22
1MRS 750616-MUM
Directional or Non-Directional Earth-Fault Relay
Technical Reference Manual
REJ 527
RD-type characteristic
The RD-type characteristic is a special characteristic which is principally used in
earth-fault protection and which requires a high degree of selectivity even at high
resistance faults. The protection can operate in a selective way even if it is not
directional. Mathematically the time/current characteristic can be expressed as
follows:
where
t = operate time
k = time multiplier
I
0
= earth-fault value
I
0
> = set start value
The RD-type characteristic is illustrated in
.
t s
[ ]
5.8
1.35
–
log
e
×
Io
k
Io>
×
------------------
=
Содержание REJ 527
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