In the case of single busbars with one defined incoming feeder and otherwise only defined outgoing feeders, fast busbar protection can be provided with no major additional effort by means of reverse interlocking. Such busbar configurations are common in medium-voltage systems and in auxiliary supply networks. The time-overcurrent relays already available for feeder protection are used.

In case of Single Bus Single Breaker with Bus Sectionalizer the Reverse Interlocking Busbar Protection can be done as shown in the below figure:

Cases:

o If the fault at F3, the summation of Incomer and Section CTs will be approximately zero or little bit difference as the loads may draw small current values.

o If the fault at F2, the summation of Incomer and Section CTs will be higher enough and will exceed the value I>> and the Relay1 would Trip the Incomer and Bus-Section “Busbar Fault”.

o If the fault at F3 the summation of Incomer and Section CTs will be higher enough and will exceed the value I>> but at the same time, I> stage of Feeder-01 will pick-up and thus will activate the Relay-1 Binary input which would block the Busbar Protection Tripping “Tripping of Incomer and Bus-Section”.

For busbars with one incoming feeder and radial outgoing feeders, i.e. without back-feeding, the reverse interlocking principle grants an effective and fast busbar protection