Smart distribution protection using current-only directional overcurrent relay

Overcurrent relays are widely used for power systems protection. Transmission side uses more directional type relays, while distribution systems, e.g., radial and ring-main subtransmission systems use non-directional types. The fault direction may be forward (between relay and grid), or reverse (between relay and source), the normal power flow being from source to the grid. Traditional directional overcurrent relays utilize the reference voltage phasor for estimating the direction of the fault. This requires measurement of both current and voltage using respective sensors. This makes the directional overcurrent relays more costly than the non-directional type. In this paper, a novel current-only directional detection possibility is highlighted along with theoretical and test signal analysis. Possible utilization of the current-only directional relay for intelligent directional protection in the distribution systems are described. Directional protection for distribution systems is a key focus area for enabling the smart grid.