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Section 8
Impedance protection
8.1.3.2
8.1.3.3
190
The following basics should be considered, depending on application, when doing
the setting calculations:
•
Errors introduced by current and voltage instrument transformers, particularly
under transient conditions.
•
Inaccuracies in the line zero-sequence impedance data, and their effect on the
calculated value of the earth-return compensation factor.
•
The effect of infeed between the IED and the fault location, including the
influence of different Z0/Z1 ratios of the various sources.
•
The phase impedance of non transposed lines is not identical for all fault
loops. The difference between the impedances for different phase-to-earth
loops can be as large as 5-10% of the total line impedance.
•
The effect of a load transfer between the IEDs of the protected fault resistance
is considerable, the effect must be recognized.
•
Zero-sequence mutual coupling from parallel lines.
Setting of zone1
The different errors mentioned earlier usually require a limitation of the
underreaching zone (normally zone 1) to 75 - 90% of the protected line.
In case of parallel lines, consider the influence of the mutual coupling according to
section
"Parallel line application with mutual coupling"
are valid in your application. We recommend to compensate setting for the cases
when the parallel line is in operation, out of service and not earthed and out of
service and earthed in both ends. The setting of earth fault reach should be selected
to be <85% also when parallel line is out of service and earthed at both ends (worst
case).
Setting of overreaching zone
The first overreaching zone (normally zone2) must detect faults on the whole
protected line. Considering the different errors that might influence the
measurement in the same way as for zone1, it is necessary to increase the reach of
the overreaching zone to at least 120% of the protected line. The zone2 reach can
be even higher if the fault infeed from adjacent lines at remote end are considerable
higher than the fault current at the IED location.
The setting must not exceed 80% of the following impedances:
•
The impedance corresponding to the protected line, plus the first zone reach of
the shortest adjacent line.
•
The impedance corresponding to the protected line, plus the impedance of the
maximum number of transformers operating in parallel on the bus at the
remote end of the protected line.
If the requirements in the bullet—listed paragraphs above gives a zone2 reach less
than 120%, the time delay of zone2 must be increased by approximately 200ms to
1MRK 506 369-UEN B
and select the case(s) that
Line distance protection REL670 2.2 IEC
Application manual
SEMOD168247-15 v2
SEMOD168247-19 v3
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