BEE108S

Unit Description and General Aims

The objective of this unit is to familiarise students with the fundamental principles of electrical motors operating from DC and AC power supplies, their operation, control techniques, construction/components, and ratings. Additionally, the determination of the efficiency of these motors, common problems, troubleshooting methods, testing of the machines for commissioning and during operation to ascertain their performance, condition monitoring, and essential maintenance aspects, will also be covered. The emphasis will be on AC motors since these types of motors are more widely used in industry.

Learning Outcomes

On successful completion of this Unit, students are expected to be able to:

1. Explain the fundamental principles behind electro-mechanical energy conversion and calculate the relation between motor rated power and torque.
   Bloom’s Level 3
2. Describe the principle of operation of DC motors, the function of the commutator, and the different types of DC machines based on field winding connections.
   Bloom’s Level 2
3. Explain the theory of 3-phase synchronous motors and the relation between excitation and motor power factor.
   Bloom’s Level 2
4. Explain the fundamental theory of 3 phase and single phase induction motors, the various types of motors, and their control aspects.
   Bloom’s Level 2
5. Discuss the construction of AC motors and the ways of enhancing motor efficiency.
   Bloom’s Level 4
6. Describe the procedure for testing AC motors and perform these tests in a simulated environment to calculate motor parameters.
   Bloom’s Level 3

Student assessment

Prescribed and Recommended Readings

Suggested Textbook

1. S. Umans, Fitzgerald and Kingsley's Electric Machinery, 7th Edition. McGraw Hill Education, 2013 - ISBN-13: 978-0073380469

Reference Materials

1. Bird J, 2013, Electric Circuit Theory and Technology, Newnes (Elsevier Science), Chapters 21 and 22, ISBN 978-0415662864
2. AC Motors and Protection (MP). IDC Technologies.

Unit Content

Topic 1

Electro-mechanical energy conversion principles

1. Forces and torques in magnetic fields
2. Energy balance
3. Determination of magnetic field, torque, and direction of force generated
4. Permanent magnet field systems
5. Single and multiple-excited magnetic systems
6. Dynamic equations and analytical principles

Topics 2 and 3

DC motors

1. Basic concepts
2. Force/Torque produced in a DC machine
3. Back EMF in rotating coils in a magnetic field
4. Commutator action
5. Effect of armature MMF and armature reaction
6. Need for inter-poles and compensating windings
7. Speed/torque characteristics
8. Shunt, series, and compound motors and their characteristics
9. Starting of DC motors
10. Speed control of a DC machine
11. Armature voltage control
12. Effect of field weakening
13. Applications of DC motors for variable speed requirement

Topics 4 and 5

Polyphase motor theory and synchronous motors

1. Basic concepts
2. MMF of distributed windings
3. Generated voltage
4. Salient and cylindrical poles and torque development
5. Synchronous machine inductances and equivalent circuits
6. Open and short circuit characteristics
7. Power angle
8. Steady-state and dynamic behaviour
9. Direct and quadrature axis theory in salient pole machines
10. Excitation of synchronous motors
11. V-curves of synchronous motors; power factor/excitation (inverse V)-curves
12. Construction of a typical synchronous motor
13. Damper windings
14. Synchronous motor applications in industry
15. Synchronous condensers in power systems

Topics 6 and 7

Induction motors

1. Torque generation in 3-phase induction motors
2. Current and fluxes
3. Phasor diagram of an induction motor
4. Equivalent circuit
5. Leakage resistance and reactance of induction motor
6. Analysis of the equivalent circuit
7. Calculation of torque, stator, and rotor current
8. Torque and power using Thevenin’s Theorem
9. Circle diagram
10. Starting behaviour and the role of back EMF
11. Squirrel cage and slip ring types-comparison
12. Single and double cage type AC motor
13. Single phase AC motors
14. Explanation of zero starting torque in single phase induction motors
15. Split winding construction for developing starting torque
16. Universal motors (based on DC series motors)

Topics 8 and 9

Control of 3 phase motors and industrial applications

1. Torque-speed characteristics of cage and slip ring motors
2. Induction motor vs. generator operation
3. Selection of motor based on torque-speed characteristics
4. Matching the driven equipment torque requirements to motor capability
5. Stable and unstable region of motor torque-speed characteristics
6. Crawling and cogging problem
7. Impact of voltage reduction on motor torque
8. Direct-on-line starting of a 3-phase induction motor-typical control circuit
9. Reversible motor circuit
10. Need for assisted starting in weak systems
11. Star-Delta and Auto-transformer starting and their control circuits
12. Solid state soft-starters and circuitry used
13. Rotor resistance starting method for slip ring motors
14. Braking of motors
15. Electrical braking using plugging and resistance braking methods
16. Regenerative braking using induction generator principle

Topics 10 and 11

AC motor applications, testing, efficiency calculation, and troubleshooting principles

1. Application of induction motors of different types in industry
2. Insulation and varnish impregnation
3. Typical cooling and mounting configurations
4. Motor frame sizes (IEC)
5. Starting and duty cycles for different applications
6. Hoisting and crane-duty applications using slip rind motor with resistance control
7. Losses in AC induction motors and efficiency
8. Efficiency improvement methods
9. Tests on AC motors
10. Open and short circuit tests
11. Plotting the circle diagram
12. Calculating leakage impedance parameters based on tests
13. Load testing and efficiency calculation
14. Back-to-back testing for large capacity motors
15. Temperature rise tests and temperature measurement
16. Maintenance and troubleshooting of AC motors

Topic 12

Unit Review

In the final week students will have an opportunity to review the contents covered so far. Opportunity will be provided for a review of student work and to clarify any outstanding issues. Instructors/facilitators may choose to cover a specialized topic if applicable to that cohort.

Software/Hardware Used

Software

• Software: MATLAB/SIMULINK

• Version: Student version

• Instructions:  N/A

• Additional resources or files: N/A

Hardware

• N/A