I.B. 29C891B
Page 20
Effective 11/98
SECTION 3: OPERATION AND FUNCTION-
ALITY
3-1 GENERAL
This section describes the details associated with the
operation and functional use of Digitrip OPTIM Trip
Units in terms four main categories:
• Protection and Coordination
• System Monitoring
- Load Current Monitoring
- Power and Energy Monitoring
- Power Quality Monitoring
• Communications
• Testing
Four quick reference overviews outlining the features
available with the Digitrip OPTIM Trip Unit System, and
specifically OPTIM Trip Units, are provided in Tables
3.1, 3.2 , 3.3
and
3.4
.
OPTIM Trip Units provide true RMS current sensing for
proper correlation with thermal characteristics of con-
ductors and equipment. The rating plug (I
n
) determines
the continuous current rating of the circuit breaker.
3-2 PROTECTION AND COORDINATION
The Digitrip OPTIM Trip Unit provides circuit breakers with
an extensive degree of selective coordination potential,
and permits curve shaping over a wide range of current
settings. Pickup settings, delay time settings and slope
selections are addressed here with respect to their effect
on the resultant characteristic curve.
3-2.1 OVER-TEMPERATURE TRIP
The OPTIM Trip Unit is designed for use in environ-
ments where the ambient temperatures range from -
20°C to +85°C. If, however, temperatures around the
trip unit exceed this range, the trip unit performance
may be degraded. To insure that the tripping function is
not compromised due to an over-temperature condition,
the OPTIM microcomputer chip has a built-in over- tem-
perature protection feature. This protective feature is
factory set to trip the circuit breaker if the chip tempera-
ture exceeds 85°C ± 10°C.
3-2.2 CHARACTERISTIC CURVE REVIEW
As a review, certain aspects of a circuit breaker’s char-
acteristic curve are discussed here to simplify the under-
standing of later material.
The operating response of the trip unit is graphically
represented by time-current characteristic curves.
These curves show how and when a particular trip unit
will act for given values of time and current. The more
versatile the trip unit, the easier it is to accomplish close
coordination and achieve optimum protection.
A characteristic curve is represented by a band created
by a minimum and maximum value of time or current
(Figure
3-1
). Minimum and maximum values are general-
ly the result of tolerances introduced by the manufactur-
ing process for components and factory calibration
efforts. The tolerances are usually stated as the trip unit’s
accuracy and specified on the time-current curves. This
accuracy is stated in terms of a plus or minus percentage
and represents a permitted fluctuation on either side of a
selected nominal setting point for a trip unit. OPTIM Trip
Unit accuracies are specified for each protective function
(long delay, short delay instantaneous and ground fault)
and the type of circuit breaker in which the trip unit is
installed. Refer to the applicable OPTIM time-current
curves outlined in Table
A.1
of Appendix A for specific
accuracies.
The programmable or adjustable features of a trip unit
permit movement of its characteristic curve or parts of
the curve. This movement can be done in both a hori-
zontal and vertical direction on the time-current grid
(Figure
3-2
).
The actual shape of the curve can be changed by
selecting the slope, such as Flat, I
2
t and I
4
t (Figure
3-3
).
An I
2
t slope selection is used for an inverse curve, an I
4
t
slope selection for an extremely inverse curve, and a
Flat selection for a definite or fixed time curve.
Capability
OPTIM 550
OPTIM 750
OPTIM 1050
Protection and
Yes
Yes
Yes
Coordination
(10 functions)
(10 functions)
(10 functions)
IMPACC
Field Yes
Yes
Communications
Upgradeable
Ground Alarm
No
Yes
➀
Yes
➀
Contact
Zone Selective
No
Yes
Yes
Interlocking
Power Quality
No No
Yes
Energy Monitoring
No
No
Yes
➀
➀
Requires external module on K, L and N-Frame breakers
Table 3.1 Digitrip OPTIM 550, 750 and 1050 Trip Unit
Capabilities
Summary of Contents for Digitrip OPTIM 1050
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