‘Pilot’ is the reference usually given to the communication channel of wire, carrier current or microwave between the two end points of a transmission system over which information transfer takes place. The important pilot relay protection schemes are wire pilot relaying, carrier current pilot relaying and microwave pilot relaying. These schemes can be further subdivided into phase comparison scheme, directional comparison scheme, combination of phase and directional comparison schemes and remote tripping scheme. The main principle involved here is differential relaying. The equipments required for pilot relaying are pilot wires, carrier wave generators, microwave generators, current transformers, blocking terminals, circuit-breakers etc. The various relaying principles utilized here are phase comparison, directional comparison, attenuation, tripping, sensitivity, speed, detection of sleet accumulation and transient blocking.
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