Solid-State, High-Speed Phase-Comparison Relay Based on Zero Crossings: II - Design

The design of a comparison type of relay system for three-phase transmission lines based on the instantaneous position of zero crossings of the current waveforms is discussed. A composite signal based on these zero crossings is generated at both ends of a protected section and compared continuously by carrier current microwave or pilot wire means. It is extremely fast and can give as many as five clear indications of abnormal operation in the first cycle after a disturbance. Solid-state and magnetic devices are used exclusively for reliability, long life, and minimum power requirements.