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current from B might go in reverse direction from B to C depending on the system parameters
(see the dotted line in figure
), given that the distance protection in B to T will measure
wrong direction.
In three-end application, depending on the source impedance behind the IEDs, the impedances
of the protected object and the fault location, it might be necessary to accept zone 2 trip in
one end or sequential trip in one end.
Generally for this type of application it is difficult to select settings of zone 1 that both gives
overlapping of the zones with enough sensitivity without interference with other zone 1
settings, that is, without selectivity conflicts. Careful fault calculations are necessary to
determine suitable settings and selection of proper scheme communication.
7.4.3
Setting guidelines
SEMOD154496-1 v2
7.4.3.1
General
SEMOD154469-4 v7
The settings for Full-scheme distance protection, mho characteristic function (ZMHPDIS) are
done in primary values. The instrument transformer ratio that has been set for the analog
input card is used to automatically convert the measured secondary input signals to primary
values used in ZMHPDIS.
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 Z
0
/Z
1
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 terminals of the protected line, the fault
resistance is considerable and the effect must be recognized.
•
Zero-sequence mutual coupling from parallel lines.
The setting values of all parameters that belong to ZMHPDIS must correspond to the
parameters of the protected line and be coordinated to the selectivity plan for the network.
Use different setting groups 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. In this way it is possible to
optimize the settings for each system condition.
Appropriate selection of zero sequence compensation factor
KNMagx and KNAngx (where
x=1-5) when parallel line can be in service, out of service, or out of service and earthed at both
ends.
1MRK 505 343-UEN B
Section 7
Impedance protection
231
Application manual
Summary of Contents for Relion 670 series
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