IB02602004E
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Instructional Literature
Effective: May 2008
Page
151
Instructions for the FP-6000 Protective Relay
The ANSI curves are defined by ANSI C37.112, and IEC curves are
defined by lEC 255-3. These curve shapes combined with the
customized capability of the short delay and instantaneous
functions allow for very versatile coordinated protection
schemes. The thermal curve shape is also customized by the user
for any desired type of coordinated protection scheme.
These curves show how and when a particular relay will act for
given values of time and current. The more versatile the relay,
the easier it is to accomplish close coordination and achieve
optimum protection. Since the FP-6000 Protective Relay is very
versatile, the makeup of a typical curve is presented for
clarification.
For the sake of simplification, the curve discussion will center on
a single line curve. Keep in mind, however, that a characteristic
curve in reality is represented by a band of minimum and
maximum values, not a line (Figure 46, Sample Electronic Trip
Curves, below). Minimum and maximum values are generally
the result of manufacturing tolerances for components and the
relay’s accuracy. Any expected value of tripping current or time
could be the nominal value anticipated within a plus or minus
tolerance. The tolerances are usually stated in terms of the
relay’s accuracy and frequently highlighted on the actual working
curves. Accuracy is stated in terms of a plus or minus percentage
and represents a permitted fluctuation on either side of the
nominal tripping point for a family of relays, like the FP-6000.
Figure 46. Sample Electronic Trip Curves.
Adjustability
The adjustability of the relay permits movement of its
characteristic curve or parts of the curve. This movement can be
done in both a horizontal and vertical direction on the time
current grid. The actual shape of the curve can be changed along
with the curve movement. This adjustability permits distinct
curves to be established to match the electrical protection to the
application. (Figures 47 through 52.) Horizontal movement of the
ANSI and lEC curve shapes is controlled by changing the pickup
setting. Changing the pickup setting of the thermal curves moves
the point at which the relay starts to time out along the curve
shape.
Figure 47. Typical Inverse Time Overcurrent Pickup Horizontal
Movement.
NOTICE
AS SHOWN IN FIGURE 40, THE ANSI AND IEC “CURVE SHAPES”
ARE IN TERMS OF MULTIPLES OF IPU (PICKUP CURRENT OF THE CT
PRIMARY), WHEREAS, “SHORT DELAY” AND “INSTANTANEOUS”
ARE IN TERMS OF MULTIPLES OF INOM (5 A OR 1 A SECONDARY
OF CT CURRENT). THE THERMAL CURVE IS REPRESENTED IN
TERMS OF MULTIPLES OF INOM FOR ITS CURVE SHAPE, SHORT
DELAY AND INSTANTANEOUS SETTINGS. THIS MUST BE CONSID-
ERED IN THE COORDINATION STUDY AND IN THE PROGRAMMING
OF THE FP-6000 PROTECTIVE RELAY.
