A differential relay is a power system protection relay that operates when the phasor difference of two or more similar electrical quantities exceeds a pre-determined value. The two ends of overhead transmission lines are several kilometers apart, in order to compare two currents, a costly pilot-wire circuit is used.
Such pilot wires are too expensive for longer lines due to the greater length of pilot wires required. This is one of the reasons that differential protection scheme is not suitable method for protection overhead lines.
Also read:
- Fundamentals of Control Relays
- Differential Protection of Generators
- Differential Current Protection and Line Impedance Characteristics
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