ABB REG316 4 Series - Page 280

ABB Switzerland Ltd REG 316*4 1MRB520049-Uen / Rev. F
3-242
Calculation of the settings REs and MTR:
()
R 400 m 60 1.44 k
Es
2
=´=WW
MTR
N'
N'
110 V
1.7 V
12
11
=´ =112
for an injection voltage of Uis = 1.7 V.
Installations with a second star-point in the zone of
protection
The following parameters settings have to be made:
· ‘NrOfStarpt’ = 2.
· ‘2.StarptInp’ = T
in cases in which the second star-point is always connected
in parallel to the first.
· ‘2.StarptInp’ = binary system input
in cases where the second star-point is connected to the
first by a switch, the closed position of the switch being
signalled a logical ‘1’ applied to a binary input.
· REs-2.Starpt = value of the grounding resistor connected to
the second star-point.
Note:
The stator ground fault protection scheme sees the ground-
ing resistor of the second star-point as a ground fault with the
value ‘REs-2.Starpt’.
Assuming a ground fault of resistance Rfs occurs, the total
resistance of the parallel resistors Rfs and ‘REs-2.Starpt’ is
calculated first. The value of Rfs can be simply determined
from this, providing the value of ‘REs-2.Starpt’ is known.
This procedure is subject, however, to certain restrictions.
The maximum ground fault resistance that can be detected is
approximately ten times the value of ‘REs-2.Starpt’.
Assuming the grounding resistor of the second star-point to
be 1 k
W, ground faults with a resistance less than 10 kW can
be detected. For this reason, choosing a grounding resistor
‘Res-2.Starpt’
³2 kW is recommended wherever possible.