Siemens siprotec 7SA6 User Manual page 289

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3U
0
3U >
0
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3I
0
3I >
0
FNr 1309
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3I0p InrushBlk
<HV
inrush
1R
stabilization

Op. mode 3I0p
Inactive
Forward
„1" Reverse
Non-Directional
Forward
direction
Reverse
determination
Figure 6-64 Directional zero voltage time protection with non-directional back-up stage
Phase Current
Stabilization
7SA6 Manual
C53000-G1176-C133-1
&
permissive
teleprot.
&
≥1
&
switch on
to fault
Non-symmetrical load conditions in multiple-earthed systems or different current
transformer errors can result in a zero sequence current. This zero sequence current
could cause faulty pick-up of the earth current stages if low pick-up thresholds are set.
To avoid this, the earth current stages are stabilized by the phase current: As the
phase currents increase, the pick up thresholds are increased (Figure 6-65). The
stabilization factor (=slope) may be changed by means of the parameter ,SK67$%
6ORSH (setting address , Subsection 6.5.2). It applies to all stages.
3I
0
I
N
,!
Figure 6-65 Phase current stabilization
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T 0
T 0
 UÃ…r‰ÃVv‰
 "DƒÃUryrƒ7D
<HV
1R
FNr 1310
>EF Inst TRIP.
 TPUAÃPƒÃH‚qr
"DƒÃTPUAU…vƒ
PICKUP+DIRECT.
&
PICKUP
Slope:
DƒuTU67ÃTy‚ƒr
 Vv‰Àvv€ˆ€
t
&
3U
0
&
≥1
&
≥1

<HV
T 0
&
1R

TPUAÃUv€rÃ9@G6`
blocking of the
pick up
I
Phmax
I
N
Functions
FNr 1357
EF 3I0p Pickup
FNr 1369
EF 3I0p TRIP
6-107