BE1-951
Appendix
A-1
T
A • D
M
B • D + K
T =
N
+
- C
Equation A-1
T
R D
M
1
R
2
=
·
-
Equation A-2
APPENDIX A • TIME-OVERCURRENT
CHARACTERISTIC CURVES
GENERAL
Basler Electric inverse time-overcurrent relays (ANSI Device 51) provide time/current characteristic curves
that closely emulate most of the common electromechanical, induction disk relays manufactured in North
America. To further improve relay coordination, selection of integrated reset or instantaneous reset
characteristics is also provided.
CURVE SPECIFICATIONS
Timing Accuracy (All 51 Functions)
Within ±5% or ±1½ cycles (F/R response) or -1½ +3 cycles (A
response), whichever is greater for time dial settings of D greater
than 0.1 and multiples of 2 to 40 times the pickup setting but not
over 150 A for 5 A CT units or 30 A for 1 A CT units.
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 equations.
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.
These equations comply with IEEE Standard C37.112-
1996.
Table A-1 lists the time characteristic curve constants.
See Figures A-1 through A-17 for graphs of the
characteristics.
