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Section 8
Impedance protection
268
Setting of zone 1
A voltage reversal can cause an artificial internal fault (voltage zero) on faulty line as
well as on the adjacent lines. This artificial fault always have a resistive component,
this is however small and can mostly not be used to prevent tripping of a healthy
adjacent line.
An independent tripping zone 1 facing a bus which can be exposed to voltage reversal
have to be set with reduced reach with respect to this false fault. When the fault can
move and pass the bus, the zone 1 in this station must be blocked. Protection further
out in the net must be set with respect to this apparent fault as the protection at the bus.
Different settings of the reach for the zone (ZMFCPDIS, 21) characteristic in forward
and reverse direction makes it possible to optimize the settings in order to maximize
dependability and security for independent zone1.
Due to the sub-harmonic oscillation swinging caused by the series capacitor at fault
conditions the reach of the under-reaching zone 1 must be further reduced. Zone 1 can
only be set with a percentage reach to the artificial fault according to the curve in
p
%
100
80
60
40
20
0
20
40
IEC99000202 V1 EN-US
Figure 130:
Reduced reach due to the expected sub-harmonic oscillations at
different degrees of compensation
=
c degree of compensation
EQUATION1894 V1 EN-US
Generator protection REG670 2.2 ANSI and Injection equipment REX060, REX061, REX062
60
80
100 %
99000202.vsd
æ
ö
X
c
ç
÷
ç
÷
X
è
ø
l
1MRK 502 071-UUS A
GUID-69E8535D-F3E2-483D-8463-089063712C67 v2
C
(Equation 123)
Application manual
130
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