High-speed distribution protection made easy: communications-assisted protection schemes for distribution applications

Communications-assisted protective schemes in transmission applications have been in service for decades. Recommendations for scheme application are well established, depending on the type of channel. Communications typically used for transmission line applications include power-line carrier, microwave, and optical fiber. With more emphasis being placed on distribution system reliability, there is a need to establish protection methods for the varying communications being used on these systems. By their nature, distribution lines are different from transmission lines. They are generally shorter, they have more tapped loads, and load currents are frequently on the same order of magnitude as fault currents. Communications systems are also different from those used on transmission lines, with associated differences in errors, outages, and signal-transmission reliability. This paper examines different communication paths for protection signals, such as spread-spectrum radio, fiber-optic cable, phone lines, and copper pilot wire. Data transmission statistics with performance measures are given for each type of communication. Based on the communication characteristics and its performance during faults, different protection schemes are studied, with total clearing times given for each scheme. The consequences of communications failure on each type of scheme are examined, including the possibility of misoperation, as well as backup clearing times.