How critical are IEC 60034-27-3 maximum values for dielectric dissipation factor and tip-up to determine the reliability of motor stator insulation?

Abstract

The authors believe that the dissipation factor and tip-up values specified in the Technical Specification IEC 60034-27-3 are not realistic and only applicable to certain types of stator winding insulation systems. To determine how critical these dissipation factor and tip-up values are, test results of sample stator coils and bars having been exposed to long-term aging tests in accordance with IEEE Std. 1553 were studied. The samples were from various types of insulation systems having service proven life. Using Weibull statistics, characteristic life was determined at different stress levels. After determining the life for various insulation systems, an attempt was made to establish a correlation with the respective dissipation factor & tip-up values. The results clearly revealed that an insulation system with higher dissipation factor & tip-up values than the specified requirements of IEC 60034-27-3 can still be considered a reliable system in service. The absolute level of dissipation factor and tip-up are functions of the system being tested, and variation among systems can be completely uncorrelated with the long-term performance. It is therefore recommended that the best approach is to establish a database for benchmarking and to determine a normal production range. It is reasonable for an end-user to request that a new machine's stator coils or winding fall within the respective historical dissipation factor & tip-up distribution for that particular insulation system.