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
ABCDE
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
TMA
B
II
pickup
⁄()C–
------------------------------------
D
II
pickup
⁄()C–()
2
-------------------------------------------
E
II
pickup
⁄()C–()
3
-------------------------------------------++ +
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⎜⎟
⎛⎞
×=
Courtesy of NationalSwitchgear.com
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