Search

In this paper, the determination of the end space induction motor heat transfer coefficients is presented, and the methodologies used are examined closely. Two 'ad hoc' prototypes have been built and a test bench completed. This paper reports the setup of the test procedures and results obtained in detail. As the end windings are the hottest points of the motor, particular care has been devoted to the determination of the heat transfer coefficient concerning the end-winding structure. The results obtained are of fundamental importance for the determination of the thermal resistances between end windings and end caps. These can then be used in thermal networks usually adopted in thermal model analysis. Index Terms--Heat transfer coefficients, induction motors, parameter identification, thermal model.

In this paper, the authors present an extended survey on the evolution and the modern approaches in the thermal analysis of electrical machines. The improvements and the new techniques proposed in the last decade are analyzed in depth and compared in order to highlight the qualities and defects of each. In particular, thermal analysis based on lumped-parameter thermal network, finite-element analysis, and computational fluid dynamics are considered in this paper. In addition, an overview of the problems linked to the thermal parameter determination and computation is proposed and discussed. Taking into account the aims of this paper, a detailed list of books and papers is reported in the references to help researchers interested in these topics. Index Terms--Computed fluid dynamic, electrical machines, finite-element analysis (FEA), lumped-parameter thermal network (LPTN), thermal model, thermal parameter identification.

This paper deals with the formulations used to predict convection cooling and flow in electric machines. Empirical dimensionless analysis formulations are used to calculate convection heat transfer. The particular formulation used is selected to match the geometry of the surface under consideration and the cooling type used. Flow network analysis, which is used to study the ventilation inside the machine, is also presented. In order to focus the discussion using examples, a commercial software package dedicated to motor cooling optimization (Motor-CAD) is considered. This paper provides guidelines for choosing suitable thermal and flow network formulations and setting any calibration parameters used. It may also be considered a reference paper that brings together useful heat transfer and flow formulations that can be successfully applied to thermal analysis of electrical machines. Index Terms--Dimensionless correlations, electrical machines, flow analysis, thermal model.

In this paper, the stray load losses due to the air gap spatial harmonics effects on the rotor squirrel cage are considered and a simplified induction motor equivalent circuit able to include them in the machine power balance is reported. In the proposed model, an additional resistance appears in series with the stator impedance. This additional parameter has been defined on the basis of power balance considerations applied to the induction motor classical theory. The complete theoretical analysis together with the guidelines to measure the equivalent circuit parameters are reported in detail. Finally, the proposed approach has been experimentally verified using five total enclosed fan cooled induction motors. Index Terms--Equivalent circuit, parameter identification, stray load losses, total enclosed fan cooled (TEFC) induction motors.

In this paper, the authors discuss the problem concerning the determination of some thermal parameters which are very complex to compute. These parameters play an important role in thermal networks usually adopted for electrical machine thermal analysis. In particular, in this paper, the following thermal parameters are analyzed: equivalent thermal resistance between external frame and ambient, equivalent thermal conductivity between winding and lamination, forced convection heat transfer coefficient between end winding and end-caps, radiation heat transfer coefficient between external frame and ambient, interface gap between lamination and external frame, air cooling speed, and the bearings effective thermal resistance. While the information given in this paper is mainly related to induction motors, it is also of general use for the designers of other types of machine. The reported results have been validated using induction motors with power ranges from a few kilowatts up to 1 MW. Index Terms--Electrical machines, induction motors, parameter identification, thermal model.

This paper deals with the endwinding cooling problems of totally enclosed fan-cooled (TEFC) induction motors. In order to obtain information about the phenomena involved in the motor end space, three 'ad hoc' prototypes have been build. The complete test-bench setup, together with the followed test procedures, is reported in detail. The measurement results have shown that all the motor-part overtemperatures (winding, endwindings, stator lamination, and external motor frame) decreasing, with the inner air speed increasing. The measured motor overtemperatures and losses allow the thermal-resistance identification of a simplified thermal model suitable to describe the thermal behaviors of the prototypes. By the endwinding-to-motor frame thermal resistance, the related heat-exchange coefficients have been evaluated as a function of the rotor speed. The proposed procedure allows separating the forced-convection contribution by the other thermal-exchange phenomena that occur in the end-space regions. The obtained heat-transfer coefficients are in agreement with the results reported in the past literature. Index Terms--Endwinding cooling, forced-convection heat exchange, thermal analysis, totally enclosed fan-cooled (TEFC) induction motors.

In order to predict conducted electromagnetic interference in inverter-motor drive systems, high-frequency (HF) motor models are requested and the involved parameters have to be available. In previous studies, the authors have presented an accurate HF model for induction motors and they have defined the procedures to identify the model parameters. In this paper, these results are extended to several types and sizes of industrial ac motors such as induction, synchronous reluctance (without interior permanent magnets), and brushless motors. The model parameter-identification procedure has been improved, and it is based on a least-squares data fitting applied to the measured magnitude and phase-frequency-response curves of the phaseto-ground and the phase-to-neutral impedances. The aim of this paper is to provide quick indications to select the suitable values of the HF model parameters, with reference to the size and type of the ac motor, to evaluate the HF voltage and current components in inverted-fed ac motor systems. Index Terms--AC electrical motor, high-frequency (HF) model, parameter identification.

Vector control accuracy of induction motor drives is affected by variations of motor parameters that are treated in the control algorithm as constant values, and by the phenomena that are not modeled at all and are therefore unaccounted for in the controller. Detuning sources of the first type include variations of rotor and stator resistance, mutual inductance, and leakage inductances, while the second category includes stator iron (core) losses. All these sources of detuned operation have been studied in a considerable depth in the past. It appears that the only potential source of detuned operation, which has never been studied before, is the stray load loss (SLL), which belongs to the category of unmodeled phenomena. This paper develops an analytical model that characterizes detuning due to SLLs in indirect rotor-flux-oriented (RFO) current-fed induction motor drives in steady-state operation by means of the orientation angle error, actual to reference rotor-flux ratio, and actual to reference-torque ratio. A quantitative assessment of the impact of SLL on accuracy of rotor-flux-oriented control is performed, with the necessary motor parameters obtained from IEEE 112-B standard measurements and subsequent equivalent circuit parameter fitting. Detuning is also examined in transient operation. It is shown that, although SLLs are comparable to the iron losses in the studied machine (of approximately the same value in the rated operating point), their impact on accuracy of vector control is much smaller when compared to the iron loss induced detuning. Index Terms--Induction machines, stray load losses, vector control.

With the ever-increasing pressure on electric motor manufacturers to develop smaller and more efficient electric motors, there is a need for more thermal analysis in parallel with the traditional electromagnetic design. Attention to the thermal design can be rewarded by major improvements in the overall performance. Technical papers published to date highlight a number of thermal design issues that are difficult to analyze. This paper reviews some of these issues and gives advice on how to deal with them when developing algorithms for inclusion in design software. Index Terms--Induction motors, thermal analysis, thermal models.

In this paper, the analysis of some possibilities for increasing the induction motor efficiency using production technological process modifications is reported. This approach is known as the 'no tooling cost' (NTC) strategy because it does not require a complete redesign of new laminations with a consistent cost in terms of investments. The paper shows the results obtained by a full experimental approach, using 'ad hoc' prototypes. The NTC design modification and the technological processes analyzed in this paper have been done on totally enclosed fan-cooled standard induction motors. Obviously, the original motors have been compared from the energetic point of view with these prototypes. The energetic performance has been measured in accordance with the IEEE Std. 112-96 Method B. In particular, the following modifications, for obtaining an increase in efficiency, have been taken into consideration: rotor with copper bar included in the slot before the aluminum die cast, increase of the core axial length, and annealing of the stator core. Index Terms--Efficiency, induction motors, rotor copper bars, technological process.

With the increasing pressures on electric motor manufacturers to develop smaller and more efficient electric motors, there is a trend to carry out more thermal analysis in parallel with the traditional electromagnetic design. It has been found that attention to thermal design can be rewarded by major improvements in the overall performance. Thus, there is a requirement for accurate and reliable thermal analysis models that can be easily incorporated into motor design software. In this paper, emphasis is given to thermal sensitivity analysis of totally enclosed fan-cooled induction motors. In particular, thermal parameters are modified and their effects on the temperature rise shown. The results are useful for identifying the most important thermal parameters and enable robust designs to be developed that are insensitive to manufacturing tolerances. Index Terms--Induction motors, sensitivity analysis, thermal analysis, thermal models.

Motor efficiency has to be measured or calculated in accordance with international standards. The most important standards are the IEEE 112-B, IEC 34-2, and JEC 3. In this paper, a comparison of the measurement procedures defined by these international standards is reported, together with some comments on the prescribed methodologies. The comparison is based on experimental results obtained by tests on four general-purpose three-phase induction motors. The stray-load loss measurement represents a critical key for the correct evaluation of the motor efficiency. For this reason, a critical analysis of this type of losses has been performed. In particular, in order to understand which are the most critical quantities that influence their evaluation, the stray-load loss sensitivity to the measurement errors is analyzed. In the final part of the paper the temperature influence, on the conventional iron losses, is experimentally analyzed. The performed tests show that the temperature difference between the no-load test and the motor real operative conditions is not negligible. Index Terms--Efficiency, induction motors, international standards, stray-load losses.

In this paper, a simplified thermal model for variable-speed self-cooled induction motors is proposed and experimentally verified. The thermal model is based on simple equations that are compared with more complex equations well known in the literature. The proposed thermal model allows one to predict the over temperature in the main parts of the motor, starting from the measured or the estimated losses in the machine. In the paper, the description of the thermal model setup is reported in detail. Finally, the model is used to define the correct power derating for a variable-speed pulsewidth-modulation induction motor drive. Index Terms--Induction motors, thermal models, thermal tests.

We propose a new approach for predicting iron losses in soft magnetic materials with any voltage supply, starting from the knowledge of the iron losses with a sinusoidal or pulsewidth modulation supply. The model is based on the separation of the loss contributions due to hysteresis, eddy currents, and excess losses with the two supplies. Since any contribution depends on the voltage supply characteristics, it is possible to find a direct mathematical relationship between the iron loss contribution and the voltage supply characteristics. As a consequence, an iron loss prediction can be obtained with any voltage supply if it does not produce a hysteresis minor loop. The energetic model is based on coefficients that depend on the magnetic material characteristic. We performed an accurate analysis of the model on eight magnetic materials used for electrical machine construction, of different thicknesses and alloy compositions. In this way, we found the main coefficients for a large spread of magnetic materials. As a consequence, our approach can be a useful support for electrical machine designers when the energetic performance of a magnetic material has to be predicted for a voltage supply different from the sinusoidal one. Index Terms--Electrical machine design, iron losses, soft magnetic materials.

The aim of this paper is the comparison of the axial flux (AF) structures versus the conventional radial flux (RF) structures for permanent-magnet synchronous motors. The comparison procedure is based on simple thermal considerations. Two motor typologies are chosen and compared in terms of delivered electromagnetic torque. The comparison is developed for different motor dimensions and the pole number influence is put into evidence. The paper reports the complete comparison procedure and the related results analysis. The obtained results show that, when the axial length is very short and the pole number is high, the AF motors can be an attractive alternative to the conventional RF solutious. Index Terms--Axial flux machines (AFMs), electromagnetic torque, permanent magnets (PMs), synchronous motors.

This paper presents different measurement and identification approaches applied to a nonconventional permanent-magnet (PM) synchronous machine, namely, the novel axial flux interior PM (AFIPM) synchronous motor. The nonconventional geometry of the AFIPM motor requires a dedicated discussion on the parameter identification subject. In the paper, the standstill frequency-response test and the standstill time-response test on the AFIPM prototype are presented. On the basis of these tests, the d- and q-axes circuit parameters are chosen. To confirm the validity of the standstill tests, the load tests have also been performed. Furthermore, the load tests provide some preliminary AFIPM machine performance results and additional information on the saturation phenomena. The d- and q-axes equivalent circuits parameters obtained by the performed measurements are analyzed and compared. Finally, the most appropriate AFIPM machine model is selected. Index Terms--Axial flux, interior permanent-magnet synchronous motor, parameters identification.