Frequency-Domain Model for Calculation of Voltage Distribution Through Random Wound Coils and Its Interaction With Stray Capacitances

Modern pulsewidth-modulation (PWM) low-voltage drives are recognized as one of the most demanding applications for a motor. Pulses facing motor terminals are responsible for turn-to-turn high electrical stresses that lead to unexpected failures in stator windings. In this paper, an accurate new model for frequency-domain voltage distribution calculation through random wound coils is presented. In addition to checking its applicability for varnished coils, the role of stray capacitances in turn-by-turn voltage propagation is analyzed as well. Model accuracy is proved using experimental data in an experimental test cell. Finally, the same model is applied successfully to real random wound coils inserted in a motor stator core, and the ability to change turn-to-turn electrical stresses by means of changes in stray capacitances values will be quantified.