9400200990 Rev I DGC-2020 Time Overcurrent Characteristic Curves A-1
APPENDIX A • TIME OVERCURRENT
CHARACTERISTIC CURVES
INTRODUCTION
The inverse time overcurrent characteristic curves provided by the DGC-2020 (style xxxxxxExx only)
closely emulate most of the common electromechanical, induction-disk, overcurrent relays sold in North
America.
CURVE SPECIFICATIONS
Timing Accuracy: Within ±500 milliseconds of indicated operating
point.
Sixteen inverse time functions and one fixed time
function can be selected. Characteristic curves for
the inverse and definite time functions are defined
by the following equation:
KDB
CM
DA
T
N
T
+⋅+
−
⋅
= Equation A-1
T
T
= Time to trip when M ≥ 1
T
R
= Time to reset if relay is set for integrating
reset when M < 1. Otherwise, reset is 50
milliseconds or less
D = TIME DIAL setting (0.0 to 9.9)
M = Multiple of PICKUP setting (0 to 40)
A, B, C, N, K = Constants for the particular curve
This equation complies with IEEE Standard
C37.112-1996.
Table A-1 lists time characteristic curve
constants. See Figures A-1 through A-16 for
graphs of the characteristics.
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