Setting Guidelines - ABB RELION RET670 Applications Manual

Section 8
Impedance protection
8.12.3
8.12.3.1
384
Fault resistance
The performance of distance protection for single phase-to-ground faults is very
important, because normally more than 70% of the faults on transmission lines are
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-US
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 RFPGZx and phase-
to-phase RFPPZx 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 (ZMFPDIS) 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 ZMFPDIS .
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 /Z ratios of the various sources.
0 1
1MRK 504 163-UUS A
GUID-83E3E475-3243-4308-9A91-B8DD9B47C276 v4
(Equation 283)
GUID-BA20D421-4435-44CA-A6E9-743E461F8C59 v2
Transformer protection RET670 2.2 ANSI
Application manual
IP14962-1 v1