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1MRS 755310
Feeder Protection Relay
Technical Reference Manual
Table 4.1.4.9-2 Values of constants α and β
Time/current curve group
Normal inverse
Very inverse
Extremely inverse
Long-time inverse
According to the standard, the normal current range is 2...20 times the set start value
at normal inverse, very inverse or extremely inverse characteristic. The relay is to
start before the current exceeds the set start value by 1.3 times. At long-time inverse
characteristic, the normal current range is specified to be 2...7 times the set start
value, and the relay is to start before the current exceeds the set start value by 1.1
times.
Table 4.1.4.9-3 Operate time tolerances specified by the standard
2)
Normal
I/I>
2
2,22E
5
1,13E
7
-
10
1,01E
20
1,00E
1)
E = accuracy in percent; - = not specified
2)
or I 0 /I 0 >
Within the normal current range the inverse-time stage fulfils the tolerance
requirements of class 5 at all degrees of inversity.
The time/current curve groups based on the IEC standard are illustrated in
Fig. 4.1.4.9.-1...Fig. 4.1.4.9.-4.
Note!
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.
α
β
0.02
0.14
1.0
13.5
2.0
80.0
1.0
120
Very
Extremely
2,34E
2,44E
1,26E
1,48E
-
-
1,01E
1,02E
1,00E
1,00E
REF 610
1)
Long time
2,34E
1,26E
1,00E
-
-
35
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