A Modified Formula for Distance Relaying of Tapped Transmission Lines with Grounded Neutrals

Protection of tapped transmission lines with grounded neutrals has been always a challenging problem, usually resulting in compromise solutions. This type of lines may be protected by pilot relaying requiring dedicated and reliable telecommunication links. This paper proposes a modified distance relaying for protection of tapped lines with grounded neutrals under single-phase-to-ground (1-ph-g) faults. The proposed method uses only local measurements similar to conventional distance relays. Nonetheless, it facilitates fast fault clearing from both line ends over a wider portion of the protected line length. Regardless of whether or not the tapping transformer is in service, the method performs desirably with no need for signaling. The proposed method is extensively tested on a large number of test-systems using the sinusoidal steady-state analysis. It is also implemented into the National Instrument Compact-RIO embedded hardware that has been suitably coupled with the RT-LAB real-time digital simulator by Opal-RT. This setup is used to conduct extensive hardware-in-the-loop (HIL) testing. The improved performance together with simplicity of the proposed distance relaying makes it an attractive option to include in numerical protective relays.