Insulation Performance Evaluation of High Temperature Wire Candidates for Aerospace Electrical Machine Winding Application

The More Electric Aircraft (MEA), complete with the More Electric Engine (MEE) is a concept that has been introduced by aircraft and engine manufacturers to reduce the reliance on hydraulic and pneumatic systems while reducing fuel costs. However, these concepts have brought a requirement to increase system voltage which in turn challenges electrical insulation systems. The insulation system must withstand these higher voltages in more severe conditions such as the high temperature environment present in the engines. Electrical machines are critical on the more electric aircraft and the reliability of these machines must be high while the weight and volume are constrained. For MEE high temperature applications (up to 450 degrees C), inorganic materials will be used as wire insulation since traditional organic materials cannot withstand such high temperature. Although inorganic insulation materials have been used for extended periods in other high voltage applications, their electrical behavior are not fully understood especially as part of aerospace electrical machine insulation system. This paper will detail the results of initial testing that seeks to understand the basic electrical performance of three inorganic wire candidates. The results will be used as a benchmark for further tests in order to evaluate critical ageing mechanisms for inorganic electrical machine insulation systems used in an aerospace environment. The performance of the electrical insulation used in all candidate wires is presented and compared. SEM scanning has been performed to examine differences in the insulation layer structures of the materials. Analysis has then been based on both measurement data and scanning results. All the tests have been performed before and after a limited number of thermal cycles and at the low pressure conditions in which the actual system is expected to operate.