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To determine the
Slope
, the restraint current of both sides (400 kV and 230 kV) must be used. The rated
current is used as starting value for the gradient. Since side 2 (230 kV) is the reference side for the normaliza-
tion, the value of the 400 kV side must be adapted to this rated current. The adaptation factor results from the
inverse ratio (230 kV/400 kV). The following restraint current goes into the calculation:
[fostbrst-231012-01.tif, 1, en_US]
Siemens recommends using the setting value 0.07.
•
Recommended setting value
(_:105) Slope
=
0.07
Protection of a Resistance-Grounded Star Winding (Y Side)
[dwrefspa-170712-01.tif, 1, en_US]
Figure 6-280
Application with Resistance-Grounded Neutral Point
To also capture faults in the resistance to ground, a current transformer must be installed at the neutral point
of the protected object (see
). The pickup values can be derived from the data in the example. As
side rated value, the following results:
140 MVA/(√3 · 20 kV) = 4042 A
The following threshold value results as lower limit:
Protection and Automation Functions
6.43 Restricted Ground-Fault Protection
SIPROTEC 5, Overcurrent Protection, Manual
875
C53000-G5040-C017-8, Edition 07.2017
Содержание 7SJ82
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