From the above it can be deduced:
•
Error is proportional to the mutual coupling factor K
0m
•
The error increases with the parallel line earth current in relation to the relay current
•
The relay underreaches when I
EP
is in phase with I
ph
+ K
N .
I
E .
For a remote end terminal fault, this underreaching effect can be as high as 25%.
The distance protection zone reaches vary with the switching state of the parallel line
configuration. We consider the three most common operation modes:
1.
Case 1: Parallel line out of service and earthed at both ends
2.
Case 2: Parallel line switched off and not earthed or earthed only at one line end
3.
Case 3: Both lines in service.
The reach of the distance protection zone 1 will be different depending on the operation
condition of the parallel line.
Compensation of the mutual zero sequence impedance of parallel circuit can be achieved by
appropriate selection of zero-sequence compensation factor K
N
when parallel line can be in
service, out of service, or out of service and earthed at both ends.
Five zone distance protection, mho characteristic function (ZMHPDIS) can compensate for the
influence of a zero sequence mutual coupling on the measurement at single phase-to-earth
faults in the following two ways, by using:
•
Different setting values that influence the earth -return compensation for different
distance zones within the same group of setting parameters.
•
Different groups of setting parameters for different operating conditions of a protected
multi circuit line.
7.4.2.8
Tapped line application
SEMOD154453-265 v2
1MRK 505 343-UEN B
Section 7
Impedance protection
229
Application manual
Summary of Contents for Relion 670 series
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