How to understand any electric drawings. Understand different ferrule and its meaning. Different symbols of electrical equipment.Remote operation circuit of a circuit breaker.

1. Understanding Electrical Drawings
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First step of understanding electric drawing of any equipment or panel is
understanding different symbols used for different equipment like C.T,
C.B,C.V.T,L.A, terminal block, Buzzer etc and next is understanding what ferrule
(tag) written on several wires mean. In the diagram shown below most of the
symbols of different equipment have been mentioned. Single line or three line
diagram can also be drawn using these symbols.

2. Understanding different ferrules :
Several wires run from control room to different equipment in the switchyard of a
substation to operate and monitor these equipment from remote i.e from the
control room. These wires are laid usually through underground cable trenches
.These wires are also tagged for identification as well as rectification of fault if any
, faulty cable or wire can be traced easily with name tags on it. Tags are also
called ferrule and they appear on wires as K1,C11,D33,U11,E31 etc .The first
Alphabet K,C,D,U,E etc of these tags have specific meaning and one can know for
what specific purpose they are being used.
Following is Ferrule numbering standards:
Ferrule “A” used for: CT circuit -Main Protection
Ferrule “B” used for : CT circuit -Busbar Protection
Ferrule “C” used for : CT circuit -Backup Protection
Ferrule “D” used for : CT circuit-Metering circuit
Ferrule “E” used for : PT circuit-Protection/Metering circuit
Ferrule “G” used for: PT circuit-Synchronizing
Ferrule “H” used for: Auxiliary AC circuit
Ferrule “J” used for: Auxiliary DC circuit
Ferrule “K” used for: Control circuit (DC)
Ferrule “L” used for: Alarm and Indication circuit
Ferrule “P” used for: DC circuit-Busbar Protection

3. Ferrule “S” used for: Event logger/SCADA/BCU circuits
Ferrule “U” used for: Spare Cont
Now that we have understanding of different symbols and ferrules ,let us try to
understand the diagram below which is of circuit breaker closing circuit from
remote i.e from control panel :
52 CB in the drawing below is a Circuit Breaker which is usua
switchyard and 195,295, 86 relays etc are housed in a control and relay panel
which is located in Control room.
From the diagram it is clear that +Ve DC supply for remote closing is taken from
Circuit breaker itself ,it first enters the panel in the terminal block(T.B) shown as
HV52TB4.03 , name of T.B is HV52TB4 and the wire connects in no.03 position of
this T.B. A terminal block looks like this and it is numbered serially from 1 to its
max capacity:
Ferrule “S” used for: Event logger/SCADA/BCU circuits
Ferrule “U” used for: Spare Contacts
Now that we have understanding of different symbols and ferrules ,let us try to
understand the diagram below which is of circuit breaker closing circuit from
remote i.e from control panel :
52 CB in the drawing below is a Circuit Breaker which is usually located in the
switchyard and 195,295, 86 relays etc are housed in a control and relay panel
which is located in Control room.
From the diagram it is clear that +Ve DC supply for remote closing is taken from
first enters the panel in the terminal block(T.B) shown as
HV52TB4.03 , name of T.B is HV52TB4 and the wire connects in no.03 position of
this T.B. A terminal block looks like this and it is numbered serially from 1 to its
Now that we have understanding of different symbols and ferrules ,let us try to
understand the diagram below which is of circuit breaker closing circuit from
lly located in the
switchyard and 195,295, 86 relays etc are housed in a control and relay panel
From the diagram it is clear that +Ve DC supply for remote closing is taken from
first enters the panel in the terminal block(T.B) shown as
HV52TB4.03 , name of T.B is HV52TB4 and the wire connects in no.03 position of
this T.B. A terminal block looks like this and it is numbered serially from 1 to its

4. From the mentioned T.B ,ferrule K310 is the wire which carries +Ve DC supply
ahead and it connects with the DC fuse shown as FS27-6A , after this fuse it
enters into protective relays -195,295 & 86 relay and then further to Trip and
Close (TNC) switch of the Panel. Only when the relay contacts of 86 HV ,86 LV
&195 is closed , +Ve DC supply will reach TNC switch terminal for closing the
breaker. When any relay is in operated condition, the relay contacts will open and
it will not allow DC voltage to pass through it and close the C.B. Therefore for
closing the C.B all relays should be reset. As soon as the +Ve DC voltage is
available on ferrule K314 , it will be available on one end of TNC switch, and when
this switch is moved to close position ,+Ve DC voltage reaches the closing coil in
the Circuit breaker which turns on the breaker. It is to be noted that trip and
closing coil of breaker is given -Ve supply at all times and +Ve supply is extended
through relays and TNC switch.
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