Induction motor stray losses and inter-bar currents

This paper presents measured bar-to-lamination contact resistance values for eight, 10 hp cast copper induction motors. The contact resistance values are compared to full load stray loss values determined using the IEEE input-output method. The stray losses generally decrease with decreasing contact resistance. This result is consistent with the general theory explained by Odok that rotor losses can peak at an intermediate value of contact resistance. For contact resistance values below the maximum loss value, decreasing the contact resistance would decrease the rotor losses. However, additional calculations and test results on skewed and non-skewed 5 hp cast aluminum cage motors are less consistent with the inter-bar loss calculations. The values of the two slot harmonic leakage reactance terms significantly impact the calculated rotor inter-bar losses.