Explosion protected electrical machines with type of protection “e” and “nA” requirements, risk analysis, type tests, conclusions

Abstract

In the late 1980s severe explosions of motors used on off shore oil platforms forced manufacturers of explosion protected electrical machines to make their products safer, although they were still built according to the latest standards. They started investigations that identified several features of design and operation of machines with negative influence on the explosion risk. The implementation of risk analysis tables in product standards enabled manufacturers to recognize an explosion risk in advance as well as to define measures to minimize it. Additionally, rotor and stator type tests were required to prove that machines are not even able to ignite an explosive gas atmosphere inside of them. After performing these tests successfully manufacturers are sure that explosion protected machines provide a very high security level and that normal partial discharges on stator winding insulation systems do not cause an ignition of explosive gas atmospheres. Moreover, plant operators may now profit from the manufacturers knowledge to secure the safe operation of motors in hazardous areas due to gas.