Basler Electric BE1-851 - Manual (Page 331)

APPENDIX A • TIME OVERCURRENT
CHARACTERISTIC CURVES
General
Basler Electric inverse time overcurrent systems (ANSI Device 51) provide time/current characteristic
curves that very closely emulate most of the common electro-mechanical, induction disk relays that were
manufactured in North America. To further improve proper 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, whichever is greater,
for Fundamental and RMS sensing, and -1½ to
+3 cycles for Average sensing, for time dial
settings 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 and 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 and comply with IEEE Std
C37.112 - 1996 - IEEE Standard Inverse-Time
Characteristic Equations for Overcurrent Relays.
K D B
C M
D A
T
N
T
+ ⋅ +
−
⋅
= Equation A-1
1 M
D R
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.
Table A-1 lists time characteristic curve
constants. See Figures A-1 through A-16 for
graphs of the characteristics.
9289900990 Rev R BE1-851 Time Overcurrent Characteristic Curves A-1