Simplification of polyphase line protection

The term `polyphase line protection´ refers to a solid state line protection system in which the measuring units use sequence quantities. Such schemes are designated `polyphase´ since generally each measuring unit can respond to faults of a given type (e.g., phase-to-ground) on all phases or phase-pairs, and some measuring units can respond to different types of faults. Traditionally most GE solid state directional and distance measuring units have employed phase angle comparator circuits. This has been the basic approach used in solid distance relays from the early SLY/SLCG to the latest modular TLS relays. However, these units may also be implemented using an amplitude comparator as well as a phase angle comparator. The use of amplitude comparators is not entirely new in GE designs. They have been used for many years in the SLYP/SLYN and SLYP/SLCN polyphase relay schemes. The operating principles of phase and comparators and the existing amplitude comparators are reviewed followed by an introduction to the new features of the `energy comparators´ to be used in the polyphase line system relay system