Updated Transmission Line Protection Communications

The telecommunications revolution has increased the options and capabilities available for communications-based protection of transmission lines. To improve tripping speeds on long and short lines, protection engineers can select from a host of media, protocols, and logic schemes. The question to address is what communications scheme is best for which circumstances. This paper begins by establishing performance baselines of protection scheme operating times measured in event reports for a variety of in-service lines. It includes various successful systems and takes into account all of the elements that must be addressed when engineering a protection scheme, such as relay pickup time, communications interface and latency, coordinating time delays, and sequential tripping times. These in-service schemes are compared with laboratory tests of new systems, using radio and fiber-optic communications with serial and Ethernet protocols. Methods of optimizing different systems are tested and evaluated; the final results are tabulated and compared. No single scheme is best for all circumstances. With comparison data, the protection engineer can select the best options to improve the overall power system performance. Recognizing the strengths and weaknesses of different schemes assists the engineer in addressing new situations. Comparing laboratory tests and in-service performance provides a tool for evaluating a transition to new technologies.