Answer / kamal ghasemi

When the line isolator is open and the voltage from cvt to
distance relay is absent and the bus isolator and breaker
are closed; if a fault occurs between the line isolator and
the ct a feature in dist. relay called stub protection
which is an instatanious none diretional oc relay sends
trip command to breaker.This is usually in test and service
conditions.

Answer / vishvajeet sharma

above written is right, one more thing stub protection will
be active only when it get the status of line isolator as
open.

Answer / furqan ahmad

stub protection is used to protect the part of one and half breaker scheme which is not protected by distance protection.
it is active only when line isolator is open, and there is no voltage from cvt for distance protection.it is an over current relay which sense the fault and trip bus breaker under such condition.

Answer / abdelrahman hussein

The stub bus element protects for faults between two breakers in a breaker-and-a-half or ring bus configuration when the
line disconnect switch is open. At the same time, if the line is still energized through the remote terminal(s), differential
protection is still required (the line can still need to be energized because there is a tapped load on a two-terminal line or
because the line is a three-terminal line with two of the terminals still connected). Correct operation for this condition is
achieved by the local relay sending zero current values to the remote end(s) so that a local bus fault does not result in
tripping the line. At the local end, the differential element is disabled and stub bus protection is provided by a user-selected
overcurrent element. If there is a line fault, the remote end(s) trips on differential but local differential function and the DTT
signal (if enabled) to the local end are blocked by the stub bus logic, allowing the local breakers to remain closed.

Answer / m.balaji

When the line isolator is in open condition in between ct &
line isolator protection is called stub protection.when the
line isolator open condition then only stub protection enable,
if it's line isolator closed protection it will not check
distance protection relay operation required voltage so that
without voltage it will not operate ,so that time going to
fourth stage of over current it will happen only at the time
of ct saturation (or) surge.

Answer / anil

The above said is dead zone protection not stub

Answer / m. usman ali

During a line open condition with the station breakers
closed, the bus between the station breakers and line
disconnect for ring bus and breaker and a half/third
configurations may not be protected. The line protection
system shall be capable of protecting the open stub through
the use of overcurrent protection. This protection shall
also function correctly for the case where the potential
transformers for the line protection are located on the
line side of line disconnect whether or not the line is
energized from the remote end.

Answer / saadiq

STUB PROTECTION IS USED AGAIST THE POSSIBLE FOR THE
UNPROTECTED ISOLATOR WITH EARTH SWITCH ( WHICH IS BEYOUND
CT)

Answer / engr.irfan sajid

In one and half circuit breaker scheme,when the bus bar side
CB opened ,the area between central/tie breaker and bus bar
side breaker is called stub area where only voltages are
available but no current flowing i.e tee branch.When a fault
occurs in this area the over current element of bus bar
protection activated which after time delay i.e 100ms, trip
the central breaker and also send direct transfer trip
signal to remote end feeder to isolate the faulty area.

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