Single-Phase

BE1-87T Single-Phase relays require phase angle compensation to be accomplished externally by proper

connection of the system CT secondaries. A wye/delta transformer requires that the CT secondaries be

connected in delta for the wye winding and in wye for the delta winding. This type of connection also

eliminates the zero-sequence component of current which could cause a false trip (operation) during

external ground fault conditions on the wye system.

Three-Phase

BE1-87T Three-Phase relays can provide zero-sequence filtering and compensation for phase shifts

introduced by the connections of the power transformer. This 30° Phase Shift compensation (either ±30°

or no compensation) is field selectable. Additionally, this feature allows sharing the transformer differential

relay CTs with other relays or instrumentation.

BE1-87T relays use the highest input current (in per unit values) to operate on maximum restraint. The

relay does not have a conventional operate winding in the internal magnetics. Operating current is

developed within the electronics of the relay.

Unrestrained Trip

Severe internal transformer faults may cause CT saturation. Under such circumstances, harmonic

restraint transformer differential relays may fail to trip because of the extremely high harmonic content in

the waveform. Lack of operation can result in severe transformer damage.

BE1-87T relays provide an independent unrestrained tripping function. When set above the possible

inrush current magnitude, this function provides high-speed protection for the most severe internal faults.