Page 333 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Nut and bolt connectors are of two types

Nut connector
This is in Fig 9. It has a transverse hole through which the conductors to be joined are inserted and then tightened
by the bolt.

Split bolt connector: This is in Fig 10. It is split at the stem. The conductors to be joined are to be inserted into
the split and then tightened by the external nut.

Fig 9 Fig 10

Types of relays and its operation

Objectives: At the end of this lesson you shall be able to
• state the classification of relays
• list the types of relays and their uses
• explain the principle of operation of over current, differential, earth fault, distance and non directional relays
• state the characteristics of relays
• explain the principle of operation of a over voltage under voltage relay
• state the necessity of time multiplier setting of relay.

Introduction

The relays is the element that senses as abnormal condition in the circuit and commands the operation of the
breaker. It interpret the fault quantities ie, CT output current and PT output voltage and sending the command to
the tripping circuits of breaker for operation in accordance with the characteristic set in the relay and the value of
the time multiplier setting.
Classification of Relays
Relays are classified mainly in three categories; they are according to:

1 Quantity sensed: Current, Voltage, active power, reactive power & impedance
2 Tripping: Instantaneous trip, delayed trip inverse time response and definite time
3 Operating principle: Electro magnetic relays, Induction relays, Thermal relays and static or digital relays
Types or relays: Various types of relays are used as per the requirement; they are:

1 Over current relay
2 Over voltage relay
3 Under voltage relay
4 Differential relay
5 Earth fault relay

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CITS : Power - Electrician & Wireman - Lesson 106-116