Core Balance Transformer
The Core balance current transformers are intended
for providing earth leakage protection on 3-phase
In insulated or compensated neutral networks, earth
leakage currents are small and generally very much
less then the nominal load current. Such earth leakage
current should not be allowed to exist for long
periods of time, since eventually it leads to insulation
failure on the healthy phase and subsequent
development into phase to phase or double to earth
faults, to protect cable circuits and also overhead
transmission line with cable transmissions, core
balance current transformers are commonly employed.
Core Balance current transformers are manufactured
with one core and one secondary winding. The no.
of secondary turns does not need to related to the
cable rated current because no secondary current
would flow under normal balanced conditions. This
allows the no. of secondary turns to be chosen such
as to optimize the effective primary pick-up current.
Core Balance Current Transformers are used with
suitable relays for the earth leakage protection
purposes. C.B.C.T. encircles a 3 Phase, 3 core cable
or 3 single core cables. During healthy conditions
i.e. when there is no earth leakage current, the
secondary of C.B.C.T. does not carry, any current
as there is no magnetic flux in the core. In the
event of occurrence of earth leakage an unbalance
current sets up flux in the core of the C.B.C.T.
and current flows through the secondary winding,
causing the relay to operate.