ABB Relion 620 Series, Technical Manual

Page: 586 / 1224

Figure 304: Phase-segregated bus differential protection based on high-impedance
principle
CT secondary winding resistances (R
in
) and connection wire resistances (R
m
/2) are
also shown in
Figure 305
.
Figure 305
demonstrates a simplified circuit consisting only of one incoming and
outgoing feeder. To keep it simple, the voltage-dependent resistor (R
u
) is not
included. The wiring resistances are presented as total wiring resistances R
m1
and R
m2
.
R
m1
is the maximum wiring resistance concerning all incoming feeder
sets, whereas R
m2
is the maximum wiring resistance concerning all
outgoing feeder sets.
The lower part of
Figure 305
shows the voltage balance when there is no fault in the
system and no CT saturation.
Protection functions 1MRS757644 H
586 620 series
Technical Manual