ABB REJ 527 Technical Reference Manual page 20

REJ 527
20
Technical Reference Manual
Table 2: The operate time tolerances specified by the standard
I /I > Normal
0 0
2 2,22E
5 1,13E
7 -
10 1,01E
20 1,00E
E = accuracy in per cent; - = not specified
In the normal current range, specified above, the inverse-time stages of the
directional or non-directional earth-fault relay fulfil the tolerance requirements of
class 5 at all degrees of inversity.
The time/current characteristics according to the IEC and BS standards are
illustrated in Fig. 4.1.3.5.-1...Fig. 4.1.3.5.-2.
RI-type characteristic
The RI-type characteristic is a special characteristic that is principally used for
obtaining time grading with mechanical relays. The characteristic can be expressed
mathematically:
k
t s [ ]
= ------------------------------------------------ -
0.339 0.236 –
where t = operate time in seconds
k = time multiplier
I = phase current
0
I > = set start current.
0
The RI-type characteristic is illustrated in Fig. 4.1.3.5.-3.
Very Extremely
2,34E 2,44E
1,26E 1,48E
- -
1,01E 1,02E
1,00E 1,00E
Io>
×
-------- -
Io
ABB Substation Automation
Products and Systems
Long time
2,34E
1,26E
1,00E
-
-
1MRS750616-MUM