Losses In Electrical Machines Research Articles

Computation of additional losses due to rotor eccentricity in electrical machines

This study investigates the effect of eccentric rotor on the power losses in electrical machines. The investigations are carried out for an induction machine with PWM-voltage supply and in the cases of dynamic and static eccentricity. The time-stepping two-dimensional finite element method, with coupled field and circuit equations, is used for the simulations. The iron losses are computed through a dynamic loss model. It is shown that the operation of the machine under eccentricity fault results in an increase of both resistive and iron losses. Further the eccentricity causes additional torque modulation and unbalance magnetic pull that result in additional bearing friction losses and wearing.

Development of a High-Precision Calorimeter for Measuring Power Loss in Electrical Machines

This paper is concerned with the development of a high-precision 30-kW (40-hp) calorimeter and is specifically focused on how experimental errors resulting from calorimeter design and operating procedures are eliminated or mitigated. A complete calibration for the calorimetric system using a DC heater is conducted, and two induction motors rated at 5.5 and 30 kW (7 and 40 hp, respectively) are carefully tested both within and outside of the calorimeter. Loss segregation is in accordance with the IEEE 112 method B. Experimental results for the comparison of calorimetric and input-output methods clearly confirm the effectiveness of the calorimeter in terms of accurate power loss measurement. The accuracy of the calorimeter is approximately 5.6 W in the measurement of power loss of up to 4.5 kW with a resolution of 0.1 W.

Identification of Flux Density Harmonics and Resulting Iron Losses in Induction Machines With Nonsinusoidal Supplies

Accurate prediction of iron losses in electrical machines requires detailed information of flux density waveforms in the iron. In the case of an induction machine operating at partial load, many supply cycles must be modeled to obtain accurate flux density waveforms on the rotor. This may be particularly troublesome when nonsinusoidal supplies are used and many small time steps are required. This paper presents an approach to predict rotor flux density harmonics with data from a finite-element model of a single supply cycle. Using this approach, the influence of particular harmonics on total iron loss can be extracted. Predicted rotor losses are compared with those obtained using direct calculation of losses from time-stepped data and with test measurement.

Losses and forces due to eddy currents in a magnetically non-linear conductive half space

A simple soft magnetically non-linear moving conductor model (“iron”) as “half-space” is presented under the inducing effect of a sinusoidal distributed current loading at different current amplitudes, covering the low to very high saturation level of 1–4 T. Eddy current losses, penetration depth of field and tangential braking and normal attractive forces are compared with the results for a linear conductor with constant saturation (relative permeability 100) for a velocity range, described by magnetic Reynolds numbers 1–300. Eddy current losses and the braking force are bigger for the non-linear case (typically 160–200%) and the penetration depth is bigger by 200–400%. The attractive force is smaller, first due to field compression at higher velocity, second due to the increased saturation level, which gives lower relative permeability values than the assumed constant value of 100 in the linear case. For a rough estimate of either eddy current effects in eddy current brakes and linear induction motors with massive secondary or of eddy current losses in electrical machines and apparatus often a constant saturation is assumed. The here presented results allow a preliminary correction due to the non-linear conductor effect, before a detailed non-linear numerical analysis of the investigated geometry is done.

Computation of Core Losses in Electrical Machines Using Improved Models for Laminated Steel

Two new models for specific power losses in cold-rolled motor lamination steel are described together with procedures for coefficient identification from standard multifrequency Epstein or single sheet tests. The eddy-current and hysteresis loss coefficients of the improved models are dependent on induction (flux density) and/or frequency, and the errors are substantially lower than those of conventional models over a very wide range of sinusoidal excitation, from 20 Hz to 2 kHz and from 0.05 up to 2 T. The model that considers the coefficients to be variable, with the exception of the hysteresis loss power coefficient that has a constant value of 2, is superior in terms of applicability and phenomenological support. Also included are a comparative study of the material models on three samples of typical steel, mathematical formulations for the extension from the frequency to the time domain, and examples of validation from electrical machine studies.

An improved method for predicting magnetic power losses in SMC electrical machines

This paper presents an improved method for predicting magnetic power losses in electrical machines with soft magnetic composite (SMC) cores. Different formulations are used for magnetic power loss prediction with purely alternating, purely circular rotating, and elliptically rotating flux density vectors, respectively. A series of three-dimensional (3D) finite element analyses is conducted to determine the flux density locus in each element in a claw pole permanent magnet SMC electrical machine when the rotor rotates. The predicted results are compared with the experimental data of the prototype.

Modelling of electromagnetic losses in asynchronous machines

This paper deals with the numerical modelling of electromagnetic losses in electrical machines, using electromagnetic field computations, combined with advanced material characterisations. The paper gradually proceeds to the actual reasons why the building factor, defined as the ratio of the measured iron losses in the machine and the losses obtained under standard conditions, exceeds the value of 1.

Design and implementation of a calorimetric measurement facility for determining losses in electrical machines

The measurement of the total losses of electrical machines is of most interest to designers for verifying their calculations. We show the limitations of the conventional input-output procedure leading to loss figures. An alternative method is proposed. For this purpose, a calorimetric measurement facility was designed and implemented. This paper is intended to present the calibration procedure for this facility, as well as results of tests performed on a 10 hp (7.5 kW) induction motor.

Iron losses in electrical machines: influence of different material models

The paper presents a comparative analysis of different theoretical iron losses evaluation techniques, coupling finite-element calculations and material modeling. This coupling can be performed at different levels: as a postprocessing step or inside the nonlinear solution loop. Comparisons on an induction machine structure are performed and results are compared and discussed.

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.

Evaluation and analysis of iron losses in electrical machines using the rain-flow method

Iron losses in electrical machines are evaluated and analyzed in this work using the time-stepping finite elements method. The three components of total losses, i.e., eddy currents, excess or anomalous and hysteresis are considered. Concerning hysteresis losses, the influence of minor loops are considered. In order to compute the changes in flux densities during excursions around these minor loops, the "rain-flow method" is used. Results on several typical machines are presented and discussed.

A method to evaluate effects of eccentricity and anisotropy on iron losses of electrical machines. Application to an induction motor

Effects of eccentricity and magnetic anisotropy on total and local iron losses in electrical machines are investigated. The method used combines a finite element simulation and a dynamic hysteresis modelling. The study is performed on a 4 kW induction motor. Eccentricity is shown to have influence only on the local loss distribution and not on the global losses. On the contrary, magnetic anisotropy appears to increase losses remarkably. Different prototypes are designed to compare simulations with experiments. While eccentricity results are very satisfying, anisotropy effects are hard to quantify experimentally and necessitate further investigations.

Methods for predicting rotational iron losses in three phase induction motor stators

Iron losses in electrical machines are difficult to predict. Discrepancies between tested and calculated no-load core losses are sometimes large. In induction motors, a large portion of the stator core is subjected to flux that rotates in the plane of the laminations. Losses due to rotating flux differ from those observed under alternating flux conditions. This paper describes direct approaches for coupling rotational iron loss measurements with finite element analysis (FEA) results that yield the distribution of rotational flux in induction motor cores. Using these methods, the prediction of no-load core loss can be made to include the effects of rotational iron losses.

Determination and designation of the efficiency of electrical machines

According to IEC 34-2 and the harmonised European standards derived from it, the additional losses in electrical machines are taken into account by an estimated 0.5% P1 in the indirect determination of efficiency. In the USA, extensive measurements are made to this effect (IEEE/NEMA), whereas in Japan the additional losses are ignored. Depending on the frame size, the actual efficiencies of four-pole squirrel cage motors <200 kW may generally be slightly lower (up to 1-2% at around 10 kW), those of large machines (700 kW) slightly higher than the nominal values obtained by indirect determination in accordance with IEC 34-2. Since, however, influences of the same order of magnitude due to temperature and measurement technology overlie this tendency, it becomes questionable whether the expenditure on precise determination of additional losses according to IEEE/NEMA is justified. On the other hand, the IEC method is easy to use and to reproduce and has proved in practice to be very worthwhile. To realistically assess the behaviour of an electrical machine in terms of energy efficiency, one has to know, in addition to the nominal efficiency, the loss distribution which influences the efficiency at partial loads, as well as the dependence of this efficiency against load curve on temperature and supply-voltage fluctuations.

Double chamber calorimeter (DCC): a new approach to measure induction motor harmonic losses

Direct measurement of electric machine losses using the principle of the calorimetric method is described in this paper. The design and construction of a double chamber calorimeter (DCC) that can be used for measurement of harmonic losses of a 7.5 kW cage induction motor is discussed. The advantages of this approach are highlighted as compared with a single chamber type calorimeter. Conducted heat leakage through the calorimeter walls is estimated accurately by developing a simple thermal model and compared with the experimental results. Accuracy and reliability is investigated by performing experimental tests using a known heater. Limits for the air flow rate and temperature rise inside and across calorimeter chambers are derived, The calorimeter is capable of measuring a heat loss up to 1 kW corresponding to the 7.5 kW machine with an overall accuracy of /spl plusmn/15 W. This provides a high resolution required for measurement of motor harmonic losses caused by distorted waveforms.

Computational methods for the evaluation of the electromagnetic losses in electrical machinery

This paper deals with the numerical modelling of electromagnetic losses in electrical machines, using electromagnetic field computations, combined with advanced material characterisations. Due to the complexity of this objective, simplified settings, deliberately choosen by physical arguments, must be considered first. The idea is to proceed gradually to the actual problem of an electrical machine through intermediate models showing physical relevance on their own. The numerical methods used to solve these various problems mainly involve modified finite element-finite difference discretisations, which properly take into account the nonlinear and memory properties of the magnetic material. To this end, one must start from suitable variational formulations of the underlying magnetic field problems. The combined magnetodynamic-hysteresis models are validated in several ways, particularly by comparison of numerically obtained electromagnetic losses with experimental results.

Prediction of mechanical stress effects on the iron loss in electrical machines

Iron losses can account for a significant portion of the total loss in electrical machines. Nevertheless, although analytical and numerical techniques have been developed for predicting the iron loss density distribution and the total iron loss of various types of machine under any operating load condition, to date these have neglected the effect of mechanical stress. However, during the manufacture of many electrical machines, a significant radial compressive stress can be imposed on the stator lamination stack, by shrink fitting/pressing an outer frame, for example. This paper describes a technique that has been developed for predicting the effect of compressive stress on the iron loss density in lamination materials, and demonstrates its use in calculating the iron loss of a permanent magnet brushless dc motor.

Rotational magnetization-problems in experimental and theoretical studies of electrical steels and amorphous magnetic materials

Flux rotating in the plane of laminations of amorphous materials or electrical steels can cause additional losses in electrical machines. To make full use of laboratory rotational magnetization studies, a better understanding of the nature of rotational flux in machine cores is needed. This paper highlights the need for careful laboratory simulation of the conditions which occur in actual machines. Single specimen tests must produce uniform flux over a given measuring region and output from field and flux sensors need careful analysis. Differences between thermal and flux sensing methods are shown as well as anomalies caused when the magnetisation direction is reversed in anisotropic specimen. Methods of overcoming these problems are proposed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Magnetic properties of roller-quenched high silicon steel ribbons

The magnetic properties of high silicon steel ribbons prepared by the roller-quenching method were investigated, and this new material was considered to offer the potential of reducing core losses of electrical machines and power transformers.

Tooth-ripple losses in electrical machines. Some basic measurements

An experimental investigation has been carried out of the eddy-current loss generated at the face of a stack of ferromagnetic laminations by a travelling wave produced by permeance variations, the conditions reproducing those which may exist at the pole face of an alternator. Measurements cover a range of values of lamination thickness, slot pitch, flux density and frequencies up to 3kHz. Experimental results are compared with calculated values based on linear theory. Certain of the phenomena of flux penetration are studied experimentally, and qualitative explanations are offered.