ABB REF 610 Technical Reference Manual page 52

REF 610 REF 610
52
Feeder Protection Relay
Technical Reference Manual
RI-type characteristic
The RI-type characteristic is a special characteristic which is principally used for
obtaining time grading with mechanical relays. The relationship between time and
current is expressed as follows:
k
[ ]
=
t s
−
0 339 0 236 . .
t = operate time
I = phase (or earth-fault) current value
k (or k ) = time multiplier
0
I> (or I >) = set start value
0
The actual operate time of the relay (see Fig. 5.1.4.9.-8), 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.
The RI-type characteristic is illustrated in Fig. 5.1.4.9.-8.
>
I
×
I
1MRS755310
(6)