ABB RELION 620 Series Technical Manual page 481

1MAC504801-IB E
620 series ANSI
Technical Manual
GUID-C5514DFD-9FE8-4BF7-93D8-14186867D0F8 V1 EN
Figure 223: Phase-segregated single busbar protection employing high-impedance
differential protection
Figure 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.
When the bus coupler is in the open position, each section of the busbar handles the current
flow independently, that is, the instantaneous incoming current is equal to the total
instantaneous outgoing current and the difference current is negligible. The difference
current is no longer zero with a fault in the busbar and the protection operates.
With the bus coupler in the closed position, the current also flows from one busbar section
to another busbar section. Thus, the current flowing through the bus coupler needs to be
Section 4
Protection functions
475