The principle of zero-sequence voltage polarization with zero-sequence current
compensation is described in figure
. The same also applies for the negative-sequence
function.
In some applications the zero and/or negative source impedance may be so small
compared to the protected line impedance, that sufficient polarizing voltage cannot be
produced for far line end faults. In these cases the sequence voltage can be compensated
with an additional voltage KI
0
(for zero sequence polarizing) where K is a setting. The
resulting polarizing voltage is then -(V
0
+KI
0
) and V
0
is very small. The setting criteria for
K is that for a reverse fault |V
0
| > |KI
0
| (I
0
is reverse) and the compensated polarizing
voltage -(V
0
+KI
0
) is sufficient to operate for reverse faults. This is usually the case where
the line impedance is much greater than the source impedance.
Z0
SA
Z0
SB
Z0
Line
V0
I0
IF
I0
V0
K*I0
V0 + K*I0
Characteristic
angle
en06000418_ansi.vsd
ANSI06000418 V1 EN
Figure 75:
Principle for zero sequence compensation
Note that the sequence based additional directional element cannot give per phase
information about direction to fault. This is why it is an AND-function with the normal
directional element that works on a per phase base. The release signals are per phase and
to have a release of a measuring element in a specific phase both the additional directional
element, and the normal directional element, for that phase must indicate correct direction.
en06000419_ansi.vsd
Normal
directional
element
A, B, C
Additional
directional
element
Release of distance
measuring element
A, B, C
AND per
phase
AND
ANSI06000419 V1 EN
Figure 76:
Ground distance element directional supervision
Section 6
1MRK 506 335-UUS A
Impedance protection
164
Technical manual
Содержание REL650 series
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