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REF 610
4.1.4.9.
34
Feeder Protection Relay
Technical Reference Manual
Inverse definite minimum time characteristics
The low-set overcurrent and earth-fault stages can be given an inverse definite
minimum time (IDMT) characteristic. 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.
REF 610 provides eight IDMT characteristics, of which four comply with the IEC
60255-3 and three with the IEEE C37.112 standard. One is a special characteristic
according to ABB praxis and is referred to as RI.
The time/current characteristics can be selected either via the HMI or the SPA bus
as follows:
Table 4.1.4.9-1 Time/current characteristic settings
Value
Time/current characteristic
0
Definite time
1
IEC Extremely inverse
2
IEC Very inverse
3
IEC Normal inverse
4
IEC Long-time inverse
5
RI-type
6
IEEE Extremely inverse
7
IEEE Very inverse
8
IEEE Moderately inverse
IDMT characteristics according to IEC 60255-3
REF 610 provides four time/current curve groups which comply with the IEC
60255-3 standard: normal inverse, very inverse, extremely inverse and long-time
inverse. The relationship between time and current is expressed as follows:
β
×
t s ]
[
---------------------- -
=
α
I
---- -
–
1
I>
where
t = operate time
I = phase (or earth-fault) current value
k (or k
) = time multiplier
0
I> (or I
>) = set start value
0
Note!
The actual operate time of the relay (see Fig. 4.1.4.9.-1...Fig. 4.1.4.9.-4), includes an
additional filter and detection time, and the operate time of the trip output contact.
When the operate time of the relay is calculated as above, approximately 30 ms
should be added to the result.
k
1MRS 755310
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