Propagation of surges in stator winding of large AC motors

The impedance and admittance matrices of the ten-turn coils of a 3.3 kV, 1 MW induction motor stator winding are calculated using a finite-element package. Using multiconductor transmission line theory the Z and Y matrices are manipulated to explain the modal propagation of step-fronted surges entering the winding. Some modes are seen to have similar structures in both the slot and overhang regions. Two of these modes propagate at a velocity approximately equal to C/√ε_r while a third mode propagates at a much lower velocity. This difference in velocity is likely to be significant for surges having risetimes of less than 1 μs