Improved method for multiterminal line protection based on reverse distance backup zones

Multiterminal lines can be protected by distance protection and/or unit protection schemes. A well known fact of multiterminal lines, equipped with distance protection, is the inherent complexity for current in-feed and backup zone coverage. Prior to this millennium most relays (for this particular application) were unable to achieve the desired backup coverage due to limitations in zoned technologies. With the advent of numerical relays, these technical limitations have already been overcome. This paper challenges the current industry practices by examining the backup zone application and proposes a new approach to the backup zone application philosophy. By applying two reverse looking zones, multiterminal lines can be safely and reliably protected. This method will improve the stability of these lines and not restrict the ability of the line to carry large loads. Hence the remote backup functionality can be provided in the form of distance protection with reduced reverse looking settings reach. This method is not limited to multiterminal lines, but also lends itself to simpler applications. In this paper the author proposes a new method, by employing the latest technologies, to complement the availability of the existing schemes and application practices and will present the additional advantages of this proposal.