The paper deals with analytical method of design and prediction of performance characteristics for induction motors with solid steel rotor coated with copper layer. On the basis of the distribution of the 2-D electromagnetic field, the equivalent impedance of the rotor has been derived. The edge effect and nonlinear magnetic permeability of solid steel have been included. The presented analytical method has been verified with laboratory test results. A 300 kW, 60 000-rpm, three-phase solid-rotor induction motor for the next generation air compressor has been investigated. The accuracy of analytical approach is acceptable and can be recommended for rapid design of solid-rotor induction motors.

Performance Calculation for a High-Speed Solid-Rotor Induction Motor

Recent concern over abnormal stresses imposed on the shafts of large turbine-generators, due to high speed switching of network faults, has led to intensive investigation of this phenomenon. Elaborate computer programs were developed for simulated model studies which revealed that hitherto unexpectedly high shaft stresses can occur merely by tripping a three-phase short circuit near the power station at an unfavorable instant. The effects of circuit breaker reclosing, both successful and unsuccessful, were also investigated together with those due to faulty synchronizing. Test data on a 780 MVA unit gained by telemetric means verified the calculated torques and established the damping coefficients in a running unit. The adverse influence of numerous repetitive instances of such over-stressing on life expenditure of rotor materials is being evaluated.

Effect of clearing short circuits and automatic reclosing on torsional stress and life expenditure of turbine-generator shafts

Thesis for the degree of Doctor of Science (Technology) to be presented with due permission for public examination and criticism in the Auditorium 1382 at Within the latest decade high-speed motor technology has been increasingly commonly applied within the range of medium and large power. More particularly, applications like such involved with gas movement and compression seem to be the most important area in which high-speed machines are used. In manufacturing the induction motor rotor core of one single piece of steel it is possible to achieve an extremely rigid rotor construction for the high-speed motor. In a mechanical sense, the solid rotor may be the best possible rotor construction. Unfortunately, the electromagnetic properties of a solid rotor are poorer than the properties of the traditional laminated rotor of an induction motor. This thesis analyses methods for improving the electromagnetic properties of a solid-rotor induction machine. The slip of the solid rotor is reduced notably if the solid rotor is axially slitted. The slitting patterns of the solid rotor are examined. It is shown how the slitting parameters affect the produced torque. Methods for decreasing the harmonic eddy currents on the surface of the rotor are also examined. The motivation for this is to improve the efficiency of the motor to reach the efficiency standard of a laminated rotor induction motor. To carry out these research tasks the finite element analysis is used. An analytical calculation of solid rotors based on the multi-layer transfer-matrix method is developed especially for the calculation of axially slitted solid rotors equipped with well-conducting end rings. The calculation results are verified by using the finite element analysis and laboratory measurements. The prototype motors of 250 – 300 kW and 140 Hz were tested to verify the results. Utilization factor data are given for several other prototypes the largest of which delivers 1000 kW at 12000 min-1. Graduate School of Electrical Engineering is greatly acknowledged. Most of all, to Maiju, Samuli and Julius: Your simple child's enthusiasm and your laugh gave me strength and kept me smiling. I am indebted to Saila for her love and patience during the years. Finally, my dear friends, without your warm support, endless patience and belief I would never have roamed this far.

High-speed solid -rotor induction machine : electromagnitic calculation and design

Transmission system events and operations which have the potential for removing significant fatigue life fram turbine-generator shafts are described. The factors which limit the fatigue capability of turbine-generator shaft systems are presented, along with a discussion of analytical models and their limitations for estimating the shaft fatigue duty following a defined electrical disturbance. The basis for a screening guide value for planned switching operations presented to the IEEE Working Group studying the effects of high speed switching is also discussed.

Torsional Vibration and Fatigue of Turbine-Generator shafts

Direct- and quadrature-axis equivalent circuits are developed for solid-rotor turbine generators. The equivalent circuits model, in considerable detail, important current-carrying paths in the rotor in addition to the excitation winding. Impedance equations are formulated so that a valid representation can be obtained over a wide range of frequencies. Operational solution of the equivalent circuits provides a powerful means for accurate analytical description of generator performance during many types of transient conditions, such as faults and other system disturbances, excitation system forcing, and asynchronous operation. In addition to providing improved accuracy of representation of generator terminal characteristics, solution of the circuits provides a wealth of valuable generator design information.

Direct- and Quadrature-Axis Equivalent Circuits for Solid-Rotor Turbine Generators

Synchronous-machine torques due to out-of-phase synchronizing may be quite large; larger in fact than those encountered during a 3-phase short circuit. Previous works have presented various forms of equations to calculate these torques.1-3,6 With the advent of the widespread use of systems analyzers and computers, it becomes convenient to use more exact equations to calculate synchronous machine transient performance. The objectives of this paper are to present the derivation of the equations for the currents and electrical torques which occur when turbine generators are synchronized out of phase; to show how these electrical torques arise; to illustrate the application of these equations to the problem of calculating the transient mechanical torques in a large, multiunit turbine-generator set under these conditions.

Synchronizing out of Phase

The first two parts of this series have developed the analysis of solid rotor machines for both flat and cylindrical models of infinite length. 1,2 The objective of this part is to present a representation of a finite length, flat model so that a correction for end effects may be incorporated in the operational impedance expressions. The correction presented gives a first-order approximation for this effect. The field analysis considering finite length is also of value in calculating air gap and rotor body spatial distributions of field quantities.

An Analysis of Solid Rotor Machines Part III. Finite Length Effects

One of the most important problems in the theory of rotating electric machinery is that of accounting for saturation effects. This paper adapts the results of the analysis of eddy current effects in semi-infinite solid saturated iron to develop the high-frequency operational and equivalent circuit impedances of a solid rotor machine. Parts I, II, and III of this series have presented a development of the basic theory, an investigation of the effects of curvature and a consideration of end effects, respectively. 1-3 Another paper has investigated the effects of field leakage. 4 This paper utilizes the electromagnetic model of Part I, neglecting the minor effects of curvature and finite length, except that the rotor iron is assumed to have a rectangular saturation curve.1 With the aid of this model, operational-and equivalent-circuit impedance equations are developed for conditions with relatively high-frequency eddy currents wherein the air gap fields are essentially one dimensional. Per-unit numerical data are given which illustrate the theoretical effect of saturation in increasing the resistive rotor impedance components over those obtained from a linear analysis.

An Analysis of Solid Rotor Machines Part IV. An Approximate Nonlinear Analysis

An Economic Study of High-Voltage Transmission [includes discussion]

In 1945, a systematic program aimed at reducing the noise level of their small and medium size 2-pole turbine generators was undertaken by the company with which the authors are associated. Factory tests on over 110 air-cooled generators ranging from 1,000-kw to 12,500-kw rating indicate that the average noise level of this line of machines has been reduced over 6 decibels. This noise level reduction has been brought about primarily by reducing sound energy transmission. One of the most important methods of reducing sound transmission is to keep the natural mechanical frequency of any part well away from any of the forcing frequencies. A discussion is given of the analytical work, the design program, the test equipment, and the development of a test procedure for obtaining consistent test results. The methods used in this program are general, and are applicable to the reduction of noise generated by other electrical apparatus.

A. J. Wood

Papers

Synchronizing out of Phase

An Analysis of Solid Rotor Machines Part III. Finite Length Effects

An Analysis of Solid Rotor Machines Part IV. An Approximate Nonlinear Analysis

An Economic Study of High-Voltage Transmission [includes discussion]

Reduction of Noise Produced by Small and Medium 2-Pole Turbine Generators [includes discussion]