ABB Relion 670 series - Page 190

The relative phase position of fault current I
F
compared to the source voltage V
S
depends
in general on the character of the resultant reactance between the source and the fault
position. Two possibilities appear:
1
1
0
0
- + >
- + <
S C L
S C L
X X X
X X X
EQUATION1935 V1 EN (Equation 54)
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
84. 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
55
1
> +
C S L
X X X
EQUATION1936 V1 EN (Equation 55)
en06000608_ansi.vsd
I
F
V
S
V
’
M
=
H
V
L
H
V
S
With bypassed
capacitor
I
F
H
V
L
V
S
H
V
C
V
M
H
V
S
With inserted
capacitor
ANSI06000608 V1 EN
Figure 84: Phasor diagrams of currents and voltages for the bypassed and inserted
series capacitor during current inversion
It is a common practice to call this phenomenon current inversion. Its consequences on
operation of different protections in series compensated networks depend on their
operating principle. The most known effect has current inversion on operation of distance
IEDs (as shown in section "Distance protection" for more details), which cannot be used
for the protection of series compensated lines with possible current inversion. Equation
55
Section 8 1MRK 506 369-UUS -
Impedance protection
184 Line distance protection REL670 2.2 ANSI
Application manual