A complete lumped equivalent circuit of three-phase squirrel-cage induction motors using two-dimensional finite-elements technique

The paper presents the use of the finite element technique for determining the parameters of a three-phase squirrel-cage induction motor. The common parameters in addition to the core losses and ratio of number of turns are obtained from the finite-element field solutions. The magnetizing characteristic and core losses curve are used to determine the flux distribution within the motor structure. The linear time harmonic vector potential field solution is used for the inductances computation. The accuracy of the finite-element application is verified using the available precise results.     

A novel finite-element transient computation of two-axis parametersof solid-rotor generators for use in power systems

An original finite element method for calculating the two-axis transient parameters of solid rotor turbine-generators is presented. Eddy current effects are lumped into equivalent damper circuits, representing layers of massive conductors within the rotor. The time variation of machine parameters of a two-axis model is determined and the equivalent circuits obtained are tested by comparing the two-axis and finite element simulations. The two-axis equivalent circuits can simulate a wide range of operating conditions, with appropriate modification of the magnetizing inductances     

An improved computational technique of the inductance parameters ofreluctance augmented shaded-pole motors using finite element method

An improved technique for calculating the inductance parameters of reluctance augmented shaded-pole motors, including the saturation effect, is described. The method is based mainly on the use of finite element (FE) field calculation and partly on some analytical derivations. Equations are provided for saturated inductance components in terms of relevant winding currents, in order to facilitate the inclusion of the saturation effect into the performance evaluation. The computed values of several inductances are compared with their measured counterparts for verification     

A comprehensive method for the calculation of inductance coefficients of cage induction machines

In this paper, a new comprehensive method for the calculation of inductance coefficients of squirrel cage induction machine based on combined winding function approach (WFA) and magnetic equivalent circuit (MEC) is presented. By taking into account machine geometry, rotor skewing, stator and rotor slots effects and type of windings connection, this method is able to model most of the important features of an induction machine. The effects of each machine parameter on the inductance coefficients are verified. Also, effects of several rotor asymmetries on these inductances are shown. Simulation results are verified by more elaborate nonlinear finite element model and finally with experimental results.     

Three dimensional magnetic field computation by a coupledvector-scalar potential method in brushless DC motors with skewedpermanent magnet mounts-the no-load and load results

The coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) method of computation of 3D magnetic fields by finite elements (3D-FE) is applied here to a brushless DC motor with skewed permanent magnet mounts on its rotor. Results of the CMVP-MSP and 3D-FE computation of the magnetic field and associated motor parameters (EMFs and armature inductances) are detailed in this paper. These results demonstrate vividly the three dimensional nature of the computed flux distributions, caused by the torque ripple reduction design employing skewed magnet mounts on the rotor. Experimental evidence supporting the validity of the BD-FE field computations, through comparison between computed and measured armature EMF waveforms is also provided in this paper     

Lumped modelling of open-circuit turbogenerator operationalparameters

Solid-rotor turbine-generators have commonly been derived from the fitting of curves to terminal characteristics obtained by measurement or from finite element simulations. The paper presents a new method to represent the open-circuit operational inductances of a large turbogenerator of 150 MVA. The method differs from current estimation techniques because the lumped model and its parameters are determined simultaneously. It is based on a finite-element electromagnetic linear analysis of the solid-rotor machine cross section in the frequency domain. Network theory is used to characterise the quadrature-axis model where the problems of model structure and parameter determination are treated. A q-axis equivalent circuit with one damper winding and frequency dependent parameters is found. In addition, an analysis of the machine d-axis is presented. It is based in an electromagnetic study of the “black box” two-port network, where the open-circuit operational inductances are represented by frequency dependent parameters     

燃气轮机涡轮盘温度及应力场计算分析

用通用有限元计算程序ANSYS对某燃气轮机透平第一级涡轮盘的轴对称原模型温度和应力场进行稳态计算。计算中考虑了材料的非线性,惯性力和温度边界条件。分析了温度和应力场,根据计算结果对结构进行了修改,对修改前后的数据作了对比,提出了改进设计建议。本计算结果为涡轮盘疲劳寿命预测提供了依据。     

Characterising the d-axis machine model of a turbogenerator usingfinite elements

An analysis of a long established fundamental assumption is presented. The assumption that superposition is valid in frequency response derived models is shown to be wrong, because eddy current losses in the solid rotor cannot be superimposed in the machine direct-axis. This implies that network theory is not valid in characterising the d-axis machine model. A machine model structure with one damper winding in the d-axis is derived from finite element analysis. Unequal mutual inductances in the machine d-axis are determined and hence the so-called differential leakage inductances are found and they are frequency dependent. The study is made on a 150 MVA turbine generator by simulating the standstill frequency response test with finite elements     

A Finite Element based State Model of Solid Rotor Synchronous Machines

In this work, a state model which portrays the dynamic electromagnetic characteristics of a synchronous machine is derived based upon the first order finite element method. The method of finite elements is used to determine the axial component of magnetic vector potential throughout the cross section of the machine. Algebraic relationships between the winding voltages and the magnetic vector potentials are derived. These are used to establish a state model which admits winding voltages as inputs. The resulting model consists of a set of first order, ordinary differential equations which predict vector potentials at grid nodes along with the winding currents as time proceeds following arbitrary disturbances in stator or rotor voltages. As an initial verification step, this method has been applied in two linear examples. The first involves a simplified geometric representation of the synchronous machine for which an analytical solution of the defining field equations can be obtained. The second involves a more detailed geometry which includes stator and rotor slots. Numerical solutions are shown to be in excellent agreement with analytical solutions for the simplified structure. In the detailed geometry, numerical solutions are shown to compare favorably with the classical equivalent circuit representation.     

Static characteristics of a new doubly salient permanent magnetmotor

In this paper, magnetic field analysis of a new doubly salient permanent magnet (DSPM) motor is carried out based on the finite element method (FEM). Hence, the corresponding static characteristics, including PM flux linkage, self-inductance, mutual inductance, and static torque are deduced (the interaction between the PM field and armature field are taken into account). New methods for measuring the motor inductance are also proposed. The theoretical analysis is verified by experimental results     

Finite element calculation of double-cage rotor equivalent circuitparameters

This paper describes the use of a saturable single slot finite element model to determine the resistances and reactances of a double-cage rotor, allowing for the MMF balancing effect of the stator currents. The method is verified by comparing the impedances calculated for an unsaturated rotor with rectangular bars with their analytically determined counterparts. The model requires the user to specify both rotor frequency and current per slot. The effect of magnetic saturation is examined, and it is demonstrated that care must be taken in the choice of current at low frequencies, to avoid conditions of excessive saturation, leading to unrealistic values for inductances     

Analytical model for permanent magnet motors with surface mounted magnets

This paper presents an analytical method of modeling permanent magnet (PM) motors. The model is dependent only on geometrical and materials data which makes it suitable for insertion into design programs, avoiding long finite element analysis (FEA) calculations. The modeling procedure is based on the calculation of the air gap field density waveform at every time instant. The waveform is the solution of the Laplacian/quasi-Poissonian field equations in polar coordinates in the air gap and takes into account slotting. The model allows the rated performance calculation but also such effects as cogging torque, ripple torque, back-EMF form prediction, some of which are neglected in commonly used analytical models.     

燃机涡轮盘三维瞬态温度及应力场计算分析

用通用有限元计算程序ANSYS对某燃气轮机启动过程中透平第一级涡轮盘的三维模型瞬态温度和应力场进行计算.计算中考虑了材料的非线性,惯性力和温度场边界条件.分析了温度和应力场特点,提出了改进设计的建议.计算结果可为涡轮盘疲劳寿命预测提供依据.图6参3     

A Complete Time Domain Model of the Induction Motor for Efficiency Evaluation

The saturation of mutual and leakage inductances as well as the eddy currents effects are taken into account to represent an almost complete model of the induction motor. These effects are not trivial, when the stator voltage and/or frequency changes considerably. Therefore, the model is suitable for the motor performance studies under nonsinusoidal voltage waveform supplies. The effects of eddy currents are represented by a simple double cage model equivalent to the deep bar cage. A practical method for finding the double cage parameters is outlined and the results obtained were used in the simulation. The accuracy of the model is emphasized by comparing the simulation results with test results of the stator inrush current during starting under no-load conditions. The model is used for calculating the induction motor losses in the time domain, when the motor is fed from nonsinusoidal voltage waveform supplies. Samples of the obtained results from different voltage waveforms are given together with that of a pure sinusoidal voltage supply for comparison.     

GROUNDWATER FLOW EFFECTS IN PROCESSES OF SOIL FREEZING

The influence of groundwater flow effects on freezing processes in soil is analyzed by means of finite element method. The latent heat involved in a phase change is taken into account by virtue of the enthalpy, which is defined as the integral of heat capacity with respect to temperature. The analyses are carried out in an example of a two-dimensional freezing process with a groundwater flow field.     

Skew and linear rise of MMF across slot modelling-winding functionapproach

A method of calculation of the inductances of an induction machine is proposed. The skewing of the rotor bars of the machine and the resultant linear rise of MMF across the slot, together with the nonsinusoidal distribution of the stator winding are taken into account. The method is based on the winding function approach, which allows for all harmonics of the MMF to be taken into account. The results obtained by the proposed method have been compared with those obtained by a conventional manner, which take into account the above phenomena by means of scale factors applied to the harmonics. A very good agreement between them is demonstrated     

Identification of parameters for superconducting generators havingfree or fixed outer rotor, based on tests and calculations

The generator, with its concentric and in part solid and conductive parts, is represented by a shell model, and the parameters of the system of equivalent windings are first obtained approximately using a two-dimensional analytical field calculation. The effect of the finite length, which is neglected in this field calculation, is taken into account by variation of the model geometry and material conductivity so that Nyquist plots of the model impedances are optimally matched to those of the real system. The resulting machine model is checked and confirmed by comparing the simulation results with test measurements. It is further shown that an outer damper cylinder (that is free to rotate independently) provides significant mechanical relief of the shaft line during transient processes     

Coupled finite-element/state-space modeling of turbogenerators inthe abc frame of reference-the short-circuit and load cases includingsaturated parameters

In this paper, a coupled finite-element/state space modeling technique is applied in the determination of the steady-state parameters of a 733 MVA turbogenerator in the abc frame of reference. In this modeling environment, the forward rotor stepping-finite element procedure described in a companion paper is used to obtain the various machine self and mutual inductances under short-circuit and load conditions. A fourth-order state-space model of the armature and field winding flux linkages in the abc frame of reference is then used to obtain the next set of flux linkages and forcing function currents for the finite-element model. In this process, one iterates between the finite-element and state-space techniques until the terminal conditions converge to specified values. This method is applied to the determination of the short-circuit, and reduced- and rated-voltage load characteristics, and the corresponding machine inductances. The spatial harmonics of these inductances are analyzed via Fourier analysis to reveal the impact of machine geometry and stator-to-rotor relative motion, winding layout, magnetic saturation, and other effects. In the full-load infinite-bus case, it is found that, while the three-phase terminal voltages are pure sinusoidal waveforms, the steady-state armature phase currents are nonsinusoidal and contain a substantial amount of odd harmonics which cannot be obtained using the traditional two-axis analysis     

Simulation and application of temperature field of carbon fabric wet clutch during engagement based on finite element analysis

The temperature plays a significant role in the tribology properties and failure of friction materials during engagement of wet clutch. In order to obtain the temperature field of carbon fabric wet clutch, the thermal model was developed and the finite element analysis was conducted with the heat flux, convective and conductive heat-transfer taken into account. The predicted temperatures of thermometer hole were compared with experimental values. The effects of the thermal parameters on the temperatures of engagement and the damage of carbon fabric composites were investigated. Results show the thermal is evaluated as effective and can well predict the temperature field. The lower skeletal density, lower specific heat capacity and higher thermal conductivity are indispensable for the purpose of lowering the temperature of engagement. The highest temperature appears at R = 0.0509 m, where the damage of friction lining easily occurs.