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Instruction Leaflet
I. L. 29-889B
Effective June 2011
Instructions for Digitrip RMS 910 Trip Unit
eaton corporation
www.eaton.com
important Safety instructions
WARNING
DO NOT ATTEMPT TO INSTALL OR PERFORM MAINTENANCE ON
EQUIPMENT WHILE IT IS ENERGIZED. DEATH OR SEVERE PERSONAL
INJURY CAN RESULT FROM CONTACT WITH ENERGIZED EQUIPMENT.
ALWAYS VERIFY THAT NO VOLTAGE IS PRESENT BEFORE PROCEEDING
WITH THE TASK, AND ALWAYS FOLLOW GENERALLY ACCEPTED
SAFETY PROCEDURES. EATON CORPORATION IS NOT LIABLE FOR THE
MISAPPLICATION OR MISINSTALLATION OF ITS PRODUCTS.
It is strongly urged that the User observe all recommendations,
warnings and cautions relating to the safety of personnel and equip-
ment, as well as all general and local health and safety laws, codes,
and procedures .
The recommendations and information contained herein are based
on experience and judgment, but should not be considered to be
all-inclusive or covering every application or circumstance which
may arise . If you have any questions or need further information
or instructions, please contact your local representative, or the
Customer Support Center for the type of circuit breaker you have .
1 General Description - Digitrip rMS 910
trip Unit
1.1 Basic Digitrip RMS 910 Trip Unit
The Digitrip RMS 910, illustrated in Figure 1, is a Trip Unit suitable
for use in types DS and DSL Low-Voltage AC power circuit breakers
and type SPB Systems Pow-R circuit breakers and Series C R-Frame
molded case circuit breakers . The Digitrip RMS 910 Trip Unit pro-
vides five basic functions:
Function
Section
Protection
1 .1 .2 – 1 .1 .5 and 3
Information
1 .1 .1 and 1 .2
Monitors
1 .2 .1
Current
1 .2 .1 .1
Voltage
1 .2 .1 .2
Power, Power Factor and Energy
1 .2 .1 .3
Harmonics and [THD]
1 .2 .1 .4 and 5 .7
Testing
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Communications
1 .4 and 5
Remote CLOSE / OPEN Control
5 .8
Digitrip RMS 910 provides true RMS current sensing for proper cor-
relation with thermal characteristics of conductors and equipment .
Interchangeable rating plugs are provided to establish the continuous
current rating of each circuit breaker . The Digitrip RMS 910 Trip Unit
is designed for use in industrial circuit breaker environments where
the ambient temperatures can range from -20°C to +85°C (-4°F to
185°F) and rarely exceed 70 to 75°C (158 to 167°F) . If, however,
temperatures in the neighborhood of the Trip Unit do exceed this
range, the Trip Unit performance may be degraded . In order to
insure that the tripping function is not compromised due to an over-
temperature condition, the Digitrip RMS 910 microcomputer chip has
a built-in over-temperature protection feature, factory set to trip the
breaker if the chip temperature is excessive . If over-temperature is
the reason for the trip, the Long Delay Time LED will light "RED", and
the word "TEMP" will appear in the display window .
The Trip Unit employs the Eaton custom designed integrated circuit
microprocessor which includes a micro-computer to perform its
numeric and logic functions . The principle of operation is described
by the block diagram shown in Figure 2 .
In the Digitrip RMS 910 Trip Unit, all required sensing and tripping
power to operate its 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 protector func-
tions, as well as tripping power, whenever the circuit breaker is
carrying current . These signals develop analog voltages across the
appropriate sensing resistors including:
1 .
Phase currents;
2 .
Ground current or Neutral current (when supplied);
3 .
Rating plug; and
4 .
Phase Voltages .
The resulting analog voltages are digitized by the custom designed
integrated circuits . The micro-computer, in cyclic fashion, repeatedly
scans the voltage values across each sensing resistor and enters
these values into its Random Access Memory (RAM) . The data used
to calculate true RMS current values, which are then repeatedly
compared with the protection function settings and other operat-
ing data stored in the memory . The software program then deter-
mines whether to initiate protection functions, including tripping the
breaker through the low energy trip device (Flux Transfer Shunt Trip
or Direct Trip Actuator) in the circuit breaker .
