Consider the possible enlarging factor that might exist due to fault infeed from adjacent
lines. Equation 50 can be used to calculate the reach in reverse direction when the zone is
used for blocking scheme, weak-end infeed, and so on.
EQUATION1525 V4 EN (Equation 50)
Where:
ZL is the protected line impedance
Z2rem is zone 2 setting at remote end of protected line.
In many applications it might be necessary to consider the enlarging factor due to fault
current infeed from adjacent lines in the reverse direction in order to obtain certain
sensitivity.
Setting of zones for parallel line application
Parallel line in service – Setting of zone 1
With reference to section
"", the zone reach can be set to 85% of the protected line.
However, influence of mutual impedance has to be taken into account.
Parallel line in service – setting of zone 2
Overreaching zones (in general, zones 2 and 3) must overreach the protected circuit in all
cases. The greatest reduction of a reach occurs in cases when both parallel circuits are in
service with a single phase-to-ground fault located at the end of a protected line. The
equivalent zero sequence impedance circuit for this case is equal to the one in figure
54 in
section
"Parallel line in service".
Parallel line is out of service and grounded in both ends
Apply the same measures as in the case with a single set of setting parameters. This means
that an underreaching zone must not overreach the end of a protected circuit for the single
phase-to-ground faults.
Setting of reach in resistive direction
Set separately the expected fault resistance for phase-to-phase faults RFPPx and for the
phase-to-ground faults RFPGx (where x is 1-5 depending on selected zone) for each zone.
For each distance zone, set all remaining reach setting parameters independently of each
other.
These settings are useful only when the distance protection is set to quadrilateral
characteristic.
Section 6 1MRK 506 334-UUS A
Impedance protection
134
Application manual
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