ABB RELION 670 Series Applications Manual page 328

Section 7
Impedance protection
Current inversion
Figure 192
source. It is generally anticipated that fault current I
power source towards the fault F on the protected line. Series capacitor may change the
situation.
Source voltage
Source
~
IEC06000607 V1 EN-US
Figure 192: Current inversion on series compensated line
The relative phase position of fault current I
general on the character of the resultant reactance between the source and the fault position.
Two possibilities appear:
-
X X
S
-
X X
S
EQUATION1935 V1 EN-US
The first case corresponds also to conditions on non compensated lines and in cases, when
the capacitor is bypassed either by spark gap or by the bypass switch, as shown in phasor
diagram in figure 193. The resultant reactance is in this case of inductive nature and the fault
currents lags source voltage by 90 electrical degrees.
The resultant reactance is of capacitive nature in the second case. Fault current will for this
reason lead the source voltage by 90 electrical degrees, which means that reactive current will
flow from series compensated line to the system. The system conditions are in such case
presented by equation
>
X X
C
EQUATION1936 V1 EN-US
322
presents part of a series compensated line with corresponding equivalent voltage
U
M
With bypassed
capacitor
U'
M
X
S
X
I
F
Z<
+ >
X 0
C L 1
+ <
X 0
C L 1
343
+
X
S L 1
flows on non-compensated lines from
F
With inserted
capacitor
U
Pre -fault voltage
Fault voltage
X
L1
F
C
en06000607.vsd
compared to the source voltage U
F
1MRK 504 152-UEN B
GUID-9F7FDF59-D0B4-4972-9CB0-B3D56DACA09E v1
depends in
S
(Equation 342)
(Equation 343)
Application manual