Current-Only Directional Overcurrent Protection for Distribution Automation: Challenges and Solutions

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 sub-transmission systems use nondirectional 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 nondirectional type. In this paper, a novel current-only directional detection possibility is highlighted along with theoretical, test signal analysis, challenges and associated solutions. Possible utilizations of the current-only directional relay in the distribution side protection are described, which is a key focus area for enabling the smart grid.