Squirrel-Cage Induction-Motor Core Losses

An experimental method is presented for segregating the various no-load losses of a squirrel-cage induction motor. It is shown that for insulated rotor bars the losses consist principally of stator fundamental-frequency losses, rotor surface losses and eddy-current losses in the rotor bars due to radial and tangential slot-leakage fluxes in the rotor slots caused by reluctance pulsations in the air-gap between stator and rotor teeth. The pulsation losses vary about as the square of the air-gaP induction and about as the 1.2 power of the frequency. The surface losses for the particular slots described are from ¼ to ⅓ of the total pulsation losses. The pulsation losses are approximately the same whether or not the rotor bars are connected by end rings, and are approximately equal to the stator fundamental-frequency losses.