DET-653C
EntelliGuard
®
G Circuit Breaker Application Guide
24-May-12
Section 3. EntelliGuard
®
TU Trip Unit System
©2012 General Electric All Rights Reserved
24
Reduced Energy Let-Through Switch Wiring
The RELT switch may be connected to a manually operated
two-position switch, a remote sensor, or both
simultaneously. The EntelliGuard TU trip unit provides a
feedback capability directly from the trip so the user is able
to verify that the signal was received by the trip unit and the
settings have changed. Optionally, an indicating light may
also be connected to the source of control power so the user
knows if control power is available to change the setting.
The trip unit does not require its own control power to
accept a RELT input and change the Instantaneous trip
pickup according to the user settings. However, if control
power is available to the trip unit, the feedback signal will
function immediately, rather than when the trip unit
becomes self-powered through its load current (Fig. 3.10).
Figure 3.10. Integrated Switch and LED, Spring Return
from “Test” to “Off,” Latched in “On”
•
This configuration provides positive indication that the trip unit has
received and processed the RELT "On" signal. It Also provides a control
power check. Caution: It is recommended that RELT output be wired to
an appropriate annunciation when remote activation control of RELT is
used.
NOTE: When using the RELT function in conjunction with
remote enable/disable control, it is strongly recommended
that the trip unit be provided with permanently connected
control power and that the RELT status output be assigned
to a trip output contact. The trip output contact should be
wired to appropriately located annunciation. The trip unit will
accept a command to enable the RELT instantaneous pickup
setting via local HMI control, a 24Vac/dc voltage applied at
the input terminals or serial communication. Regardless how
the enable command is received, the trip unit will be in the
RELT mode when protection is required. However, the status
indicating contacts will only close if the trip unit is powered
through the internal current transformers or 24Vdc control
power. Lack of 24Vdc control power could provide unreliable
indication of RELT status due to low load conditions on the
circuit breaker.
Zone Selective Interlocking (ZSI)
The EntelliGuard TU trip unit’s ZSI capability differs from that
found in other circuit breaker trips in two significant ways:
1. It allows independent and separate settings of the
unrestrained (in zone protection) and the restrained
(back up protection) bands.
2. It provides simultaneous and independent ZSI of both
the Short Time and Instantaneous protection. This
allows each circuit breaker to zone interlock with upper
tier circuit breakers between ST band to ST band,
Instantaneous to Instantaneous, or Instantaneous to
Short Time.
The EntelliGuard TU trip unit's fast ZSI system is able to
interlock Ground Fault, Short Time and Instantaneous. When
required for feeder selectivity the main is able to be set
faster than the feeder without any sacrifice in selectivity. As
long as the main breaker's pickup is set above the feeder's
pickup the two devices will remain selective. Each circuit
breaker in a ZSI scheme allows separate user settings for
the restrained (backup) and unrestrained (in zone
protections) for ground fault and short time protection. For
the lowest tier device in the scheme the restrained and
unrestrained are set to the same values. For instantaneous
protection there is only one pickup setting required.
Instantaneous protection may also be interlocked such that
all circuit breakers above the one whose zone has the fault
will shift from Instantaneous clearing to a 0.058msec time
band. Since it is expected that faults of enough magnitude
to engage the Instantaneous pickup are dangerously high,
all zone selective interlocked Instantaneous trips that
receive a restraint signal are shifted to the same band.
Should the bottom circuit breaker fail to clear for whatever
reason, quick back up protection from both ties and feeders
is provided.
Short Time and Ground Fault bands for zone interlocked
circuit breakers may be set to any band available to the trip.
Figure 3.11 shows two circuit breakers set to protect at their
unrestrained settings. Figure 3.12 shows the same two
circuit breakers while a fault is detected below the lower
circuit breaker in the system and after a restraint signal is
received by the upper circuit breaker’s trip unit. The upper
circuit breaker’s Short Time band has shifted from the user
setting of 0.025sec to a user set restrained band of 0.092sec.
The Instantaneous has shifted from the adjustable selective
Instantaneous band clearing in 0.050sec to the fixed
restrained band of 0.058sec, clearing in 0.113sec. This allows
the lower circuit breaker to clear faults within their zone of
protection above 7,000A RMS and 11,000A RMS respectively,
clearing under 100msec, while maintaining full selectivity for
faults up to 85,000A.