How safe is the insulation system of rotating machines operating in gas groups B, C & D?

Abstract

The safe operation of electrical rotating machines in Chemical, Oil and Gas industrial environments where hazardous gas may be present is of primary concern. There are numerous publications available on the subject of arc and spark at various locations within rotating electric machines. Various techniques have been used to minimize corona discharge activity in high voltage stator windings. To understand the impact of discharge activity in a hazardous environment, few manufacturers have tested or provided such data. To ensure safe operation of machines in these environments, it is necessary to determine and understand the levels of partial discharge (PD) and corona discharge activities. PD and corona discharge activities are phenomena related to the applied voltage. There are many other design and environmental related factors that can cause variation in the level of discharge activity. It is believed 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 assess the safe operation of insulation systems of 6.6 kV to 13.8 kV, the steady state ignition tests, called Incendivity testing was performed on stator windings in gas groups B, C, and D as specified in IEC Std. 60079-15. The contributing factors and mitigation of discharge activity will also be discussed in this paper.