Functions
2.8 Earth Fault Protection in Earthed Systems (optional)
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
238
During the selection of the current and time settings, regard must be taken as to whether a stage should be
direction dependent and whether it uses teleprotection. Refer also to the margin headings „Determination of
Direction“ and „Teleprotection with Earth Fault Protection“.
Figure 2-115
Curve parameters in the logarithmic–inverse characteristic
Zero-Sequence Voltage-controlled Stage with Inverse Characteristic
If you have configured the zero-sequence voltage controlled stage (address
131
Earth Fault O/C
=
U0
inverse
), you set the operating mode first: Address
3140
Op. mode 3I0p
. This stage can be set to operate
Forward
(usually towards line) or
Reverse
(usually towards busbar) or
Non-Directional
(in both direc-
tions). If the stage is not required, set its mode to
Inactive
.
Address
3141
3I0p PICKUP
indicates the minimum current value above which this stage is required to oper-
ate. The value must be exceeded by the minimum earth fault current value.
The voltage-controlled characteristic is based on the following formula:
U
0
is the actual zero-sequence voltage. U
0 min
is the setting value
U0inv. minimum
(address
3183
). Please
take into consideration that the formula is based on the zero-sequence voltage U
0
, not on 3U
0
. The function is
illustrated in the Technical Data.
Figure 2-116 shows the most important parameters.
U0inv. minimum
displaces the voltage-controlled char-
acteristic in direction of 3U
0
. The set value is the asymptote for this characteristic (t
→
∞
). In Figure 2-116,
a'
shows an asymptote that belongs to the characteristic
a
.
The minimum voltage
3U0>(U0 inv)
(address
3182
) is the lower voltage threshold. It corresponds to the line
c
in Figure 2-116. In characteristic
b
(asymptote not drawn) the curve is cut by the minimum voltage
3U0>(U0
inv)
(line
c
).
In address
3184
, an additional time
T forw. (U0inv)
that is added to the voltage-controlled characteristic
can be set for directional-controlled tripping.
With the non-directional time
T rev. (U0inv)
(address
3185
) a non-directional back-up stage can be gen-
erated.
