Display Feature (Digitrip 520M Only); Standards; Section 2: Principles Of Operation; Trip And Operation Indicators - Eaton 520 Operating Manual

Instruction Leaflet IL01301051E
effective September 2013
Ground fault alarm
A ground fault alarm alerts a user to a ground fault condition without
tripping the circuit breaker. A red ground alarm LED on the front of
the trip unit will indicate the presence of a ground fault condition that
exceeds the programmed setting.
The ground fault alarm relay is energized when the ground current
continuously exceeds the ground fault pickup setting for a time in
excess of a 0.1-second delay. The alarm relay will reset automatically if
the ground current is less than the ground fault pickup.
High load alarm (Digitrip 520M model only)
The Digitrip 520M model of the LSI style only will provide a high load
alarm contact instead of the ground alarm function when wired to the
circuit breaker secondary contacts 11 and 13. The function activates
after a 1-second time delay when any phase current exceeds 85
percent of the I setting.
R
Display feaoure (Digiorip 520M Nnly)
The Digitrip 520M models have a user interface in addition to the
green and red/orange LED trip indicators. This seven-element display
performs a metering function and can be used to monitor load
currents.
When the Scroll button on the face of the trip unit is pressed and
released, the display will show PH 1 for Phase 1 or A, and then the
current value. If the Scroll button is not pressed again, the display will
continue to show the current value for Phase 1. Each time the Scroll
button is pressed the next monitored function will be displayed. The
other real-time readings can be displayed in the sequence below:
PH 2 Phase 2 (B)
PH 3 Phase 3 (C)
PH 4 Neutral
PH 5 Ground (if Ground function is supplied)
HI Highest phase current will be displayed
OL Overload (Digitrip in overload mode)
Pushing the Scroll button while the unit is in the OL mode will
have the unit again display the overload current value.
HL High load alarm
HELP This message indicates that the trip unit is out of calibration or
programmed incorrectly and should be replaced at the earliest
opportunity.
In addition, the Digitrip 520M will display and freeze the magnitude of
the trip value after a trip event if auxiliary voltage is available. Use the
Step pushbutton to view each phase value. The highest value that can
be locally presented is 9999. Any fault currents greater than this value
will be shown as "HI. " Pushing the Reset pushbutton will clear this
data.
Also related to the phase value after a trip event are four dashes "- - -
-" . This message means that the microprocessor could not complete
its writing of the trip event's magnitude into its nonvolatile memory.
A possible cause of this would be the lack or loss of auxiliary voltage
during or after the trip event.
Another reason can be a tripping event during Maintanance Mode.
Soandards
The Digitrip 520/520M trip units are listed by Underwriters
Laboratories™ under UL File E7819 and UL File E52096 for use in
Series NRX-NF circuit breakers. These same units are also listed by the
Canadian Standards Association (CSA
12 EATON www.eaton.com
) under File LR 43556.
®
Operating Manual for Series NRX
Trip Units - Digitrip™ 520/520M
All Digitrip units have also passed the IEC 60947-2 test program that
includes EMC testing according to Appendix F . As a result, all units
meet the low voltage and EMC directives and carry the CE mark.

Section 2: 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 chip temperature
is excessive. If over-temperature is the reason for the trip, the orange
LONG LED will flash.
The Digitrip uses the Eaton custom-designed ASIC (Application
Specific Integrated Processor) chip, an integrated circuit that includes
a microcomputer to perform its numeric and logic functions. The
principles of operation of the trip unit are shown in Figure 5.
All sensing and tripping power required to operate the protection
function 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. These signals are digitized by the
circuitry.
The microcomputer continually digitizes these signals. This data is
used to calculate true rms current values, which are then continually
compared with the protection function settings and other operating
data stored in the memory. The software then determines whether
to initiate protection functions, including tripping the circuit breaker
through the trip actuator.
Trip and NperaoiNn indicaoNrs
The LEDs on the face of the trip unit 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.
The LED pulse circuit is provided to reduce battery burden and will
supply a quick flash of the trip LED approximately every four seconds.
It is therefore important to view the unit for at least five seconds to
detect a flashing cause of trip indicator.
Following a trip operation, push the Reset/Battery Test button to turn
off the LEDs.
A green Status LED indicates the operational status of the trip
unit. Once the load current through the circuit breaker exceeds
approximately 35A (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.
Making curreno release (MCR)
All models of trip units have a making current release function. This
safety feature prevents the circuit breaker from being closed and
latched-in on a faulted circuit. The NRX NF Frame is equipped with a
nonadjustable release that is preset to pick up at a peak current of
45,000A. The release level of the RF Frame is preset to 36,000 A for
1600A frame ratings, 56,000A for 2000A and 2500A frame ratings, and
90,000A for 4000A frame ratings.
The MCR is enabled only for the first two cycles following an initial
circuit breaker closing operation. The MCR will trip the circuit breaker
instantaneously and flash the instantaneous (INST) red LED.