Audio Tone Relaying Tests on Telephone Channels in the Presence of Induced Voltage

Wire-line channels are often used for transmission of high-speed protective relaying signals at power stations. In situations where the communications plant is exposed to severe environmental stress during a power fault, special engineering of plant protection is necessary. A series of staged faults in an inductive environment was conducted jointly by the Bell System and Public Service of Colorado. The purpose of these tests was to observe the operation of the relaying terminals and monitor the communication system during a fault. A series of steps was taken to ensure cable dielectric integrity and eliminate sources of transmission interference. The communications system was stressed with up to 3800 V. rms generated by electromagnetic induction from a parallel faulted ll5-kV power line. The resulting specially engineered communications system withstood the induced voltage and allowed reliable transmission of relaying signals.