Evaluation Of Eddy Current Losses Research Articles

Visualization and quantitative evaluation of eddy current loss in bar-wound type permanent magnet synchronous motor for mild-hybrid vehicles

This paper describes the conductor eddy current loss that occurs in a permanent magnet type synchronous motor with a distributed winding stator using a rectangular copper wire designed for mild hybrid system applications for small vehicles. Compared with the conventional round wire inserter method, the space factor can be improved and the coil-end length can be shortened by applying a so-called hairpin windings using a pre-formed into hairpin shape of bar conductor, and as a result, DC current resistance of the armature winding can be reduced. However, since the conductor cross-sectional area tends to increases, the conductor eddy current loss generated by the space harmonics linkage becomes too large to ignore. In order to study the reduction of the conductor eddy current loss, it is important to visualize the spatial leakage flux distribution which causes loss and finely analyze how the magnetic path is formed. Therefore, analysis of the conductor eddy current loss distribution generated in the bar-wound conductor is performed using the CAE model that faithfully reproduces the coil-end shape of the actual machine. Furthermore, it was qualitatively clarified what ratio of conductor eddy current loss at various driving points. Finally, the results of preliminary study on reduction of conductor eddy current loss are reported.

Finite-Element Calculation of 3-D Transient Electromagnetic Field in End Region and Eddy-Current Loss Decrease in Stator End Clamping Plate of Large Hydrogenerator

The stator clamping plate is an important component of hydrogenerators used to fasten the stator end core. Due to the complex leakage electromagnetic field in the end region, eddy-current loss in the stator clamping plate is usually very large, which will lead to partial overheat. Evaluation of eddy-current losses in stator clamping plates and reasonable structure design are the premise of ensuring the safe and stable operation of a large hydrogenerator. A 278-MVA hydrogenerator is taken as an example in this paper, and the calculation model of 3-D transient electromagnetic field of end region is established and validated by temperature test value. Then, a new arch-shaped clamping plate structure is presented. The transient electromagnetic field and eddy-current losses of end regions with traditional fan-shaped and new arch-shaped stator clamping plate structures are calculated by time-stepping finite-element method and are compared. Calculation results indicate that the new arch-shaped clamping plate structure can effectively reduce the eddy-current loss of stator clamping plate.

Finite-Element Evaluation and Eddy-Current Loss Decrease in Stator End Metallic Parts of a Large Double-Canned Induction Motor

Large double-canned induction motor has high power density and usually works in a closed environment. Compared with a common induction motor, there are many contacted metallic parts in the stator end region of a large double-canned induction motor, in which eddy current will exist not only in end metallic parts themselves but also between contacted metallic parts. Evaluation of eddy-current losses in stator end metallic parts and reasonable end structure design is the premise of ensuring the safe and stable operation of a large double-canned induction motor. A 5-MW-scale double-canned induction motor is taken as an example in this paper, and the 3-D eddy-current field finite-element calculation model of its stator end is established and solved. Then, the eddy current in stator end metallic parts and between different contacted stator end metallic parts is analyzed in detail. On this basis, the eddy-current losses' decrease method through cutting off the eddy-current path between contacted stator end metallic parts is proposed and validated by experimental results of temperature.

Using Neural Networks for Simulating and Predicting Core-End Temperatures in Electrical Generators: Power Uprate Application

Power uprates pose a threat to electrical generators due to possible parasite effects that can develop potential failure sources with catastrophic consequences in most cases. In that sense, it is important to pay close attention to overheating, which results from excessive system losses and cooling system inefficiency. The end region of a stator is the most sensitive part to overheating. The calculation of magnetic fields, the evaluation of eddy-current losses and the determination of loss-derived temperature increases, are challenging problems requiring the use of simulation methods. The most usual methodology is the finite element method, or linear regression. In order to address this methodology, a calculation method was developed to determine temperature increases in the last stator package. The mathematical model developed was based on an artificial intelligence technique, more specifically neural networks. The model was successfully applied to estimate temperatures associated to 108% power and used to extrapolate temperature values for a power uprate to 113.48%. This last scenario was also useful to test extrapolation accuracy. The method is applied to determine core-end temperature when power is uprated to 117.78%. At that point, the temperature value will be compared to with the values obtained using finite elements method and multivariate regression.

Electromagnetic modelling of short circuited coreplates

PurposeCoreplates in large generators may suffer from local short circuits. An accurate analysis is required to avoid these failures and detect them when occurring. The purpose of this paper is to develop a lamination stack model compliant with interlamination default analysis.Design/methodology/approachAn electromagnetic model should account for the eddy‐current in the lamination stack. To avoid the modelling of the insulation between the steel sheets, the authors propose to introduce a condition on the fields applied between each sheet. In the case of electric fault between several sheets, the conducting domain, i.e. the sheets, is not simply connected. Then, T‐Ω formulation must be adapted to solve such problem.FindingsThe model allows to account for thin plates, insulating layers and electrical faults in electromagnetic modeling of core plates. This study leads to a first evaluation of eddy current losses in steel laminations with defaults.Research limitations/implicationsThe present study does not take into account thermal effects. The next step will consist in a magneto‐thermal computation. Thus, an electromagnetic finite element software must be coupled with a thermal one. An other improvement will rely on the study of actual situation in order to evaluate the accuracy of industrial sensors and to compare with measurements.Originality/valueThe paper develops a lamination stack model compliant with interlamination default analysis. As far as the authors know, this is the first study on 3D electromagnetic modeling.

Evaluation of eddy current losses in the cover plates of distribution transformers

The elimination of hot spots and the reduction of eddy current losses in bushing mounting plates is an important consideration in transformer design. The currently used bushing mounting plates are either mild steel plates, or mild steel plates with non-magnetic stainless steel inserts or stainless steel plates. The authors calculate the eddy current losses in bushing mounting plates using four different methods; (i) an analytical formulation; (ii) a three-dimensional finite element method (FEM); (iii) from measured values of the initial temperature rise; and (iv) from measured values of the steady-state temperature rise. There is a close agreement between the loss values obtained using these four methods. The analysis has resulted in a detailed understanding of the loss pattern and temperature rise phenomenon in bushing mounting plates. The authors also analyse tank plates of small pad-mounted distribution transformers. It is shown that judicious use of non-magnetic stainless steel can result in considerable energy savings for pad-mounted transformers. FEM simulations are performed to find out cost-effective materials for the tank plates of the pad-mounted transformers. A T-shaped stainless steel plate is found to significantly reduce the load loss. The results of the simulations have been verified on a 225 kVA pad-mounted transformer.

Approximate Expressions for Maximum Values of Transient Magnetic Fields and Electromagnetic Forces Imposed on Windings in Superconducting Generators

AbstractAs superconducting generators have a number of advantages, the investigations for such machines have actively been carried out throughout the world.In the superconducting generator, it is very important to support the field winding and to protect it from quenching. On the other hand, since the armature winding is of air core, the evaluation of eddy current loss in the winding and the way it is supported arc inevitable. Thus, the magnetic fields and the electromagnetic forces acing on both the field and the armature windings at the early stages of the machine design should be known.In previous papers the transient behavior of magnetic fields and electromagnetic forces acting on the windings of a superconducting generator based on a computer simulation for a sudden 3‐phase fault have been discussed in part. However, the behavior of magnetic fields and electromagnetic forces during transient period is very complicated and many calculations are required to determine their maximum values.In this paper, for practical use at the early stages of the machine design, approximate expressions are derived to calculate the maximum values of the magnetic fields and electromagnetic forces on the windings in the case of a 3‐phase fault. To check these expressions numerically, a 1000‐MVA superconducting generator was conceptually designed. The numerical results obtained by using these expressions agree well with the computer simulation results.

Field Distribution and Evaluation of Eddy-Current Loss in Solid-Magnetic Cores Subjected to Time Varying Magnetic Fields

In the study of field distribution in solid magnetic cores subjected to a time-varying magnetic field, the field distribution inside the core is created by a magnetising winding that results in current flow within the material. These eddy currents, as they are called, depend on the geometry of the medium, on the electric and magnetic properties of the material and on the rapidity of alteration of the flux. It is obvious, therefore that the study of eddy current phenomena should centre round the determination of the field and current distribution in a conducting medium subjected to a time-varying field. The paper examines the field distribution for different boundary conditions. Based on these solutions formulae are derived for the evaluation of eddy current loss. The paper further examines the usefulness of the concept of Poynting vector for the evaluation of eddy current loss and thus offers an alternative method.

Approximate Expressions of Maximum Values of Transient Magnetic Fields and Electromagnetic Forces Imposed on Windings in Superconducting Generator.

As superconducting generators have a number of advantages, the investigations for such machine have been actively carried out throughout the world.In the superconducting generator, it is very important to support the field winding and to protect it from quenching. On the other side, as the armature winding is of air core, the evaluation of eddy current loss in the winding and the way of its support are inevitable. Thus, we should know the magnetic fields and the electromagnetic forces acting on both the field and the armature windings at the early stages of the machine design.We have partially discussed in previous papers the transient behavior of magnetic fields and electromagnetic forces acting on the windings of a superconducting generator based on a computer simulation for a sudden 3-phase fault. However, the behavior of magnetic fields and electromagnetic forces during transient period is very complicated and many calculations are required in order to find their maximum values.In this paper, for practical use at the early stages of the machine design, we derived approximate expressions to calculate the maximum values of the magnetic fields and electromagnetic forces on the windings in the case of a 3-phase fault. In order to numerically check these expressions, we conceptually designed a 1, 000 MVA superconducting generator. The numerical results obtained by using these expressions agree well with the computer simulation results.

A Simple and Accurate Evaluation of Eddy-Current Loss in Magnetic Pipe of a Cable

Two analytical methods for calculating eddy-current loss in a magnetic pipe of a pipe-type cable have been developed. The first is a simplified but accurate procedure which can be used as a very convenient tool in the cable design, the second is based on integral equation. In both methods, a uniform current distribution in cylindrical cable cores is assumed. The magnetization characteristic of the pipe material is assumed linear and hysteresis loss is neglected. Calculations have been made for some practical cable systems and for different configurations of the conductors in the pipe. The results are Presented in a series of graphs for various conductivities and permeabilities of the pipes. Experimental data reported by other workers are quoted to confirm the theoreticai calculations.

A Simple and Accurate Evaluation of Eddy-Current Loss in Magnetic Pipe of a Cable

A Simple and Accurate Evaluation of Eddy-Current Loss in Magnetic Pipe of a Cable

Equivalent circuit and evaluation of eddy-current loss in solid cores subjected to alternating and rotating magnetic fields

In the study of eddy-current distribution in solid cores subjected to a pulsating or rotating magnetic field a general 2-dimensional current distribution exists and is created by a magnetizing winding that restricts the current flow through it in only one direction. Under such situations, the method of evaluation of the equivalent impedance of the system as a whole is difficult to visualize and has not so far been attempted in the literature. Such an evaluation calls for a concept of the power factor of the magnetizing winding. This is the special feature of the paper. The paper further examines the usefulness of this concept for the evaluation of eddy-current loss in solid cores and thus offers an alternative method. To give more validity to several of the formulae deduced in the paper, the analysis is applied to compute the performance characteristics of a solid-rotor induction machine and certain conclusions are drawn.