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CHAPTER 5: SETPOINTS
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
5–31
IAC Curves
The curves for the General Electric type IAC relay family are derived from the formula:
(EQ 0.6)
where:
T
= Trip Time in seconds
M
= Multiplier setpoint
I
= Input Current
I
pickup
= Pickup Current setpoint
A
,
B
,
C
,
D
,
E
= Constants
FlexCurve™
The custom FlexCurve™ has setpoints for entering times to trip at the following current
levels: 1.03, 1.05, 1.1 to 6.0 in steps of 0.1 and 6.5 to 20.0 in steps of 0.5. The relay then
converts these points to a continuous curve by linear interpolation between data points. To
enter a custom FlexCurve™, read off each individual point from a time overcurrent
coordination drawing and enter it into a table as shown. Then transfer each individual
point to the 489 using either the EnerVista 489 Setup software or the front panel keys and
display.
Table 5–4: IAC Inverse Time Curve Constants
IAC Curve Shape
Constants
A
B
C
D
E
Extreme Inverse
0.0040
0.6379
0.6200
1.7872
0.2461
Very Inverse
0.0900
0.7955
0.1000
–1.2885
7.9586
Inverse
0.2078
0.8630
0.8000
–0.4180
0.1947
Short Inverse
0.0428
0.0609
0.6200
–0.0010
0.0221
T
M
A
B
I I
pickup
⁄
(
)
C
–
------------------------------------
D
I I
pickup
⁄
(
)
C
–
(
)
2
-------------------------------------------
E
I I
pickup
⁄
(
)
C
–
(
)
3
-------------------------------------------
+
+
+
⎝
⎠
⎜
⎟
⎛
⎞
×
=