Setting Guidelines - ABB RET670 Applications Manual

Section 3
IED application
3.6.9.2
332
single phase-to-ground faults. At these faults, the fault resistance is composed of three
parts: arc resistance, resistance of a tower construction, and tower-footing
resistance.The resistance is also depending on the presence of ground shield conductor
at the top of the tower, connecting tower-footing resistance in parallel. The arc
resistance can be calculated according to Warrington's formula:
×
28707 L
=
Rarc
1.4
I
EQUATION1456 V1 EN
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-groundRFPG and phase-to-
phase RFPP should be as high as possible without interfering with the load impedance
in order to obtain reliable fault detection.

Setting guidelines

General
The settings for Distance measuring zones, quadrilateral characteristic ((ZMRPDIS,
21) are done in primary values. The instrument transformer ratio that has been set for
the analogue input module is used to automatically convert the measured secondary
input signals to primary values used in (ZMRPDIS, 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
• 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 from load transfer together with fault resistance may be considerable in
some extreme cases.
• Zero sequence mutual coupling from parallel lines.
/Z ratios of the various sources.
0 1
1MRK504116-UUS C
(Equation 262)
Application manual