Electrical Symbols and 1 Standards -...
Transcript of Electrical Symbols and 1 Standards -...
1.1 NEED OF ELECTRICAL SYMBOLS
Drawing is the language of engineers. For proper communication people must use the same language so that a particular word or symbol means the same thing to every one. In engineering drawing it is common practice to employ graphical symbols to denote the various accessories used. These symbols must convey the same meaning to everyone who reads the drawing. Symbols are, therefore, standardized by the Bureau of Indian Standards (BIS), as far as possible according to internationally agreed conventions as adopted by the International Electrotechnical Commission.
An important consideration in selecting symbols is that they should be, as far as possible, self explanatory and easy to draw.
It must be realized that even though the Bureau of Indian Standards has standardized the symbols for nearly all accessories/components used in the field of electrical engineering, these symbols are not yet universally used. Therefore, it is possible that the reader may come across, in other books, different symbols from the ones used in this text. However, in an attempt to encourage standardization, symbols approved by the Bureau of Indian Standards (BIS) have been used in this text. The reader is advised to make it a habit to refer to the Indian Standard Specifications to ensure the correctness of a symbol. IS: 2032 gives a list of standard symbols.
1.2 LIST OF SYMBOLS
1.2.1 Kind of Current
Direct current — Alternating current Power frequency Apparatus and machines suitable either for d.c. or a.c. (universal)
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1.2.2 System of Distribution
a.c. of m-phase and frequency m fExample
( ) a.c., single phase, 50 Hz 1 50 Hz
(b) a.c., three-phase, 50 Hz 3 50 Hz
(c) a.c., three-phase, 50 Hz, 415 V 3 50 Hz, 415 V
NeutralExample
(a) a.c., three-phase, with neutral, 50 Hz 3N 50 Hz
(b) a.c., three-phase, with neutral, 50 Hz 3N 50 Hz, 415 V
415 V (240 V between phase and neutral)
d.c. two conductors 110 V 2 — 110 V
d.c., three conductors, including neutral,220 V, (110 V between outer conductors
2N — 220V
and neutral)
Positive polarity +
Negative polarity –
1.2.3 Symbols of Lines
Line or cable: existing —
planned
Underground cable
Overhead line (general symbol)
1.2.4 Conductors
Conductors or a group of several conductors —
Flexible conductor
Note: Use one or several half circles reversely drawn; two half circles are never to be used because of a possible confusion with symbol for alternating current.
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Two conductors:
(a) Single line representation
(b) Multiline representation
Three conductors: (a) Single line representation
(b) Multiline representation
n conductors: n
ExampleFour conductors:
Single line representation 4
Multiline representation
Indication of conductor particulars (a) Example: d.c. circuit, 110 V, two conductors of 125 mm2 of aluminium
Single line representation – 110 V2 × 125mm A2
Multiline representation – 110 V
2 × 125mm A2
(b) Example: d.c. circuit 220 V (110 V between outer conductors and neutral), two conductors of 50 mm2 with neutral of 25 mm2
Single line representation 2N – 220 V
2 × 50mm + 1 × 25mm2 2
Multiline representation 2N – 220 V
2 × 50mm + 1 × 25mm2 2
(c) Example: Three-phase circuit 50Hz 6 kV, three conductors of 50 mm2
Single line representation 3 50 Hz, 6 kV3 × 50mm2
Multiline representation 3 50 Hz, 6 kV
3 × 50mm2
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(d) Example: Three phase circuit, 50 Hz 3 conductors of 125 mm2 with neutral of 50 mm2:
Single line representation 3N 50 Hz3 × 125mm2 + 1 × 50mm2
4
Multiline representation 3N 50 Hz
3 × 125mm2 + 1 × 50mm2
Changing over from a single line 4
4Or representation to a multiline
representation.
Example: Four conductors Group of n conductors which n follow the same way on the diagram.
1.2.5 Terminals and Connections of Conductors
Terminal OR
Junction of conductors
Double junction of conductors Or Or
Crossing without electrical connection
Crossing and connecting conductors
Single line representation
Multiline representation
1.2.6 Circuit Elements
Non-reactive resistance or non-reactive resistor R
Impedance Z
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Inductance, inductor L
Winding
Capacitance, capacitor
Note: The distance between the plates should not be greater than one-fifth of the length of the plates.
Earth
Frame or chassis connection
Frame or chassis earth connection
Fault
Example: Position of fault to frame
Screen – – – – – – –
Example: Screened conductor or screened cable
Magnetic core
Laminated core
1.2.7 Variability
Note: (a) Variability is ‘inherent’ when the variable quantity depends on qualities
of the device itself, for example, when the resistance changes with the change of voltage or with change of temperature.
(b) Variability is ‘non-inherent’ when the variable quantity is controlled by an external device, for example, when the resistance is controlled by a regulator.
(c) The sign of variability should be drawn across the main symbol at about 45° to the centre line of the symbol.
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Examples of variable resistors
(a) General symbol
(b) Continuously variable
(c) Variable in steps
(d) With moving contact (general symbol)
(e) With moving contact continuosly variable
(f ) With moving contact, variable in steps
(g) Voltage divider with moving contact
1.2.8 Rotating Machines
Mechanically coupled machines:
d.c. two wire series generator (G) Mor motor (M)
d.c. two wire generator (G) or G motor (M), separately excited.
d.c. two wire shunt generator (G) M
or motor (M),
d.c. two wire generator (G) or
Gmotor (M), compound excited,short shunt
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Symbol showing terminals, brushes and numerical data:
G 240V
30kWExample: d.c. two wire generator, compound excited, short shunt, 240V, 30 kW
a.c. series motor single phase M1
a.c. series motor three phaseM
3
Synchronous generator (GS) or synchronous motor (MS) single-phase.
GS1
Synchronous generator (GS) or synchronous motor (MS), three-phase, star connected, neutral not brought out.
GSY
Synchronous generator (GS) or synchronous motor (MS), three-phase, star connected, neutral brought out.
GSY
Synchronous generator (GS) or synchronous motor (MS), three-phase, both leads of each phase brought out.
GS
Or
GS
GS
Or
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Symbol showing terminals, brushesand numerical data:
Example: Synchronous Generator 6600 V1000 kVA, 50Hz
120 V–GS(GS) or synchronous motor (MS), three-phase, both leads of eachphase brought out, 6600 V, 1000 kVA,50 Hz, 120 V d.c.
Induction motor, Squirrel cage M1single-phase.
Induction motor, squirrel cage, M1single-phase, leads of split phase
brought out.
Induction motor, squirrel cage, Mthree phase delta connected.
Induction motor, three phase, M3
Or
M3
squirrel cage, both leads of eachphase brought out.
Induction motor, three-phase, M3wound rotor.
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1.2.9 Transformers
single line representation
multiline representation
Single phase transformers, with two- or three-phase windings:
11000 V250 KVA
50Hz4%
415VExample: 11,000/415 V, 250 kVA, 50Hz short circuit voltage 4%
Three phase transformer with two separate windings:Example: Star delta 6600/1100 V, 4000 kVA, 50 Hz. Connection Y d 11
Y
6600V4000KVA
7.5%YD11
11000V
50 Hz
Short circuit voltage 7.5%
Auto–transformer: single line representation
multiline representation
(a) Auto-transformer, single-phase.
(b) Auto-transformer, three-phase, star connected.
(c) Auto-transformer, single-phase, with continous voltage regulation.
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1.2.10 Switchgear
Switch-general symbol
(a) Two way
(b) Intermediate
Three-pole switch, multiline representation
Three-pole switch, single line representation
Circuit breaker
Isolator
Terminal strip 11121314 15 11121314 15
Link
Open link
Distribution board cubical box
1.2.11 Contacts
Socket
Plug
Plug and socket
Relay or contactor contact, normally Oropen (NO)
Relay or contactor contact normally Or
closed (NC)
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Push-button with momentary closed
Orcontact (normally open contact)
Push-button with momentary open
Orcontact (normally closed contact)
Thermal overload relay contact
Time-delay relay contact
Limit switch (NC contact)
Limit switch (NO contact)
Or
1.2.12 Relays and Contactors
Coil of electro-magnetic relay or contactor
Thermal overload relay
Electrically operated three-pole contactor
Electrically operated three-pole contactor with thermal overload device in all three-poles
Time delay relay (TDR)
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1.2.13 Fuse-boards
Lighting circuit fuse-boards: (a) Main fuse-board without switches
(b) Main fuse-board with switches
(c) Distribution fuse-board without swithces
(d) Distribution fuse-board with switches
Power circuit fuse-boards: (a) Main fuse-board without switches
(b) Main fuse-board with switches
(c) Distribution fuse-board without switches
(d) Distribution fuse-board with switches
1.2.14 Switch and Switch Outlets
One way switch (a) Single pole
(b) Two-pole
(c) Three-pole
Two-way switch
Intermediate switch
Push-button or bell-push
1.2.15 Socket Outlets
Socket outlet, 5 A
Socket outlet, 15 A
Combined switch and socket outlet, 5 A