Answer / perservance

it is used for earth fault protection,this kind of C.T
covers all the phases ,the secondary side of it is
connected to trip coil of CIRCUIT BREAKER.Under no fault
conditions the vector sum of all the three phase currents
is zero so no output to c.t secondary but when there is a
earth fault ,the sum would not remain zero and the trip
coil would act and circuit breaker would trip.
the disadvantage being that it would not detect phase to
phase fault,seldom used,not seen anywhere in my plant.

Answer / veerachary

CBCT stands for Core balance current transformer, it is
used in Main incommer pannels as of my experience.

Answer / sarbani

Core balance CT (CBCT): The CBCT, also known as a zero sequence CT, is used for earth leakage and earth fault protection. The concept is similar to the RVT. In the CBCT, the three core cable or three single cores of a three phase system pass through the inner diameter of the CT. When the system is fault free, no current flows in the secondary of the CBCT. When there is an earth fault, the residual current (zero phase sequence current) of the system flows through the secondary of the CBCT and this operates the relay. In order to design the CBCT, the inner diameter of the CT, the relay type, the relay setting and the primary operating current need to be furnished.

Answer / maharajan

CBCT is core balance c.t it is used at where we could not
use earth.because at balance condition Ir+Iy+Ib=0 when
balance will be distrube current will be induced in cbct
secondary.

Answer / abhishek singh

Core balance CT (CBCT): The CBCT, also known as a zero
sequence CT, is used for earth leakage and earth fault
protection. The concept is similar to the RVT. In the CBCT,
the three core cable or three single cores of a three phase
system pass through the inner diameter of the CT. When the
system is fault free, no current flows in the secondary of
the CBCT. When there is an earth fault, the residual current
(zero phase sequence current) of the system flows through
the secondary of the CBCT and this operates the relay. In
order to design the CBCT, the inner diameter of the CT, the
relay type, the relay setting and the primary operating
current need to be furnished.

Answer / parthsharathi

cbct is core balance current transformer it for earthfault .
sum of all phases zero it ok, if any difference . So trip bkr

Answer / guru

first time i seen this core balance current transformer from mcc panel. all output cables from through via this cbct. because any earth fault occurs, this cbct generate a current and give to earth fault relay. this relay automatically switch off a rccd breaker.

Answer / srinivasan rengarajan

it is used for sensitive earth fault protection , especially when the feeder CT ratio is very large & max EF current to be sensed is very low as much as 5A or 10A.. This kind of C.T namely ring type CT encompases all the phase cables ,the secondary side of it is
connected to a sensitive EF relay, whose contact will in turn be connected to trip coil of CIRCUIT BREAKER.Under no fault
conditions the vector sum of all the three phase currents
is zero; so no output to c.t secondary but when there is an
earth fault ,the sum would not remain zero (it would be 3 I0- namely 3 times Zero phase sequence currents) and the trip
coil would act and circuit breaker would trip.
The fact that it would not detect phase to
phase fault,is not a disadvantage, because the very purpose of CBCT is that it is specifically designed for sensitive earth faut protection or earth leakage protection.

Answer / sakka

cbct is very good device. i shall be very thankfull to who invent cbct.
thank u,
your obediently
yatin shah

Answer / lola pondu

cbct is used to protect the system from earth fault or leakage earth current. Three phases cable passes through the inside the cbct and secondary of cbct connected to the earth fault relay.Under normal condition the vector some of three phases current will zero & while earth fault or leakage occurring the current will passes through the secondary of the cbct which sensed the relay and trip the breaker for protection.

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