Rockwell Automation Publication 1407-UM002B-EN-P - February 2019
177
Appendix
A
Time Over-current Characteristic Curves
General
The CGCM-DLR unit time over-current protection function provides
time/current characteristic curves that closely emulate most of the common
electromechanical, induction disk relays manufactured in North America. To
improve further 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…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 can be selected. The
following equations define the characteristic curves for the inverse and definite
time functions.
Figure 41 - Equation 1
Figure 42 - Equation 2
–
TT = Time to trip when M = 1
–
TR = Time to reset if relay is set for integrating reset when
M < 1. Otherwise, reset is 50 ms or less
–
D =T IME DIAL setting (0.0…9.9)
–
M = Multiple of PICKUP setting (0…40)
–
A, B, C, N, K = Constants for the particular curve
–
R = Constant that defines the reset time.
These equations comply with IEEE Standard C37.112-1996.
The
51P and 51N Time Characteristic Curve Constants
table lists the time
characteristic curve constants.
T
T
A D
⋅
M
N
C
–
------------------
B D K
+
⋅
+
=
T
R
R D
⋅
M
2
1
–
-------------------
=