The type 87B single-phase differential relay with high input impedance offers high-speed and sensitive protection against faults within the protected zone of substations or equipment. It is used in well known differential circuits with standard current transformers. The protection can be conveniently expanded to more CT's if breakers are added to more CT's if breakers are added to the existing scheme.
The type 87B is a high-speed or instantaneous differential voltage device intended primarily for bus differential protection. High current sensitivity also allows the relay to be used for differential protection of resistance grounded systems and machines or reactors.