Acionamentos Eletromecânicos

Electrical Circuits Theory I

Electrical Circuits Theory II

Electrical Machines

(THIS SUBJECT IS TEACHED ONLY IN PORTUGUESE)

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.

Practical / Laboratory Classes. These classes are of two types: Exercise resolution classes, with analysis and dimensioning of electromechanical drives, including their command and protection; and laboratory experimentation classes where different electromechanical drives are tested, controlled and connected. 
The UC organization, carefully balancing comprehensive theoretical knowledge with resolution of theoretical-practical exercises and laboratory practice, makes this one of the most successful UCs in LEE,
with a very high approval rate for the students evaluated. For the motivation of the students, it also contributes the attribution of one or two certificates (depending on the results obtained in the UC and in the laboratories) awarded by SEW Eurodrive, under the protocol between ISEC and this reference company in the area of electromechanical drives.

Goals

To give students theoretical, practical and experimental skills on electromechanical drives and on the respective protection, command and control devices.

Skills

At the end of this course unit, the student is expected to be able to use, design, analyze, optimize, protect and implement electromechanic drives, integrating three-phase induction motors, soft-starters, variable-speed drives, contactors, protection devices and mechanical transmission.

The learning outcomes, associated with those acquired in other course units, contribute for the understanding of the operation of electric motors and of the respective control equipment, the capability of design and implementation of command and protection systems of industrial equipment and the respective electric power networks, the knowledge of relevant aspects of industrial electric power networks and equipment maintenance, and the capability to define maintenance schemes for electromechanical equipment.

1- Sizing and applications of powertrain systems.
Introduction to drives
Energy conversion in electromechanical drives.
Electromechanical drives of constant speed and variable speed. Main industrial applications and power range of electromechanical drives. Evolution of the distribution of the drives by DC and AC motors.
Standardization of electrical circuits: Symbology for electromechanical drives.
Used but outdated symbology; symbology according to IEC 1082-1. Comparison of the main symbols of International (IEC) and US standards.
Reference to developed electrical circuits.
Rules for implementation of electrical circuits.
Control and power circuits for motor starters.
Currents and binaries during motor starting: direct start, star-triangle. Curves for slip and speed. Typical representations. Typical control and power circuits.
Other starting:
• Motors with partial winding (“part-winding”).
• Stator-Resistor.
• By autotransformer.
• Wound rotor motors.
• Starters-inverters.
• Direct starting of single-phase motors.
• Separate winding 2 speed motors.
• 2-speed motors with pole switching. Dahlander: Binary const. and variable; Constant power.
Drive control equipment
Contactors. Particular aspects of the coil supply in alternating current and direct current (consumption reduction devices). Forces in alternating current. Function of the shading coil; parallel with the operating principle of shaded pole motors.
Other types of contactors: low consumption contactors. Relays and static contactors.
Examples of choice of contactors depending on the application.
Coordination of contactors with short-circuit protection devices
Electromagnetic and thermal effects of short-circuits.
Notion and types of coordination (nonexistent, type 1, type 2 and total) and their consequences, advantages and disadvantages.
The different motor control and protection solutions. Solutions with 1, 2 or 3 devices to perform the basic functions of a motor output. Advantages and disadvantages.

2- Optimization of electromechanical drives
Introduction
Nature of electromechanical drives. Functional scheme of an electric drive. Steps for design / selection of drives.
Mechanics of Drives: Description and modeling
Fundamental equation of dynamics. Inertia, friction and elastic effects. Friction binaries.
Description and resistant torque of some types of loads.
Organs for transmission and adaptation of movement. Principle of additivity. Mechanical gears. Transmission ratio. Various types of gear units and their gear ratio.
Determination of the mechanical parameters: calculation of the moment of inertia and coefficient of viscous friction; determination of the parameters from the tests.
Service requirements, dynamic regime
Service requirements. Operating quadrants.
Cases study.
Restrictions imposed by the electric machine / converter.

3- Speed variation and position control
Transducers
Analog speed and position transducers: tachymetric dynamos and resolvers.
Digital speed and position transducers: pulse counters with inductive detectors, incremental and absolute encoders (natural binary code and Gray code). Advantages and disadvantages. Current transducers: current transformers and Hall effect sensors.
Electronic starters and variable speed drives
Differences and fields of application of controlled rectifiers, frequency converters and voltage graders.
Constitution: power module and control module. Main functions of electronic starters and variable speed drives.
Variation of voltage with fixed frequency
Soft starters.
Variable Frequency Drives
Simultaneous voltage and frequency variation (“V / f” and “E / f” technique).
Simultaneous variation of current and frequency.
Speed and position control: vector control
Introduction to the Generalized Theory of Electric Machines.
Models of asynchronous three-phase machine in various references.
Equations of the voltages in phase values.
Park transformation applied to a three-phase asynchronous machine.
Principle of Vector Control.

4- Dynamic systems analysis
Reference to the application of Park’s Transformation to the three-phase asynchronous machine, for dynamic study and application to vector control.

5- Complementary aspects of electromechanical drives
Potential for energy savings.
Advances and future trends: in electric machines; in drives with induction motors.
Motor mounting positions and insulation classes.

6- Special powertrain systems
Use of Linear Induction Motor and BLDC Motor.
Application of drives in electric traction.

NOTE: In order to ensure the coordination of measures between the theoretical and laboratory practice, the teaching sequence of the materials may not be exactly the shown above.

NAO

Lessons presentations delivered by the instructors.

Problems and Laboratory Guide (in Portuguese), ISEC.

The indicated above for the portuguese students.