GE Industrial Solutions EntelliGuard TU Trip Units - Manual (Page 24)

EntelliGuard TU Trip Units: UL/ANSI Models DEH-4567B
Protection
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The serial register indicating the state of the Current Alarm
will assume a value 1 when the alarm is triggered, and a
value of zero if the alarm is cleared. If a digital output is
mapped to the Current Alarm, it will be open if the alarm is
clear, and closed if the Current Alarm is active. The alarm
indications do not latch; they follow the state of the Current
alarm.
ZONE SELECTIVE INTERLOCKING
Zone -selective interlocking coordinates breakers so that
the downstream breaker is allowed the first opportunity to
clear a fault or overload event.
The optional Zone Selective Interlocking (ZSI) function
operates with a group of series-connected breakers. ZSI is
achieved with the use of the TIM1 module or an equivalent
GE qualified and recommended device.
There are two sets of settings in a breaker used in a Zone
Selective Interlocking system. The normal or “unrestrained”
setpoints are the main over current protection setpoints. A
second set of ZSI or “restrained” setpoints are included for
each interlocked protection element – GF, ST, and
Instantaneous.
If a protection element, such as Ground Fault, goes into
pickup and the Zone Selective Interlock input is active, the
“restrained” or ZSI settings will be in effect. If the Zone
Selective Interlock input is not active when the GF element
enters pickup, the normal or unrestrained GF pickup
setpoints will be effect.
If the Zone Selective Input goes off while the restrained
settings are in effect, they will remain in effect for 50
milliseconds. After that, the unrestrained settings will go
into effect.
Unrestrained, normal mode ST setpoints: If
the trip unit enters Short Time pickup and the
ZSI input is OFF, these settings are in effect. In
a ZSI configuration these settings are
optimized for protection of the cable/bus
directly below the breaker, and not for
selectivity with downstream breakers.
Restrained settings: If the trip unit enters
Short Time Pickup and the ZSI input is ON,
these settings are in effect. This setting is
intended to provide selectivity with the
downstream breaker, so it will typically be set
longer, to give the downstream breaker a
chance to clear the fault.