Effect of rotor winding mass on the temperature rise and performance of increased safety HT induction motor for hazardous area

The main objective of the design of high tension (HT) increased safety (Ex e) motor is to prevent the arc/spark and control the temperature of any part of Ex ‘e’ HT motor which cannot act as source of ignition in the explosive atmospheres. The time tE is the time taken by motor windings to reach the limiting temperature of winding insulation which is very important for increased safety motor. The time tE of rotor or stator winding can be affected by increasing the mass of rotor winding of motor. The time tE is very critical for any HT Exe motor and it should be at least 5 seconds as per requirement of IS/IEC 60079-7:2006. A study has been conducted in this paper to discern the effect of increased mass of normal rotor winding on the time tE and the performance characteristic of motor. The Ex ‘e’ high tension induction motors mentioned in this paper have been manufactured by Bharat Heavy Electricals Ltd. (BHEL), Bhopal, India during the project as per the design and guidance of main author as project leader.