Abstract
This work shows the results obtained from studying the influence of equivalent circuit resistances on three-phase induction motors. The stator resistance, rotor resistance, and iron losses resistance affect the different motor operating variables (output power, current, speed, power factor, starting ratios, and maximum torque). These influences have been quantified, paying particular attention to the losses affected and their impact on efficiency. The study carried out does not apply optimization techniques. It evaluates the different influences of the equivalent circuit’s different resistances on its operation by evaluating applicable constructive modifications concerning available motors. The work has been limited to three-phase induction motors up to 50 kW and low voltage, with the nominal powers of the selected motors being 0.25 kW, 1.5 kW, 7.5 kW, 22 kW, and 45 kW. The tools used to carry out the study are analyzing the equivalent circuit and the simulation of the electromagnetic structure using a finite-element program. The variations proposed in each resistance for all the motors studied is not purely theoretical, as it is based on applying feasible constructive modifications, appropriately analyzed and simulated. These modifications are the variation of the conductor diameter in the stator coils, the change of the section of the rotor cage, and the selection of different ferromagnetic steel types.
Highlights
Three-phase induction motors are the most widely used in industrial applications, especially in pumps, fans, compressors, manufacturing, and processing of materials and refrigeration equipment [1]
The resistors evaluate the different types of losses appear: Joule losses on the stator and the rotor, and the iron losses [7,8]: the stator resistance depending on the diameter of the conductor being used, the rotor resistance depends on the variation of the section of the rotor cage, as well as the iron losses resistance and how it is affected by the type of ferromagnetic steel selected and its specific iron losses
To simplify the number of results and graphs to be shown, of all the calculations made, those that follow a similar trend for all the motors studied and in all the proposed construction modifications have been selected to be presented here. We understand that these cases allow possible action strategies to be established in the design or redesign of induction motors in the range of powers covered by the study
Summary
Three-phase induction motors are the most widely used in industrial applications, especially in pumps, fans, compressors, manufacturing, and processing of materials and refrigeration equipment [1]. Different market studies establish that the drives that use alternating current motors are approximately 75% of the total installed motors, where 89%. That small and medium power motors are the principal consumers of electrical energy globally [2]. For these reasons, the influence of the efficiency on these motors is of great importance in the efficient use of electrical energy, being one more vector to consider in ecodesign and sustainable development policies associated with electrical energy consumption [3]. The study proposed in this article is limited to motors with powers up to 50 kW and low voltage. Mechanical losses and additional load losses are not included in this study
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