Siemens siprotec 7SA522 User Manual page 170

Functions
6-22
Resistance ratio:
R
1
M
-- -
------- - =
3
R
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 pro-
tection 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
rent 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 suf-
ficient. 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
a smaller setting may be useful. A more detailed explanation of parallel line compen-
sation can be found in section 6.2.2.1, under distance protection.
I
I
EP
I
E
II
Figure 6-12 reach with Parallel Line Compensation at II
The current ratio may also be calculated from the desired reach of the parallel line
compensation and vice versa. The following applies (refer to Figure 6-12):
Reactance ratio:
R
0M
⋅
---------- -
R
1
x
l
X
X
1
0M
M
⋅
-- - ----------
------- - =
3 X
X
1
L
/I for the earth cur-
E EP
/X below approximately 0.4),
M L
7SA522 Manual
C53000-G1176-C119-2