GE Multilin 489 Instruction Manual page 140

5–30
Courtesy of NationalSwitchgear.com
ANSI Curves
The ANSI time overcurrent curve shapes conform to industry standard curves and fit into
the ANSI C37.90 curve classifications for extremely, very, normally, and moderately
inverse. The 489 ANSI curves are derived from the formula:
⎛
B
T M × ⎜ A
----------------------------------- -
= +
( I I ⁄
⎝
pickup
where: T = Trip Time in seconds
M = Multiplier setpoint
I = Input Current
I = Pickup Current setpoint
pickup
A, B, C, D, E = Constants
Table 5–2: ANSI Inverse Time Curve Constants
ANSI Curve Shape
A
Extremely Inverse 0.0399
Very Inverse 0.0615
Normally Inverse 0.0274
Moderately Inverse 0.1735
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:
T
where: T = Trip Time in seconds
M = Multiplier setpoint
I = Input Current
I = Pickup Current setpoint
pickup
K, E = Constants
Table 5–3: IEC (BS) Inverse Time Curve Constants
IEC (BS) Curve Shape
IEC Curve A (BS142)
IEC Curve B (BS142)
IEC Curve C (BS142)
Short Inverse
D
------------------------------------------ - ------------------------------------------ -
+ +
) C 2
( ( ⁄ ) C ) ( (
I I
–
–
pickup
Constants
B C
0.2294 0.5000
0.7989 0.3400
2.2614 0.3000
0.6791 0.8000
⎛ ⎞
K
M × ⎜ ------------------------------------- - ⎟
=
E
( ⁄ )
⎝ I I 1 ⎠
–
pickup
Constants
K
0.140
13.500
80.000
0.050
489 GENERATOR MANAGEMENT RELAY – INSTRUCTION MANUAL
CHAPTER 5: SETPOINTS
⎞
E
⎟
(EQ 0.4)
3
⎠
⁄ ) C )
I I
–
pickup
D E
3.0094 0.7222
–0.2840 4.0505
–4.1899 9.1272
–0.0800 0.1271
(EQ 0.5)
E
0.020
1.000
2.000
0.040