| Summary: | 碩士 === 國立臺灣科技大學 === 電機工程系 === 106 === In response to the upgrade of global energy efficiency standards, the efficiency of low-voltage three-phase squirrel-cage induction motor is mandatorily upgraded to class IE3. Therefore, this thesis proposes to reduce the iron and rotor copper losses by using low-loss silicon steel sheet material and copper-bar rotor to replace silicon steel sheets and cast-aluminum rotor, respectively. Two 6-pole, 250HP, three-phase induction motors are designed and built, and the experimental as well as its counterpart groups are formed for benefit improvement analysis. The empirical formula and silicon iron loss curves are introduced to calculate the range of iron loss reduction. The measured results agree closely with the predicted values, and indicate that the core loss can be effectively improved. As to the reduction of rotor copper loss, copper-bar and its end ring resistance are calculated to assess the proportion that the copper loss of the rotor can be decreased. In addition, finite element method of Flux 2D is used to analyze the static magnetic field of the stator and rotor slots to ensure smooth flux line distribution with flux density lower than the saturation value.
The IEEE 112-A, IEEE 112-B and CNS 5421, which are the methods for dynamometer evaluation, measurement of stray-load loss as well as the efficiency test with circle diagram, respectively, are adopted to evaluate the motor designed. The corresponding efficiencies are 95.97%, 95.90% and 96.10%. All are higher than the minimum efficiency of 95.80% required by IE3. Meanwhile, since efficiency improvement needs to take motor starting performance into consideration, real test yields the starting torque of 270.1 kg-m for the motor with copper-rotor bar, which is larger than the rated torque of 183.1 kg-m as required by NEMA standard. Besides, starting current measurement gives 2,108A for the motor with copper-bar rotor, which is smaller than 2,191A as specified by Code G. Both the starting torques and currents obtained from real test for the motors with cast-aluminum rotor as well as copper-bar rotor are further confirmed by the three calculation methods proposed by CNS 5421. In short, the efficiency of the proposed low-voltage three-phase squirrel-cage induction motor is upgraded to class IE3 with its starting torque and starting current comply with international standard.
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