Protection application considerations for northern transmission

Two transmission systems in northern Saskatchewan, which have weak sources, long lines, high ground impedances, system harmonics and possible machine self-excitation, are discussed. These conditions create problems with protection applications. The weak nature of the system, coupled with long lines, makes it difficult to set the relays sensitive enough to detect faults. On the other hand, the expected harmonics and system self-excitation problems require the relays to be set less sensitively. These two points are conflicting requirements. The author discusses these problems, presents the solutions chosen, and provides a protection performance analysis