Load Losses In Induction Motors Research Articles

An Evaluation of Induction Machine Stray Load Loss From Collated Test Results

The international standards for determining induction motor efficiency are not in agreement with each other. At the heart of the differences is the stray load loss (SLL). The way this loss is quantified is continuously debated. For many years, the IEC standard for motor efficiency measurement has assigned a fixed percentage to stray load loss. This fixed percentage value has been criticized throughout the history of the standard. A new version of the standard published in September 2007 replaced the fixed percentage with one that is dependent on motor kW rating through a specific relationship. One of the goals of this paper is to determine whether the new formula for assigning the SLL can be confirmed with actual test data. This paper presents a collection of test data on about 1000 motors to show the distribution of stray load losses in induction motors. The analysis clearly demonstrates the need for determining stray loss from test measurements rather than assigning an arbitrary value.

電磁界解析による誘導電動機の漂遊負荷損及び高調波トルクを考慮した等価回路の構築

In this paper, we describe the construction of an equivalent circuit that considers harmonics and stray load loss in induction motors. First, harmonic losses in the motors are investigated by electromagnetic field analysis. Using the obtained results, several equivalent circuits that consider harmonics and stray load loss are proposed and the circuit parameters are determined. Next, the best circuit is determined from the viewpoint of practical use. Finally, the motor characteristics calculated by using the proposed circuit are compared with those of experiments. It is concluded that the accuracy of the proposed equivalent circuit is considerably higher than that of the conventional circuit, particularly at high rotational speeds.

Evaluation of Stray Load Loss in Induction Motors With a Comparison of Input–Output and Calorimetric Methods

This paper investigates the input-output and the calorimetric methods of evaluating stray load loss in induction motors. It highlights the difficulties of accurately measuring stray load loss experimentally and thereby declaring the correct machine efficiency. The standard experimental approach of input-output power measurement with loss segregation is widely used but has some limitations. Fifteen induction motors ranging between 11 kW (15 hp) and 200 hp have been carefully studied in this paper mainly using IEEE 112 Method B. Additional results obtained by calorimetric methods have been used to validate the standard test methods. The objectives of this paper are to quantify the stray load loss, to identify possible sources of error in such a process, and to provide indications of how some of these errors may be mitigated. The conclusion drawn confirms that the only valid way is to evaluate stray load loss directly and any arbitrary allowance for stray load loss is unfounded. The importance of this work is in improving measurement techniques and instrumentation accuracy

Evaluation of additional loss in induction motors consequent on repair and rewinding

The effect on the efficiency, and particularly the effect on the stray load loss of induction motors due to the process of repair and rewinding, are considered. To assess these changes, a range of induction motors covering powers between 5.5 and 225 kW has been very carefully tested both before and after rewinding. The sources of loss in induction motors are several, and all apart from stray load loss can be determined experimentally with reasonable accuracy. Stray load loss, however, is more challenging. The standard experimental approach of input-output power measurement, using the IEEE 112-B or C390 technique, is frequently used to evaluate stray load loss but has limitations. A limited set of results obtained by calorimetric methods has been used to validate the standard test methods. The most significant changes to the loss in induction motors caused by the repair process would be expected to be to stator copper loss, to core loss and to stray load loss. This is shown to be the case but the overall effect is normally less than 0.5% loss of efficiency. Occasionally efficiency loss up to 0.7% occurs for motors with core faults from new. With random-wire-wound machines, it is possible to compensate somewhat for this increase in core and stray load loss by using a 'tight' winding to reduce the copper loss. The trade associations of machine repairers EASA (USA) and AEMT (UK) sponsor the work as part of research into the influence of electric motor repair on machine losses.

Stray Load Loss Analysis of Induction Motor—Comparison of Measurement Due to IEEE Standard 112 and Direct Calculation by Finite-Element Method

The purpose of this paper is to specify the main components of the stray load loss of induction motors from both results of measurement and analysis. The IEEE standard 112 Method B is applied to the cage induction motor for the measurement of the stray load loss. On the other hand, the losses generated at the stator core, the rotor core, and the rotor cage are calculated directly by the finite-element method considering the magnetic saturation and the harmonic fields, which vary due to the load condition. The measured and the calculated torque, losses, and efficiency agree well. It is clarified that the main parts of the stray load loss in the case of the analyzed motor are the increase of harmonic losses due to load, which are the harmonic Joule losses of the rotor cage and the harmonic core losses of the stator and the rotor. The relationships between the losses separated by the measurement and the losses calculated directly by the finite-element method are also clarified.

Stray load losses in induction motors: a challenge to academia

In the February 1997 issue of Power Engineering Journal, Prof. Stephen Williamson published a short article entitled `Stray losses-a residue of ignorance'. In a paper by the author published at the Lisbon Conference on 'Energy efficiency improvements in electric motors and drives' in October 1996, it was concluded that the subject of stray load losses had suffered from academic neglect. This article steers a path between the accusations of neglect and ignorance and presents the challenging case for revisiting the problems and issues with the benefit of new technologies. The author discusses the sources and effects of stray load losses, standards and levels of stray load losses, and the need for energy conservation. The author concludes that the following are urgently needed: to be able to accurately calculate stray load losses; to be able to define and control the material and process variables associated with the generation of stray load losses; to be able to accurately measure stray load losses; and new theories, technologies and work programmes to achieve the above.

Measurement of iron and stray load losses in induction motors using the temperature-time method

In recent years there has been a shift towards the development of highly efficient and high torque inertia electrical machines. The limiting factors in these designs are the losses which effectively reduce the output capability and, possibly, the life span of the machine. To limit these undesirable effects a prior requirement is to accurately assess the iron losses, and understand their nature and, ideally, their spatial location. An experimental method for measuring the iron and stray load losses is presented. The test motor is a 3 phase, 4 pole, 4 kW induction motor which was heavily instrumented with thermocouples to map the loss distribution. The nature and distribution of the stray losses in various parts of the motor are also described.

Novel approach to the measurement of iron and stray load losses in induction motors

Successful design of electrical machines hinges on a knowledge of the likely temperature rise within the machine. The ability to predict an accurate temperature distribution, in turn, requires a knowledge of the iron loss distribution, thermal characteristics of the materials, and the cooling conditions, all of which are very difficult to quantify. A temperature–time method is proposed to evaluate accurately the iron loss density distribution in the stator of an induction motor by measurement of temperature gradients in the machine. This method is used to determine the iron loss density distributions, under various load conditions, in a specially constructed 3-phase, 4-pole, 4 kW frameless induction motor. Accurate stray load losses are then computed from the resulting loss density distributions. The experimental results were validated against those obtained with standard test procedures, as well as predicted results from finite element analysis.

Origins of load losses in induction motors with cast-aluminium rotors

Origins of load losses in induction motors with cast-aluminium rotors

Discussion on “Origins of load losses in induction motors with cast-aluminium rotors”

Discussion on “Origins of load losses in induction motors with cast-aluminium rotors”

Origins of load losses in induction motors with cast aluminium rotors

The theory presented in the paper attempts to explain the origins of load losses in detail. It includes an analysis of the losses produced, at any given value of slip, by current flow through the rotor iron between two adjacent bars, owing to the imperfect insulation of the squirrel cage. The theory also includes a calculation of the eddy-current and hysteresis losses in the rotor teeth, caused by the high-frequency harmonic fluxes that penetrate them. It shows how eddy currents in the iron surface can reduce the value of the differential harmonic leakage of a bar, thus allowing more harmonic bar current to flow, and hence more I2R losses to be produced. It discusses how the effective skew differs from its geometrical value, depending upon the width of the rotor bars. The theoretical formulas developed are used to predict the torque/slip characteristics of three 7½hp squirrel-cage induction motors, and the results show good agreement with the experimental curves, thus verifying the validity of the theoretical argument. A simplified theory of interbar currents is finally given, and the effect of skew and slot combination on the magnitude of the load losses, under normal operating conditions, is discussed.

Power losses in induction machines

Losses in induction machines have been subjected to a detailed study by many investigators, but due to the complex nature of some of these losses, particularly several forms of load loss in induction motors, a clear understanding of their nature, has not been available. Since the majority of such losses are connected with the magnetic flux in the machine, a study of the distribution of magnetic flux in the stator and rotor is necessary; such a study is presented herewith. The flux losses considered are divided into 2 groups, those occurring at the fundamental frequency, and those occurring at tooth frequency.

Power Losses in Induction Machines

Losses in induction machines have been subjected to a detailed study by many investigators, but due to the complex nature of some of these losses, particularly several forms of load loss in induction motors, a clear understanding of their nature, has not been available. Since the majority of such losses are connected with the magnetic flux in the machine, a study of the distribution of magnetic flux in the stator and rotor is necessary; such a study is presented herewith. The flux losses considered are divided into 2 groups, those occurring at the fundamental frequency, and those occurring at tooth frequency.

Measurement of Stray Load Loss in Polyphase Induction Motors

The purpose of this paper is to present the results of experiments carried out to establish a practical method of measuring stray load loss in induction motors. The nature of stray load losses is discussed, methods of measuring these losses are described, and proposals for the revision of the Institute Standards to include stray load losses are made.