Basler Electric BE1-700 - Manual (Page 455)

APPENDIX D
• OVEREXCITATION (24) INVERSE
TIME CURVES
GENERAL
This appendix contains the inverse time curves for the overexcitation element (24). Equations D-1 and D-
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 D-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
T
T
1
Nominal Hz / V
Measured Hz / V
D
T






−
Equation D-1, Time to Trip
FST
E
D T
T
R R
∗ =
Equation D-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
E
T
= Elapsed time
n = Curve exponent (0.5, 1, 2)
FST = Full scale trip time (T
T
)
E
T
/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 V/Hz rises above a pickup threshold, the pickup element becomes TRUE and an
integrating or definite time timer starts. If the V/Hz 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 V/Hz drops below pickup before timeout to trip, either an
instantaneous or a time delayed integrating reset can be selected.
The following sets of curves (Figures D-1 through D-6) are shown first with the time axis on the vertical
and then on the horizontal for ease of use.
9376700990 Rev M BE1-700 Overexcitation (24) Inverse Time Curves D-1