Abstract
The prediction of partial discharge (PD) occurrence in electrical motors at the design phase is key to the development of future devices. As a result, there is a growing interest for predictive numerical tools to help assess partial discharge risk. Currently, most efforts rely on Paschen's law as a criterion for partial discharge occurrence between two neighboring wires. Its use requires field lines data obtained with finite element electrostatic simulations. In this paper, we explore the extent to which these finite element simulations can be simplified without losing accuracy regarding subsequent partial discharge risk assessment using Paschen's law. First, we examine whether partial discharge risk predictions between two turns are influenced by the presence of other turns nearby. Our results suggest that the partial discharge is mostly a local phenomenon hardly affected by the surroundings. Performing simulations for an isolated pair of conductors may thus be sufficient to determine the maximum allowable constraints between two turns, at least for large wires. Also, we show that neglecting field line curvature in the calculation does not alter predictions, vindicating the straight line assumption which has been adopted in the literature for the sake of simplicity.
Highlights
Current trends in the electrical engineering industry lead to increasingly severe stresses on the windings of inverter-fed motors [1], [2]
OVERVIEW The general aim of a predictive tool for partial discharge (PD) risk assessment at the design phase is the determination of the maximum electrical constraints that the stator windings of a prospective motor can bear without damage
We can see that there is little to no difference for conductors with radii larger than 0.1 mm, whereas a large deviation from the reference can be seen for smaller radii. This deviation is due to the fact that PDs between wires 1 and 2 are predicted to occur along field lines which paths draw near to the third wire where its electrostatic influence is felt
Summary
Current trends in the electrical engineering industry lead to increasingly severe stresses on the windings of inverter-fed motors [1], [2] This is in part due to the increase in bus voltages to achieve higher power density and to the impact of steep voltage fronts typical of pulse width modulation power supplies. Originally devised for uniform and stationary electric fields, Paschen’s law is routinely used in the context of electrical windings [7]–[12] This has overall led to satisfactory prediction results despite lingering concerns over its validity in some circumstances, such as high pressure [17] or very small gap lengths [18]–[20]
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