GE Multilin G650 Manual page 175

5.4 PROTECTION ELEMENTS
5.4.2.2 IEC CURVES
This family of curves follows the European standard IEC 255-4, and the British standard BF142 for IEC Curves A, B and C,
IEC Long-Time Inverse and IEC Short-Time Inverse. The formulas that define these curves are as follows:
Where:
t = Operation time in seconds
Dial = multiplying factor
I = Input current
Itap = Current pickup value
K, E = constants defined by the standard
T
RESET
t = characteristic constant.
r
5
Table 5–31: CONSTANTS FOR IEC CURVES
5-32
= reset time in seconds (assuming 100% of power capacity and that the reset is activated)
IEC CURVE SHAPE
IEC Curve A
IEC Curve B
IEC Curve C
IEC Long-Time Inverse
IEC Short-Time Inverse
G650 Generator Protection & Control System
NAME K
IEC Curve A 0.140
IEC Curve B 13.500
IEC Curve C 80.000
IEC Long-Time Inv 120.000
IEC Short-Time Inv 0.050
5 SETTINGS
E tr
0.020 9.7
1.000 43.2
2.000 58.2
1.000 120.0
0.040 0.5
GEK-113285A