and in figure
a three phase fault occurs beyond the capacitor. The resultant IED impedance seen from the
D
B
IED location to the fault may become negative (voltage inversion) until the spark gap has
flashed.
Distance protections of adjacent power lines shown in figure
are influenced by this
negative impedance. If the intermediate infeed of short circuit power by other lines is taken
into consideration, the negative voltage drop on X
C
is amplified and a protection far away
from the faulty line can maloperate by its instantaneous operating distance zone, if no
precaution is taken. Impedances seen by distance IEDs on adjacent power lines are presented
by equations
1
2
3
= +
+
I
I
I
I
EQUATION1915 V1 EN-US
(Equation 394)
X
X
I
I
X
X
DA
A
F
A
C
1
1
1
11
=
+
⋅
−
(
)
EQUATION1916 V2 EN-US
(Equation 395)
X
X
I
I
X
X
DA
A
F
A
C
2
2
2
11
=
+
⋅
−
(
)
EQUATION1917 V2 EN-US
(Equation 396)
X
X
I
I
X
X
DA
A
F
A
C
3
3
3
11
=
+
⋅
−
(
)
EQUATION1918 V2 EN-US
(Equation 397)
en06000621.vsd
B
A1
A2
A3
D
B
D
A3
D
A2
D
A1
jX
11
I
A1
I
A2
I
A3
I
F
-jX
C
jX
1
jX
2
jX
3
F
IEC06000621 V1 EN-US
Figure 228: Distance IED on adjacent
power lines are influenced by
the negative impedance
Normally the first zone of this protection must be delayed until the gap flashing has taken
place. If the delay is not acceptable, some directional comparison must also be added to the
protection of all adjacent power lines. As stated above, a good protection system must be able
to operate correctly both before and after gap flashing occurs. Distance protection can be
used, but careful studies must be made for each individual case. The rationale described
applies to both conventional spark gap and MOV protected capacitors.
Special attention should be paid to selection of distance protection on shorter adjacent power
lines in cases of series capacitors located at the line end. In such case the reactance of a short
1MRK 505 343-UEN B
Section 7
Impedance protection
349
Application manual
Summary of Contents for Relion 670 series
Page 1: ...RELION 670 SERIES Line differential protection RED670 Version 2 1 IEC Application manual...
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