Time/Current Characteristics - ABB REJ 527 Technical Reference Manual

REJ 527
4.1.4.5.
20
Directional or Non-Directional Earth-Fault Relay
Technical Reference Manual
The resetting time can be set to 80, 100, 500 or 1000 ms in SGF5. When the resetting
time is set to 100 ms or above, earth-fault stage I
earth-fault stage.
1RWH
If the CBFP function is in use and a resetting time longer than 80 ms is selected, a
CBFP operate time longer than the resetting time is recommended.

Time/current characteristics

The low-set earth-fault current stage can be given either a definite-time or an inverse
definite minimum time (IDMT) characteristic whereas the high-set earth-fault
current stage and the voltage stage(s) feature the definite-time characteristic alone.
The settings of switches SGF4/1...6 determine the operation mode of the stage.
Refer to section Settings for additional information.
At IDMT characteristic, the operate time of the stage is dependent on the current
value: the higher the current value, the shorter the operate time. Six time/current
curve groups are available, of which four comply with the IEC 60255 standard: the
normal inverse, very inverse, extremely inverse and long-time inverse. The two
additional inverse-time curve groups, referred to as RI and RD, are special curve
groups according to ABB praxis.
Characteristics according to the IEC 60255 standard
The relay module incorporates four internationally standardized time/current curve
groups called extremely inverse, very inverse, normal inverse and long-time inverse.
The relationship between time and current is in accordance with the IEC 60255-3
standard and can be expressed as follows:
k β ×
t s [ ]
= --------------------------
α
 
Io
-------- - – 1
 
Io>
where
t = operate time
k = time multiplier
I = earth-fault current value
0
I > = set start value
0
Table 4.1.4.5-1 The values of constants α and β
Time/current curve group
Normal inverse
Very inverse
Extremely inverse
Long-time inverse
> will operate as an intermittent
0
α β
0.02 0.14
1.0 13.5
2.0 80.0
1.0 120
1MRS 750616-MUM