ABB RET670 Applications Manual page 226

Section 3
IED application
220
E
(
w l j
= × × + -
i G sin t
L
Z
SC
æ
w
= + × -
2
Z R L
ç
SC L L
è
E
(
l j
= - ×
K I G sin
=
1 L t ( 0)
Z
SC
é
( )
l
×
E sin
ê
G
1
ê
=
K
2 b ê
× ×
L E R
- ×
G L
L
ê
×
ë 2 Z
SC
R
a
=
L
×
2 L
L
2
1 R
b
= -
L
× × 2
L C 4 L
L L L
EQUATION1996-ANSI V1 EN
The transient part has an angular frequency b and is damped out with the time-constant
.
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 89.
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 89 at approximately 21ms) is much slower than on non-
compensated line. This occurs due to the energy stored in capacitor before the fault.
[
) ( )
b
+ × × +
K cos t K
1
2
ö
1
÷
w
×
C
ø
L
)
-
R
- - × -
V L I
= =
C t ( 0) L t ( 0)
2
( )
l j
-
sin
1MRK504116-UUS C
]
( )
b a
× × × - ×
t
sin t e
2
w
× ×
E L
( )
l j
× - -
G L
cos
Z
SC
Application manual
ù
ú
ú
ú
ú
û
(Equation 135)