Basler Electric DGC-2020 - Manual (Page 411)

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. To further improve proper relay coordination, selection of integrated reset or instantaneous reset
characteristics is also provided.
Curve Specifications
Timing Accuracy: Within
±500 milliseconds of indicated operating
point.
Sixteen inverse time functions, one fixed time
function, and one programmable time function
can be selected. Characteristic curves for the
inverse and definite time functions are defined by
the following equation:
Equation A-1
1 M
RD
T
2
R
−
=
Equation A-2
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
R = Constant defining the reset time
This equation complies with IEEE Std C37.112 -
1996 - IEEE Standard Inverse-Time
Characteristic Equations for Overcurrent Relays.
∗ Timing range is 0.0 to 7,200 seconds when the
F (fixed) curve is selected.
Table A-1 lists time characteristic curve
constants. See Figures A-1 through A-16 for
graphs of the characteristics.
K BD
(M
N
–C)
Q
AD
T
T
+ + =
9400200990 Rev X DGC-2020 Time Overcurrent Characteristic Curves A-1