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4-22 489 Generator Management Relay GE Multilin
4.6 S5 CURRENT ELEMENTS 4 SETPOINTS
4
c) IEC CURVES
For European applications, the relay offers the four standard curves defined in IEC 255-4 and British standard BS142.
These are defined as IEC Curve A, IEC Curve B, IEC Curve C, and Short Inverse. The formula for these curves is:
(EQ 4.5)
where: T = Trip Time in seconds
M = Multiplier setpoint
I = Input Current
I
pickup
= Pickup Current setpoint
K, E = Constants
d) IAC CURVES
The curves for the General Electric type IAC relay family are derived from the formula:
(EQ 4.6)
where: T = Trip Time in seconds
M = Multiplier setpoint
I = Input Current
I
pickup
= Pickup Current setpoint
A, B, C, D, E = Constants
Table 4–3: IEC (BS) INVERSE TIME CURVE CONSTANTS
IEC (BS) CURVE SHAPE CONSTANTS
KE
IEC CURVE A (BS142) 0.140 0.020
IEC CURVE B (BS142) 13.500 1.000
IEC CURVE C (BS142) 80.000 2.000
SHORT INVERSE 0.050 0.040
Table 4–4: IAC INVERSE TIME CURVE CONSTANTS
IAC CURVE SHAPE CONSTANTS
ABCDE
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
TM
K
II
pickup
⁄()
E
1–
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×=
TMA
B
II
pickup
⁄()C–
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D
II
pickup
⁄()C–()
2
-------------------------------------------- -
E
II
pickup
⁄()C–()
3
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⎜⎟
⎛⎞
×=