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0.1
0.12
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10
5
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10
t[ms ]
I[
pu
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en06000610.vsd
IEC06000610 V1 EN-US
Figure 99: Short circuit currents for the fault at the end of 500 km long 500 kV line
without and with SC
Location of instrument transformers
SEMOD168320-261 v2
Location of instrument transformers relative to the line end series capacitors plays an
important role regarding the dependability and security of a complete protection scheme. It is
on the other hand necessary to point out the particular dependence of those protection
schemes, which need for their operation information on voltage in IED point.
Protection schemes with their operating principle depending on current measurement only,
like line current differential protection are relatively independent on CT location. Figure
shows schematically the possible locations of instrument transformers related to the position
of line-end series capacitor.
-jX
C
CT 1
CT 2
VT1
VT 2
en06000611.vsd
IEC06000611 V1 EN-US
Figure 100: Possible positions of instrument transformers relative to line end series
capacitor
Bus side instrument transformers
SEMOD168320-266 v2
represent the case with bus side instrument transformers. The
protection devices are in this case exposed to possible voltage and current inversion for line
faults, which decreases the required dependability. In addition to this may series capacitor
cause negative apparent impedance to distance IEDs on protected and adjacent lines as well
for close-in line faults (see also figure
LOC=0%), which requires special design of distance
measuring elements to cope with such phenomena. The advantage of such installation is that
the protection zone covers also the series capacitor as a part of protected power line, so that
line protection will detect and cleared also parallel faults on series capacitor.
Line side instrument transformers
SEMOD168320-271 v2
represent the case with line side instrument transformers. The
protective devices will not be exposed to voltage and current inversion for faults on the
protected line, which increases the dependability. Distance protection zone 1 may be active in
most applications, which is not the case when the bus side instrument transformers are used.
1MRK 505 343-UEN B
Section 7
Impedance protection
169
Application manual
Summary of Contents for Relion 670 series
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