EQUATION1456 V1 EN (Equation 129)
where:
L represents the length of the arc (in meters). This equation applies for the distance protection zone 1.
Consider approximately three times arc foot spacing for the zone 2 and to give extra margin to the
influence of wind speed and temperature.
I
is the actual fault current in A.
In practice, the setting of fault resistance for both phase-to-ground RFPE and phase-to-
phase RFPP should be as high as possible without interfering with the load impedance in
order to obtain reliable fault detection. However for zone1 it is necessary to limit the reach
according to setting instructions in order to avoid overreach.
8.3.3 Setting guidelines
8.3.3.1 General
The settings for Distance measuring zones, quadrilateral characteristic (ZMQPDIS, 21)
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 ZMQPDIS (21).
The following basics must 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 ground-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-ground 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.The load transfer on the protected line
should be considered for resistive phase to ground faults
• Zero-sequence mutual coupling from parallel lines.
1MRK 506 369-UUS - Section 8
Impedance protection
Line distance protection REL670 2.2 ANSI 241
Application manual
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