Stator End Windings Research Articles

Extended End-Winding Cooling Insert for High Power Density Electric Machines With Concentrated Windings

Concentrated windings are favourable in electric motors with a high torque density because of the achievable high winding filling factor and their short end-windings. Nevertheless, the performance of the cooling system has the biggest impact on the reachable torque density limits. This article introduces a thermally conductive insert piece that encloses the stator end-windings with extensions in the stator slots. This results in an extended contact surface between the stator windings and the machine housing, which is advantageous for the conductive heat transfer. The introduced indirect cooling concept is compatible with traditional cooling techniques such as forced air and water jacket cooling. The concept is illustrated with 3D thermal finite element simulations, including the anisotropic thermal material properties, as well as ad hoc measurements on a stator pole unit mock-up of a 6-4 switched reluctance machine. Where the stator with reference cooling system was only able to handle a continuous current density of 19.0 A/mm $^2$ , 26.5 A/mm $^2$ could be obtained in the winding of the stator with the extended end-winding cooling inserts.

Improved Thermal Management and Analysis for Stator End-Windings of Electrical Machines

In an electrical machine design, thermal management plays a key role in improving the performance and reducing size. End-windings are commonly identified as the machine hot-spot. Hence, lowering and predicting end-windings temperature are crucial tasks in thermal management of electrical machines. This paper proposes and investigates a noninvasive but effective cooling method that aims for a uniform cooling of a machine's winding by implementing direct cooling on its end-windings. Modeling and experimental results show that a 25% hot-spot temperature reduction on a particular application can be achieved. To analyze the proposed technique in detail, an accurate but computationally economic lumped parameter thermal network is developed. Comparison between a “standard” thermal network and its simplified equivalent (with less nodes) is presented where the models are developed and fine-tuned based on experimental data. All the above is used to investigate the potential of the proposed end-winding cooling method with different configurations of the methodology.

Optimization of Generator Stator End Winding Structure Based on Improved PSO and SVM

The selection of parameters in the support vector machine (SVM) approximation model plays an important role in the performance of the model. Therefore, the support vector machine parameters need to be optimized. Because the particle swarm algorithm is easy to be premature and easy to fall into the local optimal solution, the improved particle swarm optimization algorithm is used to optimize the parameters, and the support vector machine approximation model with optimal parameters is established. Finally, the support vector machine approximation model of optimal parameters and particle swarm optimization algorithm are combined and used in the optimization of stator end winding structure of large steam turbine generator. The validity of the method is verified by the analysis of the results, and good optimization results are obtained.

New topology of direct current claw-pole machines for stop-start application

PurposeThis paper aims to propose a new topology of direct current (DC) machine using claw-pole stator to replace standard DC starter in micro-hybrid vehicles. The main interest of such a topology is the reduction of copper volume.Design/methodology/approachThe design of the claw-pole machine is based on a multi-objective optimization of several topologies, based on a three-dimensional (3D) reluctance network modeling. The 3D finite element (FE) model is used to check the results of the optimization, and a prototype is manufactured and tested with satisfactory results.FindingsThe claw-pole topology with wave-shape windings allows to replace the current DC series classical starter because of to its copper volume saving.Research limitations/implicationsThis model is only limited to the optimization of the claw-pole stator for a fixed geometry of the rotor.Practical implicationsThe research outcome shows that claw-pole machine can replace the series-excited DC machines of starters and at the same time achieve the same performance at reduced copper volume.Originality/valueThe paper deals with a new DC machine topology to reduce the copper volume through the suppression of the classical stator end-windings. The use of Claw-Pole inductors ensures this copper reduction.

Wafter design for totally enclosed electric machines

A computational fluid dynamics (CFD) model representing the effect of wafters in a totally enclosed electric machine is presented, introducing the most relevant theoretical assumptions and simplifications. The validation of the model is conducted through experimental measurements. From the CFD simulation data, a second-order response surface is developed using statistical tools, from which the wafters’ influence on the convective heat transfer from the stator end windings is predicted. Wafter design criteria are obtained from the response surface information. Finally, a specific case is analysed, showing through CFD simulations that temperatures in the machine are reduced by including wafters in the design.

The Application of Surface Potential Test on Hand-making Insulation for Generator Stator End-winding

This paper presents the advantage of surface potential test on hand-making insulation for generator stator end-winding insulation detection, compared with DC or AC withstand voltage test, also details the test principle, connection method and test notes. And through the case, surface potential test on hand-making insulation proved effective for insulation quality detection after generator stator end-winding maintenance, and the experimental data is useful and reliable for the electrical equipment operation and maintenance in the power plant.

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.

多目的最適化手法を用いた構造物の動的問題における実験同定

Dynamic FEM analysis is valid for designing rotating machinery to reduce its vibration problem when we may ensure enough accuracy of the analysis. Surrogate multiple objective optimization method is one of the most effective methods for structural identification improving the FEM analysis model of a structure to adjust the natural frequency analysis results to the experimental results. In this study the structural identification method is applied to stator end-windings of a turbine generator to determine the Young's modulus of the principal components on the FE model minimizing the analysis errors of the natural frequencies of the 2-lobe and 4-lobe circular modes to the corresponding experimental results. The accurate FE model of the end-windings is obtained by this method.

Optimal Scheme for Structural Design of Large Turbogenerator Stator End Winding

A three-dimensional (3-D) electromagnetic model of the end region of a 600 MW turbogenerator is set up. The variations of electromagnetic force densities of the stator end winding under rated load and three-phase short circuit from full load are obtained by numerical simulation. Then, the electromagnetic forces varying with time and space on the end winding are applied to the 3-D fine finite-element model established in ABAQUS/CAE for structural analysis, and the deformation and stress distributions of the stator end winding during rated load and three-phase short circuit are numerically analyzed by means of the ABAQUS software. Furthermore, the influences of structural and material parameters of the end winding on its dynamic responses under rated load are numerically investigated. Based on the numerical results, an optimal scheme for the design of the turbogenerator stator end winding is proposed.

Anti-vibration optimization of the key components in a turbo-generator based on heterogeneous axiomatic design

With the increasing demand for the cleaner production of electric energy, many countries around the world strive to develop new turbo-generators with advanced parameters and large capacities. In the design of a new turbo-generator, it is important to optimize the anti-vibration performance of its key components in order to ensure its safe and reliable operation. The anti-vibration optimization of the key components in a turbo-generator when a set of alternative schemes are provided for selection is a heterogeneous multi-attribute decision making (HMADM) problem involving deviation attributes, which cannot be solved by present HMADM approaches. To solve such a HMADM problem, a novel heterogeneous axiomatic design (HAD) method is developed by introducing the distance measure into axiomatic design for computing the information contents of the alternative schemes. With the attribute data in various mathematical forms unified as triangular fuzzy numbers, their probabilities of success can be conveniently calculated by a unified formula once their corresponding positive and negative ideal solutions are determined. As a result, the complexity and computational cost involved in computing the information contents of alternatives can be greatly reduced, which enables the efficient solution of the HMADM problem involving deviation attributes. A case study on the fixture scheme optimization for the stator end windings in a large turbo generator demonstrated the feasibility and effectiveness of proposed HAD. The ninth fixture scheme with the structural manufacturability being very good (VG), the natural frequencies at the turbine and exciter ends being [68.2, 78.5]Hz and [72.5, 83.2]Hz, the maximum amplitudes at the turbine and exciter ends being 67 μm and 72 μm was chosen as the optimal scheme from nine alternatives according to the HMADM results.

Modeling and Diagnostic of Incipient Interturn Faults for a Three-Phase Permanent Magnet Synchronous Motor

This paper discusses incipient end-winding interturn faults in the stator winding of a permanent magnet synchronous motor caused by the mechanical vibrations of the concerned turns. With aging, the end-winding blocking system becomes weaker and turns insulation degrades until its breakdown. The fault is modeled by an intermittent interturn short circuit between the turns of the stator end winding. Intermittent fault occurrence disturbs the stator currents as well as the reference voltages leaving a specific fault signature. The detection method uses a pattern-adapted wavelet to detect fault occurrence. In this paper, it is applied to the quadrature reference voltage. Simulation and experimental results confirm the effectiveness of the proposed approach.

Finite element modelling of turbine generator stator end windings for vibration analysis

In this study, the authors present methods for accurately modelling the bindings and the stator bars of turbine generator stator end windings for vibration analyses. The bindings are modelled with beam elements and multipoint constraint equations to take account of the bending, twisting, and shearing rigidities of the bindings. To reproduce the spatial distribution of rigidity in a cross-section of the stator bar, the bar is modelled as a composite material comprising a conductor bar with equivalent elastic moduli and ground insulation. The accuracies of the developed binding and stator bar models are verified by comparing measured natural frequencies of binding test pieces and stator bar specimens with calculated values. The developed models and conventional models are applied to the natural frequency analyses of stator end windings, and then the effects of the modelling methods on the calculation accuracy are investigated. While the maximum calculation errors of the conventional models are more than 12%, the calculation results of the developed models agree with the measured values within an error of 7%. Accordingly, for accurately calculating the end winding natural frequencies, end winding finite element models need to take the binding rigidities into account and reproduce the rigidity distribution of the stator bar.

Calculation and Analysis of the Surface Heat-Transfer Coefficient and Temperature Fields on the Three-Dimensional Complex End Windings of a Large Turbogenerator

With increased turbogenerator capacity and electromagnetic load, overheating of the complex end parts has become one of the main problems affecting safe and stable turbogenerator operation. In this research, a flow network was built representing the structural and ventilation characteristics of a 330-MW turbogenerator. The fan inlet velocity and pressures (boundary conditions) of each end-region outlet were obtained by the flow network method. The 3-D transient electromagnetic field in the turbogenerator end was calculated, and the eddy current losses (heat sources) of the end parts were obtained by the finite-element method. To study the surface heat-transfer coefficient distribution on the stator-end winding surface, fluid and thermal mathematical and geometric models of the whole turbogenerator end region were given. Using the finite-volume method, the surface heat-transfer coefficient distribution on the complex 3-D stator-end winding surface, fluid-flow distribution, and temperature distribution of the end parts were investigated under rated-load conditions. The calculated temperature results match well with measured data. This research can provide a theoretical basis for calculating the heat-transfer coefficients of the outer surfaces of large turbogenerators.

India’s largest short circuit generator & its salient features

Short circuit test is one of the very important tests on electrical power equipment to verify its design aspects to withstand the critical severities under the condition of actual fault. To perform these tests a high power source is required. This source can be a grid supply with a high fault level or can be a high power short circuit generator. This paper gives the salient features of high power generator installed at Central Power Research Institute (CPRI), Bangalore. This 2500MVA short circuit generator is of highest capacity in the sub-continent of South Asia as on date. The design features are intricate in nature and complex in terms of stator, rotor damper winding and stator end winding. This paper presents the specification, design concept, constructional features, comparison between salient pole and turbo type of generators and other auxiliaries of the generator. Mechanism of achieving the maximum short circuit current is broadly discussed in this paper. This rare facility at CPRI meets high power testing requirement for the electrical industry and utilities of India and other part of the world. In this paper attempts are also made to bring out the highlights of operational features of capital intensive 2500 MVA SC generator. This generator has been used for short circuit testing of various power system components over the period of time.

INVESTIGATION ON ELECTROMAGNETIC FORCES AND EXPERIMENTAL VIBRATION CHARACTERISTICS OF STATOR END WINDINGS IN GENERATOR

This paper investigates the electromagnetic forces acting on the stator end windings, by using the stator end windings structure of a 600 MW large-capacity turbo-generator as the analysis object. Firstly, based on the method of images, the Biot–Savart Law and superposition theorem, the calculation model of the stator end windings is proposed. Then, the average electromagnetic forces acted on the end windings and the relationship between radial and tangential electromagnetic force densities are analyzed. The result shows that the tangential electromagnetic force should be treated as radial one and should not be ignored. Finally, the radial and tangential vibrations are measured to verify the theoretical analysis. The investigation results will be beneficial to the binding and fault diagnosis of stator end windings.

Black-Out Test Versus UV Camera for Corona Inspection of HV Motor Stator Endwindings

As part of a factory acceptance test program for high-voltage (HV) motors, end users sometimes specify a black-out test. This is a traditional offline inspection where the stator is placed in complete darkness, each phase is energized to 115% of rated line-to-neutral voltage, and both ends of the stator are observed to determine the presence, location, and severity of endwinding surface partial discharges (PDs). The setup for the test may be complex and risky due to the need for observers to be standing in darkness close to the energized parts of the stator. The test results are qualitative and strongly depend on the observer's eyesight and individual perception. A safer and more accurate alternative is to use an ultraviolet (UV) camera or viewer. The observed PD activity may be observed in ambient lighting, recorded, and quantified through simultaneous offline PD measurements. This paper describes the two inspection techniques and presents experimental validation of the UV corona camera inspection method as a suitable replacement for a black-out test. Sample 13.8-kV coils were wound in a fixture simulating their relationship in a stator winding and subjected to high-potential tests while observed under black-out conditions and with a UV corona camera in ambient lighting. The stator windings from two HV compressor motors were inspected using the same camera. Recorded images of the observed discharges and measured PD activity in the sample coils and stator winding were used to compare the evaluation by each test method.

Parametric Study on Dynamic Characteristics of Turbogenerator Stator End Winding

The material properties, including Young's modulus, Poisson's ratio, and density, of the structural components in the stator end winding of a typical 600-MW turbogenerator were experimentally measured; the equivalent bending stiffness of the conductor bars are determined by the three-point bending test, and the lower orders of natural frequencies and mode shapes were measured by modal test. The finite-element model of the stator end winding is set up, and its dynamic characteristics are numerically analyzed by means of the ABAQUS software. The numerical model is validated by the consistence of the numerically determined natural frequencies corresponding to the modes with elliptic shape with those measured by the modal test. With the finite-element model, parametric study on the natural frequencies and modes of the end winding is performed, which behaves instructive significance for the design and improvement of the turbogenerator stator end windings.

Numerical Calculation and Analysis of Three-Dimensional Transient Electromagnetic Field in the End Region of Large Water–Hydrogen–Hydrogen Cooled Turbogenerator

Due to the complexity of the structures and magnetic field distribution in the end region of large turbogenerators, using a 330-MW water-hydrogen-hydrogen cooled turbogenerator as an example, the 3-D mathematical and geometry models of the nonlinear transient eddy current field were given. Taking the nonlinearity of the core material and the influences of noncontact between the copper screen and the clamping plate, as well as the shape of stator end windings into consideration, the 3-D transient electromagnetic field was calculated, and the losses of different metal parts were obtained by the finite-element method. The calculated power losses were applied to the thermal field as heat sources. Temperatures of the copper screen were gained. The calculated results of copper screen were well coincident with the test data. Hence, the calculated results are accurate, and the method of calculation is effective.

Robust Optimization for Dynamic Characteristics of Mechanical Structures Based on Double Renewal Kriging Model

Present optimization approaches for the mechanical structures usually neglect the uncertainty of material characteristics and the influence of their dynamic characteristics on the overall performance. Moreover, the algorithms for solving the optimization problems are often inefficient. To overcome the above shortcomings, the robust optimization method of the dynamic characteristics of mechanical structures based on double renewal Kriging models is proposed. A robust optimization model including both the means and variances of the mechanical structures' dynamic characteristics in the objectives is established. The model includes the deformation of mechanical structures as constraints. The kriging models that can accurately and efficiently obtain the values of objective and constraint functions are constructed based on the Latin hypercube experimental design, double update strategy, and the sample point encryption technology in both the local area of maximum error and the neighborhood of the approximate optimal solution. And then all the Pareto optimal solutions to the robust optimization problem of the mechanical structures' dynamic characteristics are located by integrating a neighborhood cultivation-based genetic algorithm with the double renewal Kriging model. The robust optimal design of the dynamic characteristics of the cone-shape fixed structure of a large turbogenerator's stator end windings verifies the validity of the proposed method as well as its superiority over the deterministic ones.

Analysis of Electromagnetic Force Distribution on End Winding of Electrical Submersible Motor During Starting Transient Operation

Generally, an electrical submersible motor generates a current with high magnitude and long interval during starting transient operation. This paper aims to analyze the electromagnetic forces on the stator end windings of an electrical submersible motor during the starting transient operation by a 3-D finite element method (FEM). A 3-D model was conducted and some complex support structures in the end regions were simplified. Then we analyzed the electromagnetic field in the end region according to the governing equations and the boundary conditions. The analysis shows that the forces on the outer layer especially in 1st and 5th coil are larger than those on the other parts. Furthermore, the force distributions on the coils in the same phase belt are different and the force distribution in each segment varies with the position and the direction. Finally, the analysis of stresses indicates that the stresses in a coil end are not small but within the yield strength of the copper coils.