GE 489 Instruction Manual page 56

4.6 S5 CURRENT ELEMENTS
b) 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:

K
×

T M -------------------------------------- -
=
( ⁄

I I
pickup
where: T = Trip Time in seconds
M = Multiplier Setpoint
I = Input Current
I = Pickup Current Setpoint
pickup
K , E = Constants
Table 4–3: IEC (BS) INVERSE TIME CURVE CONSTANTS
IEC (BS) CURVE SHAPE
IEC CURVE A (BS142)
IEC CURVE B (BS142)
4
IEC CURVE C (BS142)
SHORT INVERSE
c) IAC CURVES
The curves for the General Electric type IAC relay family are derived from the formula:

×

T M A
= + ------------------------------------ -
( ⁄

I I
where: T = Trip Time in seconds
M = Multiplier Setpoint
I = Input Current
I = Pickup Current Setpoint
pickup
A , B , C , D , E = Constants
Table 4–4: IAC INVERSE TIME CURVE CONSTANTS
IAC CURVE SHAPE
IAC EXTREME INVERSE
IAC VERY INVERSE
IAC INVERSE
IAC SHORT INVERSE
4-18


)

E
1
–
CONSTANTS
K
0.140
13.500
80.000
0.050
B D
+ -------------------------------------------- -
) C
( ( ⁄ ) C )
2
–
I I
–
pickup
pickup
A
0.0040
0.0900
0.2078
0.0428
489 Generator Management Relay
E
0.020
1.000
2.000
0.040

E

+ -------------------------------------------- -
( ( ⁄ ) C ) 
3
I I
–
pickup
CONSTANTS
B C
0.6379 0.6200 1.7872
0.7955 0.1000 –1.2885
0.8630 0.8000 –0.4180
0.0609 0.6200 –0.0010
4 SETPOINT PROGRAMMING
D E
0.2461
7.9586
0.1947
0.0221
GE Power Management