Protective Relaying Systems Using Pilot-Wire Channels

This paper has presented a variety of pilot-wire relaying systems. Each has its field of application which is influenced by technical and economic factors, as listed in the previous section. In many cases, particularly where tapped or multiterminal lines are concerned, combinations of the various systems will be necessary for high-speed simultaneous clearing of faults. Experience has indicated that well-designed private-wire circuits are likely to be more reliable than leased circuits. A basic reason for this is the difference in philosophy between communication and power system engineers as to what constitutes a reliable channel. However, given a specific channel, there are no significant differences in the expected reliability of the vanrous relaying systems. The reliability and security of pilotwire relaying can be improved by the following: 1. The use of fault detectors to supervise conventional a-c pilot-wire relay tripping, where their use will not compromise the relay system performance. 2. Supervision of the receiver-relay contact of the transferred-tripping schemes by fault detectors. 3. Channel-failure supervision of the trip circuit with blocking schemes. Table III gives the salient features of the pilot-wire relaying systems described in this paper.