Flammable vapor ignition initiated by hot rotor surfaces within aninduction motor-reality or not?

摘要

Work by the IEEE P1349 Working Group (Motors in HazardousnLocations), which is working on a “recommended practice” fornapplication of motors in Class I, Division 2 areas, has questioned ifnthe rotor of an induction motor becomes too hot for safe application inna classified area. API Publication 2216, Ignition Risk of HydrocarbonnVapors by Hot Surfaces in the Open Air, concludes that ignition ofnvapors on hot surfaces in open air requires temperatures well above (atnleast 200° C) the laboratory-determined (ASTM E 659) minimum ignitionntemperature of the material involved. This paper tests the validity ofnthe API Publication's premise as applied to hot surfaces within anninduction motor. Several motors of various sizes are instrumented withnthermocouples, a flammable concentration of a material of lownautoignition temperature (e.g., diethyl ether, n-hexane, n-heptane, orntetrafluoroethylene) is introduced to the motor interior, and the motorsnare subjected to a series of short-duration locked-rotor tests where thenrotor surface temperature is brought, in defined increasing steps, aboventhe material's listed autoignition temperature. The temperatures atnwhich ignition occurred are reported. These tests are intended tonsimulate the condition of a fully-loaded motor being suddenly stopped innan atmosphere of flammable gas or vapor, such as during an emergencynshutdown of a processing unit during a release. Other tests werenconducted on running motors at overload to heat the rotor well abovennormal operating temperature to simulate somewhat abnormal operatingnconditions