ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-74
E. Setting instructions
Settings:
Current pick-up Current
Delay Delay
Undervoltage Hold-Voltage
Reset delay Hold-Time
The voltage controlled overcurrent function comprises a definite
time overcurrent unit which latches when the undervoltage unit
responds.
The protection is intended for generators and genera-
tor/transformer units, for which a fault current can fall below the
pick-up of the overcurrent protection before it has an opportunity
to trip.
Apart from the influence of a DC component, a decaying AC
component can only occur on a generator, the steady-state fault
current of which is very low because of the large synchronous
reactance X
d
typical of modern generators (see Fig. 3.5.5.1).
This function is largely insensitive to DC component and har-
monics.
i
t
n
i
HEST 905 012 C
1
2
3
4
5
6
-1
-2
-3
-4
-5
-6
Fig. 3.5.5.1 Generator fault current
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