Induction machine efficiency is defined as the ratio of output power to input power. The efficiency determined from this ratio is known as the direct efficiency. Alternatively, the efficiency is often determined by first determining the losses and using either the input power or the output power to calculate the efficiency. This method, known in standards as the loss segregation method is an indirect method that is known to yield a more accurate result if the stray load losses are properly determined. However, the indirect method is complicated; it requires skilled operator and is time consuming. On the other hand, the direct method is relatively simple and less time consuming. The question is by how much the efficiency numbers produced by these two methods differ. This paper presents a comparison of the two methods from a collection of test data of about 1000 induction motors, rated 1–250hp, to show the relative accuracy of the direct method. The Bland-Altman procedure for comparing measurement methods is used in the analysis.

A Comparison of direct and indirect measurement of induction motor efficiency

A comparison of the direct and indirect measurements of induction machine efficiency from a collection of test data is presented in this article. The efficiency is computed from 1,000 induction motors rated 1-250 hp to show the relative accuracy of the methods. The Bland-Altman procedure for comparing measurement methods is used in the analysis.

Induction Motor Efficiency

This paper presents a high-level overview of the issues and challenges relating to high efficiency induction machine design for industrial applications. First, a brief overview of the classical approach to machine design is presented, followed by a commentary on contemporary design using finite element method and design optimization techniques. The issues, challenges and opportunities of improving the efficiency of induction motors are discussed and some interesting results of stack lengthening investigations are presented.

High efficiency design of induction machines for industrial applications

The IEEE standard 112B is widely used as the method for determining induction motor efficiency. However, there is sparse work about the repeatability of this measurement method. This paper presents an analysis of a set of measurements of motor efficiency using the IEEE 112B standard in order to assess the repeatability of the method. The measurements were repeatedly performed on four different motors of varying sizes over a number of years. The conditions of the tests and variations in measurements of efficiency of the motors are presented in this paper and the repeatability coefficient is discussed. The accuracy of the IEEE 112B method is also discussed and causes of the variations are highlighted for future revisions of the standard. This work is important for comparison of the standard with other standards and for interpreting induction motor efficiency measurements.

The repeatability of IEEE standard 112B induction motor efficiency tests

The literature in recent years has numerous references to methods of testing large induction machines at the factory to demonstrate conformance with contractual efficiency and loss statements. The authors do not intend to rehash, or even to shed more light upon, this particular aspect of the situation; their purpose is to demonstrate that there are means of measuring efficiency in the field to obtain information relative to the operating costs of equipment under actual load conditions.

Determining Motor Efficiency by Field Testing

With the continuing escalation of the cost of electrical energy, motor manufacturers and appliers are increasingly concerned with the energy conservation available from high efficiency electrical motors. The revised NEMA Standard on Motor Efficiency is described, as well as its use by motor manufacturers and users and the several years of work invested in preparing and validating the standard.

John R. Keinz

Papers

NEMA Nominal Efficiency-What Is It and Why