Thermal classification of an epoxy integral insulation

Epoxy integral insulation applied in powdered form by means of a spray or fluidized bed process to fractional and integral H.P. electric motors is replacing conventional ground insulation at a rapid rate. Since many of these motors with integral insulation are destined for the appliance market, the Underwriters´ Laboratories, Incorporated responded to requests for U.L. listing of such appliances by instituting: 1. A test program for determining the suitability and thermal classification of the epoxy integral insulations - to be carried out by the epoxy resin vendor, and 2. a rigid inspection program of the motor manufacturer´s insulating process and finished motors. The test procedure drafted by Underwriters´ Laboratories for thermal classification of epoxy integral insulation is described in this paper with an analysis of test data determined on a hydrazide quick curing epoxy resin system. The test method developed by the Underwriters´ Laboratories in conjunction with resin suppliers to classify integral insulation is patterned to a great extent after the AIEE No. 510 Test Procedure. The test specifies exposure of the insulation specimens to heat, mechanical stress, thermal shock, and moisture representing an accelerated, cumulative deteriorating effect of service on the integral insulation. Periodic voltage checks are used to establish the end point of insulation life.