Siemens SIPROTEC 7SA522 Manual page 295

Parallel Line Mea-
sured Value Correc-
tion (optional)
Correction of Mea-
sured Values for
Load Current on
Double-end Fed
Lines
7SA522 Manual
C53000-G1176-C155-3
Note
The distance can only be applicable in the form of kilometres, miles or percent if the
relevant line section is homogeneous. If the line is made up of several sections with
different reactances, e.g. overhead line - cable sections, then the reactance calculated
by the fault location can be evaluated for a separate calculation of the fault distance.
In the case of earth faults on double circuit lines, the measured values obtained for
calculation of the impedance are influenced by the mutual coupling of the earth imped-
ance of both parallel lines. This causes measuring errors in the result of the imped-
ance computation unless special measures are taken. The device is therefore provid-
ed with a parallel line compensation function. This function takes the earth current of
the parallel line into consideration when solving the line equation, thereby compensat-
ing for the coupling influence as was the case with the derivation of the distance by
the distance protection (refer to Subsection 2.2.1 at "Correction of Measured Values
for Parallel Lines"). The earth current of the parallel line must, of course, be connected
to the device and the current input I
6\VWHP 'DWD  (Subsection 2.1.3.1 at "Current Transformer Connection").
The parallel line compensation only applies to faults on the protected feeder. For ex-
ternal faults, including those on the parallel line, compensation is impossible.
When faults occur on loaded lines fed from both ends (Figure 2-119), the fault voltage
U is influenced not only by the source voltage E
F1
if both voltages are applied to the common earth resistance R
ance measuring errors since the current portion I
suring point M. This measuring error in the X-component of the fault impedance (de-
cisive for distance calculation) may be considerable in long and heavily loaded lines.
A load compensation feature in 7SA522 is provided for the fault location calculation
which largely corrects this measurement inaccuracy for single-phase short-circuits.
Correction for the R–component of the fault impedance is not possible; but the result-
ant inaccuracy is not critical, since only the X–component is critical for the distance to
fault indication.
Load compensation is effective for single–phase faults. For single–phase to earth
faults, positive and zero phase sequence components of the symmetrical components
are used in the compensation.
Load compensation can be switched on or off. Off-switching is useful, for example,
during relay testing, in order to avoid influences caused by the test quantities.
must be configured correctly in the 3RZHU
4
but also by the source voltage E
1
can not be detected at the mea-
F2
2.17 Fault locator
,
2
. This causes imped-
F
295