17
Instructional Leaflet
IL70C1037H05
Effective October 2009
Digitrip models 520, 520i; and 520M, 520Mi,
520MC, 520MCi trip units for use only in
Magnum and Magnum DS circuit breakers
eaton corporation
www.eaton.com
Currtno stnsNrs (Magnum soandard framts)
The three (three-pole) or four (four-pole) primary current sensors are
installed internally in the circuit breaker on the lower conductors of
the breaker. The current sensor rating defines the breaker rating (I
n
).
For example, 2000A:1A sensors are used on a 2000A rated breaker.
There are four auxiliary current transformers with a ratio of 10:1 that
further step down the rated current to 100 milliamperes, which is
equivalent to 100% (I
n
) to the Digitrip.
The primary current sensors produce an output proportional to
the load current and furnish the Digitrip with the information and
energy required to trip the circuit breaker when functional protection
settings are exceeded.
If a set of current sensors with a different ratio are installed in the
field, the rating plug must also be changed. The associated rating
plug must match the current sensor rating specified on the plug
label. The current sensor rating can be viewed through openings in
the back of the breaker.
Currtno stnsNrs (Magnum dNublt-widt framts)
The six (three-pole) or eight (four-pole) current sensors installed
in the circuit breaker are located on the lower conductors. The
poles are paralleled and the corresponding current sensors are also
paralleled (see
Figurt 8
). For example, a 4000A breaker phase rating
has two 2000:1 current sensors wired in parallel, which provides
an overall ratio of 4000:2. The auxiliary current transformers have
a ratio of 20:1 for this size breaker that further step down the
rated current to 100 milliamperes and is equivalent to 100% (I
n
)
to the Digitrip.
Section 3: principles of operation
Gtntral
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 in the neighborhood of 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 overtemperature
condition, the microcomputer chip has a built-in overtemperature
protection feature, factory set to trip the breaker if the chip
temperature is excessive. If overtemperature is the reason
for the trip, the red Long Delay Time LED will flash.
The Digitrip uses the Eaton custom-designed CHip™ (Cutler-
Hammer 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
Figurt 15
.
All sensing and tripping power required to operate the protection
function is derived from the current sensors in the circuit breaker.
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 CHip chip.
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 breaker through
the trip actuator.
Trip and NptraoiNn indicaoNrs
The LEDs on the face of the trip unit, shown in
Figurt 1
and
Figurt
16
to
Figurt 27
, 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, the backup battery continues to supply power to
the LEDs as shown in
Figurt 15
. The LED pulse circuit, shown
in
Figurt 15
, 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,
shown in
Figurt 1
, to turn off the LEDs. A green LED, shown in
Figurt 1
, indicates the operational status of the trip unit. Once the
load current through the circuit breaker exceeds approximately 10%
(three-phase power) of the current sensor rating, the green LED will
flash on and off once each second to indicate that the trip unit is
energized and operating properly.
Note:
N
A steady green Status LED typically indicates that a low level of load
current, on the order of 5% of full load, exists.
Making Currtno Rtltast
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 nonadjustable release
is preset at to a peak current of 25 x I
n
, which correlates to
approximately 11 x I
n
(rms) with maximum asymmetry.
The Making Current Release is enabled only for the first two cycles
following an initial circuit breaker closing operation. The Making
Current Release will trip the circuit breaker instantaneously and
flash the Instantaneous LED.
ZNnt inotrlNcking
m
NOTICE
THE PROVISION FOR THE ZONE SELECTIVE INTERLOCKING FUNCTION IS
STANDARD ON CIRCUIT BREAKERS WITH DIGITRIP TRIP UNITS FOR SHORT
TIME AND GROUND FAULT (EARTH FAULT) FUNCTIONS.
FOR ANSI/UL CIRCUIT BREAKERS WITH DIGITRIP TRIP UNITS, THE
APPROPRIATE JUMPER TO TERMINAL B8 AND B9 MUST BE ADDED ON
THE CIRCUIT BREAKER IF ZONE INTERLOCKING IS NOT DESIRED OR FIELD
TESTING IS DESIRED.
FOR IEC CIRCUIT BREAKERS WITH DIGITRIP TRIP UNITS, THE ZONE
INTERLOCKING FUNCTION IS NOT WIRED OUT TO THE CIRCUIT BREAKER
SECONDARIES (I.E., ZONE FUNCTIONALITY IS NOT PRESENT IN
SECONDARIES B7, B8, AND B9). THE TRIP UNIT WILL ALWAYS FOLLOW
THE PROGRAMMED SHORT TIME OR GROUND TIME SETTING. THIS IS
ACCOMPLISHED VIA A WIRING HARNESS INTERNAL TO THE CIRCUIT
BREAKER. IF THE ZONE INTERLOCKING FUNCTION IS DESIRED FOR IEC
CIRCUIT BREAKERS WITH DIGITRIPS, PLEASE REFER TO EATON FOR
APPROPRIATE INSTRUCTIONS ON HOW TO ADJUST THE INTERNAL
WIRING HARNESS TO ACTIVATE THE ZONE INTERLOCKING FUNCTION
ASSOCIATED WITH SECONDARIES B7, B8, AND B9 OF THE CIRCUIT
BREAKER.
