Siemens siprotec 7SA6 User Manual page 202

Functions
Parallel Line Mutual
Impedance
6-20
 . ! = and  $QJOH, . ! = apply to the remaining zones Z1B
and Z2 up to Z5 (as seen from the relay location).
Note:
If a combination of values is set which is not recognized by the device, it operates with
preset values K = 1·e
0
(FNo ) or "'LV(UURU. =
„'LV(UURU. !=
"
If the device is applied to a double circuit line (parallel lines) and parallel line
compensation for the distance and/or fault location function is used, the mutual
coupling of the two lines must be considered. A prerequisite for this is that the earth
(residual) current of the parallel line has been connected to the measuring input I
the device and that this was configured with the power system data (Section 6.1.1) by
setting the appropriate parameters.
The coupling factors may be determined using the following equations:
Resistance ratio:
R
R
1
0M
M
⋅
-- - ---------- -
------- - =
3 R
R
1
L
with
R — mutual zero sequence resistance (coupling resistance) of the line
0M
X — mutual zero sequence reactance (coupling reactance) of the line
0M
R — positive sequence resistance of the line
1
X — positive sequence reactance of the line
1
These values may either apply to the entire double circuit line length or be based on
a per unit of line length, as the quotient is independent on length. Furthermore it makes
no difference if the quotients are calculated with primary or secondary values.
These setting values only apply to the protected line and are entered in the addresses
 505/ 3DUDO/LQH and  ;0;/ 3DUDO/LQH.
For earth faults on the protected feeder there is in theory no additional distance
protection or fault locator measuring error when the parallel line compensation is used.
The setting in address  5$7,2 3DU &RPS is therefore only relevant for earth
faults outside the protected feeder. It provides the current ratio I
current balance of the distance protection (in Figure 6-12 for the device at location II),
above which compensation should take place. In general, a presetting of 85% is
sufficient. A more sensitive (larger) setting has no advantage. Only in the case of a
severe system un-symmetry, or a very small coupling factor (X
approximately 0.4), a smaller setting may be useful. A more detailed explanation of
parallel line compensation can be found in section 6.2.3.1, under distance protection.
I
I
EP
I
E
II
Figure 6-12 reach with Parallel Line Compensation at II
0°
. The event logs
show the following information:
Reactance ratio:
X
M
------- -
X
x
l
(FNo )
"
X
1
0M
⋅
-- - ----------
=
3 X
1
L
/I
E EP
/X below
M L
C53000-G1176-C133-1
of
4
for the earth
7SA6 Manual