Solid Iron Rotor Research Articles

Effect of Exciter and AVR on Transient and Dynamic Stability of an Alternator Using State Space Model

Transient stability of an alternator under fault condition and after removal of the fault has been studied in great details by many authors. The stability studies have been made either on grid systems or on one machine on infinite bus idealization. The saliency effect, saturation and damping (due to both damper winding and solid iron rotor) have been accounted for by many authors. But in many cases, the effect of fast-acting control systems like automatic voltage regulator and exciter has not been considered. Transients caused by the turbine governor are slow and may be neglected, but not the fast-acting exciter control. This paper is devoted to assessment of stability in the presence of AVR exciter. A suitable model of IEEE has been chosen for the specific case study, which has been subsequently mapped to state space. The composite model has been developed from which both transient stability and dynamic stability have been assessed. The boiler and firing control is extremely sluggish—hence their effect has been neglected.

Application of Nonlinear Complex Polyharmonic Finite-Element Models of High-Speed Solid-Rotor Induction Motors

In this article, the application of a nonlinear complex De Gersem-type polyharmonic finite-element (FE) model in the steady-state analysis of three-phase solid-iron rotor induction motors is discussed. Effective magnetic permeability, dependent on the fundamental time harmonic of the magnetic field, is used for the representation of the magnetic saturation effects. A new coupling scheme for the air-gap mesh nodes is proposed in order to make the model more time-competitive with the time-stepping model in cases where the number of air-gap nodes must be high. By means of comparative analysis of computed electromagnetic torque and harmonic losses, it is shown that omitting some nodes at the interface boundary results in the reduction of the execution time by a factor of 100 with only a slight loss of accuracy.

Design Consideration of Eddy-Current Loss for Rotor of HIA With Rectifier and Capacitive Loads

Homopolar inductor alternator (HIA) with rectifier and capacitive loads is a promising choice for pulsed power supply. The solid-iron rotor of HIA can rotate at a very high speed, but this causes serious eddy-current loss in the rotor and results in local overheating on rotor face. In this paper, the analytical method was used to calculate the rotor eddy-current loss for HIA with rectifier and capacitive loads, and the effect of eddy-current shielding on the rotor eddy-current loss was also discussed. The analytical results are coincided with the results simulated by a simplified 2-D field-circuit coupled simulation. This paper shows that in order to reduce the rotor eddy-current loss, the air-gap length and the pole number should be as large as possible and the windings should be distributed and short-pitch. Meanwhile, an important conclusion is that the eddy-current shielding cannot decrease the eddy-current loss for HIA with rectifier and capacitive loads; on the contrary, it increases the eddy-current loss, compared to the case with the rectifier and resistive load.

Estimators of induction motor electromechanical quantities built on the basis of a machine secondary multi-loop equivalent circuit

Abstract Contemporary sensorless AC drives require the use of electromechanical quantities estimation. The skin effect occurring in AC machines with solid secondary or with solid secondary elements causes machines of this type to be represented by equivalent circuits containing distributed elements, which makes the analysis of machine electrodynamic states more complicated and hinders the construction of relatively simple and effective estimators of electromechanical quantities. The variability of rotor parameters is modelled, with a good approximation, by the machine secondary multi-loop equivalent circuit with lumped elements. In this paper the construction procedure of electromechanical state variable estimators basing on this type of equivalent circuit will be presented. The simulation investigations of the created electromechanical quantities estimators, performed for the selected states of solid iron rotor AC machine operation will be shown as well.

Geometry optimization of solid rotor eddy current brake by using sensitivity analysis and 3D finite elements

The paper presents an optimization procedure for eddy current brakes, considering both copper and solid iron rotors. The rotor geometry optimization has been performed based on analytical solutions and 3D finite elements combined to sensitivity analysis technique. Optimum dimensions of copper parts and solid iron slots have been investigated.

Temperature rise within the rotor of squirrel cage induction machines with solid iron and laminated rotors during run up and standstill

The electrical and thermal behaviour of induction motors with solid and laminated rotors is compared. In particular, temperature rises within the rotor during standstill and run ups are investigated. The investigation is based on a finite difference time-stepping method, which takes the motion of the rotor into account. The calculation method is verified by comparison with measurements on a 22 kW induction motor. The temperature rise depends upon the position of the rotor bars compared with the stator winding during standstill. Differences up to 50% occur on account of the position. Specialities in the temperature distribution are elaborated for the solid iron rotor and are compared with the results of laminated induction motors.

Finite element simulation of a magnetic brake with a soft magnetic solid iron rotor

A magnetic brake with a solid iron cylinder rotating at high speeds is considered. The rotor iron is both conductive and permeable. The magnetisation curve is non‐linear. Special attention is paid to the correct integration of the angular velocity term. A Newton‐Raphson scheme dealing with the non‐linear material characteristics is applied. The numerical oscillations appearing in the finite element model at high velocities are overcome by an adaptive mesh refinement technique combined with the artificial diffusion upwind technique. End effects due to the finite length of the rotor are incorporated by an electric circuit coupling. Simulations are performed to study the influence of the saturation of the moving rotor upon the speed‐torque characteristic of the magnetic brake. It is remarkable that in the case of this solid rotor magnetic brake, the saturation of the rotor iron has a beneficial influence on the device performance.

Non-linear models for the design of solid rotor induction machines

Two finite element methods are used to calculate the steady-state performances of solid iron rotor induction machines. They are applied to both smooth and slitted rotors and are used to define the rotor form which provides the maximum torque for the rated value of the slip. The mean torque-slip characteristics calculated under constant voltages are compared to experimental results.

Practical detailed model for generators

The Parks equation is currently used for mathematical expressions of the state of synchronous generators connected to power systems. The calculation results using the Parks equation, however, differ greatly from the results of measurement on the real generator when the Parks equation is applied to an event where the flux linking the generator undergoes a very large change as when the generator is suddenly disconnected from a load during normal operation. The difference between the field test result and the calculation result is larger for a turbogenerator with a solid iron rotor than for a salient synchronous machine. To deal with this problem, this paper introduces a mathematical expression of generating machines, which is an extension of the Parks equation and which is practically applicable to an event in which the flux within the generating unit changes sharply as when it experiences a load rejection. The newly introduced expression takes the following considerations: (1) a magnetic flux saturation coefficient k is applied to d- and q-axis; and (2) T'/sub q0/ that corresponds to T'/sub d0/ of d-axis is introduced to q-axis. A generator model incorporating the magnetic flux saturation coefficient k and another parameter T'/sub q0/ has proved capable of providing a good simulation representing a load rejection whose calculation results coincide satisfactorily with the measurements of actual generators.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Determination of damper winding and rotor iron currents in convertor- and line-fed synchronous machines

The damper winding currents of a synchronous machine with a solid iron rotor are analyzed. Based on the self and mutual inductance modelling technique, the damper currents are described by a detailed damper model taking the damper cage and the rotor iron into account. The model's component elements are determined by the finite element method. Theoretical results are verified by measuring damper bar currents of a six-phase synchronous machine fed by two six-pulse converters. For a number of different operating modes the model is used to calculate the damper current distribution of a six-phase machine. >

Optimal control of the torque of solid iron rotor induction motor

The optimal control of an asynchronous motor with a solid iron rotor is considered. The objective of the control is to obtain a given torque in minimum time with, naturally, constraints on currents. The idea is to use a model formulated in terms of the potentials of the electromagnetic field, whose evolutions are described by a nonlinear diffusion equation, in order to determine the domain of validity of the classical techniques of field oriented control. Equations are approximated via a finite element formulation which leads to a finite-dimensional dynamical system to which the techniques of optimal control may be applied. The criterion is a norm of the difference between the electromagnetic torque and a given reference torque.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Calculation Method for Starting Characteristics of a Solid-Rotor Induction Motor with End-Rings.

The three-phase induction motor with solid-iron rotor has advantages in case of manufacture, in high torque per ampere at standstill, and in withstanding high rotational stresses. Recently there has been wide interest in the possible use of such a solid-rotor induction motor for ultrahigh-speed inverter drives with suitable high stator frequency. However, the copper loss of the solid-rotor induction motor becomes large, because it is designed with a high resistance rotor. Accordingly, the efficiency and the power factor of the motor are lower than those of conventional induction motor.In this paper, it is clarified experimentally that starting and running characteristics of the solid-rotor induction motor are improved considerably by providing narrow slits and end-rings on the rotor. Then, a new equivalent circuit for the solid-rotor induction motor is derived considering the behavior of the solid-iron rotor as that of the double-cage rotor, and a method of determining the circuit constants for the motor is proposed. The starting characteristics for the solid-rotor induction motor with narrow slits and end-rings on the rotor is calculated using the proposed equivalent circuit. The results calculated for starting characteristics from the equivalent circuit method agreed satisfactorily with results obtained. from the measurement.

Subsynchronous resonance phenomena considering skin effects in solid iron rotor turbo-generators

The question of how the skin effects of the eddy current in the rotor of a synchronous generator influence the induction generation modes and the torsional interaction modes of the subsynchronous resonance (SSR) phenomena is addressed. The 3-D magnetic diffusion equation is solved in a round solid iron rotor to provide data for comparison and discussion purposes. The problem of representing skin depth, which is frequency dependent, in the time-domain stability analysis based on dx/dt=(A)x is examined. >

The Application of the Duality of Equivalent Circuits to Modelling Cylindrical Solid-Iron Rotors of Synchronous Machines at Asynchronous

ABSTRACT By means of the duality of magnetic and electric equivalent circuits, an equivalent circuit is derived for the machine with slotted solid-iron rotor at asynchronous speeds. All impedances are calculated from geometrical data. The saturation, the magnetic field in slots and the impedance of the rotor ends are taken fully into consideration.

Transient and steady-state behaviour of solid rotor induction machines

The paper illustrates a two dimensional, finite element analysis of a three-phase induction motor with smooth solid-iron rotor under voltage-forced operation. In order to take saturation completely into account, each steady-state operating point is calculated as the asymptotic solution of the electro-magnetic field equation for a fixed constant speed. The study is supported by experimental results.

Asynchronous Performance of Slitted Rotor Reluctance Machines: Saturation Effects

Analytical investigation based on limiting nonlinear theory presented here for the asychronous performance of a slitted solid iron rotor reluctance machine include the effect of rotor iron saturation. Characteristic curves depicting nondimensional expressions developed for the rotor impedance factor and the power factor enable a visualization of the effects of 1) ratio of depth of saliency to depth of penetration, 2) slit number and depth, and 3) effective resistivities and saturation flux densities of different regions of the rotor on rotor parameter variations. Further predicted values are compared with experimental values and conclusions are drawn.

Synchronous Machine Models by Standstill Frequency Response Tests

An approach to determining synchronous machine parameters by low-voltage frequency response tests with the machine stationary will be described. The tests are simple and safe. In addition, they provide a more detailed and complete model of the machine than the accepted standard methods/1/. The standard tests rely heavily on the measurement of large transients. As such, they are susceptible to any changes in saturation during the course of the measured transient. Furthermore, the accuracy and resolution with which a single transient can be measured are frequently insufficient to provide the detail required to model the solid iron rotor of a turbogenerator. The test method described herein avoids both of these problems as well as providing complete q-axis data which is not done by the standard tests.

Use of numerical analysis of nonlinear eddy current problems by finite elements in the determination of parameters of electrical machines with solid iron rotors

This paper reports on the application of the concept of effective permeability using the finite element technique, to the solution of eddy current problems, and the determination of damping resistances as well as the characteristics of the solid iron rotors in rotating machinery during transients. The formulation is based on the concept of magnetic vector potential in phasor form, coupled with effective permeability which is related to the average magnetic energy throughout an a.c. cycle. The technique is applied to the solid iron rotors of turbogenerators for the determination of equivalent damping resistances, etc., during asynchronous operation. Sample eddy current loss results compare favorably with experimental test data. Instantaneous change in damping resistances during machine transients are obtained and reported on here based on this technique.

Current-density distribution in solid-rotor induction motor

The interaction between the eddy currents induced in the solid cylindrical rotor steel structure and the revolving field of the airgap produces the electrodynamic torque. The polyphase induction machine with solid-iron rotor offers advantages in ease of manufacture, in high torque per ampere at standstill, in withstanding high rotational stresses, and in operating in unusual environments. It is the purpose of this paper to present an approximate three-dimensional nonlinear numerical analysis of the solid-rotor induction motor for finding the three-dimensional current-density distribution in the solid rotor, in order to calculate the performance characteristics, based on finite-difference iterative techniques.

Electromagnetic Fields in Solid-Rotor Induction Motor

The most elementary type of rotor for the polyphase induction machine is the solid-iron rotor, which offers advantages in ease of manufacture, in high torque per ampere at standstill, in withstanding high rotational stresses, and in operating in unusual environments. Since conventional induction machine theory has proven inadequate for such machines, the need has arisen for improved methods of investigation. It is the purpose of this paper to present an approximate three-dimensional nonlinear numerical analysis for the solid-rotor induction motor, based on magnetostatic assumptions and finite-difference iterative techniques.