29247 - Electrical Machines T

Learning outcomes

The course is proposed to supply the basic knowledge for the study of the widely used electric machines.  The operating principles and the performance in different operating conditions will be analysed.

After passing this course, students will be familiar with issues involved in electromechanical energy conversion, use of mathematical models to predict the machine behaviour, analysis of usual operating conditions.

Course contents

Recalls on the laws of the electromagnetism and on the main property of the conducting, dielectrics and ferromagnetic materials employed in the accomplishment of the electric machines.

Transformers

Basic definitions and construction elements, principle of operation, machine equations, equivalent circuits and performance.

Machine parameter determination by laboratory tests.

Analysis of the no-load behaviour with reference to primary and secondary winding connections. Harmonic content of primary currents and magnetic fluxes at no-load. Analysis of the transformer behaviour with unbalanced load: Y/Y, D/Y,Y/Yn, Y/Z. Calculation of the homopolar impedance of transformer.

Unbalanced duty of three-phase transformers, parallel operation, autotransformers, transformers, test transformers.

External characteristic of transformer with R-, L- and C-type load. Output voltage variations due to load current variations. Kapp diagram.

Parallel operation of transformers having different voltage transfer ratio.

Triple-wound transformers. Machine equations, equivalent circuit. Short circuit tests. Analytical calculation of machine parameters.

Measurement transformers: Voltage and current transformers. Relationships between machine parameter values and measurement errors. Basic design criteria.

 

Rotating Machines

General information on AC machines. Windings for alternating current machines.

Harmonic analysis of the air-gap magnetic flux distribution produced by a distributed winding. Magnetic flux distribution produced by a system of balanced currents flowing in a symmetric poly-phase winding. Existing rotating fields.

Electromotive force produced by a harmonic rotating field in a distributed winding.

 

Induction machines

Analysis of the induction machine behaviour taking the mmf harmonic content into account. Generalized equivalent circuit. Leakage reactance contributions.

Ttorque characteristics. Starting of three-phase induction motors, speed control. Single-phase induction motors.

Double cage rotor.

The single-phase induction motor: principle of operation, equations, equivalent circuit. Starting problems.

The calculus of the equivalent circuits of a.c. machines. Leakage reactance of a.c windings of coil- and and bar-type. Equivalent circuit and parameter calculation of the double squirrel cage motors.

 

Synchronous machines

Basic types of synchronous machine and operating principle, armature reaction, voltage diagrams, torque production, parallel operation, oscillations of synchronous machines.

Reactance calculation, Torque of a salient-pole and non-salient pole machines. Mathematical models of the two types of machine with saturated magnetic circuit.

Permanent magnet machines.

 

DC machines
Basic types of DC machines, magnetic circuit, windings, emf calculation, machine equations. Armature reaction, commutation, compensating windings. Characteristics of DC motors and generators.

Basic relationships for D.C. winding design. Equalizers.

The commutation process. Reactive e.m.f. calculation. Compoles design. Compensating winding.

Readings/Bibliography

B. Brunelli: Conversione elettrica ed elettromeccanica dell'energia, Pitagora, Bologna

A. E. Fitzgerald, C. Kingsley, A. Kusko: Macchine elettriche. Franco Angeli

E. Di Pierro: Costruzioni elettromeccaniche (vol. I e II). Eedizioni Scientifiche Siderea, Roma

L. Fusco, D. Iannuzzi, E. Pagano, L. Piegari: Macchine elettriche. Liguori Editore, Napoli

M. Kostenko, l. Piotrovsky: Electrical machines, (vol. I e II). Mir Publishers Moscow
P. L. ALGER: THE NATURE OF POLIPHASE INDUCTION MACHINES JOHN WILEY NEW YORK CHAPMAN & HALL LONDON

Paper copy of the PowerPoint presentation.

 

Teaching methods

The course includes hours of lesson and hours of exercise where application examples are presented.

The proposed exercises need the use of pocket calculators together with tables and graphs from commercial data.

Assessment methods

The final test consists in the overcoming of a written exercise and of an oral discussion based on three of the basic issues of the Course.

Teaching tools

Blackboard, overhead projectors and PC based presentations are employed during lessons.

Simulation software and running models of electrical machines are also available

Office hours

See the website of Giovanni Serra