APPENDIX B • OVEREXCITATION (24) INVERSE
TIME CURVES
GENERAL
This appendix contains the inverse time curves for the overexcitation element (24). Equations B-1 and B-
2 represent the trip time and reset time for constant volts per hertz level. Normally, the V/Hz pickup is set
to a value greater than the V/Hz nominal. This ensures that V/Hz measured divided by V/Hz nominal is
always greater than 1.000 throughout the pickup range.
CURVE SPECIFICATIONS
If the pickup is set less than nominal, then measured values above pickup and below nominal will result in
the maximum time delay. The maximum time delay is determined by equation B-1 with (V/Hz measured /
V/Hz nominal) set equal to 1.001. The overall inverse time delay range is limited to 1,000 seconds
maximum and 0.2 seconds minimum.
n
NOMINAL
MEASURED
T
T
1
Hz
V
Hz
V
D
T
/
/
Equation B-1,
Time to Trip
FST
E
D
T
T
R
R
X 100
Equation B-2,
Time to Reset
where:
T
T
= Time to trip
T
R
= Time to reset
D
T
= Time dial trip
D
R
= Time dial reset
ET = Elapsed time
n
= Curve exponent (0.5, 1, 2)
FST = Full scale trip time (T
T
)
ET/FST = Fraction of total travel toward trip that integration had progressed to. (After a trip, this value
will be equal to one.)
When the measured volts/hertz rises above a pickup threshold, the pickup element becomes TRUE and
integrating or definite time timer starts. If the volts/hertz remains above the pickup threshold and the
integration continues for the required time interval as defined by the equations shown above and the set
time dial, the trip output becomes TRUE. If the measured volts/hertz drops below pickup before timeout to
trip, either an instantaneous or a time delayed integrating reset can be selected.
The following sets of curves are shown first with the time axis on the vertical and then on the horizontal for
ease of use.
9365200990 Rev F
BE1-CDS240 Overexcitation (24) Inverse Time Curves
B-1
Summary of Contents for BE1-CDS240
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Page 349: ...Figure 12 5 Horizontal Rack Mount Front View 9365200990 Rev F BE1 CDS240 Installation 12 5 ...
Page 361: ...Figure 12 17 Typical DC Connection Diagrams 9365200990 Rev F BE1 CDS240 Installation 12 17 ...
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