User`s guide

V3-T9-208 Volume 3—Power Distribution and Control Assemblies CA08100004E—November 2013 www.eaton.com
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9.4
Metering Devices, Protective Relays, Software and Connectivity
Protective Relays
Zone Selective Interlocking (Phase and Ground)
Note: For the phase time
overcurrent element, the current
sensed by the Digitrip 3000 must
exceed 300% (3 x I
n
) for the zone
selective interlocking to initiate an
immediate trip signal.
Zone Selective interlocking
is a protection function to
minimize equipment damage
resulting from a phase or a
ground fault in an area where
long-time and/or short-time
delay is in use.
When the “Ground Zone
Interlocking” feature is
utilized, an immediate trip
is initiated when the fault
is in the breaker’s zone of
protection, regardless of its
preset time delay. When the
“Phase Zone Interlocking”
feature is utilized, the time
overcurrent and short delay
phase elements work as
follows. The short delay
phase element will initiate an
immediate trip when the fault
is in the breaker’s zone of
protection, regardless of its
preset time delay. For the
time overcurrent phase
element, the current sensed
by the Digitrip 3000 must
exceed 300% (3 x I
n
) for the
zone selective interlocking
to initiate an immediate trip
signal when the fault is in the
breaker’s zone of protection.
Upstream Digitrip 3000
protected breakers are
restrained from tripping
immediately by an
interlocking signal from the
downstream Digitrip 3000
relay. This interlocking signal
requires only a pair of wires
from the downstream breaker
to the upstream breaker.
The Upstream Digitrip 3000
provides time delayed
standard coordinated
tripping when the fault is
located outside the zone
of protection.
In the sample zone
interlocking system shown
below, circuit breakers A, B
and C are equipped with
Digitrip 3000 overcurrent
relays.
Fault Location Zone 3
Note: For the phase time
overcurrent element, the current
sensed by the Digitrip 3000 must
exceed 300% (3 x I
n
) for the zone
selective interlocking to initiate an
immediate trip signal.
If a fault occurs at a point in
Zone 3, the Digitrip 3000 of
Downstream Breaker C
senses the fault and sends
a restraining signal to the
upstream Digitrip 3000 of
Feeder Breaker B.
Having received this signal,
the Digitrip 3000 of Feeder
Breaker B begins timing for
normal final delay tripping. As
a result, only Downstream
Breaker C is tripped.
Fault Location Zone 2
Note: For the phase time
overcurrent element, the current
sensed by the Digitrip 3000 must
exceed 300% (3 x I
n
) for the zone
selective interlocking to initiate an
immediate trip signal.
If a fault occurs at a point in
Zone 2, the Digitrip 3000 of
Feeder Breaker B senses the
fault and sends a restraining
signal to the upstream
Digitrip 3000 of Main
Breaker A.
The Digitrip 3000 of the
Downstream Breaker C does
not see this fault since it is
situated on the downstream
side of the fault. As a result,
the Digitrip 3000 of
Downstream Breaker C does
not send a restraining signal
to the Digitrip 3000 of Feeder
Breaker B.
Since there is no restraining
signal from the Digitrip 3000
of Downstream Breaker C,
the Digitrip 3000 of Feeder
Breaker B identifies that
the fault is in Zone 2 and
immediately trips Feeder
Breaker B, regardless of its
time setting.
Fault Location Zone 1
Note: For the phase time
overcurrent element, the current
sensed by the Digitrip 3000 must
exceed 300% (3 x I
n
) for the zone
selective interlocking to initiate an
immediate trip signal.
If a fault occurs in Zone 1, no
restraining signal is received
by the Digitrip of Main
Breaker A. As a result, Main
Breaker A is immediately
tripped by its Digitrip
overcurrent relay, regardless
of its time setting.
Sample Zone Selective Interlocking System
Main
Breaker
“A”
Feeder
Breaker
“B”
Downstream
Breaker
“C”
Interlocking
Wire
LOAD
Zone 1
Zone 2
Zone 3