GE Power Management 745 Transformer Management Relay 5-95
5 SETPOINTS 5.9 TIME OVERCURRENT CURVES
5
5.9.5 IAC CURVES
The curves for the General Electric type IAC relay family are derived from the formula:
where:
T
= Operate Time (seconds)
M
= Multiplier Setpoint
I
= Input Current
I
pkp
= Pickup Current Setpoint
A
,
B
,
C
,
D
,
E
= Constants
Table 5–14: IAC CURVE CONSTANTS
IAC CURVE SHAPE CONSTANTS
A B C D E
IAC EXTREME INVERSE 0.0040 0.6379 0.6200 1.7872 0.2461
IAC VERY INVERSE 0.0900 0.7955 0.1000 –1.2885 7.9586
IAC INVERSE 0.2078 0.8630 0.8000 –0.4180 0.1947
IAC SHORT INVERSE 0.0428 0.0609 0.6200 –0.0010 0.0221
T
MA
B
1.03
C
–
----------------------
D
1.03
C
–
()
2
-----------------------------
E
1.03
C
–
()
3
-----------------------------
++ + , for 1
I
I
pkp
--------- 1.03
<≤×
MA
B
II
pkp
⁄
C
–
-------------------------
D
II
pkp
⁄
C
–
()
2
---------------------------------
E
II
pkp
⁄
C
–
()
3
---------------------------------
++ + , for 1.03
I
I
pkp
---------
20.0
<≤×
MA
B
20.0
C
–
----------------------
D
20.0
C
–
()
2
-----------------------------
E
20.0
C
–
()
3
-----------------------------
++ + , for
I
I
pkp
---------
20.0
≥×
=
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