The L90, a member of the UR family of protection relays, is a digital current differential relay system which provides protection for transmission lines. It may be applied on or adjacent to series compensated lines for three phase tripping. The L90 utilizes an innovative current differential scheme with adaptive restraint that allows the relay to operate correctly even when fault currents are distorted by harmonics or CT saturation. Models are available for application on transmission lines with 2 or 3 terminals. The relay may be used as a standalone device or as a component of an automated substation control system.
