Answer / hari

If u have the fault mva and the voltage level at which the
CB is to be installed then :
Normal current would be the continuous current flowing in
the line ( u can take the next higher value from standard
values to take care of over current)
Breaking capacity would be tha fault MVA.
Rated symmetrical breaking current in kA would be Fault
MVA*1000/(1.732x Voltage in kV)
Rated making ct would be peak value of symmetrical breaking
current i.e 2.55 times breaking current
Short time rating would be rated symm breaking ct for 3 secs

Answer / ravi kumar singh

Breaking capacity will be always iN MVA= 1.732*Voltage in KV * cerrent in KA

making capacity = 2.55 * symmetrical breaking capacity


note:-( 1.41*1.8=2.55)

full load current= 1.8 * KVA


ravi kumar singh

Answer / nighot jagdish

Rated symmetrical breaking current in kA would be Fault
MVA*1000/(1.732x Voltage in kV

Answer / karthik

BREAKING CAPACITY OF CIRCUIT BREAKER
=SQRT(3) x V x I x 10-6
V is supply voltage
I is circuit breaker capacity
answer appears in MVA.

Answer / usama badran ali

el salamo aleekom

to calculate circuit breaker breaker capacity...there are
four steps :
1-indicate all actual nominal voltages and MVA of your
system
2-indicate the location of circuit breaker.
3-calculate the actual impedance between the known supply
to the point of fault at which near to circuit breaker.
4-then calculate:
a- short circuit current =
voltage of supply/((3^0.5)actual impedance)
b-MVA short citcuit=
(3^0.5)*voltage of supply*short circuit current
c c-breaking capacity=
MVA short citcuit*assymetry factor.
or
short circuit current*assymetry factor
notes:
Assymetry factor:1.5~1.6 for midium voltage
1.25 for low voltage
MVAshort circuit= fault level
breaking capacity: it is the value of peak current where
the circuit breaker is breaking.

Answer / s.venkatesh

we can consider circuit breaker capacity for particular
feeder depend upon the 1.2 times of full load current for
receiving end equipments

Neutral CT for 45MVA 132/11 KV YNd11 Transformer. NCT REF CLASS-PS or 5P20 with 20VA burden which is suitable.

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