Coil groundwall insulation system evaluation for a large motor wound rotor application

The rotor rewind of large wound rotor motors for NASA presented a number of challenges with respect to the rotor coil ground insulation characteristics. Both electrical and mechanical requirements were difficult to meet using some of the standard insulation systems generally used and accepted today, The winding is a 4600 volt AC winding with a unique end turn support structure. The end turn handing process subjects the coil insulation to very high compressive forces. Through testing and analysis, it was found that an insulation system using polyester impregnating resin and glass backed mica paper tape were not suitable for this application. The insulation system that was found to meet all the requirements is an epoxy impregnating resin and mica splittings tape. This paper details the approach taken in the insulation design and the test methods used to verify the design before actual coil production and slot winding took place. Many insulation systems were evaluated and the approach to best fit the rigid design requirements were found