Effective 11/2003
Page 15
I.L. 66A7535H02
Following a trip operation, push the
Reset/Battery Test
button, shown in Figure 1.1, to turn off the LEDs and reset
the trip unit.
3.2.1 Status/Long Pickup LED
The green Status LED will indicate the operational status
of the protection CHip A microprocessor of the trip unit.
Even with no external power present, if the load current
through the circuit breaker exceeds approximately 12 per-
cent (3 phase power) of the current sensor rating, the LED
will flash on and off once each second indicating that the
trip unit is energized and operating properly
(See Figure
3.1).
In an overload (Long Pickup) condition this status LED
flashes at approximately 4 times per second while the
overload persists.
3.2.2 Alarm LED
In addition to the green status LED, a yellow alarm LED is
provided to indicate real time alarm conditions existing on
the power system. See Appendix D-16 for the programing
of these alarms. Also, if an unusual condition is detected
within the Digitrip’s hardwire or firmware, this LED will light
along with an ALARM message.
3.2.3 Trip LED
The trip LED is illuminated upon any trip condition. It is
also a real time display and incorporates the breaker’s
Aux. Switch input for its logic. Pushing the Reset
pushbutton or closing the breaker will clear this LED.
3.3 Zone Interlocking
CAUTION
IF ZONE INTERLOCKING IS NOT TO BE USED (I.E.
ONLY STANDARD TIME-DELAY COORDINATION IS
INTENDED), THE ZONE INTERLOCKING TERMINALS
MUST BE CONNECTED BY A JUMPER FROM TERMI-
NAL B8 TO B9 OF THE BREAKER SECONDARY TERMI-
NALS SO THAT THE TIME-DELAY SETTINGS WILL
PROVIDE THE INTENDED COORDINATION.
Zone Selective Interlocking (or Zone Interlocking) is
available on the Digitrip 1150V for the Short Delay and
Ground Fault protection functions
(See Figure 3.1).
The
zone interlocking signal is wired via a single set of wires
labeled Zone In (Zin) and Zone Out (Zout) along with a Zone
Common wire. The Zone Selective Interlocking function
combines the interlocking of Short Delay and Ground
Fault. A zone out signal is issued if the ground fault pick-
3.0 PRINCIPLES OF OPERATION
3.1 General
The Digitrip 1150V trip unit is designed for circuit breaker
environments where the ambient temperatures can range
from –30
°
C to +85
°
C, but rarely exceed 70
°
to 75
°
C. If,
however, temperatures in the neighborhood of the trip unit
exceed 85
°
C, the trip unit performance may be degraded.
In order to insure that the tripping function is not compro-
mised due to an over-temperature condition, the Digitrip
1150V trip unit has a built-in over-temperature protection
feature, factory set to trip the breaker if the chip tempera-
ture is excessive. If over-temperature is the reason for the
trip the red “Long Delay Time” LED will flash and the Over-
Temp trip message will appear on the display.
The Digitrip 1150V uses an integrated circuit that includes
a microcomputer to perform its numeric and logic func-
tions. The principles of operation of the trip unit are shown
in Figure 3.1.
All power required to operate the current based protection
functions are derived from the CH Type-V current sensors
in the enclosure behind the circuit breaker.
(See Figure
1.4)
The secondary currents from these sensors provide
the correct input information for the protection functions, as
well as tripping power, whenever the circuit breaker is
carrying current. These current signals develop analog
voltages across the “current viewing” resistors. The
resulting analog voltages are digitized by the microproces-
sor.
The microcomputer continually digitizes these signals.
This data is used to calculate true RMS current values,
which are then continually compared with the protection
settings. The embedded software then determines whether
to initiate protection functions, including tripping the
breaker through the Trip Actuator (TA).
3.2 Trip and Operation Indicators
The LEDs on the face of the trip unit
(See Figures 1.1, 3.2
& 3.3)
flash red to indicate the reason for any automatic
trip operation. Each LED is strategically located in the
related segment of the time-current curve depicted on the
face of the trip unit. The reason for the trip is identified by
the segment of the time-current curve where the LED is
illuminated. Following an automatic trip operation and if the
auxilary power is not available, the backup battery contin-
ues to supply power to the LEDs as shown in Figure 3.1.
The LED pulse circuit, shown in Figure 3.1, is provided to
reduce battery burden and will supply a quick flash of the
trip LED approximately every 4 seconds. It is therefore
important to view the unit for at least 5 seconds to detect a
flashing cause of trip indicator.
