Siemens SIPROTEC 7SA6 Manual page 321

Zero Sequence
Voltage Stage with
Inverse
Characteristic
7SA6 Manual
C53000-G1176-C156-2
t
3I0p MaxT-DELAY
3I0p MinT-DELAY
0
3I0p Startpoint
1
Figure 6-75 Setting parameter characteristics in the logarithmic–inverse curve
For the zero sequence voltage controlled stage (address 131 Earth Fault O/C =
U0 inverse ) the operating mode is initially set: address 3140 Op. mode 3I0p . This
stage can be set to operate Forward (usually towards line) or Reverse (usually to-
wards busbar) or Non-Directional (in both directions). If this 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 operate. The value must be exceeded by the minimum earth fault
current value.
The voltage-controlled characteristic is based on the following formula:
2 s
---------------------------------------------------------- -
t =
⁄
0,25 U V U
–
0 0 min
U is the actual zero sequence voltage. U
0
(Address 3183 ). Please take into consideration that the formulae is based on the zero
sequence voltage U , not on 3U
0
tion (10.5, Figure 10-5).
Figure 6-76 shows the most important parameters. U0inv. minimum displaces the
voltage-controlled characteristic in direction of 3U
this characteristic (t → ∞ ). In Figure 6-76 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 6-76. In characteristic b the curve is cut by the
minimum voltage 3U0>(U0 inv) (line c ).
An additional time T forw. (U0inv) (address 3184 ) that is added to the voltage-
controlled characteristic can be set for directional-controlled tripping. The directional
additional time is usually not required and set to 0 .
With the non-directional time T rev. (U0inv) (Address 3185 ) a non-directional
back-up stage can be generated.
3I0p Time Dial
⁄
V
is the setting value U0inv. minimum
0 min
. The function is illustrated in the Technical Data Sec-
0
0
3I
0
. The set value is the asymptote for
Functions
/3I0p PICKUP
6-131