discharge inception voltage (RPDIV) and repetitive partial discharge extinction voltage (RPDEV) are defined as parameters that are used to characterize the lifetime of the insulation. Measuring these variables proves to be a challenge during operation. It is necessary to disconnect the frequency inverter and couple the varying pulse source. Both RPDIV and RPDEV exhibit a significant temperature dependence. As an alternative to RPDEV, the newly defined parameter repetitive partial discharge extinction temperature (RPDET) is defined. RPDET is determined by keeping the pulse voltage constant while continuously reducing the temperature. Changing the temperature can easily be done in most industrial drives making RPDET a good candidate for in-service monitoring of insulation without the need for disconnecting the machine and using special equipment like pulse voltage generators. As part of the analysis, RPDEV and RPDET are examined and subsequently compared with each other.