Assessment and control of ignition risk of HT induction motor for increased safety Ex ‘e’ as per Indian standard for explosive atmospheres

It is very difficult to manage ignition risk by operational procedures to ensure that there has not been a hazard gas release in the area prior to starting the motor or and stator sparking which may occur during running; this procedure may be less appropriate than an automatic interlock. As per Indian Standard rotor cage potential sparking and potential stator winding discharge of induction motor are to be considered for risk assessments of increased safety motor. Risk assessment is done based on construction, operation, protection, and environmental conditions of the motor and ignition risk factor are assigned based on its characteristics. The sum of assigned risk factors should not be more than 5. If it is greater than 5 the motor should be type tested where no incendive sparking should occur during ignition risk assessment test for Ex `e' motor. The paper discuses about the control of ignition risk and assessment of risk factor. The paper also describes the ignition risk assessments test of HT (High Tension) Ex `e' motor as per Indian Standard, conducted successfully first time in India by Central Institute of Mining and Fuel Research Institute (CIMFR), Dhanbad jointly with Bharat Heavy Electricals Limited, India.