Protection symbols used in circuit diagrams

-,' ..... , Fuse Control or selector switch t . . . . . I

- tW i O - Link - readily separable T N C Note: the position of the I I I rectangle represents the

contact -O I lIT]O-- position in which the I I I circuit is completed

Link - bolted contacts -O[]]1 I O - between the associated terminals

- O ~ ~ Link - hinged or sliding /

- plug-in type [~] Circuit breaker Link !

' - " >-- Plug and socket t

Auxil iary switch or relay ~ Circuit breaker normally contacts " [ " open

-~_ O- Make contact

Break contact ,~ Withdrawable metal-clad

"qD_..A O-- Make contact with delayed ~ circuit breaker make

Break contact with delayed ~/ Switch disconnector break I

Changeover contact ]

Push button switches J Centre rotating post disconnector

O . O Make contact I . . .a t . ,

Break contact

Telephone type relay contacts

Make contact unit

j . Break contact unit

Changeover (break before make) contact unit

Changeover switch break before make

Make contactor

Mechanical coupling

~#~ _~ Example - double pole contactor

Indirectly-heated bimetallic thermal element

_..f3r"v'X._ Operating coil for contactors and relays - general

Coil with flag indicator

Series coil

Machine windings General and shunt

..../'W"V'X._ Series

AC generator

Motor

Core (/./'desired to indicate)

_t-v'v'v-x_ Transformer or reactor winding

Protection symbols used in circuit diagram,

I Single-break disconnector or earth switch

I Additions to symbol for , power-operated

disconnector: NA - Non-Automatic

N~A A - Automatic

I '~] Fault throwing switch

Summation current transformer

Power and voltage transformers

Two winding

Simplified form

3 Auto-transformer

Simplified form - with delta tertiary

Transductor

) c Spark gap

- ~ gas d~scharge Protective tube

l Capacitor T

Power system protection

Current transformer

Current transformer with tapping

~ ~ Interposing transformer current or voltage Fixed resistor

- ~ Variable resistor

Resistor, with non-linear current/voltage characteristic

Impedance

Impedance, with non-linear current/voltage characteristic

Earthing resistors h

~.j Dry type

Liquid type

Arc suppression coil

] Earth m

- -~ Rectifier

cF_r_q~ri_~i-coupling equipment Line I

' z To carrier equipment

Fault

t ~ pn diode or semiconductor ~__~ rectifying diode

Zener diode

Thyristor

@ pnp transistor

npn transistor

t Envelopes may be omitted

Thermionic valve, triode, indirectly heated

(~ Cold cathode discharge tube (e.g., neon lamp)

- ~ Cold cathode trigger tube

O Coaxial line I'~ ~ Cable sealing ends t J "-q

+ ->-

33_

Rectifier equipment in bridge connection

Amplifier

Buchholz - single float

Buchholz - two float

Winding temperature single switch

Winding temperature double switch

High speed ammeter

Alarm flag relay

Trip flag relay

Relay - general symbol

Feeder protection

Power line carrier phase comparison protection

Distance protection

High speed distance (Mho) protection

Electric bell

Signal lamp

Protecthgn

G symbols used in circuit diagrams

Electromotive force (emf)

Private pilot protection

Post Office pilot protection

Transformer protection

Biased differential protection

Plain balance differential protection

Transformer HV connection protection

Circulating current

Busbar protection

Mesh corner protection

High speed auto-close relay

Overvoltage relay

High speed distance (reactance) protection (inverse definite minimum time)

Three-pole overcurrent re!a.y (inverse definite minimum time

Two-pole overcurrent and single pole earth fault re!ay.se (inverse definite minimum time)

Powersystemprotection

m One-pole overcurrent relay (inverse definite minimum time) Earth-fault relay (inverse definite minimum time)

Three-pole two stage overcurrent relay (inverse definite minimum time)

Three-pole directional overcurrent relay (inverse definite minimum time)

Three-pole overcurrent relay (instantaneous)

Three-pole overcurrent relay (extremely inverse definite minimum time)

Earth-fault relay (instantaneous)

Three-pole high set overcurrent relay

Standby earth-fault relay (long time inverse definite minimum time)

Two-stage standby earth-fault relay (long time inverse definite minimum time)

Reverse power relay

Restricted earth-fault relay

7q Tripping relay Intertrip relay

Intertrip relay (send)

Intertrip relay (receive)

Definite time relay

Negative phase sequence

Lost excitation

Three-pole voltage-controlled overcurrent relay (inverse definite minimum time)

Three-pole overcurrent interlocked relay (inverse definite minimum time)

Breaker fail current check

LV connection protection

Front MatterTable of ContentsProtection Symbols Used in Circuit DiagramsIndexABCDEFGHIJKLMNOPRSTUVWZ