Electrical Maintenance:  Relays II

TDRE2

Overview

The purpose of this unit is to continue the development begun in Relays 1 by introducing differential and pilot relays and discussing routine relay maintenance.  The relays examined are differential relays and pilot relays used for differential comparison, phase comparison, and transfer tripping. The unit demonstrates how to inspect and maintain relays and how to put them in and out of service. At the conclusion of this unit, trainees should be able to explain how differential and pilot relays work and give examples of situations where they are used. They should also be able to describe how to approach routine inspection and maintenance and how to put a relay in or out of service.

Objectives

Introduction to relays

• Identify five common relay elements.

• Identify the functions of overcurrent, directional overcurrent, reclosing, voltage, and auxiliary relays.

Differential relays

• Identify what differential relays typically protect.

• Describe the condition that causes a differential relay to operate.

• Describe the basic operating principles of differential relays.

Transfer tripping

• Describe the function of transfer tripping.

• Identify the main components of a transfer tripping system.

• Identify four communication channels used for transfer tripping and explain how they work.

• Identify the main equipment associated with transfer tripping communication channels and describe the function of each type of equipment.

Distance relays

• Identify what distance relays typically protect.

• Describe the condition that causes a distance relay to operate.

• Describe the basic operating principles of distance relays.

Pilot wire relaying

• Describe the function of a pilot wire relaying system.

• Identify the main components of a pilot wire relaying system.

• Describe the basic operating principles of a pilot wire relaying system.

Breaker failure relaying

• Identify the function and the main components of a breaker failure relaying system.

• Describe the general operation of a breaker failure relaying system.

• Describe the basic operating principles of a breaker failure relay.

• Describe the basic operating principles of a timing relay in a breaker failure relaying system.

Subjects

Introduction to relays

• Relay elements

• Plunger element

• Clapper element

• Induction disc element

• Induction cup element

• Solid-state circuitry

• Basic protective relay functions

• Overcurrent relays

• Directional overcurrent relays

• Reclosing relays

• Voltage relays

• Auxiliary relays

Differential relays

• Differential relay operation

• Current backfeed and differential relay operation

• Types of differential relays

• Differential relay with an induction disc element

• Differential relay with plunger elements

Transfer tripping

• Function of transfer tripping

• Transfer tripping example

• Communication channels and equipment

Distance relays

• Function of distance relays

• Zoned protection

• Construction and operation of a distance relay

Pilot wire relaying

• Pilot wire relaying system components and operation

• Pilot wire relay components and operation

Breaker failure relaying

• Breaker failure relaying system components and operation

Breaker failure relay components and operation

• Timing relay components and operation