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EATON
www.eaton.com
Section 4: Principles of operation
General
All models of trip units are designed for industrial circuit
breaker environments where the ambient temperatures can
range from –20°C to +85°C but rarely exceed 70°C to 75°C. If,
however, temperatures near the trip unit exceed this range,
the trip unit performance may be degraded. In order to ensure
that the tripping function is not compromised due to an over-
temperature condition, the microcomputer chip has a built-in
over-temperature protection feature, factory set to trip the
circuit breaker if the trip unit temperature is excessive. If over-
temperature is the reason for the trip, the LONG LED will flash
on and off with an orange color.
The Digitrip uses an integrated circuit that includes a Digital
Signal Processor (DSP) to perform its numeric and logic
functions. A block diagram of the major components of
operation of the trip unit are shown in
Figure 8
.
All sensing and tripping power required to operate the current
protection functions is derived from the current sensors in
the circuit breaker. The signals from these sensors provide the
correct input information for the protection functions, as well as
tripping power, whenever the circuit breaker is carrying current.
The DSP microcomputer continually digitizes the signals from
the sensors even when the circuit breaker is open. This data is
used to calculate the true RMS current values, which are then
continually compared with the protection function settings and
other operating data stored in the memory. The trip unit then
determines whether to initiate protection functions, including
tripping the circuit breaker using the trip actuator.
Trip and operation indicators
The LEDs on the face of the trip unit, shown in
Figure 12,
flash red or orange to indicate the reason for any automatic trip
operation. Following an automatic trip operation, the backup
battery continues to supply power to the LEDs. An LED pulse
circuit is provided to reduce battery burden and will flash a trip
LED approximately once every four seconds. It is therefore
important to view the unit for at least five seconds to observe a
flashing cause of trip indicator.
Following a trip operation, push the Reset/Battery Test button to
turn off the cause of trip LED.
A Status LED, shown in
Figure 12,
indicates the operational
status of the trip unit. Once the load current through the circuit
breaker exceeds approximately 50A (NF Frame) or 100A (RF
Frame) three phase power, the green LED will flash on and off
once each second to indicate that the trip unit is energized and
operating properly.
Note:
A steady green STATUS LED typically indicates a low level
of circuit breaker load current indicating that the trip unit is not fully
powered up.
Alarm LED
An orange Alarm LED is provided to indicate real-time alarm
conditions are existing on the power system. See
Appendix
D: Display, Indicators and Menus
for the programing of these
alarms. If an unusual condition is detected within the Digitrip’s
hardware or firmware, this LED will light with a message on the
display indicating the type of alarm.
Effective September 2013
Instructional Leaflet IL01301064E
Operating Manual for Series NRX
Digitrip Trip Units 1150 / 1150i
PT
Module
Com
Com
+
24 V dc
–
+
24 V dc
–
Analog
Circuits
Voltage Signals
Figure 8. Block Diagram With Breaker Interface