BEE207S

Unit Description and General Aims

The objective of this unit is to: provide students with detailed knowledge of power system protection and its role in the safe and reliable operation of a power system; and, to impart the ability to choose and apply protection systems in a given context. Information covered in this unit will include: the different types of protective devices and their applications; the coordination between different protective devices and the different forms of grading that are possible; protection of individual types of equipment such as motors, generators, transformers, and switchgear; and, the approach to setting these protective devices. Students will also undertake project work involving protection applications and settings for a typical industrial power network.

Learning Outcomes

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

1. Explain the fundamentals of electrical power system protection and its components.
   Bloom’s Level 2
2. Describe protection devices used in LV systems, relays, and IEDs.
   Bloom’s Level 2
3. Evaluate short circuit current values of simple industrial systems using equivalent diagrams.
   Bloom’s Level 3
4. Explain the time/current characteristics of DMT and IDMT types and calculate coordinated settings in practical circuits.
   Bloom’s Level 6
5. Explain the concept of unit protection and compare its applications.
   Bloom’s Level 5
6. Describe protection systems specific to each type of equipment.
   Bloom’s Level 3

Student assessment

Prescribed and Recommended Readings

Required textbook(s)

EIT reference book on power system protection (Course code PS)

Reference Materials

Number of peer-reviewed journals and websites (advised during lectures)

For example:
Simple, easy to follow explanations can be seen from the webpage:
http://www.electrical4u.com/protection-system-in-power-system/ : Protection System in Power System by electrical4u.com Online Electrical Engineering.

Unit Content

One topic is delivered per contact week, with the exception of part-time 24-week units, where one topic is delivered every two weeks.

Topics 1 and 2

Basics of power system protection

1. Objectives of protection systems
2. Attributes of protection systems
3. Functional components in a protection system
4. Protection – basic approaches: fuses, release integrated with breakers, and relays
5. Instrument transformers and their application in protection
6. Reliable, battery-based power supply for protection systems
7. Fuses and their application in the protection of feeders
8. Types of protective release integrated systems with LV circuit breakers

Topics 3 and 4

Faults: types and calculation of fault current

1. Reason for faults in electrical circuits
2. Types of faults
3. Principle of fault current calculation
4. Limiting the fault current magnitude – methods of determining this
5. Ohmic and per unit impedance, and the calculation of impedance per unit values
6. Equivalent diagrams for fault current evaluation
7. Calculation of 3-phase fault current using reduction of equivalent diagram
8. Maximum and minimum fault currents, implication for protection design
9. Symmetrical components and application in calculating the current for unbalanced faults

Topics 5 and 6

Protection relays and IEDs, their setting and coordination

1. Types of protection relays based on construction
2. Time-current characteristics and relay types based on the characteristic
3. Intelligent electronic devices - essential components
4. IEC/ANSI equations for time/current characteristics
5. Determining current setting based on circuit parameters and fault current values
6. Grading of protection needs and methods (current, time, energy, impedance, direction)
7. Current/time grading and the different approaches used
8. Calculation of coordinated setting on current relays using a spreadsheet program

Topics 7 and 8

Principles of unit protection and protection of feeders

1. Unit or differential protection
2. Comparison with other methods of protection
3. Applications of unit protection and pitfalls
4. Feeder protection using current relays
5. Feeder protection using unit principle
6. Protection by comparison of phase angle
7. Distance protection and comparison with unit protection
8. Distance protection with PLCC or other inter-communication for fast operation

Topic 9

Transformer protection

1. Transformer faults
2. Over-current protection
3. Differential protection
4. Earth fault/REF protection
5. Temperature based protection
6. Gas protection
7. Mounted DGA monitoring for early detection

Topics 10 and 11

Protection of electrical switchgear and rotating machines (generators and motors)

1. Busbar protection in outdoor and indoor substations using current relays and unit protection
2. LV busbar protection with optical (arc) sensing
3. LV busbar protection with zone selective relaying and communication interlinks
4. Faults in motors
5. Winding protection using unit protection approach
6. Thermal protection
7. Stall protection
8. Over-current, earth fault and negative sequence current protection
9. Generator faults
10. Protection using current relays
11. Winding protection using unit approach and sensitive earth fault protection
12. Temperature based protection
13. Loss of field and pole-slip protection

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: ETAP 19; PSCAD

• Version: PSCAD Version 5

• Instructions:  N/A

• Additional resources or files: N/A

Hardware

• N/A