Losses In Induction Motors Research Articles

Stray losses due to inter-bar currents of skewed cage induction motors at no-load

In accordance with present-day efforts to reduce power losses in electrical machines, an analytical approach to estimate the influence of contact resistances between the skewed rotor cage and its laminated iron core on the amount of stray losses of induction motors is made in this paper. Equations for calculation of resistances of the rotor iron core, with which the stray losses due to inter-bar currents are taken into account, are presented.

Computation of the core loss in an induction motor using the vector Preisach hysteresis model incorporated in finite element analysis

This paper deals with the computation of the magnetic field and core losses in a squirrel-cage induction motor. The computational algorithm consists of the vector Preisach model incorporated in two-dimensional time-stepping finite element analysis. The hysteretic nonlinearity is handled by the fixed-point iterative technique. The comparison between the calculated and measured core losses for a 37 kW motor at no-load is given and indicates a reasonable agreement.

Effects of broken bars/end-ring connectors and airgap eccentricities on ohmic and core losses of induction motors in ASDs using a coupled finite element-state space method

In this paper, effects of rotor abnormalities such as broken squirrel-cage bars, broken cage connectors and airgap eccentricity on ohmic and core losses of induction motors are presented. In this investigation, a comprehensive time-stepping coupled finite element-state space (TSCFE-SS) model was fully utilized to compute the time-domain elemental flux density waveforms and various time-domain waveforms of motor winding currents useful for core loss and ohmic loss computations. Such investigation is feasible by use of the TSCFE-SS model due to its intrinsic nature and characteristics. The results obtained from the simulations of an example 1.2-hp induction motor clearly indicate that faults due to broken squirrel-cage bars/end-connectors can increase motor core losses in comparison to the healthy case. The results also give the effect of saturation on the core loss distributions within the cross-section of the motor, and indicate the potential for possible excessive loss concentrations and consequent hot spots near zones of bar and connector breakages in the rotor.

Analysis of axially non-uniform loss distribution in 3-phase induction motor considering skew effect

This paper discusses the phenomena of the axially nonuniform distribution of magnetic flux densities and losses in a three-phase squirrel cage induction motor of which the rotor bars are skewed. A 2-D complex finite element method, taking account of the effects of the skewed rotor bars, is utilized for the analysis of characteristics such as copper and iron losses and the loss distributions are examined. The summing up values of nonuniform losses resulted from the finite element analysis are compared with measurements.

Inclusion of interbar currents in a network-field coupled time-stepping finite-element model of skewed-rotor induction motors

In order to include the interbar currents of skewed-rotor inductor motors in finite-element analysis, a three-dimensional (3-D) model is usually necessary. In this paper a two-dimensional multislice time-stepping finite element method of skewed-rotor induction motors is presented to solve such complicated 3-D problems. It is shown that the network of the rotor cage is coupled to finite-element equations so that the interbar currents in the rotor can be taken into account. By arranging the unknowns and mesh-current equations ingeniously, the resultant coefficient matrix of the global system equations are made symmetrical. Compared with 3-D finite-element methods, the computation time for solving field equations with the proposed method is significantly shorter. The model can be used to estimate the high-order harmonic stray losses in induction motors. A comparison between computed and tested results is also given.

A thermometric approach to the determination of iron losses in single phase induction motors

This contribution describes a novel technique for evaluating the iron loss density distribution in a single phase induction motor using the temperature time method. This is achieved by measuring the temperature gradient which exists at any point within the machine when it is isolated from the supply. This method was used when the motor was lightly loaded. The measurements were carried out on a 200 W, 220 V, 4-pole, 1.6-A single phase induction motor.

A novel method for rapid efficiency measurement of three phase induction motors

This paper describes a novel method for rapid full load efficiency evaluation of three phase induction motors using the synthetic loading technique, without the need to connect a load to the machine's drive shaft. The new method uses a digital signal processor (DSP) controlled high switching frequency power electronic inverter to synthetically load the induction machine, while using a new real time data acquisition system to accurately determine and record the machine's performance. The method proposed considerably reduces the testing time compared with conventional methods of efficiency measurement and the accuracy of the result is maintained. Moreover the use of the power electronic inverter allows a comprehensive control over all the quantities which determine the rate at which the power is dissipated inside the induction machine. This method can also directly quantify rotational losses of the induction motor under test.

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.

Estimation of stray losses of skewed rotor induction motors using coupled 2-D and 3-D time stepping finite element methods

A precise estimation of stray losses in skewed rotor induction motors is an important and yet very challenging topic for machine designers. Methods for evaluating the stray losses in skewed rotor induction motors by coupling a 2-D multi-slice time stepping finite element model into a 3-D time stepping finite element method are presented in this paper. The model can take into account the inter-bar currents which are ignored if a 2-D finite element model only is used. New formulae, which are based on the actual changes in the magnetic flux densities and can be easily coupled into a time stepping finite element method for estimating the iron losses, are also described.

Influence of rotor skew on cage motor losses

A technique for calculating the total losses in a skewed induction motor, based upon a multi-slice finite-element model, is presented. The ability of this model to predict the axial variation in flux-density in the motor is initially verified. The model is then used to investigate how skew affects the losses in one induction motor. It is shown that skew alters the balance between the rotor iron loss and high-frequency rotor joule loss in the machine.

Influence of Switching Frequency and Squirrel Cage Design on Audible Noise and Losses in Variable Speed Induction Motor Drives with Transistor and IGBT Inverters

A large number of experiments are performed to analyse the influence of the inverter type and the switching frequency on the audible noise, losses and overall efficiency in induction motor drives. Temperature measurements both in stator and rotor give an indication of the required derating, if any. Results for a standard design motor, consecutively supplied by a transistor based inverter and IGBT inverter are compared with the behaviour when the machine is directly connected to the mains. To analyse the influence of the rotor design, a special rotor with no current redistribution is constructed and mountedin a rewound stator. Higher switching frequencies have a large influence on audible noiseand temperature, but the overall efficiency remains nearly constant. However the distribution of losses is influenced.

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.

Harmonic losses of single-phase induction motors under nonsinusoidal voltages

Parameters of a capacitor-start, capacitor-run single-phase induction motor with closed or semi-closed rotor slots are measured and a model for the investigation of the performance of the machine in the frequency domain under the influence of harmonic voltages is presented. An algorithm, taking into account the nonlinear rotor leakage inductance, is established. This algorithm is applied to estimate the current in the time domain, and the harmonic losses at rated-load operation without and with run capacitors are calculated. Computational results are compared with those from experimentation and the differences between both are discussed.

Influence of the inverter characteristics on the iron losses in PWM inverter-fed induction motors

In this paper, the authors deal with the effects of inverter characteristics on iron losses in induction motors fed by pulsewidth modulation (PWM) controlled power converters. Laboratory tests based on no-load input power measurements were carried out and in order to avoid the influence of mechanical losses and rotor copper losses, which are difficult to be measured or computed, a special test bench with an unconventional test device was employed. In particular, the influence of the following inverter parameters are considered: modulation index; modulation waveform; and switching frequency. Complete experimental results are presented and discussed.

Loss minimization in induction motor adjustable-speed drives

A loss model controller (LMC) for determining the optimal air-gap flux that minimizes the losses in scalar controlled induction motor drives is presented. The suggested LMC is simple, and its implementation does not affect significantly the cost and the complexity of the drive. Although the conception of the suggested LMC is based on the loss model of the induction motor, it is shown that its realization does not require knowledge of the loss model.

Eddy-current losses in a tubular linear induction motor

Primary core and solid secondary eddy-current losses are determined in the electromagnetic topology of a tubular linear induction motor (TLIM). The nonlinear B-H characteristic, hysteresis and skin effect are considered in deriving formulas for eddy-current losses. A means to reduce these losses in the primary core laminations is presented. In addition, techniques for parameter determination of the equivalent circuit and performance predictions are developed by extending the theory presented in the paper. Experimental results show good agreement with calculated values. >

No-load induction motor core losses using a combined finite-element/state-space model

A combined finite-element/state-space (CFE-SS) modeling is used to compute the no-load core losses in three-phase induction motors. The CFE-SS is totally within the embrace of the ABC frame of reference. Consequently, the current, flux linkages, winding magnetomotive forces, and flux density waveforms include as many space harmonic terms, caused by motor magnetic circuit geometries and winding layouts, as necessary. The resulting harmonically rich flux density waveforms are used to calculate the no-load core losses (hysteresis and eddy current losses) of a case-study three-phase, 1.2-hp, squirrel-cage induction motor. In addition, those results are compared with conventionally computed core losses obtained using only the fundamental components of the flux density waveforms. A substantial increase in the core losses due to the significant harmonic contents of the flux density waveforms is reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Calculation of stray losses in a single-sided linear induction motor

The paper describes a method of the stray losses calculation in single-sided linear induction motors (LIMs). The stray losses produced by the higher space harmonics of the primary winding and by the primary slots are discussed. Examples of calculations for a small and a large-scale LIM have been included.

A Calculation Method for Starting Characteristics of a Solid-Rotor Induction Motor with End-Rings.

The three-phase induction motor with solid-iron rotor has advantages in case of manufacture, in high torque per ampere at standstill, and in withstanding high rotational stresses. Recently there has been wide interest in the possible use of such a solid-rotor induction motor for ultrahigh-speed inverter drives with suitable high stator frequency. However, the copper loss of the solid-rotor induction motor becomes large, because it is designed with a high resistance rotor. Accordingly, the efficiency and the power factor of the motor are lower than those of conventional induction motor.In this paper, it is clarified experimentally that starting and running characteristics of the solid-rotor induction motor are improved considerably by providing narrow slits and end-rings on the rotor. Then, a new equivalent circuit for the solid-rotor induction motor is derived considering the behavior of the solid-iron rotor as that of the double-cage rotor, and a method of determining the circuit constants for the motor is proposed. The starting characteristics for the solid-rotor induction motor with narrow slits and end-rings on the rotor is calculated using the proposed equivalent circuit. The results calculated for starting characteristics from the equivalent circuit method agreed satisfactorily with results obtained. from the measurement.

Losses influenced by third-harmonic flux in induction motors

The trend toward increasing flux density in modern induction motors results in the increase of third-harmonic flux in the magnetic paths. The effects of third-harmonic flux on energy losses in induction motors are discussed. The shapes of flux distributions in various sections of an induction motor are interrelated. The most saturated section normally has a flattened shape of flux density distribution. The effects of the shapes of flux density distribution on losses are compared from the third-harmonic flux standpoint. The losses influenced by the third-harmonic flux may be controlled through lamination punching designs and winding connections.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>