ABB REL670 2.2 IEC - Page 182

compensation degree has been considered for a particular case), but the low
frequency oscillation is also obvious. The increase of fault current immediately
after the fault incidence (on figure 84 at approximately 21ms) is much slower than
on non-compensated line. This occurs due to the energy stored in capacitor before
the fault.
0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2
10
5
5
10
t[ms ]
I[pu]
en06000610.vsd
IEC06000610 V1 EN-US
Figure 84: 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
85 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 85: Possible positions of instrument transformers relative to line end
series capacitor
Section 8 1MRK 506 369-UEN B
Impedance protection
176 Line distance protection REL670 2.2 IEC
Application manual