The Stuck Protection is applied mainly in Low and Medium voltage systems. The concept based on the differential protection by connecting all CTs of all sources in parallel then connected to a simple Overcurrent relay that has an Overcurrent setting above 120% of the Full Load current of the Transformer Incomer of the Section with a time delay typically 0.1 Sec.

Current Transformers to be connected in parallel are:

o Transformer Incomer

o Bus Section / Bus Tie / Bus Coupler

o Metered Feeder (Feeders connected with another Substation Switchgear)

o Auxiliary Transformer Feeder that is connected to Aux Transformer through Ring Main Unit.

o Any other source.

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 trip faster than the Busbar Relay.