Field Coil Insulation Testing for Pulse Power Alternators

Current pulse power alternator designs operate at high speeds and high current densities. The field coil insulation systems for pulse power alternators must provide sufficient stand-off voltage while limiting the amount of thermal resistance for actively cooled designs, and also withstand the strain excursions experienced at full operating speed. Repetitive cycling of the strain excursion overtime may induce cracks in the surrounding field coil matrix. The primary insulation surrounding the field coil conductors must be able to stop crack propagation that may develop in the surrounding matrix material and provide voltage hold-off. Thermally conductive thermoplastics are currently being investigated for the field coil matrix materials where decreased thermal resistance is necessary for actively cooled field coil designs. In order to evaluate conductor insulation and thermoplastic matrix filler quickly, small coupon motorettes were developed per previous designs. The motorettes simulate the hoop strain the conductors would experience due to rotor growth at high rotational speeds. Once the motorettes had been mechanically loaded, the coupon was hi-potted to verify insulation integrity under strain. This paper will discuss the design and testing of these motorettes to evaluate thermally conductive thermoplastics as filler material for the field coil matrix