Stray Load Losses Research Articles

Stray Load Losses in Induction Machines A Review of Experimental Measuring Methods and a Critical Performance Evaluation

Stray Load Losses in Induction Machines A Review of Experimental Measuring Methods and a Critical Performance Evaluation

高力率昇圧形ハーフブリッジコンバータの試作と評価

This paper shows a result which evaluated a half-bridge converter for the purpose of the improvement in power factor and efficiency about an X-ray high-voltage generator. By making the inverter input voltage higher by the boosting function of the converter, the current flowing through the IGBTs of the inverter can be reduced. Thereby, the current rating of the device can be reduced. Moreover, boosting inverter input voltage can make the turn ratio of the high-voltage transformer smaller, which leads to reduction in stray load loss originated from leakage magnetic flux and in copper loss.

Comparative analysis of IEEE 112-B and IEC 34-2 efficiency testing standards using stray load losses in low-voltage three-phase, cage induction motors

Since 1998, 817 motor efficiency test data sets, in the 1-500 hp (0.75-375 kW) range have been collected from several sources in different countries around the world, for 50 and 60 Hz. The test data include the motor efficiency using the IEC 34-2 and IEEE 112-B test standards, and the quantification of the stray load losses (SLLs), using the IEEE 112-B method. In 125 cases, the test data include the efficiency computed with both methods. The aim of this paper was the quantification of the discrepancy between the two mentioned standards, and to establish an approximate method to allow the comparison between motors tested with the two standards. Based on the significant number of collected motor data sets, it was concluded that, when compared to the IEEE 112-B standard, the IEC 34-2 standard is less accurate, and gives typically higher efficiency values, mainly because of the SLLs estimation procedure. The IEEE 112-B SLLs computed values are typically higher than the IEC SLLs predefined values, on average of 1.0 and 0.8 percentage points for 50-Hz and 60-Hz motors, respectively. Also, the average SLLs values vary slightly with the motor power. Using efficiency measurements made with both standards on the same motors, it was possible to confirm that the SLLs are the main reason for the observed discrepancy in the efficiency values. The results of the analysis carried out in this paper offer the possibility of comparing the efficiency of motors tested under the IEC 34-2 standard with motors tested with IEEE 112-B, leading to a choice of the most cost-effective option. This paper also provides a key contribution to the ongoing revision of the IEC 34-2 standard.

Optimal Robot Speed Trajectory by Minimization of the Actuator Motor Electromechanical Losses

This paper considers the control problem of a robotic manipulator with separately excited dc motor drives as actuators. An innovative method is proposed which achieves robot speed-control requirements, with simultaneous minimization of total electromechanical losses, while the drives follow the desired speed profiles of the robot joints under various loads and random load disturbances. If there is no demand for a specific speed profile, the optimal speed trajectory is determined by minimizing an electromechanical losses criterion. Controllable energy losses, such as armature copper losses, armature iron losses, field copper losses, stray load losses, brush load losses, friction and windage losses, can be expressed proportionally to the squares of the armature and the field (exciting) currents, the angular velocity and the magnetic field flux. The controllable energy loss term is also included in the optimal control integral quadratic performance index, defined for the whole operation period. Thus the appropriate control signals required for following the desired trajectory by simultaneous energy loss minimization for the whole operation interval are achieved. Two case studies of optimal robot control with and without minimization of actuator energy losses are presented and compared, showing the energy savings that can be achieved by the proposed methodology.

Thermal effects of stray load losses in induction machines

Additional heat produced in induction machines due to stray load losses could influence the plant rating, winding insulation design, operating limit and the machine protection design. Quantifying this additional heat and stray load losses accurately and, hence, investigating the extent of some of these influences are the concerns of this paper. Two experimentally verified models, electrical and thermal, are presented. Results of a practical exercise on the measurement of stray load losses by different test methods are reported. The study, thereafter, gives insight into the relationship between stray load losses and the influences mentioned above and contribute results, which are useful to the design and operation of this machine and its protection.

Harmonic Analysis and Loss Comparison of Microcomputer-Based PWM Strategies for Induction Motor Drive

The results presented in this paper were specially chosen to provide a comparative basis for assessing the performance of induction motor drive operating on PWM strategies that have been suitably modified to facilitate real-time implementation using microcomputers. The comparison is made for harmonic copper loss with and without skin effect, end leakage losses, and stray load losses. The simulation results confirm that for low speed operation, Selective Harmonic Elimination (SHE) Technique is unsuited. The regular sampled strategies, in general, are superior to harmonic elimination technique in low and mid frequency range, and associated harmonic losses could be as low as one fourth of the losses occurring with SHE strategies. Sensitivity of the optimal regular sampled strategies for relative phase shift is also investigated. Reduction of 6% in harmonic copper losses occurs for phase shift of 180 at modulation depth of 1.2. teaching tool, and its open architecture would permit the expansion to customize specific requirements. More importantly, users can get

Comparison of standards for determining efficiency of three phase induction motors

The paper describes a set of experiments and discusses their results for determining the efficiency of low voltage, three phase squirrel cage induction motors. The measured efficiency of an induction motor directly connected to the grid, strongly depends on the method used to evaluate the results and the standard according to which the measurements are performed. Different standards as IEEE 112 and IEC 32 are mentioned and their similarities and differences are discussed. The main discrepancies between the various standards is the way in which the values for the stray load losses are obtained at different load levels. A short description of the measurement setup is given and measurement results for motors of several manufacturers accounting for different standards are proposed. The results clearly demonstrate the necessity to handle the efficiency data given by the manufacturer with a lot of care.

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.

DETERMINATION OF IRON AND STRAY LOAD LOSSES IN INDUCTION MOTORS USING A THERMOMETRIC METHOD

In an induction motor, losses in the magnetic materials account for 10% to 20% of total losses. The iron loss effectively reduces both 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 determining 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.

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.

Input Impedance and Losses of Induction Motors Operating from Inverters

Abstract A method for calculating the harmonic input impedance ZH and harmonic losses WH of induction motors operating from PAM- and PWM inverters is presented. The method is derived by use of six test motors, of ratings from 1.5 KW to 900 KW. A simple method is given for calculating the skin effect coefficients KR and KX. The method indicates that it is necessary to consider the skin effects and the stray load losses. Effects of harmonic order, and carrier frequency on ZH and WH are discussed,

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.

Comparison of the nature of torque production in reluctance and induction motors

The nature of torque production is different in reluctance and inductance motors. One significant difference occurs in a reluctance motor that has nonsalient stator punching and a salient motor. When the flux per pole is small in such a motor, the torque can still be high, as long as the rate of energy change with respect to the rotor angular displacement at the rotor pole fronts and pole ends is high. A theoretical foundation to improve the torque capability of reluctance motors is provided. Effects of saturation and stray-load loss are also studied. Experimental results show agreement with theoretical conclusions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Experimental study of high speed induction motor varying rotor core construction

An experimental study of a high-speed induction motor with various rotor constructions is described. The electrical characteristics of a solid-core-type induction motor are inferior to those of a laminated-core-type motor. A new equivalent circuit for a solid-core-type motor is presented. The behavior of the solid core as secondary conductors is considered. The stray load loss with respect to the rotor construction and the influence of the supply frequency are discussed. >

Experimental study on harmonic magnetic fluxes of small squirrel cage induction motor.

The small squirrel cage three-phase induction motors have been used in all fields of industries for many years. Recently, further detailed studies about magnetic noise and stray load losses have been urged in relation to noise reduction and energy saving.Searchcoil voltage on stator and rotor were analyzed for frequency and harmonic flux orders, and its derivation were experimentally clarified. As a result, it was confirmed that time and space saturation harmonic flux had a different order and rotor mmf. included harmonic fluxes caused by stator harmonic fluxes.From experimental comprehensive analysis of harmonic magnetic fluxes, it was found that it was enough for harmonic flux to consider up to order 5.Experimental formulas were also confirmed to evaluate magnetic flux in the airgap due to stator mmf., permeance of airgap and slots, and iron core, considering saturation of iron (time and space separately). The formulas of magnetic flux due to rotor mmf. induced by current which depends on stator mmf. were similarly derived.The frequencies and magnitude of magnetic fluxes such as time, space and saturation (time and space) harmonic fluxes calculated by these formulas were examined with experimental results.As a result, most frequencies of magnetic fluxes of induction motor could be predetermined with these formulas.

No load method of estimating stray load loss in small cage induction motors

The paper refers to the principal methods that have been used for measuring losses in cage induction motors and their assessment by Schwarz [1] and later investigators. Some claims have been contradictory and almost the only consensus is that the existing BS 4999 [2] method is inadequate for small motors; no satisfactory alternative has been suggested. The paper describes a no load test method which is simpler to perform and has fewer theoretical objections than other methods that have been used previously. Typical test results for three motors in the size range 0.25 to 5 kW are shown.

Study on Reliable Reduction of Stray Load Losses in Three-Phase Induction Motor for Mass Production

In 1983, the Japanese Industrial Standard, Lowvoltage Three-phase Squirrel-cage Induction Motors for General Purpose (JIS C 4210) was revised to achieve an internationalization of that Standard. Main contents of the revision include the addition of B-class and F-class insulation to conventional E-class insulation, as well as regulations on torque characteristics, starting input characteristics, and noise level, in alignment with IEC and NEMA Standards. Since Japanese three-phase standard motors possess special characteristics of common use for both 50Hz and 60Hz, to realize frame assignment that enables use of the same horsepower as previously or even more, and to improve starting characteristics and efficiency, study and new technique on stray load losses, other than conventional design engineering, have been necessary. To reduce stray load losses, rotor slot insulation and nonmachining of rotor outer surfaces have been newly developed for mass-produced motors. This new manufacturing method is being applied to new types of motors. In applying these new methods, materials and their treatment for rotor slot insulation were developed that have proved to be appropriate for mass production and that reveal minimized dispersion. Also, studies on further improved accuracy of core dimensions have been conducted. Presented in this paper are the results of these studies.

Study on Reliable Reduction of Stray Load Losses in Three-Phase Induction Motor for Mass Production

Study on Reliable Reduction of Stray Load Losses in Three-Phase Induction Motor for Mass Production

Experimental verification of stray losses in cage induction motors under no-load, full-load and reverse rotation test conditions

The stray load losses of polyphase squirrel-cage induction motors have hitherto rarely been measured at rated voltage and full-load, owing to the great difficulties in achieving the required measuring accuracy; instead, mostly the reverse rotation test is used. This paper primarily deals with the question whether the reverse rotation test yields representative results. It is also examined to what extent it is possible to predetermine the stray losses by means of a series of new investigations on space harmonics of flux density and harmonics of rotor current. For this purpose the stray losses of a four-pole 11 kW polyphase induction machine with semi-closed and open stator slots as well as rotors with a varying number of unskewed and skewed slots are measured under no-load and full-load conditions and in the reverse rotation test and computed for machines with unskewed slots.

Three Dimensional Flux Calculation on a Three-Phase Transformer

Increases in the ratings of large power transformers have demanded more accurate methods of predicting leakage fields which give rise to excessive losses in the devices. This paper addresses the issue, giving the development of a technique which can be used with minimal computing power to determine the distribution of the magnetic fluxes. Estimates for the additional stray load losses in the iron parts can be calculated with reasonable accuracy after the flux distribution has been found. For developing large transformers and reactors, it is necessary to know the distribution of the magnetic leakage field to calculate the electro-dynamic forces and the stray losses due to eddy currents in the winding conductors and in steel parts such as core, tank, pressing beams, etc. In general, the magnetic field in the transformer is calculated using the assumption that the structure is two-dimensional. But actual transformers are three-dimensional. Thus, the customary two-dimensional approximations are inadequate. In this paper, the three-dimensional magnetic flux distribution on the tank wall of a three phase transformer has been calculated. In order to perform the calculation, a finite element scheme has been adopted to obtain a two-dimensional solution at 15 meridian planes of the transformer coil of a single phase transformer for any arbitrary value of current density. Using the actual values of current densities, the magnetic field has been computed for each phase at two selected instants of time in the cycle. Then, the results are manipulated to obtain an overall solution.