Siemens 7SJ82 Manual page 598

Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
System Type/
Neutral-Point Treat-
ment
Isolated
Resistance-
Grounded
Parameter: α1 reduction dir. area, α2 reduction dir. area
•
Recommended setting value (_:105) α1 reduction dir. area = 2°
•
Recommended setting value (_:106) α2 reduction dir. area = 2°
With the α1 reduction dir. area and α2 reduction dir. area parameters, you specify the angle
for the limitation of the direction range. Siemens recommends using the default setting of 2°.
598
Description
In the isolated system, the capacitive ground reactive current 3I0 · sin φ is decisive for
the direction determination.
To evaluate the capacitive ground reactive current, set the parameters as follows:
•
Dir. measuring method = B0
•
φ correction = 0.0°
In isolated systems, a ground fault allows the capacitive ground-fault currents of the
entire electrically connected system, except for the ground current in the faulty cable
itself, to flow through the measuring point as the latter flows directly away from the
fault location (that is, not via the measuring point). The following formula can be used
to determine the pickup value of the Polarized G0/B0 threshold parameter.
where:
I : Ground current in the healthy case
0min
V0>: Pickup threshold of the residual voltage ≈ 0.02
In healthy operation, B0 ≤ 0.
For the 3I0> release thresh. value parameter, select around half of this capac-
itive ground-fault current flowing via the measuring point.
In the resistance-grounded system, the ohmic-inductive ground-fault current is decisive
for the direction determination.
To evaluate this short-circuit current, set the parameters as follows:
•
Dir. measuring method = G0
•
φ correction= -45.0°
For the setting of the Polarized G0/B0 threshold parameter, the rule of thumb
is: Set the pickup value according to the following formula where only the active
ground-fault current can be put into use.
where:
k : Safety margin, k = 1.2 (cable networks), k
s s
I : Active component of the ground-fault current of the protected line
0active
V : Secondary rated voltage in the healthy case
rated
I : Min. ground current in the healthy case, 5 mA to 10 mA (core balance current
0min
transformer), 50 mA to 100 mA (Holmgreen transformer)
V0>: Pickup threshold of the residual voltage ≈ 0.02
The 3I0> release thresh. value parameter must be set to a value below the
minimum expected ground-fault current.
= 2.0 (overhead lines)
s
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017