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,
with 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,
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
C37.112 - 1996.
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-17 for
graphs of the characteristics.
9365200990 Rev F
BE1-CDS240 Time Overcurrent Characteristic Curves
A-1
Summary of Contents for BE1-CDS240
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