Design, ignition risk assessment and testing of increased safety high tension induction motor for explosive atmospheres

Increased safety (Exe) motors are widely used in zone 1 and 2 areas. Exe high tension (HT) motor is designed in such a way that it cannot produce any arc/spark and temperature of any part of motor in normal operating condition and specified abnormal condition. The risk assessment of Exe HT motor was introduced in the year of 2008 by ET22 Committee of Bureau of Indian Standards in IS:6381-2004 standards in India. The Exe motors were designed and risk assessment of ignition was carried out as per new standards. All necessary test on the Exe HT designed motors are also described in this paper. The starting time or blocking time in normal or abnormal condition of Exe motor depends on the insulation system of motor. Time t_E of rotor or stator winding depends on some design parameters like mass of rotor winding, rotor copper loss, starting torque etc. Time t_E is very critical for any HT Exe motor and it should not be less than 5 s as per IS:6381-2004 and IS/IEC 60079-7:2006. The Exe motors mentioned in this paper have been manufactured by Bharat Heavy Electricals Ltd. (BHEL), Bhopal, India during the project and main author was project leader.