Behaviour of an insulation system in gas groups IIA, IIB & IIC

Safe operation of electrical rotating machines in explosive gas environments often present in the petrochemical industry is of primary concern. To ensure safe operation of machines in these environments, the working group committees of IEC standards continue to develop state of the art test methods to assure that electric machinery built to these standards will be safe to operate in such crucial environments. Partial discharge (PD) and corona discharge activities are phenomena related to the applied voltage. There are many other design and environmental related factors that can additionally cause variation in the level of corona discharge activity. It is understood that if the PD or corona discharge activity exceeds certain limits, it may ignite a specific explosive gas or vapor of gas as defined in the IEC Std. 60079-15. To understand the behavior of insulation systems in explosive environments, a steady state ignition test also known as an “Incendivity test” was performed on a partially wound stator in gas groups IIA, IIB, and IIC as specified in the IEC standard. The factors contributing to discharge activity and their mitigation are also discussed in this paper.