Three-phase Cage Research Articles

Critical Slip of Three-phase Cage Induction Motor Supplied from Limited Power Source

The peculiarities and characteristics of a cage induction motor supplying from limited power source (mobile electric power station, diesel power plant, wind power station and etc.) change virtually in comparison with the case when motor is supplied from unlimited voltage source. The critical slip expression of the cage induction motor operating from the limited power-supply source taking into account the inner complex impedance of power-supply source and other cable parameters has been derived. It is shown that critical slip formula, when motor is supplied from a high-capacity power-supply source (the inner complex impedance is not taken into account) and through short cable (the cable impedance is not taken into account) absolutely coincides with well-known formula. The algorithm for calculations of the induction motor characteristics taking into account the parameters of the supply circuit and the suitable length and cross-section of the supply cable has been created. Ill.1, bibl. 6 (in English; summaries in English, Russian and Lithuanian).

Optimal stator slot design of inverter-fed induction motor in consideration of harmonic losses

This paper proposes optimal design method of stator slot for three-phase cage induction motor fed by six-step inverter output voltage by using proposed analysis method. The finite-element method (FEM) on one phase band stator periodic condition is coupled with harmonic equivalent circuit. Using the FEM, the stator slot is optimally designed and the result is presented. Stator core loss and copper loss including harmonic loss are reduced by the proposed optimum slot design method. The analysis result is verified by experimental measurement.

Transient model of the three-phase cage asynchronous machine with saturation and space harmonics effects

Three-phase induction machines are excessively used and their control has been widely developed. The machine model often used in the control system is the linear 2-axes d-q machine equations. There is a need for improved methods of analysing the dynamic behaviour to check the validity of the control system. We propose a real three-phase model including space harmonics effects by Fourier analysis of the air-gap induction and taking into account simultaneously the non-linearity of the ferromagnetic parts by using a complete permeance network.

Theory and design of part-winding starting

When a three-phase cage induction motor is started on a half winding, space harmonic MMFs occur, and the machine usually fails to accelerate beyond the speed of the principal harmonic. A mathematical theory is presented in this paper which not only explains such behavior observed in the past, but also predicts whether, and at what speed, a motor will hang up or crawl on any particular arrangement of half winding. The theory also provides a basis for the design of harmonic-free half windings on which the machine will accelerate smoothly to full speed. This is illustrated by application to a 6-pole motor.

Self-excited induction generator controlled by a VS-PWM bidirectional converter for rural applications

This paper concerns an application of a three-phase cage induction machine (IM) as a self-excited generator connected to the AC side of a voltage-source PWM bidirectional inverter. The generator is supposed to be driven by a low-head unregulated shaft hydraulic turbine. The proposed system is intended to be applied in rural plants as a low-cost source of high-quality AC sinusoidal regulated voltage with constant frequency. Simulation results are obtained based on the /spl alpha//spl beta//spl gamma/ stationary reference frame model of the IM. The experimental results demonstrated that the system presents satisfactory behavior when feeding AC loads and during the startup of induction motors.

Calculation of two-axis induction motor model parameters using finite elements

The paper presents the use of the finite element method for determining the parameters of a two-axis model of a three-phase cage induction machine. The model parameters are obtained from the finite element field solutions. The saturation of the motor is taken into account in calculation of the flux distribution by using a static nonlinear vector potential solution. The linear time harmonic vector potential field solution is used for the inductances determination. All the inductances are determined as functions of the magnetizing current. Rotor skew is also taken into account. The accuracy of the described identification procedure is verified through laboratory measurements of the parameters.

Dynamic harmonic field analysis of a cage type induction motor when magnetic slot wedges are applied

Applying magnetic slot wedges to stator slot openings is an effective means to reduce the slot ripple harmonic components in the magnetic field. To investigate the effect of the wedges in detail, this paper proposes a new harmonic field analysis method that considers the rotor movement dynamically and the harmonic components of the secondary current as induced current by a two-dimensional finite element method (2D-FEM) using a time stepping technique. The differences in harmonic characteristics due to the use of plural wedges (a nonmagnetic wedge and magnetic slot wedges in different dimensions) for the stator slot opening of a three-phase cage induction motor are evaluated using the method. Suitable wedge dimensions to reduce the slot ripple harmonics are determined. From the comparison of calculated and experimental results of secondary current, the proposed method is shown to be appropriate and useful for the quantitative estimation of harmonic fields for induction motors.

3-D electro-magnetic analyses of a cage induction motor with rotor skew

The paper studied the performance characteristics of a three-phase cage induction motor using a 3D finite element technique. Especially, the effects of rotor skew and the rotor end-rings and the distribution of the electromagnetic field toward the axial direction, which have not been able to be analyzed accurately by 2D analysis, were investigated. Since the 3D analysis enabled the analysis of the continuity of the air gap flux density at the core ends and to take into consideration the rotor end-ring impedance, the motor parameters were calculated with high accuracy, compared with 2D analysis. Firstly, the authors made the relation of the rotor end-ring current with the rotor bar current clear, by analyzing the harmonics of the rotor bar current and the rotor end-ring current in the cases of motors without rotor skew and with rotor skew. Secondly, the torque and the rotor axial force were calculated from the distribution of the electromagnetic field obtained by the 3D analysis in the case of rotor skew. They also calculated the axial forces on the both end-rings in the case of rotor skew. The results obtained in the paper show the importance of 3D analysis for the design of induction motors.

Calculation of cage induction motor equivalent circuit parameters using finite elements

A means by which the finite-element method can be used in conjunction with the conventional equivalent circuit model to determine the equivalent circuit components for a three-phase cage induction motor is described. The method uses separate finite-element models for the rotor and the stator, consisting of one slot pitch and one phase band, respectively. The use of minimal models leads to a fast execution time. The method is illustrated by comparing computer predictions of performance with test measurements made on four motors, ranging in size from 4 to 150 kW.

Excitation balancing of a self-excited induction generator for maximum power output

Using symmetrical component techniques the steady-state behaviour of a self-excited three-phase induction generator under unbalanced loading is examined. Particular reference is made to single-phase loading, a practical application being the use of standard three-phase cage machines in micro-hydro plants. An unbalanced excitation scheme is proposed which improves balance overall and maximises the allowable power output of a particular machine. A method is presented by which de-rating factor and voltage regulation can be predicted for a general unbalanced condition. The results of modeling are in good agreement with experiment. Possible further applications of the method are to the behaviour of induction generators in networks and the operation of three-phase motors from single-phase supplies.

Modeling and Analysis of Induction Machines Containing Space Harmonics Part III: Three-Phase Cage Rotor Induction Machines

This part of the paper deals with the application of the general model and equations derived in Parts I and II to the common three-phase, cage rotor induction machines. It describes the procedure used to identify the significant harmonics for a reasonable representation with a low order model. The effects of MIF harmonics on the steady-state and transient behaviors of three sample cage rotor induction machines that have rotors designed to give varying amounts of asynchronous and synchronous torques are examined. Skin effect, skewing of rotor bars, and the influence of slot opening on the MMF are all taken into account in the derivation of the parameters for-these machines. The computational requirement for the solution of the original phase equations is compared with those for the solution of the a-P and d-q component equations.

Modeling and Analysis of Induction Machines Containing Space Harmonics, Part III: Three-Phase Cage Rotor Induction Machines

Modeling and Analysis of Induction Machines Containing Space Harmonics, Part III: Three-Phase Cage Rotor Induction Machines