A novel scheme for current-only directional overcurrent relay

• The new directional relay algorithm is proposed to detect fault direction.
• The algorithm uses only current signal in relay location to detect fault direction.
• The algorithm is capable to detect fault direction in different situations.
• The algorithm is efficient in the case of close-in faults.
• The algorithm needs half cycle after fault to detect direction.

Overcurrent relays are widely used as main protection in sub-transmission and distribution systems. In mesh and multi-source networks, application of directional relay is unavoidable. Traditional directional overcurrent relays use the reference voltage phasor as the polarizing quantity to estimate the direction of the fault. Traditional direction distinguishing scheme is unreliable in the case of close-in faults. In this paper, a novel algorithm for directional overcurrent relay is proposed. The new algorithm uses only current signals for determining the fault direction. It uses superimposed component of the current signal and does not require phasor estimation. This new algorithm uses pre-fault current signal as the polarizing quantity. The proposed method is tested on simple power system in different situations. The results show it leads to fast and reliable directional protection.