ABB REJ 527, Technical Reference Manual

Page: 21 / 76

1MRS 750616-MUM Directional or Non-Directional Earth-Fault Relay
Technical Reference Manual
REJ 527
21
According to the standard, the normal current range is 2...20 times the setting value
at normal inverse, very inverse or extremely inverse characteristic. The relay is to
start before the current exceeds the setting value by 1.3 times. At long-time inverse
characteristic, the normal current range is specified to be 2...7 times the setting
value, and the relay is to start before the current exceeds the setting value by 1.1
times.
E = accuracy in percent; - = not specified
Within the normal current range the inverse-time stage fulfils 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. 4.1.4.5.-1
...
Fig. 4.1.4.5.-4
.
1RWH
If the ratio between the current and the set start value is higher than 20, the operate
time will be the same as when the ratio is 20.
RI-type characteristic
The RI-type characteristic is a special characteristic which is principally used for
obtaining time grading with mechanical relays. The characteristic can be expressed
mathematically as follows:
where
t = operate time
k = time multiplier
I
0
= earth-fault current value
I
0
> = set start value
The RI-type characteristic is illustrated in
Fig. 4.1.4.5.-5
.
Table 4.1.4.5-2 The operate time tolerances specified by the standard
I
0
/I
0
>
Normal Very Extremely Long time
2 2,22E 2,34E 2,44E 2,34E
5 1,13E 1,26E 1,48E 1,26E
7 - - - 1,00E
10 1,01E 1,01E 1,02E -
20 1,00E 1,00E 1,00E -
t s
[ ]
k
0.339 0.236 –
Io>
Io
---------
×
------------------------------------------------- =