Effect of Surge Capacitor Lead Length on Protection of Motors from Steep Switching Surges

The results reported in this paper suggest that capacitor protection of large AC motors may not be adequate to protect against motor starting switching surges when the length of the leads connecting the capacitor to the machine terminals and to ground are substantial. Accordingly, it is shown that the magnitude and shape of the switching surges appearing in the machine windings depend upon the length of the capacitor connecting leads. It is shown that steep switching surges with high rates of rise can be impressed on motor winding insulation when the surge capacitor leads to machine terminals and to ground are long.