Experimental investigation of the voltage distribution in form wound windings of large AC machines due to fast transients

This paper investigates the voltage distribution in form wound windings of large electrical machines due to fast transient voltage steps, usually produced by (multi-level) voltage source inverters. Measurements are conducted on a stator core of a large prototype machine with voltage step rise times between 0.1 and 10 The measurement results of the voltage distribution in one phase string of the stator winding are analyzed and compared to previous simulation results of an equivalent π-section lumped circuit model based on parameters determined by finite element method (FEM) calculations. Good agreement is found for the oscillating overvoltages between the coils of the winding due to the fast rising transients. Furthermore, it is shown that the effect of a non-equally distributed voltage in the winding is diminishing in the investigated machine winding for voltage step rise times longer than 10 μs.