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The coupling factors may be determined using the following equations:
Resistance ratio:
where
R
0M
X
0M
R
1
X
1
These values can be applied either to the entire double circuit line length or based on a per unit of line length,
since the quotient is independent of length. Furthermore, it makes no difference whether the quotients are cal-
culated with primary, or secondary values.
These setting values only apply to the protected line and are entered in the addresses 1126 RM/RL
ParalLine and 1127 XM/XL ParalLine.
For earth faults on the protected feeder there is in theory no additional distance protection or fault locator mea-
suring error when the parallel line compensation is used. The setting in address 1128 RATIO Par. Comp is
therefore only relevant for earth faults outside the protected feeder. It provides the current ratio I
earth current balance of the distance protection (in Figure 2-4 for the device at location II), above which com-
pensation 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 asymmetry, or a very small coupling factor (X
approximately 0.4), may a smaller setting be useful. A more detailed explanation of parallel line compensation
can be found in Section 2.5.1 under distance protection.
Figure 2-4
The current ratio may also be calculated from the desired distance of the parallel line compensation and vice
versa. The following applies (refer to Figure 2-4):
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
= Mutual zero sequence resistance (coupling resistance) of the line
= Mutual zero sequence reactance (coupling reactance) of the line
= Positive sequence resistance of the line
= Positive sequence reactance of the line
Distance with parallel line compensation at II
Reactance ratio:
Functions
2.1 General
/I
for the
E
EP
/X
below
M
L
63
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