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This article proposes an enhanced procedure for executing the standard variable load test that allows obtaining high correlation factors for indirectly measured stray-load loss during efficiency tests of induction motors. This helps to achieve the minimum values required by the international standards to consider the variable load test well executed, avoiding unwelcome test repetitions and leading to significant amount of time saved. With the machine at steady-state temperature, the enhanced procedure consists of alternatively applying load levels higher and lower than the rated load, so that the stator winding temperature zigzags around the rated value. Hence, multiple readings can be performed for each load point, having the machine in isothermal conditions. This allows averaging many measurements of the same load point to mitigate the impact of instrumentation and reading errors. The article includes load tests conducted on different induction motor sizes and pole counts, applying both the standard variable load test procedure and the proposed approach. The experimental results show that the proposed technique allows achieving higher correlation factors on the stray-load losses than the standard procedure.

This paper proposes a procedure for executing the standard variable load test aimed at obtaining valid correlation factors in the stray-load loss calculation during efficiency measurement. This helps to avoid the tests being repeated, leading to significant amount of time saved, making the proposed methodology of potential high interest for industry. The proposed procedure allows for isothermal multiple readings for each load point of the variable load test; thereby, averaging many measurements of the same load point in order to mitigate the impact of instrumentation and reading errors. Experimental tests on different induction motors show that very high correlation factors for the stray-load losses can be achieved.

MEng (Electrical and Electronic Engineering), North-West University, Potchefstroom Campus In this work, fundamental aspects regarding the efficiency of induction motors are treated. Improved efficiency is the task of the hour. Environmental challenges, which include climate change, global warming and greenhouse gas emission have been fuelling the need to increase energy efficiency in electrical rotating machinery. Furthermore, there is a need to establish a level platform for motor manufacturers globally where they can produce electric machines according harmonized standards. Not only does this establish trust with the market, but it allows legislators to enact policies which promote energy conservation and facilitate governments to provide incentives to organizations which make energy efficiency their priority. The efficiency data provided by manufacturers is measured or calculated according to different national and international standards. These standards use different means to incorporate the stray load losses and use different test methods; thus, the efficiency values obtained from different testing standards can vary. This leads to problems in competition and a potentially confusing situation for manufacturers and customers. Hence, there is a need to compare the standards and highlight the possible variations leading to these differences, their causes and recommend where possible, solutions on how they can be eliminated. A comparison of induction motor efficiency test methods according to the IEC 60034-2-1 and IEEE 112 standards is presented in this work. Standard direct-on-line squirrel cage induction motors rated at 3 Kw, 5.5 Kw, and 7.5 kW are tested according to the IEC and IEEE preferred standards. Data collected from tests carried out on the motors is used to calculate the efficiency for the various IEC and IEEE tests. The data obtained shows a similar variation in values of efficiency, stray load losses and excitation losses for the same machine, but calculated using different standards. These differences result from how stray losses are treated and calculated in the standards. As a result, there is a need to harmonize the international standards. Masters

El artículo muestra el desarrollo de un software de adquisición de datos para determinar la eficiencia de motores eléctricos de hasta 10 HP, valiéndose de equipos extras para la medición de las potencias de entrada y salida, aplicando el método directo descrito en la norma IEC 60034-2-1, y clasificando el equipo en prueba según su eficiencia, basándose en la norma IEC 60034-30-1. La metodología de la norma 60034-2-1 se aplica en las pruebas de eficiencia sobre un motor de inducción. Los resultados y la información correspondiente estarán disponibles en una plataforma que actuará como interfaz con el usuario que realice la prueba, permitiéndole arrojar un reporte de la misma This paper shows the development of a software for data acquisition in order to calculate the efficiency of up to 10hp electric engines. This software is complemented with additional equipment for input/output electrical power measurement using the direct method described in IEC60034-30-1 standard. The methodology to calculate the efficiency described in the IEC60034-30-1 standard is applied to electrical induction motor. The results of the test will be on a server and make a report about the test with these results is easier

Dissertação de Mestrado Integrado em Engenharia Electrotécnica e de Computadores apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra