Máquinas Elétricas

Base Knowledge

Electrical Circuit Theory I and II

Electromagnetism

Teaching Methodologies

Theoretical classes: with exposure of the subjects, drawing attention to the most relevant aspects and making the connection between each subject and the others. Interpellation of students on the subject in order to arouse curiosity, remember and connect previous knowledge. Presentation of some videos and animations that illustrate the concepts and / or applications.

Theoretical-practical classes: complementation of theoretical classes; problem solving, problem development and mathematical formulations.

Practical / Laboratory Classes: These classes are of two types: mainly, laboratory experimentation classes where classic tests of the studied machines are carried out, in group work; but also exercise resolution classes, which concretize the models presented in the theoretical classes, allowing to calculate the parameters of the studied machines from test results and their operating regimes.

 

Learning Results

Objectives: To understand the steady state operation of transformers and single-phase and three-phase asynchronous machines. Know its constitution, operating principle, equivalent schemes and applications. Familiarize students with the use of these machines through their use in the laboratory environment.

Skills: Knowing how to connect, use, test and calculate transformers and asynchronous machines. Know how to design and use control and protection systems, implementation and maintenance of these electric machines. Choice of technical solutions in the field of these machines and their arguments to the employer or client.

Program

Goals

The main goals of this course unit are:

To understand the basic concepts of electric machines operation in continuous (steady-state) operation. Obtain knowledge on mechanical construction, principle of operation and equivalent circuits and applications of transformers and asynchronous machines, single- and three-phase. Familiarize students with the use of these electrical machines through their use in the laboratory environment.

Skills

At the end of this course unit, it is expected that the student will be able to: calculate, connect and work with transformers and asynchronous machines; design and conduct experiments, as well as to analyze and interpret data; learn how to use control systems and protection; choose technical solutions and participate in projects to implement and maintain these kinds of machines.

Program Contents

1. Generic Principles of Electric Machines

Constitution. Materials. Main physical laws governing the operation of electric machines: Maxwell, Ampere, Faraday, Lenz, Ohm generalized. Electromechanical Energy Conversion.

2. Single-phase transformer

Constitution. Operation principle. Equations of operation. Equivalent circuits of the real transformer. Definition of characteristic quantities at rated power. Determination of voltage drops and external characteristics. Losses and efficiency. Economic tests. Grouping in parallel.

3. Three-phase transformer

Three-phase bank and three-phase unit. Three-phase transformer core. Types of three-phase transformers, regarding the connection of windings. Operation of the transformer in symmetrical mode. Economic analysis of the amount of copper used on each type of winding. Electrodynamic forces. Grouping in parallel. Study of the three-phase connections from the point of view of the 3rd harmonic and the regime of unbalanced loads.

4. Special transformers

Measurement and Protection Transformers: current transformer, voltage transformer. Autotransformer.

5. Three-phase asynchronous machines

Constitution. Operation principle. Equations of operation. Equivalent circuit. Motor powers and torque. Electromechanical and mechanical characteristics. Operating stability. Influence of parameters on motor characteristics. Circle diagram. Economic tests. Starting of induction motors: squirrel cage motors; winding rotor motors. Classes of squirrel cage motors. Inverted March. Operation of the asynchronous machine as generator. Operation of the asynchronous machine as a brake.

6. Single-phase induction motor.

 Constitution. Operation principle. Starting processes of single-phase induction motors. Locked rotor and no-load tests.

Curricular Unit Teachers

Internship(s)

NAO

Bibliography

1 – As support for the Electrical Machines classes and evaluation, please consider as main references the two books below:  

Nasar, S. A. (1998). Electric machines and Electromechanics : Schaum’s outline of Theory and problems (2nd ed.). New York : McGraw-Hill. ISBN 0-07-045994-0 (available at ISEC’s Library: Exercises book with theoretical introductory summary).

In chapters:

  • 1 – Magnetic Circuits
  • 2 – Power Transformers
  • 5 – Polyphase Induction Motors
  • 7 – Single-phase motors… (only the 2 pages of theoretical introduction about this machine: 7.1. and 7.2)

Study the theoretical summary and solve the solved exercises.

 

Nasar, S. A. (1995). Electric Machines and Power Systems: Volume I, Electric Machines. McGraw-Hill Companies. ISBN13: 9780070459588. 

More deeper theoretical explanation with some solved exercises.

Relevant chapters:

  • 1– Introduction.
  • 2 – Fields, Energy and Forces. Most important sections: (2.1.) 2.2-2.5;  2.9. (means: “quick review of 2.1; important: from 2.2 to 2.5 and 2.9”)
  • 3 – Power Transformers. Everything (less important: 3.7, 3.13, 3.15)
  • 4 – Induction Machines. Everything (except 4.14). In exercises, we use the “approximate equivalent circuit” (fig. 4-20)

Study the theoretical presentation and solve the solved exercises.

 

2 – The Bibliography above indicated for the Portuguese students.