Some methods to increase the time tE of increased safety Ex e motor for explosive atmospheres

Dr. Bhagirath Ahirwa and Dr. Tarun Kumar Chatterjee

Increased safety (Ex e) High Tension (HT) squirrel cage induction motors are being designed for safe operation in the explosive atmospheres. The motor time tE for increased safety motor is prime safety parameter. The higher value of time tE means insulating system of Ex e motor is able to withstand the locked condition for long time so motor will be more safe for long duration during in specified abnormal condition in hazardous area. The research work shows that the time tE of Ex e motor can be increased by two proposed methods; by increasing the mass of rotor bar or by increasing the stator coil pitch. Low speed and a high speed HT Ex e motor were selected to redesign with increasing rotor bar mass and stator coil pitch. The time tE and other parameters of redesigned motors have been compared with standard design of Ex e motor. It is anticipated that this study will be of immense benefit to Ex e HT motor designers.