Analysis of Turn-to-Turn Transient Voltage Distribution in Electrical Machine Windings
Keywords:electric machine, transient voltage, electric insulation, Finite Element Method
The interturn overvoltage during transient events in stator windings is an important feature to be considered during the machine’s design. In the literature there is no consensus about which turn is subjected to the highest voltage, once there are results of simulations and measurements that found the highest values across the last turns of the coil, although, there are other that verifies the highest overvoltages across the first turns of the coil. In this context, this paper aims at verifying the transient interturn voltage distribution (turn-to-turn and turn-to-ground) in the stator windings of a large motor, using a method in which transient magnetic fields and electric circuit elements (resistance, inductance and capacitance) are coupled. The transient simulation and the calculation of the electric circuit elements used in the model are performed by means of Finite Elements Method (FEM). The end-windings parameters are calculated based on a 3D geometry, which normally is modeled by using simplifications in the literature. The model used only needs of the machine’s geometry, that is, the studies can be done at design phases of the machine. Moreover, the simulations consider all coils of one winding group from the 3 phases, which is different from the other models found in the literature that consider only one or two coils in series of a single phase. To verify the interturn voltages, different numerical simulations are done by changing the surge rise time. According to the results, for the particular motor studied, the last turns were the ones submitted to the highest voltages.