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5 SETPOINTS
The curves for the General Electric type IAC relay family are derived from the 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 5–14: IAC CURVE CONSTANTS
IAC CURVE SHAPE
IAC EXTREME INVERSE
IAC VERY INVERSE
IAC INVERSE
IAC SHORT 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
0.0040
0.6379
0.0900
0.7955
0.2078
0.8630
0.0428
0.0609
745 Transformer Management Relay
5.9 TIME OVERCURRENT CURVES
I
E
≤
---------------------------- -
,
for 1
---------
(
)
I
3
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
0.6200
1.7872
0.1000
–1.2885
0.8000
–0.4180
0.6200
–0.0010
5.9.5 IAC CURVES
<
1.03
I
≤
<
20.0
---------
I
pkp
E
0.2461
7.9586
0.1947
0.0221
5-95
5
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