Surge Voltage Distribution in Line-End Coils of Induction Motors

The line-end coil of an induction motor winding subjected to steep fronted surges is examined. A multi-conductor transmission line model is developed to represent the entrance coil of the winding under surge conditions. Transmission line parameters are calculated from the geometry of the winding and from the solution of magnetic field equations, using the finite element method. The voltage at any point in the line-end coil is calculated from solution of the transmission line equations describing the model. The results are compared with those obtained from practical tests. This technique can be used to design winding insulation capable of withstanding high stresses caused by fast surges.