that flow into the protection zone, that is, currents with positive value, must
be equal to currents that flow out of the protection zone, that is, currents with
negative value, at any instant of time.
Figure 309
shows an example of a phase segregated single busbar protection
employing high-impedance differential protection. The example system consists of
a single incoming busbar feeder and two outgoing busbar feeders. The CTs from
both the outgoing busbar feeders and the incoming busbar feeders are connected
in parallel with the polarity. During normal load conditions, the total instantaneous
incoming current is equal to the total instantaneous outgoing current and the
difference current is negligible. A fault in the busbar results in an imbalance
between the incoming and the outgoing current. The difference current flows
through the protection relay, which generates a trip signal.
Figure 309: Phase-segregated single busbar protection employing high-impedance
differential protection
Figure 310
shows an example for a system consisting of two busbar section coupled
with a bus coupler. Each busbar section consists of two feeders and both sections
are provided with a separate differential protection to form different zones. The
formed zones overlap at the bus coupler.
1MRS757644 H
Protection functions
620 series
Technical Manual
589
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