ABB REG670 Applications Manual page 239

1MRK 502 071-UEN -
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual
Source voltage
With bypassed
capacitor
Source
X
S
~
I
F
IEC06000607 V1 EN
Figure 112: Current inversion on series compensated line
The relative phase position of fault current I
depends in general on the character of the resultant reactance between the source and
the fault position. Two possibilities appear:
- + >
X X X 0
S C L 1
- + <
X X X 0
S C L 1
EQUATION1935 V1 EN
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 113. 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 X
C S L 1
EQUATION1936 V1 EN
With inserted
capacitor
U
U
M
Pre -fault voltage
U'
Fault voltage
M
X
L1
F
X
C
Z<
en06000607.vsd
compared to the source voltage U
F
111
Section 8
Impedance protection
(Equation 110)
(Equation 111)
S
233