Contents I. Introduction
Last few years have seen the development of more and more electric vehicles. The embedded power growth lead to use the electrical activators with very strong environmental or electrical constraints. For example, with more than 1.4MW of embedded power, the Dreamliner is the most electric aircraft for the moment and many systems are targeted to produce a new generation of planes like braking, de-icing systems, taxiing, passenger equipment, air conditioning and pressuring. These embedded systems have to deal with the weight of the copper conductors, and thus, the trend tries to increase the value of the supply voltage much higher than usual voltage. Moreover, the enameled wires technology uses a classical combination of PolyAmide-Imide (PAI) and PolyEster-Imide (PEI) - whose thicknesses are defined in an international standard [1] - designed for industrial voltages operating points. In addition, PWM converters currently feed the motors without any filter due to weight considerations. In these conditions, the steep voltage edges imposed to the system made of the motor and the connection cable causes a voltage peak that may exceed the PDIV in the motor insulation system [2]. When they appear, partial discharges (PD) cause very fast ageing of polymer insulating layers leading to a short life expectancy for standard motors fed by these systems [3], [4]. The variable operating conditions of the embedded systems can lead to unconventional values of the PDIV. Indeed, the conditions of appearance of partial discharges are intrinsically linked to pressure, temperature or humidity. So, it is necessary to calculate a relevant value of this threshold very early during the design of the motor to adjust its EIS. The method used in this study suggests to compute the distribution of the electric field in a motor coil to compare the results with those calculated with the Paschen's theory. Previous works using this method compute straight field lines between the conductors [5]. This can be done however only with simple geometries. The originality of the proposed method is the computation of the electric field line length to improve the accuracy of the results. That also makes it possible the computation of more complex problems and more complex geometries. In a first part, the method is detailed and validated with the suitable assumptions. Then, the use of the method in the domain of the coil insulation is explained. Geometrical and environmental considerations are taken into account to refine the results quality. In the third part, the method is implemented for the determination of a twisted pair PDIV. The last part discusses the results and the ways of improvement for the study.
