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2 Functions
Parallel Line Mutual
Impedance
(optional)
52
The magnitude and angle of the earth impedance (residual) compensation factors
setting for the first zone Z1 and the remaining zones of the distance protection may be
different. This allows the setting of the exact values for the protected line, while at the
same time the setting for the back-up zones may be a close approximation even when
the following lines have substantially different earth impedance factors (e.g. cable after
an overhead line). Accordingly, the settings for the address . = and
$QJOH . = are determined with the data of the protected line while the addresses
. ! = and $QJOH, . ! = apply to the remaining zones Z1B
and Z2 up to Z5 (as seen from the relay mounting 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
´'LV(UURU. != µ (FNo 3655) appears in the event logs.
If the device is applied to a double circuit line (parallel lines) and parallel line compen-
sation 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
this was configured in the power system data (Section 2.1.3.1) by setting the appro-
priate parameters.
The coupling factors may be determined using the following equations:
Resistance ratio:
where
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 of length. Furthermore it makes
no difference whether 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
current balance of the distance protection (in Figure 2-4 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 asymmetry, or a very small coupling factor (X
. The information ´'LV(UURU. = µ (FNo 3654) or
0°
Reactance ratio:
of the device and that
4
/I
for the earth
E
EP
/X
below approximately 0.4),
M
L
7SA522 Manual
C53000-G1176-C155-3
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