Transmission line protective systems loadability: a report to the power system relay committee of the IEEE power engineering society prepared by working group D6

摘要

As transmission lines are loaded to higher and higher levels, and as the concept of open transmission access becomes a reality, the subject of load-carrying capabilities of transmission lines is becoming increasingly important. Short term ratings of lines are being applied for system operations, and conflicts with load limitations and the protection system settings are becoming more prevalent. Generally, the characteristics of the line itself should determine the limits of line loading. The level to which the protection system permits a transmission line to be loaded is based on transmission line protection design and setting philosophies, system characteristics, and protective equipment thermal ratings. A line relay load limit is established for the purpose of comparing with the line load limit to determine if steps must be taken to prevent undesirable relay operation. This paper discusses the various factors to consider concerning relays in the determination of transmission line loadability; considerations for protection design and relay setting philosophies to prevent limitations on line loadability; and utility practices for settings, equipment ratings, and methods to mitigate related problems.