Lessons Learned: Protecting Lines without Communication-Assisted Tripping

With modern communication, relays on transmission lines can clear nearly all types of faults instantaneously. However, there are many lines that do not have communication. Because of this, the need to understand and protect lines without the additional aid of communication is still a major requirement. An initial understanding of basic protection – step distance, overcurrent protection, and residual ground current – is required. For parallel lines, the concept of Mutual Coupling will have to be considered. For three-terminal lines, the effect of apparent impedance will also be examined for impedance reach and current flow.