Analysis of End-Windings Influence on the Transient Voltage Distribution in Machine Stator Windings by a Three Phase Model

Transient voltage distribution due to steep-fronted surges must be taken into account during the machine's design as it can lead to main and turn insulation failure. In medium voltage machines, the end-windings region has a considerable percentage of the coil length and plays an important role during transient studies. This article has the purpose of verifying the influence of end-windings on the transient voltage distribution by using a three-phase simulation model in which transient magnetic fields and electric circuit elements are coupled. The transient simulation and the calculation of the electrical parameters used in the model are done employing the Finite Elements Method (FEM). To verify the influence on the results, simulations for different surge rise times are performed, considering and neglecting the end-windings model. As main results, the intercoil and interturn voltages are analyzed for all turns from the three phases of one winding group. The model is validated by measurement results. It is shown that the end-windings, indeed, affect the transient voltage distribution for both, interturn and intercoil voltages, regarding the rate of rising (slope), instant, and the amplitude of the peak voltages. Moreover, all three phases are affected by the end-windings, especially for the turn-to-turn voltages.