18
Time/current
characteristics
ANSI-type
characteristic
The operation of the overload stage I
b
> is based
on ANSI and IEC inverse time characteristic.
I/Ib> t [s] standard durations [s]
1.15 1620 1800 IEC 871-1
1.20 270 300 IEC 871-1
1.30 54 60 ANSI 18-1980, IEC 871-1
1.40 13.5 15 ANSI 18-1980
1.70 0.9 1 ANSI 18-1980
2.00 0.27 0.3 ANSI 18-1980
2.20 0.10 0.12 ANSI 18-1980
Minimum operating time is 100 ms.
The graph of the characteristic is shown in Fig.5.
Phase unbalance-
type characteristic
(modified 99-10)
The operation of the phase unbalance stage ∆I
2
>
is based on inverse time characteristic near to
normal inverse. The characteristic is based on
the following mathematical expression:
t[s] = k x 101.2/[(100 x ∆I/∆I
2
>)-97]+0.02
where
t = operating time in seconds
k = time multiplier
∆I = current value
∆I
2
> = set current value
Note!
It is possible to increase the inverse time char-
acteristic by a factor 10 by setting switch SGF/6
to position 1.
The normal current range is defined as 1...2
times the setting current. Additionally the relay
must start at the latest when the current exceeds
a value of 1.05 times the setting current.
Minimum operating time is 100 ms. For cur-
rents above two times the rated current ∆I the
relay levels out to definite time operation.
The graph of the characteristic is shown in Fig.6.
To Next Page
Loading...
