Overcurrent Protection Course: Principles, Relays, Schematics and Settings

Learn how overcurrent protection works in power systems, the concept of short circuits, different types of faults, and settings. Special attention is paid to instantaneous and time delay protection types (normal, very and extremely inverse relays). 21 lessons in 3 hours and 29 minutes.
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Course Description

Overcurrent protection is by far the simplest type of protection widely used in electrical power systems. It’s estimated that more than 80% of relays in industrial and power systems are overcurrent type. Therefore it is essential to fully understand and learn the real art of overcurrent relays. The course consists of 21 lessons in 3 hours and 29 minutes.

The course starts with explaining what is short circuit and the different types of faults in power systems and continues with the concept of short circuit current, load current, and percentage impedance of generator/transformer.

The course will teach you what are primary and secondary values needed for various protection calculations (fault MVA and fault current, plug settings, pick current, etc.). The course covers current transformer (CT) basics and you will learn to calculate CTs, how CT primary and secondary current ratings are selected, CT polarity and saturation, metering and protection cores, etc.

Special attention is paid to explaining the types of overcurrent protection i.e., instantaneous and time delay. Inverse time overcurrent relay, its types (Normal Inverse, Very Inverse & Extremely Inverse relays) and settings are explained in detail.

This course covers also the following topics:

  • How to connect CT secondary wiring to Overcurrent relay
  • CT star point towards the line and towards bus connections
  • Understand how a change of the direction of current by 180 deg when star point of CT is changed
  • Single point earthing of CT secondary and its importance
  • Selectivity Sensitivity Speed Reliability
  • What it means by relay coordination and discrimination
  • Current selective discrimination
  • Time selective discrimination
  • Definite time overcurrent relay time coordination example
  • Inverse time overcurrent relay time coordination example
  • A choice between IDMT over DTOC Relays
  • What are directional overcurrent relays
  • What are zones & why zones are important for selectivity?
  • What it means by polarizing quantity
  • Self & cross-polarization
  • Zero Sequence, positive sequence, and negative sequence polarization
  • Advantages and requirement of directional overcurrent relays
  • Explained by vectors how cross-polarized relay works.
  • Maximum Torque Angel, relay characteristics angle, max forward and reverse angle explained
  • Application of DOC relays
  • Disadvantages of overcurrent relays

Course Overview

  1. Short circuit, calculation of fault MVA and fault current
  2. Current transformer essentials
  3. Overcurrent protection (Instantaneous and time delay)
  4. Normal- very- and extremely-inverse relays
  5. Connecting CT secondary wiring to relay
  6. Relay coordination and discrimination
  7. IDMT over DTOC Relays
  8. Zero, positive, and negative sequence polarization
  9. Disadvantages of overcurrent relays

Who Is This Course For

  • Practicing power system engineers
  • Electrical engineering students planning on pursuing a career in power engineering
  • Anybody with an interest in learning about power systems and power engineering


  • Understanding of power system analysis

Downloadable course materials

After purchasing the course, students can download the following documents:

  1. The Basics Of Overcurrent Protection (pdf)
  2. Overcurrent and differential digital protective relays with monitoring capabilities (pdf)
  3. Overcurrent protection study for power network (solving relay setting miss-coordination) (pdf)
  4. Phase overcurrent protection on overhead MV feeders (pdf)
  5. Preventive Maintenance And Reliability Of LV Overcurrent Protective Devices (pdf)

About Instructor

Muhammad Kashif

Muhammad Kashif Shamshad is an Electrical Engineer and has more than 17 years of experience in operation & maintenance, erection, testing project management, consultancy, supervision, and commissioning of Power Plant, GIS, and AIS high voltage substations ranging up to 500 kV HVAC & ±660kV HVDC  more than 10 years experience is with Siemens Saudi Arabia. He completed over 20 high voltage substation projects, Operation & Maintenace of Substation & Power plants in Pakistan and Saudi Arabia for different electric utilities including Saudi Electricity Company (SEC), Saudi Aramco, SABIC, Marafiq, National Transmission & Despatch Company (NTDC), WAPDA, and K-Electric. Also, he led testing and commissioning teams to implement electrical infrastructure projects for many types of industrial clients (Steel, Petrochemical, etc.) in both countries, Pakistan and Saudi Arabia.

14 Courses

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Course Includes

  • 27 Lessons
  • Course Certificate
  • Lifetime Access