Totally Enclosed Fan Cooled Research Articles

Determination of Heat Transfer Coefficient from Housing Surface of a Totally Enclosed Fan-Cooled Machine during Passive Cooling

This paper presents the analytical calculation of the heat transfer coefficient of a complex housing shape of a Totally Enclosed Fan-Cooled (TEFC) industrial machine when it works below 20% of its nominal speed or close to stall. Therefore, passive cooling is dominant, and most of the heat is extracted by the combination of natural convection and radiation phenomena. Under these conditions, the area-based composite approach was used for the development of the analytical calculation method. A test rig using a TEFC Synchronous Reluctance Motor (SynRM) was constructed, and the collected experimental data was used to validate the proposed analytical method successfully.

Determination of heat transfer coefficient of finned housing of a TEFC variable speed motor

This paper proposes the analytical calculation of the heat transfer coefficient from the housing of a totally enclosed fan cooled (TEFC) machine during the active cooling. A particular focus is on the calculation of the heat transfer coefficient from the machine’s housing for different fan rotational speeds. The paper describes the challenges and provides solutions to dominate them during the analytical calculation of the heat transfer coefficient a TEFC electrical machine. Finally, the proposed method is validated experimentally on a totally enclosed fan cooled synchronous reluctance motor, and good correspondence between the analytical and experimental results is obtained.

EFFECT OF DIFFERENT AMBIENT FACTORS ON TEMPERATURE DISTRIBUTION IN THREE-PHASE INDUCTION MOTOR

This paper adopted a thermal network method (TNM) based on Motor-CAD software for investigating of temperature distribution inside different parts of a totally enclosed fan cooled (TEFC), squirrel cage, three-phase induction motor, with taking ambient considerations like ambient temperature, altitude, relative humidity, and contamination into account. The thermal model of the test motor was done according to its design documents. The results obtained from Motor-CAD were verified by comparing it with that obtained from the finite element analysis taken from Flux2D software with a good agreement.

Thermal analysis of a three-phase induction motor based on motor-CAD, flux2D, and matlab

This paper adopted a thermal network method (TNM) based on Motor-CAD software, and Matlab/SIMULINK, with finite element method (FEM) based on Flux2D software to perform a thermal analysis of a totally enclosed fan-cooled (TEFC), squirrel cage, three-phase induction motor. The thermal analysis is achieved based on a precise knowledge of the test motor geometry, materials, and heat sources (losses). The estimation of heat distribution inside the test motor by this three software is done successfully with a good agreement between its results. The proposed triple-software methodology for this work can be adopted from the motor designer instead of using an experimental test based on a real motor.

Thermal Analysis of a Three-Phase Induction Motor with Frame Design Considerations

The present work investigates the temperature distribution inside different parts of a three-phase induction motor when motor frame dimensions (fins thickness, fins height, fins spacing) were changed, and when frame material is changed from cast iron to cast aluminum. A 2.2 kW, 2 poles, insulation class F, totally enclosed fan cooled (TEFC), squirrel cage, three-phase induction motor is modeled according to its design documents and it is analyzed by a thermal network method (TNM) based on Motor-CAD software. The results show the motor temperatures are in direct proportional with fins thickness, fins spacing, and in inverse proportional with fins height. In addition, the motor temperature will decrease when using the cast aluminum frame. The results were verified by finite element method (FEM) results obtained based on Flux2D software with a good agreement. This work will help the induction motor designer in prediction the thermal state of induction motor when modifying the frame, without needing manufacturing and testing expensive prototype motor.

Fluid flow and heat transfer analysis of TEFC machine end regions using more realistic end‐winding geometry

Here, a typical small low-voltage totally enclosed fan-cooled (TEFC) motor (output power ∼10 kW) has been studied using computational fluid dynamics. The complexity of the end-winding geometries, often consisting of several insulated copper strands bound together, provides a challenge to the modelling and analysis of heat transfer and fluid flow phenomena occurring in the end region, which typically is an area of most interest for thermal management. Approximated geometries are usually employed in order to model the end windings to reduce the analysis time and cost. This paper presents a comparison of two cases, a typical simplified geometry and a more realistic geometry of end windings, and uses these cases to highlight the challenges and impact on predicted heat transfer. A comparison of the two models indicate that the different representations of end winding geometries can affect the heat dissipation rate through the outer housing by up to 45%.

Estimation of Stator Winding Temperature of a Three-Phase Induction Motor

This paper adopted a thermal network method (TNM) based on Motor-CAD with MATLAB/Simulink software, and finite element method (FEM) based on Motor- CAD with Flux2D software, to estimate the stator winding temperature of a totally enclosed fan-cooled (TEFC), squirrel cage, three-phase induction motor. The three software packages were adopted successfully with a good agreement among their results resulting in preferring using Motor-CAD in obtaining results, and using Flux2D with MATLAB to validate these results. The success of triple-software methodology will give the induction motor designer a well-validated tool in attaining a safe motor operation without exceeding the maximum allowable stator winding temperature rise, and without using an experimental test based on an expensive manufacturing motor.

Coupled Fluid-Thermal Analysis for Induction Motors with Broken Bars Operating under the Rated Load

Thermal stress of the rotor in a squirrel cage induction motor is generated due to the temperature rise, it is also one of the factors causing the broken bar fault because the structure of the rotor would be destroyed if the stress of the rotor bars exceed the strength limit. The coupled fluid-thermal analysis for the induction motor with healthy and broken bar rotors is performed in this paper. Much concern has been committed to establishment of the fluid model on the basis of computational fluid dynamic (CFD) theory. The heat field of the prototypes is analysed so that the effect of the asymmetrical rotor on the motor heat performance can be investigated in depth. Eventually, the efficiency of the presented model and method, for the totally enclosed fan cooled (TEFC) induction motor, can be verified through experimental results. In addition, this paper reports a quantitative analysis of the heat flux distribution of the fault rotor, and the heat flux density of the bars is investigated in detail. Then, the part most likely to break in the rotor as a result of the thermal load is identified.

Fan characteristics of the self-support components of rotor ends and its performance matching

In order to perform a comprehensive study on the ventilation characteristics of an induction motor rotor end’s self-support components, and specify the relationship among its size, structure, motor loss and cooling performance, in this paper a 3D physical model of the rotor, stator and motor shell was established according to the characteristics of the total enclosed fan-cooled (TEFC) induction motor. Then the fluid field and temperature field of the TEFC induction motor was solved by combining finite volume method (FVM) and the basic principles of electric machine. By taking the rotor air friction loss and stator end windings temperature rise into consideration and comparing various solutions, the optimum solution to the length of the self-support components was determined, which provided a reference for the optimization of the motor rotor physical construction.

Stator Winding Thermal Conductivity Evaluation: An Industrial Production Assessment

The thermal conductivity between winding and lamination is one of the most critical parameters in electrical machine thermal analysis. Its value depends on the insulation material and on the manufacturing process of the winding system, and for this reason cannot be computed using analytical equations. In this paper, a practical investigation of equivalent thermal conductivity of electrical machines stator winding is presented and discussed. The fully experimental approach is based on a fast transient thermal test to evaluate the winding equivalent thermal conductivity. The test campaign is carried out on two sets of Total Enclosed Fan Cooled (TEFC) industrial induction motors produced by two different manufacturers; the rated power of the devices under test ranges from 1.5 to 55 kW.

Analysis of relevant aspects of thermal and hydraulic modeling of electric machines. Application in an Open Self Ventilated machine

Prediction of the thermal behavior of electric motors in the early design stage is crucial in any design process. The most popular prediction methods are analytical, and based on the lumped parameter model approach. These methods require experimental data in order to obtain accurate results, but this data is often not available. This paper deals with the problem of the lack of experimental data for an Open Self-Ventilated (OSV) Induction motor and reviews some of the most controversial parameters in thermal modeling, such as the bearings model and the axial conductivity of the lamination stack. Due to the nature of the OSV machine, through ventilation is also investigated, and a hydraulic model with improvements focused on rotational effects observation is presented. Moreover, the heat transfer in end spaces and ducts is studied, using dimensionless analysis correlations, along with focusing on new hydraulic phenomena, such as the development of the flow and the roughness effect. An implementation of a thermal circuit for an OSV machine that has good agreement with reference results is used to compare heat transfer coefficients used regularly for Totally Enclosed Fan Cooled (TEFC) enclosures. Finally, a sensitivity analysis is carried out on some parameters to determine their importance.

Totally Enclosed Fan-Cooled Squirrel-Cage Induction Motor Options

This paper focuses on electric motor options specific to rolling element bearing totally enclosed fan-cooled (TEFC) ac induction motors. Topics such as temperature and vibration probes, space heaters, seals and sealing practices, and various other features will be explored. Understanding how these options can benefit specific motor applications can increase user satisfaction, extend motor life, reduce maintenance, and improve operating conditions.

3D temperature field analysis of the induction motors with broken bar fault

The paper deals with 3D temperature estimation for totally enclosed fan cooled (TEFC) induction motor with healthy rotor and faulty rotor. The losses are determined from a complex finite element analysis of the magnetic field, and based on the electromagnetism analysis, the 3D thermal models of the induction motor operating at the healthy state, one broken bar fault and two adjacent broken bars fault state are built. At the above three states, the steady stator-rotor coupled thermal fields of the motor with normal full load are calculated respectively. Then the influence of the broken bar number on the motor thermal field is analyzed. The accuracy of the model is assessed by comparing the calculated temperature values of the prototype motor with the measured ones at rated load condition.

Computation of thermal condition in an induction motor during plugging

The problem of two-dimensional heat flow in the stator of induction motor is solved by use of a finite element formulation and arch-shaped elements in the r-θ plane of the cylindrical coordinate system. The shape functions and exact solution matrices are derived algebraically for utmost economy in computation. The temperature distribution has been determined considering convection from the stator frame and cylindrical air-gap surface. The model is applied to one squirrel cage totally enclosed fan cooled (TEFC) machine of 7.5 kW. Finally, the temperatures obtained by this two-dimensional approximation have been compared for different stator currents for a period of 10 seconds at time intervals of 1 sec during the transient in plugging method of braking.

Computation of thermal condition in an induction motor during reactor starting

Induction machines transient thermal analysis has been a subject of interest for machine designers in their effort to improve machine reliability. The stator being static is prone to high temperature. Therefore, the study of transient thermal behavior in the stator is useful to identify causes of failure in induction machines. The paper presents a two-dimensional transient heat flow in the stator of an induction motor using arch shaped elements in the r–θ plane of the cylindrical co-ordinate system. A temperature–time method is employed to evaluate the distribution of loss in various parts of the machine. Using these loss distributions as an input for finite element analysis, more accurate temperature distributions can be obtained. The model is applied to one squirrel cage Totally Enclosed Fan Cooled (TEFC) machine of 7.5kW. Finally the temperatures obtained by this two-dimensional approximation at different location of stator have been compared for different stator currents considering the time required for each stator current during the transient in reactor starting.

Increased Efficiency Versus Increased Reliability

The vast majority of totally enclosed fan cooled (TEFC) squirrel cage induction motors in the 1-to 20-hp range installed in the petroleum and chemical industries are National Electrical Manufacturers Association (NEMA) "T" frames built prior to 1992, NEMA "T" frames built in accordance with the Energy Policy Act of 1992 (commonly referred to as EPAct motors), and the NEMA Premium motors, introduced after the year 2000, that exceed the EPAct efficiency standards. All three types are available in accordance with the IEEE 841 recommended practice and standards. The most obvious difference in these three generations of motors is their efficiency levels. There has been some concern expressed by the users of these motors that to achieve the premium levels of efficiency it was necessary to compromise other performance characteristics and the motor reliability. This article addresses these claims and shows that they are without basis.

Analysis of the Endwinding Cooling Effects in TEFC Induction Motors

The paper deals with the endwinding cooling problems of Total 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 set up together the followed test procedures are 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 thermal resistance between the endwinding and the motor frame, 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.

Survival of the fittest

This article discusses the two motor designs namely weather-protected type II (WPII) and totally enclosed fan-cooled (TEFC) motors specifically employed in a variety of harsh, contaminated environments of the petrochemical industry. These two motor designs are fundamentally different in everything from cooling methods to maintenance. Although there are many motor applications within the industry in which both enclosures would be suitable, totally enclosed fan-cooled motors from 250-2,000 hp typically perform better in the harsher environments. Their increased reliability leads to reduced downtime caused by repair or replacement and the price differential can most often be recouped through lower life-cycle costs of the motor

TEFC Induction Motors Thermal Models: A Parameter Sensitivity Analysis

With the increasing pressures on electric motor manufactures 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 the paper emphasis is given to thermal sensitivity analysis of total enclosed fan cooled (TEFC) 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 enables robust designs to be developed that are insensitive to manufacturing tolerances.

A Simplified Thermal Model for Power Derating Prediction of TEFC Induction Motors

In this article, a simplified thermal model for variable speed total enclosed fan cooled (TEFC) induction motors is proposed and experimentally verified. The thermal model is based on simple equations that are compared with more complex equations reported in literature. The proposed thermal model allows to predict the over temperature in the main parts of the motor, starting from the measured or the estimated losses in the machine. The description of the thermal model set up is reported in detail. Finally, the model is used to define the correct power derating for a variable speed PWM induction motor drive. In fact, if variable speed PWM drive employ general purpose self cooled induction motors, a torque derating is required due to motor efficiency and cooling effect reduction. This article presents in detail a procedure to preview the derating of self cooled induction motors, based on the proposed simplified thermal model, but accurate enough for practical applications. The obtained results are experimentally verified on five standard industrial motors of the same series (4–7.5–15–30–55 kW, 4 poles, 380 V, 50 Hz). The previewed overtemperatures match the measured ones with an average accuracy better then 10% (absolute error less than ±5° C).