ABB RELION 670 Series Applications Manual page 189

1MRK 504 152-UEN B
=
c degree of compensation
EQUATION1894 V1 EN-US
X is the reactance of the series capacitor
c
p is the maximum allowable reach for an under-reaching zone with respect to the sub-
harmonic swinging related to the resulting fundamental frequency reactance the zone is not
allowed to over-reach.
The degree of compensation C in figure
series capacitor reactance X
source to the fault. If only the line reactance is used the degree of compensation will be too
high and the zone 1 reach unnecessary reduced. The highest degree of compensation will occur
at three phase fault and therefore the calculation need only to be performed for three phase
faults.
The compensation degree in earth return path is different than in phases. It is for this reason
possible to calculate a compensation degree separately for the phase-to-phase and three-
phase faults on one side and for the single phase-to-earth fault loops on the other side.
Different settings of the reach for the ph-ph faults and ph-E loops makes it possible to
minimise the necessary decrease of the reach for different types of faults.
Reactive Reach
Compensated lines with the capacitor into the zone 1 reach :
A
X
LLOC
IEC07000063 V1 EN-US
Figure 102: Simplified single line diagram of series capacitor located at X
Application manual
æ ö
X
c
ç ÷
ç ÷
X
è ø
l
and the total positive sequence reactance X1 to the driving
C
X B
C
X
L
en07000063.vsd
station
101 has to be interpreted as the relation between
Section 7
Impedance protection
(Equation 90)
ohm from A
LLOC
183