Course Details

Subject {L-T-P / C} : EE4101 : Power System Protection {3-0-0 / 3}
Subject Nature : Theory
Coordinator : Prof. Ananyo Sengupta


Overview of Power System Protection: General architecture of protection system, Evolution of relays, Attributes of a protection system, Current and potential transformer for relays, Zones of protections, Concept of primary and back-up protection.

Overcurrent Protection: Construction, Operating Principle and Characteristics of Instantaneous overcurrent relay, Definite Time overcurrent relay, Inverse Time overcurrent relay, Inverse definite minimum time overcurrent relay Co-ordination of overcurrent relays for radial lines, Overcurrent protection of three-phase feeder Construction, Operating Principle and Characteristics of Directional overcurrent relay, Directional overcurrent protection of a three-phase feeders Drawbacks of overcurrent protection.

Distance Protection: Universal Torque Equation, Construction, Operating Principle and Characteristics of Simple Impedance relay, Reactance relay, and Mho relay, performance of different impedance relays during normal loading condition, power swing and effect of arc resistance, Directional properties of various impedance relays, Impact of infeed effect Distance protection of a three-phase line, Three-stepped distance protection.

Differential Protection: Dot convention, Simple differential protection – behavior during normal load, external fault and internal fault Actual behavior of a simple differential protection scheme and Percentage Differential relay.

Busbar Protection: Differential protection of busbars, actual behavior of a protective current transformer – effect of CT saturation, High Impedance busbar protection.

Transformer Protection: Over-current protection, Percentage differential protection of transformer, Inrush phenomenon, percentage differential relay with harmonic restraint High resistance ground fault protection of a Y-? transformer Inter-turn faults in transformer, Buchholz relay Protection against over-fluxing.

Digital Relay: Architecture of a digital relay, Phasor Measurement technique, Numerical distance protection of transmission line, Elimination of decaying dc component, Distance protection by differential protection method, protection of transformer.

Circuit Breaker: Requirement of circuit breakers, Characteristics of electric arc, Principle of A.C. and D.C. arc interruption, recovery and Restriking voltage and effect of current asymmetry upon them, Interruption of capacitive currents Various types of circuit breakers - Air-breaker circuit breaker, bulk-oil circuit breaker and minimum oil circuit breaker, Air-blast circuit breaker, SF_6 circuit breaker, Vacuum circuit breaker.

Course Objectives

  1. 1. Design the overcurrent protection for a given power system
    2. Design the distance protection for a power system
    3. Design the differential protection for transformers and busbars.
    4. To understand the principles of digital relaying
    5. To understand the circuit breaker operations.

Course Outcomes

At the end of the course, students will be able to

1. Understand the construction and operating principles of overcurrent relays.
2. Understand the construction and operating principles of different types of impedance relays.
3. Co-ordinate primary and backup relays (both overcurrent and impedance relays)
4. Understand the construction and operating principles of differential relays.
5. Understand the operating principles of digital relays
6. Understand different types of circuit breaker operating principles.

Essential Reading

  1. Y. G. Paithankar and S. R. Bhinde, Fundamentals of Power System Protection, PHI
  2. Stanley H. Horowitz, Arun G. Phadke, James K. Niemira, Power System Relaying, Willey

Supplementary Reading

  1. J. L. Blackburn and T. J. Domin, Protecive Relaying: Priciples & Applications, CRC Press
  2. S. S. Rao, Switch Gear and Protection, Khanna Publishers