Further Experience with Form-Wound Motorettes

Nineteen insulation systems for form-wound motor coils were tested according to IEEE No. 275, and were successfully designated Class A, B, F, or H. Systems evaluated included mica splittings, mica papers, and non-micaceous materials in combination with resinous treatments of various kinds. It was found that not only materials, but processing procedures, have a great effect upon the thermal capability of an insulation system. Statistical techniques were used to analyze data, and it was found that excessive extrapolation can be misleading. The data presented confirm the desirability of testing at a minimum of three temperatures, one of which is within 20°C of the anticipated hot spot temperature rating. It is evident that micaceous products can be built into all temperature classes. However, the system classification of mica containing systems is dependent upon the resinous binders and processing techniques in the same manner as the non-micaceous systems.