Effect of rotor bar size on three phase induction motor performance

Abstract

This investigation is to determine the effect of rotor bar size to performance of three phase induction motor. The research was conducted in two forms, namely by using the FEM software and laboratory experiments that conducted on three fabricated rotor hardware models. The study using FEM software involves three (3) sizes, 6 mm, 8 mm and 10 mm, of rotor bar diameter. A user-friendly FEM software named Motorsolve, allowed simulation to be performed quickly and accurately. Comparison of the results from the software simulation then compared in terms of information on the name plate such as current, output power and power factor, equivalent circuit parameters, torque, efficiency, power input, power output, losses and magnetic flux density. The second part is the construction of three induction motor rotors with rotor bar size 6 mm, 8 mm and 10 mm. Construction starts with preparation of a block of non-grain steel laminations and then followed by cutting process using EDM wire cutting machine, the cut laminations then welded and followed by insertion of copper rotor bars, and finally is installation of both end rings and rotor’s shaft. The next stage is to carry out laboratory experiments such as no-load test, blocked rotor test, and direct current (DC) resistance test methods on the three rotor models that were fabricated. The information of voltage, current and power gathered allows mathematical calculation to determine the induction motor efficiency, losses and power factor, θ. Results from both investigations shows that the increment in rotor bar diameter will increase the current, power output, power factor, losses and torque at rated speed but decrease the starting torque. Results show that different sizes of rotor bar given different efficiency. Changes from 6 mm to 8 mm of rotor bar diameter increased the efficiency but changes from 8 mm to 10 mm of rotor bar diameter will decreased an induction motor efficiency. This is because increment the rotor bar size from 6 mm to 8 mm had decreased the percentage of losses to power input while further increment from 8 mm to 10 mm rotor bar size increased the percentage of losses to power input.