ABB RELION RET670, Applications Manual

Page: 225 / 1016

network with and without series capacitor. Possible effects of spark gap flashing or
MOV conducting are neglected. The time dependence of fault currents and the
difference between them are of interest.
en06000609.vsd
~
e
G
(t)
i
L
(t)
R
L
jX
L
-jX
C
F
IEC06000609 V1 EN-US
Figure 96: Simplified equivalent scheme of SC network during fault conditions
We consider the instantaneous value of generator voltage following the sine wave
according to equation
61
( )
sin
w l
= × × +
G G
e E t
EQUATION1904 V1 EN-US
(Equation 61)
The basic loop differential equation describing the circuit in figure 96 without series
capacitor is presented by equation 62
( )
sin
w l
× + × = × × +
L
L L L G
di
L R i E t
dt
EQUATION1905 V1 EN-US
(Equation 62)
The solution over line current is presented by group of equations 63
( )
( )
( )
( )
0
2
2
sin sin
w l j l j
w
w
j
- ×
=
é ù
= × × + - + - × - ×
ê ú
ë û
= + ×
æ ö
×
=
ç ÷
è ø
L
L
R
t
L
G G
L
L t
L L
L
L
E E
i t I e
Z Z
Z R L
L
atg
R
EQUATION1906 V1 EN-US
(Equation 63)
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
1MRK 504 163-UUS A
Section 8
Impedance protection
Transformer protection RET670 2.2 ANSI 219
Application manual