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5 SETPOINTS
5.9 TIME OVERCURRENT CURVES
Graphs of time-current curves on 11"x17" log-log graph paper are available upon request.
NOTE
The ANSI time overcurrent curve shapes conform to industry standard curves and fit into the ANSI C37.90
curve classifications for extremely, very, normally, and moderately inverse. The 745 ANSI curves are derived
from the following formula:
×
M
A
×
M
A
T
=
×
M
A
where:
T = Operate Time (seconds)
M = Multiplier setpoint
I = Input Current
I
= Pickup Current setpoint
pkp
A , B , C , D , E = Constants
Table 5–10: ANSI CURVE CONSTANTS
ANSI CURVE SHAPE
EXTREMELY INVERSE
VERY INVERSE
NORMALLY INVERSE
MODERATELY INVERSE
GE Power Management
B
D
+
--------------------- -
+
---------------------------- -
+
(
)
2
1.03 C
–
1.03 C
–
B
D
+
+
-------------------------
-------------------------------- -
⁄
(
⁄
)
2
I I
–
C
I I
C
–
pkp
pkp
B
D
+
--------------------- -
+
---------------------------- -
+
(
)
2
20.0 C
–
20.0 C
–
A
B
0.0399
0.2294
0.0615
0.7989
0.0274
2.2614
0.1735
0.6791
745 Transformer Management Relay
5.9 TIME OVERCURRENT CURVES
E
I
≤
,
for 1
---------------------------- -
---------
(
)
3
I
1.03 C
–
pkp
E
+
,
for 1.03
-------------------------------- -
(
⁄
)
3
I I
C
–
pkp
E
I
≥
,
for
20.0
---------------------------- -
---------
(
)
3
I
20.0 C
–
pkp
CONSTANTS
C
D
0.5000
3.0094
0.3400
–0.2840
0.3000
–4.1899
0.8000
–0.0800
5.9.1 NOTE
5.9.2 ANSI CURVES
<
1.03
I
≤
<
---------
20.0
I
pkp
E
0.7222
4.0505
9.1272
0.1271
5-91
5
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