ABB RET670 Applications Manual page 225

1MRK504116-UUS C
Application manual
E
(
w l j
= × × + -
i G sin t
L
Z
( )
2
w
= + ×
2
Z R L
L L
æ w ö
×
L
j
=
atg L
ç ÷
R
è ø
L
EQUATION1906 V1 EN
The line fault current consists of two components:
• The steady-state component which magnitude depends on generator voltage and
absolute value of impedance included in the circuit
• The transient DC component, which magnitude depends on the fault incident angle
decays with the circuit time constant
[ ]
L R s
L L
EQUATION1907 V1 EN
The basic loop differential equation describing the circuit in figure
capacitor is presented by equation 134.
2
d i di 1
× + × +
L l R L
L L
2
dt dt C
EQUATION1908 V1 EN
The solution over line current is in this case presented by group of equations 135. The
fault 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
é
E
)
+ - ×
I G sin
ê
( )
=
L t 0
ë Z
(
w w
= × ×
i t ( ) E cos
L G
L
IED application
R
ù
- × L
t
( )
l j
- × L
e
L
ú
û
88 with series
)
l
× +
t
Section 3
(Equation 132)
(Equation 133)
(Equation 134)
219