Electrical Protection and Selectivity Course

Lesson 1 • Types of Electrical Faults

Classifies fault types by cause, location, and severity. Provides the fault taxonomy learners need to select appropriate protection strategies later.

Lesson 2 • Protection System Performance Criteria

Defines speed, sensitivity, reliability, and selectivity as the four core performance metrics. Learners use these criteria to evaluate any protection design throughout the course.

Lesson 3 • Key Protection System Components

Identifies sensors, relays, circuit breakers, and communication links as the building blocks of any protection scheme. Connects component roles to overall system behaviour.

Lesson 1 • Symmetrical Components for Fault Analysis

Introduces positive, negative, and zero sequence components as the mathematical basis for analysing unbalanced faults. This framework is used in every subsequent protection chapter.

Lesson 2 • Current Transformer Principles and Classes

Covers CT construction, magnetising characteristics, and accuracy classes for protection use. Accurate CT selection is prerequisite to correct relay operation.

Lesson 3 • CT and VT Wiring and Polarity

Teaches correct polarity marking, secondary wiring practices, and earthing of instrument transformers. Wiring errors are a leading cause of protection failures in practice.

Lesson 1 • Earth Fault Overcurrent Protection

Covers residual and core-balance CT methods for detecting earth faults with high sensitivity. Earth fault settings differ from phase settings due to lower fault current levels.

Lesson 2 • Overcurrent Relay Operating Characteristics

Explains definite-time, inverse-time, and instantaneous overcurrent characteristics and their standard curves. Understanding curve shapes is essential for time-grading coordination.

Lesson 3 • Directional Overcurrent Protection

Extends overcurrent protection to meshed and looped networks using directional elements. Directional control prevents relay operation for faults in the non-tripping direction.

Lesson 4 • Pickup and Time-Dial Setting Calculations

Provides step-by-step methods for calculating pickup current and time-dial settings. Learners apply load current, fault current, and CT ratio data to derive correct settings.

Lesson 1 • Coordination in Meshed and Looped Networks

Addresses the additional complexity of bidirectional fault current in meshed systems. Directional relays and zone-selective interlocking are introduced as coordination tools.

Lesson 2 • Fuse and Relay Coordination

Covers coordination between fuses and upstream overcurrent relays, including fuse-saving and fuse-blowing schemes. Learners select fuse ratings that maintain selectivity with relay settings.

Lesson 3 • Selectivity Concepts and Grading Margins

Defines selectivity and explains how grading margins account for relay and breaker tolerances. Correct margins prevent upstream relay operation during downstream fault clearance.

Lesson 4 • Low-Voltage Selectivity Methods

Examines current limiting, energy-based, and zone-selective interlocking methods used in LV switchgear. LV coordination differs from MV due to high available fault currents and fast devices.

Lesson 1 • Power Swing Detection and Blocking

Explains how power swings cause impedance locus movement that can enter relay characteristics. Power swing blocking prevents unwanted tripping during stable and unstable swings.

Lesson 2 • Zone Reach Calculation and Setting

Provides methods for calculating Zone 1, 2, and 3 reaches based on line impedance and infeed effects. Correct reach settings prevent under-reach and over-reach maloperation.

Lesson 3 • Distance Relay Schemes and Signalling

Covers permissive underreach, permissive overreach, and blocking communication schemes. Signalling schemes extend instantaneous protection to 100% of the protected line.

Lesson 4 • Distance Protection on Special Line Configurations

Addresses challenges on series-compensated, tapped, and parallel lines where standard settings fail. Learners adapt zone settings and apply supplementary functions for these configurations.

Lesson 1 • Cable and Line Differential Protection

Covers pilot-wire and digital current differential schemes for cables and short lines. Charging current compensation is required to maintain sensitivity on long cables.

Lesson 2 • Differential Protection Operating Principle

Explains the current-balance principle and how operate and restraint quantities are derived. The percentage differential characteristic is introduced as the standard implementation.

Lesson 3 • Transformer Differential Protection

Covers CT ratio matching, vector group compensation, and inrush restraint for transformer differential relays. These features prevent false tripping during energisation and through-fault conditions.

Lesson 4 • Generator Differential and Stator Protection

Applies differential protection to generator stators and introduces 100% stator earth fault protection. Generator protection must detect high-resistance faults that overcurrent relays miss.

Lesson 1 • Motor Protection Principles and Settings

Covers thermal overload, locked rotor, phase unbalance, and undervoltage protection for induction motors. Motor protection settings must accommodate high starting currents without sacrificing fault sensitivity.

Lesson 2 • Transformer Protection Functions

Identifies overcurrent, differential, restricted earth fault, and thermal protection functions for transformers. Each function targets a specific failure mode and must be coordinated with others.

Lesson 3 • Out-of-Step and Loss-of-Synchronism Protection

Explains pole-slip detection and controlled tripping to protect generators during loss of synchronism. Uncontrolled pole-slip causes severe mechanical and electrical stress on the machine.

Lesson 4 • Coordination of Machine Protection Schemes

Integrates individual protection functions into a coherent scheme with correct time grading and backup coverage. Learners verify that no single protection failure leaves the machine unprotected.

Lesson 1 • Protection Relay Setting and Configuration

Covers relay setting file management, group switching, and parameter documentation practices. Systematic setting management prevents configuration errors that cause protection failures.

Lesson 2 • Cybersecurity for Digital Protection Systems

Addresses access control, network segmentation, and secure communication for protection systems. Cybersecurity measures must not degrade protection performance or availability.

Lesson 3 • Numerical Relay Architecture and Functions

Describes the hardware and software architecture of numerical relays including sampling, filtering, and processing. Numerical relays implement multiple protection functions in a single device.

Lesson 4 • IEC 61850 Standard for Substation Automation

Introduces the IEC 61850 data model, logical nodes, and communication services relevant to protection. GOOSE messaging enables high-speed peer-to-peer protection signalling without hardwired connections.