EQUATION1456 V1 EN (Equation 76)
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 wind speed of
approximately 30 m/h
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.
3.6.1.3 Setting guidelines
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.
• Zero-sequence mutual coupling from parallel lines.
Setting of zone 1
The different errors mentioned earlier usually require a limitation of the underreaching
zone (normally zone 1) to 75 - 90% of the protected line.
1MRK504116-UUS C Section 3
IED application
177
Application manual
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