Electrical Machines

Scholar Year: 2019/2020 - 1S

Courses

Head Teacher Responsability Silviano Francisco Santos Rafael Head

Weekly workload Hours/week T TP P PL L TC THE EL OT OT/PL TPL S Type of classes 2,5 2 Lectures Type Teacher Classes Hours Theorethical and Practical classes Totals 1 2,50 Silviano Rafael   4,00 Prática Laboratorial Totals 1 2,00 Silviano Rafael   2,00

Teaching language

Portuguese

Intended learning outcomes (Knowledges, skills and competencies to be developed by the students)

The course aims to contribute to the student's scientific training in the area of ​​electromechanical energy conversion, namely, in the steady-state study of single-phase and three-phase transformers (TR) and also of synchronous machines such as motor and three-phase alternator (MST).
The student, at the end of the study in this discipline, should be able to;
1-Understand / explain the constitution of TR and MST and justify with laws and rules the principle of operation of the same and the considerations regarding the perfect, ideal and real RT;
2 - To determine / estimate the parameters of the mathematical model of RT and MST in permanent regime;
3 - Apply / implement mathematical model of TR and MST in order to predict the consequences of parameter changes and / or analyze / predict the consequences of changes in electrical quantities and their phasor representation;
4-Analyze the power transit and efficiency of TR and MST;
5-Recommend / justify the choice of TR and MST machines to make the parallel between themselves;
6-Explain the conditions of power factor compensation in MST, as alternator and as motor;
7-Interpret the schematics, sketch, make the electrical connections and tests of the TR and MST machines. Apply Matlab in TR and MST troubleshooting.

Syllabus

I. SINGLE-PHASE TRANSFORMER.
1. Constitution. Windings. Ferromagnetic core. Coefficient of stacking.
2. Principle of operation. Convention.
3. No-load operation.
3.1. Perfect and ideal transformer.
3.2. Electromotive force. Relationship of transformation.
3.3. Real transformer. Leakage flow. Winding resistors. No load current. Component of magnetization and loss component in iron. Equivalent scheme. Phasor diagram.
4. Charging operation.
4.1. Perfect and ideal transformer. Approximate relations between currents and tensions.
4.2. Real transformer. Scheme equivalent of Steinmetz. Phasor diagram. Reduction of quantities from secondary to primary. Voltage drops on load.
5. Transformer tests. No load test. Short-circuit test. Short-circuit voltage. Tests under load. Characteristic curves. Approximation of Kapp.
6. Energy diagram. Constant and variable losses. Efficiency curve. Maximum efficiency.
7. Understanding the constitution, operation and use of autotransformers.

II - THREE-PHASE TRANSFORMER
1. Three-phase transformers. Constitution. Flows. Working principle.
2. Connection groups.
3. Parallel of three-phase transformers. Requirements for connection.

III. SYNCHRONOUS MACHINE
1. General Constitution: 1.1. Constitution. Stator. Rotor and speed. Cilindrical rotor poles (hydraulic turbines) and salient rotor poles(turboalternators) machines. 1.2. Principle of operation of alternators. 1.3. Inductive System. Independent excitation and self-arousal. 1.4. Stator windings. F.m. induced. 1.5. Cooling (air, hydrogen, water).
2. Alternator operation: 2.1. In no load space. F.m. waves and excitation flow. Test of no load. Air gap line. 2.2. On charge. Pulsating and rotating fields. Magnetic reaction of the armature in charge. Short-circuit test.
3. Permanent regime. Phasor Diagrams: 3.1. Equivalent circuit (cylindrical rotor not saturated). 3.2. Unsaturated and saturated synchronous reactance. 3.3. Effects of salients poles. 3.4. Introduction to the theory of two reactances. Phasor diagram and phasor relations. 3.5. Electromagnetic power and torque. 3.6. Losses and efficiency. Energy diagram. Alternator adjustment.
4. Characteristics of the Alternator: 4.1. No load. Short-circuit. External. 4.2. Power - load angle. 4.3. Regulation. 4.4. Mordey curves.
5. Parallel Synchronous Machines: 5.1.Conditions for connection and maneuver. 5.2. Synchronism detection (rotating, simultaneous fires and synchroscope). 5.3. Connecting the alternator to the infinite power network. 5.4. Breakdown of loads.
6. Synchronous Motor: 6.1. Operation with constant load and variable excitation. Mordey curves. 6.2. Operation with constant excitation and variable load. 6.3. Synchronous capacitor (compensator). 6.4. Synchronous motor start-up processes.

LABORATORY PART
I. SINGLE-PHASE TRANSFORMERS
1. No load and short-circuit tests for parameter determination.
2. External characteristics of a single-phase transformer.
II. THREE-PHASE TRANSFORMERS
1. Connection of transformers according to the specified time index.
2. Experimental determination of the time index of a three-phase transformer.

III. SYNCHRONOUS MACHINES
1. Tests under vacuum, and short-circuit. Determination of synchronous reactance.
2. Obtaining external characteristics for resistive, inductive and capacitive loads.
3. Alternator operating point prediction for a given load impedance.
4. Parallel connection of synchronous machines.

Software

Matlab

Demonstration of the syllabus coherence with the UC intended learning outcomes

All the programmatic contents form the platform of knowledge that will allow the student, through its interaction and internalization, to reach the referred learning objectives. The coherence is observed through the similarity of the contents with the objectives, verifying the alignment requested / desired.

Teaching methodologies

The teaching methodology used, in the context of the theoretical-practical classes, is based on the application of several active learning techniques aiming at a greater involvement and autonomy of students in the construction of their knowledge. The students work their resources in the process of critical reflection applying the laws and rules of the electrotechnics on electric machines (TR and MS). The competences acquisition is done trough the exercise of learning activities.
In the context of laboratory classes, active learning techniques are applied in a small group environment, where the individual contribution to the development / deepening of the topics and responsibility for their performance in the experimental tasks / simulation is encouraged. The laboratory work, developed by the students, will be focused on solving problems of a general nature, facilitating the understanding of the subjects. Students will use a simulation method to validate the machine model in order to predict and estimate operating regimes and recommend solutions to a real problem.

Demonstration of the teaching methodologies coherence with the curricular unit's intended learning outcomes

The application of active pedagogical techniques in a classroom environment, focusing progressively student learning is central to this teaching methodology. This methodology allows the students to interact and internalize the contents in the exercise of the learning activities, developing the skills and attitudes desired, identifying the agreement with the objectives.

Assessment methodologies and evidences

1 - Continuous Evaluation Regime
Students wishing to attend the UC on a continuous assessment basis are subject to the attendance regime and are obliged to carry out the laboratory work and all formative and summative evaluations, all with an individual quotation of 20 values.
The continuous evaluation of the theoretical-practical component is composed by the average of the formative evaluations (AF) and the average of the summative evaluations (AS).
The final classification of the theoretical-practical component (CF_TP) is calculated as follows:
CF_TP = 0.5 AF + 0.5 AS
The minimum grade of the practical theoretical component is 9.5 points. Formative assessment (PA) consists of six minitestes. Three minitestes on the transformer and three minitestes on the synchronous machine. Each training mini-course will have a duration of 30 to 45 minutes, being obligatory to reach 70% of the price of the same. If the students do not get 70% of the quotation, the minitest on the subject will be repeated, at the date and time to be agreed with the teacher.
Summative assessment (AS) consists of two tests. A summative test on transformers and another on three-phase synchronous machine. The duration of the summative test is 60 minutes, with a minimum mark of 6 values. If students, after completing all the summative tests, have not obtained the minimum grade for their approval, they may, during the examination periods, repeat the evaluation on the subject (s) of the summative test (s)
The laboratory component is mandatory and its evaluation is composed of two laboratory works L1 and L2. The work L1 is about transformers and the L2 work is about the three-phase synchronous machine and are evaluated when they are presented and discussed, in schedule to be agreed with the students. The grade of the laboratory component obtained from laboratory work is given by:
LC = 0.5 L1 + 0.5 L2.
The classifications of the tests and laboratory work are rounded to the tenths.

2 - Evaluation system for exams and laboratory work (self-assessment)
Students who choose this examination evaluation regime are subject to a minimum score of eight values ​​and follow the usual EST Setbal rules. The grade shall be the classification obtained in the examination consisting of two parts, one for transformers (TR) and the other for three-phase synchronous machines (MST). The mark obtained in the exam corresponds to the theoretical-practical component and is given by;
CF_TP = 0.5 TR + 0.5 MST.
Laboratory work, L1 and L2 or equivalent, are mandatory and are presented and discussed on the date to be agreed upon with the students. The grade obtained in the laboratory work corresponds to the laboratory component and is given by;
LC = 0.5 L1 + 0.5 L2.
The classifications of the exams and laboratory work are rounded to the tenths.
Exam dates are scheduled at School level.

3 - Final classification for the two assessment regimes
The final classification, CF, is given by weighting the classifications of each component through the expression:
CF = (CL + 2CF_TP) / 3.
Students who have achieved a final grade, CF> = 10, after unit rounding, will be approved.

Attendance system

The students to be covered by the continuous evaluation regime are required to attend in person at least 75% of the theoretical-practical classes and 75% of the laboratory classes.

By the end of the second week of classes, students covered by special statutes (student worker, associative leader, high-level athletes, etc.) shall place the UC manager in charge of their specific situation and their implications for the evaluations.

Assement and Attendance registers

Primary Bibliography

Secondary Bibliography

Observations

The contents and pedagogical materials to support the study can be found on the ME page in moodle. Students are enrolled by the head of the UC.