The solution over line current is in this case presented by group of equations
current consists also here from the steady-state part and the transient part. The difference
with non-compensated conditions is that
•
The total loop impedance decreases for the negative reactance of the series capacitor,
which in fact increases the magnitude of the fault current
•
The transient part consists of the damped oscillation, which has an angular frequency
b
and is dying out with a time constant
a
(
)
(
)
(
)
[
]
(
)
( )
(
)
(
)
1
2
2
2
1
(
0)
(
0)
(
0)
2
2
sin
cos
sin
1
sin
sin
cos
2
1
sin
2
2
1
4
a
w
l j
b
b
w
w
l j
w
l
l j
b
l j
a
b
- ×
=
=
=
=
×
× + -
+
×
× +
×
×
×
=
+
×
-
×
=
-
×
-
× ×
×
-
-
×
-
×
-
-
=
×
×
-
×
-
×
=
×
=
-
×
×
æ
ö
ç
÷
è
ø
é
ù
ê
ú
ê
ú
ê
ú
ê
ú
ë
û
t
G
L
SC
SC
L
L
L
G
L t
SC
G
L
L
G
C t
L t
SC
G
L
L
SC
L
L
L
L
L
E
i
t
K
t
K
t
e
Z
Z
R
L
C
E
K
I
Z
E
L
R
E
U
I
Z
K
E
R
L
Z
R
L
R
L C
L
2
L
EQUATION1909 V1 EN-US
(Equation 79)
The transient part has an angular frequency
b
and is damped out with the time-constant
α
.
The difference in performance of fault currents for a three-phase short circuit at the end of a
typical 500 km long 500 kV line is presented in figure
The short circuit current on a non-compensated line is lower in magnitude, but comprises at
the beginning only a transient DC component, which diminishes completely in approximately
120ms. The final magnitude of the fault current on compensated line is higher due to the
decreased apparent impedance of a line (60% compensation degree has been considered for a
particular case), but the low frequency oscillation is also obvious. The increase of fault current
immediately after the fault incidence (on figure
at approximately 21ms) is much slower than
on non-compensated line. This occurs due to the energy stored in capacitor before the fault.
Section 7
1MRK 505 343-UEN B
Impedance protection
168
Application manual
Содержание Relion 670 series
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