212
March 1996
Power Circuit Breakers Type DSII and
SPB with OPTIM Trip Units
Electronic Trip Units
General Description
Cutler-Hammer offers the most comprehen-
sive range of electronic trip units in the indus-
try for power circuit breakers. The UL listed
OPTIM electronic trip units are true RMS
sensing and can be applied in any SPB or
DSII breakers.
Digitrip electronic trip units are ac devices
that employ microprocessor-based technol-
ogy that provides a true RMS current sensing
means for proper correlation with thermal
characteristics of conductors and equipment.
The primary function of the Digitrip elec-
tronic trip unit is to provide circuit protection.
This is achieved by analyzing the secondary
current signals received from the circuit
breaker current sensors and initiating trip
signals to the circuit breaker trip unit when
pre-set current levels and time delay settings
are exceeded. By sampling the current wave-
form at various points on the wave and calcu-
lating true RMS current, the Digitrip is able to
reduce nuisance tripping events due to non-
sinusoidal wave shapes.
Electronic trip units are applied to distribu-
tion systems when high standards of protec-
tion and coordination are called for. In
addition, electronic trip units can provide fur-
ther enhanced features such as alarming,
diagnostics, system monitoring and
communications.
Cutler-Hammer RMS sensing trip units for
power breakers fall into two main categories:
●
Front adjustable trip units: Digitrip RMS
510, 610, 810, 910
●
Programmable trip units: Digitrip OPTIM
750, 1050
Programmable Trip Units
OPTIM trip units are electronic trip units that
have up to ten time-current setting options
that are programmed electronically by the
use of a programming device. Trip units are
readily accessible from the front of the break-
ers. Programmability means more settings,
better accuracy, faster configuration, remote
accessibility, higher system security, and the
ability to apply limitless software. The appli-
cation for programmable trip units would be
high integrity distribution systems that re-
quire superior levels of system coordination
coupled with system alarming, diagnostics
and monitoring.
Digitrip OPTIM for power breakers are avail-
able in three configurations:
-
Long time, short time, and instanta-
neous (LSI)
-
Long time, short time, instantaneous
and ground fault protection (LSIG)
-
Long time, short time, instantaneous
and ground fault alarm (LSIA)
For maximum selectability, OPTIM trip units
allow the user to disable either short time or
instantaneous functions, but not both.
Rating Plugs
Rating plugs provide a means to establish
the breaker’s continuous current rating. Rat-
ing plugs are unique to a particular breaker
type, and are color coded to make it easy to
match the correct rating plug with the correct
circuit breaker type. Rating plugs are fixed
type, and are interchangeable so that amp
ratings can be changed simply by changing
from one plug to another in a given breaker.
The same rating plug can be applied to both
50 and 60 Hz distribution systems. SPB plugs
are interlocked with the breaker frame to pre-
vent putting the wrong plug into the wrong
frame size.
Rating plugs are available down to an ampere
value of half the sensor rating. Sensors are
selectable on DS breakers and on SPB break-
ers are equal to the breaker frame rating. The
plug value is referred to as I
n
.
Time-Current Curve Shaping
All Digitrip OPTIM settings are continuously
adjustable, allowing virtually an infinite num-
ber of possibilities within setting ranges.
Ranges are based on the plug rating I
n
and
the long delay pickup setting I
r
. For ease of
use all pickup values are programmed in
amps rather than in multiples of I
n
or I
r
.
Table 1 illustrates available setting ranges.
For improved system coordination OPTIM
features a new setting not available on previ-
ous models of Digitrip. The I
4
t long delay
slope will provide superior coordination with
upstream fuses and transformer damage
curves.
OPTIM 750
●
RMS Sensing
●
10 Functions
●
Programmable
●
Load Monitoring
●
Diagnostics
●
Communications
OPTIM 1050
●
RMS Sensing
●
10 Functions
●
Programmable
●
Load Monitoring
●
Diagnostics
●
Communications
●
Power and Energy Monitoring
●
Harmonics
Interchangeable rating plugs establish the circuit breaker’s continuous ampere rating. Different types and
ratings are available to match the desired ampere rating and type of circuit breaker into which a Digitrip
RMS trip unit is installed. The rating plugs are suitable for use on either 50 or 60 Hz system applications.
Rating plugs may be applied as low as 50% of sensor rating.
