Winding Arrangement Research Articles

Numerical and experimental thermofluid investigation of different disc-type power transformer winding arrangements

In this paper, measurements are carried out on four different washer arrangements of an ON disc-type power transformer winding scale model. The experimental setup comprises a closed cooling loop with all the main components generally found on a power transformer and it is equipped with both thermal and flow sensors. Moreover, 3D Conjugate Heat Transfer simulations of the entire cooling circuit are performed using a commercial CFD solver and the computed oil flow rates and winding temperatures are compared with the experimental data for both uniform and non-uniform heat loss distributions. The experimental results show that the reduction of the number of washers in the tested scale model winding increases the total oil flow rate but this effect is overridden by a higher flow maldistribution in the radial ducts of a pass. Thus, the discs temperatures increase with the removal of washers and this effect is particularly marked for a non-guided winding arrangement where an almost stagnant flow is observed in several radial cooling ducts. The CFD results show the same trend but the numerical model consistently underpredicts the total oil flow rate circulating in the closed cooling circuit. This underestimation by the CFD model causes, for certain winding arrangements, significant errors in the evaluation of the average and hot-spot temperatures. For this reason, numerical simulations with a reduced computational domain (i.e., winding region only) are also performed by specifying the measured oil flow rate and temperature as inlet boundary conditions. In this case, the accuracy of the numerical model is significantly improved as the predicted average and hot-spot winding temperatures are within 3 °C of the corresponding measured values. This result is reassuring since the majority of published numerical thermofuid studies on transformer windings are performed on the windings region only and boundary conditions are specified at the inlet, thus avoiding the simulation of the entire cooling loop.

Analysis of Winding Forms for Bearingless Flux-Switching PM Motor with U-core Stator Laminations

Due to low-cost and magnet-free rotor structure, bearingless flux-switching permanent magnet motors (BFSPMs) are more applicable to high-temperature and/or disposable applications. A BFSPM with U-core stator laminations is investigated in this paper. First, the operational principle is analyzed in accordance with the influence of winding connection manners on torque and radial forces, and then the basic winding arrangement for torque windings and radial force windings is determined. The mathematical models of torque and radial forces are derived based on the basic winding arrangement. Followed by that, a method to select winding terminal connection manners is proposed by taking into account control scheme and power inverter topologies. A promising terminal connection is found from three possible candidates and a detailed current model for torque and radial force control are given for the promising winding forms. Finally, relevant electromagnetic properties of the motor are verified and analyzed by finite element analysis.

Current Harmonic Compensation for $n$ -Phase Machines With Asymmetrical Winding Arrangement and Different Neutral Configurations

Low-order current harmonics arise in ac drives due to nonlinearities, producing torque ripple and extra losses. In multiphase machines, which offer advantages over three-phase ones, the latter is aggravated because some harmonics map in low-impedance no-torque subspaces. A multiple-resonant-controller (MRC) structure, combining resonant controllers and synchronous frames, was proposed for harmonic cancellation. It permits substantial computational saving over the multiple-synchronous-frame (MSF) strategy, which includes proportional-integral control in one synchronous frame per harmonic. However, such MRC method is only suitable for symmetrical winding arrangements (SWAs), while asymmetrical winding arrangements (AWAs) are also widespread. Adapting the MRC for AWAs is not straightforward, since the harmonic mapping differs significantly from SWAs, and the effect of neutral configurations on it is more complicated and has hardly been studied. In this paper, an MRC strategy for multiphase machines with AWA is developed. Different neutral configurations are considered; particularly, it is shown and taken into account that for a single isolated neutral, unlike with SWAs, certain subspaces are coupled and unbalanced. The optimum frequencies of the resonant controllers and synchronous frames are assessed. The computational burden of the MRC and MSF schemes is compared, and the differences with SWAs are established. Experimental results are provided.

The single-active-part structure of the UHVDC converter transformer with the UHVAC power grid

The studied sending-terminal's UHVDC converter transformer with the UHVAC grid is currently one of the largest-capacity converter transformers, which is characterized by strong support for the large-scale grid power delivering out, strengthening grid's fault tolerance and backup capability, improving grid operation's flexibility and security, lowering the short-circuit currents. The proposed single-active-part converter transformer structure is well-designed, including the single-phase five-leg iron core, the special winding arrangement, the special structure of the spacers and angle rings, and so on, which is a smaller footprint, easier to install and test on site, but is more challenging in the structural design due to the critical railway transportation limitations on aspects of both size and weight. The feasibility of the proposed structure schema is verified by a series of tests, concerning the wave process, the short circuit force, the temperature field, the main insulation, and so on. Among them, the main insulation's electric fields at the import positions are verified to be reasonable, including the AC impressed voltage test, the DC impressed voltage test, and the polarity reversal test. It shows that the proposed single-active-part design scheme is practicable and conductive to manufacture and application for the UHV large-capacity converter transformers.

Direct Drive Linear Generator Designs with Aluminium Spacer and Alternate Slot Winding for Wave Energy Conversion System

This paper presents the study on direct drive linear generator designs with aluminium spacer and alternate slot winding for wave energy conversion system . The study involved the development of permanent magnet linear generator designs with the variation on aluminium spacer utilization as part of magnet assembly and alternate slot winding usage instead of conventional winding arrangement. The proposed designs were simulated using Finite Element Method (FEM) software to attain the results on flux distribution, air-gap flux density and open circuit results. The total weight and material cost of each design were also estimated. These results are significant in finding the acceptable design’s alternatives to counter the need of huge and heavy linear generator in wave energy converter system. Comparative studies on simulation results and calculated data were conducted between the alternative and conventional design. It is found out that alternate slot winding design improves the performance of conventional design with no impact on design’s weight and material cost while aluminium spacer design yields more significant negative results on the performance than the positive effects in term of design’s weight and material cost.

Development of a single-phase 330kVA HTS transformer using GdBCO tapes

With the mature of manufacture process and technology of high temperature superconductors, the critical current and stability are gradually increased. High temperature superconductors could be used in transformer, current limiter, generator, magnet and etc. This paper focuses on development and characteristic tests of a single-phase high temperature superconducting (HTS) power transformer with capacity of 330 kVA by using GdBCO tapes, which is 1/3 model of a 1 MVA / 10kV / 0.4kV HTS transformer. The specifications of iron core, HTS windings and cryostat are described in detail. The iron core is made of silicon steel plate. The arrangement of HTS windings are based on experimental and simulated results. The cryostat with a room temperature bore is manufactured using nonmetallic materials. Several characteristic tests and insulation tests are performed in liquid nitrogen of 77K. The efficiency and AC loss at rated load is 99.90% and 243.7W, respectively. In addition, an overload test was also performed.

Influence of mixed winding arrangements on torque ripples of five-phase induction machines

In this paper, the authors take a particular look at the influence of mixed stator winding arrangements on torque ripple production in a 30 stator slots, 2-pole, and five-phase induction machine. The conventional five-phase double layer windings with 14/15 and 13/15 chorded coils are compared with the proposed five-phase mixed winding arrangements. This paper presents the design consideration and calculation of winding factors of the proposed mixed winding configurations. The different five-phase winding arrangements have been modelled using Finite Element Methods. The results obtained from simulation are compared to those obtained from experimental measurements. Both simulation and practical results have proven that the combination of double and triple layer winding, mixed with coil side shift to other layer, has tremendously reduced the torque ripple factor while maintaining the torque average.

Multilayer Concentrated Windings for Axial Flux PM Machines

Coreless axial flux machines are of interest because of the absence of stator core losses and cogging torque. These machines generally employ concentrated windings. One of the challenges with such a winding is that the torque producing MMF component that corresponds to the fundamental of the magnet excitation is accompanied by substantial asynchronous components. These harmonics cause losses in the rotor core and magnets, which can become significant at high speeds. This paper proposes a new multilayer winding arrangement to eliminate the non-torque producing MMF components. This winding is applied to a 12-coil 16-pole coreless axial flux machine. The efficacy of the winding is established by 3-D finite-element analysis.

Efficient Simplified Physical Faulty Model of a Permanent Magnet Synchronous Generator Dedicated to the Stator Fault Diagnosis Part I: Faulty Model Conception

This paper proposes an original, simple, and fast permanent magnet synchronous generator model implemented with a new conception on the graphic interface of MATLAB/Simulink environment. The obtained physical model suggests a new way to easily carry out different types of stator faults such as interturns short-circuit faults, phase-to-phase faults, and phase-to-ground faults, as well as simultaneous multifaults. This is handled by connecting the two desired points in the stator on the graphic interface of Simulink exactly as they can be carried out in the experimental tests. This model has the originality to take into account the arrangement of the stator windings of a multipole machine by differentiating between the windings under the same pole-pair and those under different pole-pairs. A comparison between the simulated and the experimental results is done to verify the behavior of the proposed model in both healthy and faulty modes under different operating speeds. The good comparison results lead to validate the correct behavior of the proposed model with a satisfactory accuracy.

Short Circuit Stress Analysis Using FEM in Power Transformer on H-V Winding Displaced Vertically & Horizontally

The aim of this work was to work out the mechanical stresses within transformer resulting from the extreme short-circuit currents. The forces and stresses set up in transformer windings as the result of exterior or interior short-circuits or of switching operations, are measured in detail. A variety of arrangements of windings in large power transformers are described. Points at which mostly high mechanical stresses take place in concentric windings are discussed in detail. Analytical and FEM calculations for individual short circuit forces, axial and radial have been discussed. The result was then compared with actual measurements on a prototype 20MVA 132/11.5kV power transformer [15]. Various failure mechanisms due to these forces have been discussed. Design parameters are also discussed, whose values determine the maximum stresses which may occur in any part of the transformer. Effects of irregularity in various parts and various properties of materials have been studied and the usage of appropriate material for withstanding the dynamic effects of SC is discussed. Effect of workmanship errors on short circuit withstand capability has also elucidated. Finally, a complete model is developed.

Design and Analysis of an Electronic-Geared Magnetless Machine for Electric Vehicles

This paper proposes a new electronic-geared (EG) magnetless machine for electric vehicles. The proposed EG machine can offer the multitooth bipolar-flux (MTBF) operation for the low-gear (high-torque low-speed) situation, and the single-tooth unipolar-flux (STUF) operation for the high-gear (low-torque high-speed) situation. In particular, the balance-position winding arrangement is proposed to enable the machine having balanced flux linkages. Consequently, the proposed machine operates as the brushless ac machine for MTBF operation, leading to offer smoother torque at the low-gear situation. Meanwhile, it operates as the brushless dc machine for STUF operation, leading to produce better torque density at the high-gear situation. Various performances of the proposed EG machine are analyzed, with emphasis on the validity of electronic gearing. The experimental prototype is also built for verification.

AC Copper Losses Analysis of the Ironless Brushless DC Motor used in a Flywheel Energy Storage System

The purpose of this paper is to analyze ac copper losses of the ironless brushless dc machine (BLDCM) used in the flywheel energy storage system. The influence factors of the ac copper losses, such as the winding diameter, phase current, and machine speed, are analyzed. The research results show that the winding wire diameter has a huge effect on the ac losses in ironless BLDCM, and the shunt wound structure with multiple wires method can reduce winding ac losses effectively. However, due to induced voltage and impedance unbalance, additional circulating current losses are induced. For circulating current losses calculation, a winding circulating current equivalent calculation model is built. The circulating current losses are calculated by a simplified three-dimensional finite element method and the winding wires arrangement methods to reduce circulating current losses are explored. Three winding wires arrangements are compared and discussed. The results show that the ironless BLDCM using multiwires with suitable arrangements can reduce the copper losses.

A Numerical Method for Calculating and Optimizing the Coupling Factor of HTS Air-Core Transformer

The coupling factor is a crucial parameter for a high-temperature superconductor (HTS) air-core transformer. This paper proposes a numerical method for calculating and optimizing the coupling factor, which took the influence of insulation distance into account. To verify this method, a laboratory-scale HTS air-core transformer was fabricated and tested in liquid nitrogen. GdBCO HTS tapes were used for HTS windings. The primary windings were six single pancakes (SPs) in series, and the secondary windings were three SPs in parallel. Each SP has 32 turns. The numerical calculation and the experimental measurement were consistent. Because the HTS air-core transformer has no specific path for the magnetic flux compared with the full-core transformer, more attention should be given to optimizing the coupling factor. The relationship between the windings arrangement, the insulation distance, the radial dimension, and the coupling factor was discussed by the numerical calculation method. The conclusion of this paper will guide the design of the 1-MVA/10-kV/400-V HTS power transformer, which is going to be built later this year.

Analysis of end-winding proximity losses in a high-speed PM machine

Abstract This paper presents a finite element investigation into the proximity losses in a high-speed permanent magnet (PM) machine for traction applications. A three-dimensional (3D) finite element analysis (FEA) is employed to evaluate and identify the endwinding contribution into the overall winding power loss generated. The study is focused on the end-winding effects that have not been widely reported in the literature. The calculated results confirm that the end-winding copper loss can significantly affect the eddycurrent loss within copper and it should be taken into account to provide reasonable prediction of total losses. Several structures of the end-winding are analyzed and compared in respect to the loss and AC resistance. The results clearly demonstrate that the size of the end-winding has a significant impact on the power loss. The calculated results are validated experimentally on the high-speed permanent magnet synchronous machine (PMSM) prototype for selected various winding arrangements.

Study on the Optimum Arrangement of the Field Winding for a 20-kW Fully Superconducting Motor

The development of fully superconducting motors using $\text{Re}_{1}\text{Ba}_{2}\text{Cu}_{3}\text{O}_{7-\delta}$ (REBCO, Re: rare earth such as Y, Gd, or Eu) superconducting tapes has begun with the support of the Japan Science and Technology Agency. In this study, as the first step, the optimum arrangement of the rotating field winding for a 20-kW 600-r/min fully superconducting motor was evaluated in terms of torque. The ac loss and critical current properties of currently developed REBCO superconducting tapes were first investigated using a pickup coil method. Taking these properties into account, 20-kW fully superconducting motors with four types of ironless two-pole rotors were designed. The ac loss reduction technique for REBCO superconducting tapes, which was successfully adopted for a 66-kV 2-MVA transformer, was applied to the fixed armature winding. By numerically simulating the actual operation of the respective motors, the torque and ac loss properties were investigated. The torque, i.e., the output power of the motor, and the torque ripple were found to strongly depend on the arrangement of the field winding, despite the different arrangements having the same ampere-turn. The torque ripple becomes smaller as the rotating field winding approximates a 2-D dipole, which is indicated by the uniformity of the magnetic field inside the rotor.

Semi-analytical determination of inductances in windings with axial and azimuthal wires

Purpose – Optimizing an electromechanical device often requires a significant number of evaluations of the winding inductance. In order to reduce drastically the computing costs associated with the calculation of inductances, the purpose of this paper is to propose a semi-analytical toolbox to calculate inductances in any winding made of axial and azimuthal wires and lying in the air. Design/methodology/approach – First, this paper presents a typical rectangular, spiral winding and the way its geometry is approximated for inductance calculations. Second, the basic formulas to calculate inductances of various windings arrangements are provided. The analytical model of the inductances is exposed, and the formulas for the inductances are derived. Finally, a validation is proposed by comparing analytical predictions to 3D FE simulations results and experimental measurements. Findings – The semi-analytical predictions agree with the finite element methods (FEM) and experimental data. Furthermore, the calculation of the inductances was done using much fewer resources with the semi-analytical model than with FEM. Research limitations/implications – The analytical formula for the mutual inductance between coaxial circular arcs is a series with an infinite number of terms which should be truncated appropriately. This is necessary because the term are found using a recurrence formula which may be unstable for a high number of terms. Practical implications – The paper includes implications for the optimization of electromechanical devices comprising windings made of axial and azimuthal pieces of wires. Originality/value – The main original result resides in the analytical expression of Neumann’s integral for the inductance between two coaxial circular arcs.

Influence of Slot and Pole Number Combinations on Voltage Distortion in Surface-Mounted Permanent Magnet Machines With Local Magnetic Saturation

The local magnetic saturation in tooth-tips of surface-mounted permanent magnet (SPM) machines generates on-load terminal voltage distortion, especially when small or closed slot openings are adopted. This paper focuses on investigating the influence of slot and pole number ( N s/2 p ) combinations on this phenomenon in both fractional slot and integer slot SPM machines. The mechanism of this phenomenon and how it is influenced by current advance angle and tooth-tip geometric parameters are introduced first. Then, voltage distortion pattern is proposed to analyze the occurring time or rotor positions of voltage ripples and their relative amplitudes according to the winding arrangements of different Ns /2 p combinations, with the influence of PM leakage flux considered. By 2-D finite-element analysis, the voltage distortion of various machines is calculated and compared, such as $N_{s} \pm 1 = 2p$ , $N_{s} \pm 2 = 2p$ , N s /2 p = 3/2 (3/4), and integer slot machines with slot number per pole per phase $q = 1$ or 2. The analysis results reveal that under the same comparison conditions, the integer slot machines have less voltage distortion than the fractional slot machines, especially when $q \geq 2$ . Meanwhile, for the same slot number, the fractional slot machines with $N_{s} > 2p$ suffer from on-load voltage distortion less than their counterparts with $N_{s} . Finally, three prototype machines with 12/10, 12/14, and 12/8 slot/pole numbers are manufactured and tested to validate the analyses.

Turn–turn short circuit fault management in permanent magnet machines

This paper presents a systematic study on turn-turn short circuit fault and ways to manage them to provide a basis for comparison of the various options available. The possible methods to reduce the likelihood of the winding SC fault and the fault mitigation techniques related to such faults are discussed. A Finite Element (FE) analysis of a surface-mount Permanent Magnet (PM) machine under application of different mitigation techniques during a turn-turn fault is presented. Both machine and drive structural adaptations for different fault mitigation techniques are addressed. Amongst the investigated fault mitigation techniques, the most promising solution is identified and validated experimentally. It is shown that the shorting terminal method adopting vertical winding arrangement is an effective method in terms of the implementation, reliability and weight.

Analysis and Development of Novel Three-Phase Hybrid Magnetic Paths Switched Reluctance Motors Using Modular and Segmental Structures for EV Applications

The classical switched reluctance motors (SRMs) often suffer from drawbacks such as low power and torque densities, high torque ripple, mutual coupling, etc., which limit their industrial applications. This paper presents the analysis and development of two novel three-phase SRMs with hybrid magnetic paths comprising six E-shaped modular stators and three segmental common rotors, termed as the modular SRMs (MSRMs), for electric vehicle applications. The machine topologies with different winding arrangements are described. The voltage and output power equations are analytically derived, and some design particularities and parameters are discussed. The field distributions and static magnetic characteristics of an MSRM with double coil are analyzed by using 3-D finite-element method. After that, two MSRMs with different winding arrangements, namely a double-coil MSRM and single-coil MSRM, are analyzed and compared to evaluate the distinct features of this novel MSRM, accompanied with a classical three-phase 6/4 SRM. The comparison includes static magnetic characteristics, mass of iron core, normal dynamic, and fault-tolerant performances. It is shown that the double-coil MSRM appears to have better characteristics such as higher torque production capability, lower torque ripple and cost, higher torque and output power densities, and higher reliability and fault tolerance. For experimental verification, laboratory testing of a double-coil MSRM is developed, and the simulated and measured static inductance characteristics and dynamic performances correlate well.

Reduction of Irregular Magnetic Field Generated by Screening Current in REBCO Coil

In REBCO coils, the screening current flows in the tape in response to the normal component of the linkage flux to the tape's wide face. Generally, the radial component of the magnetic field is large at both ends of the coil winding. Therefore, changes in the winding arrangement may be expected to reduce screening current induction. Furthermore, multifilamentary or narrow REBCO tapes with widths of a few millimeters can be also expected to reduce the magnitude of the screening current. Based on the above considerations, in this paper, we numerically investigated the reduction effect on a magnetic field generated by a screening current in a REBCO coil, due to thinning tape width and varying coil winding arrangements. It was found that the screening field is inversely proportional to the number of tape filaments, whereas a smaller coil winding aspect ratio leads to a decrease in the screening field.