Low voltage control system for telephone circuit - uses low voltage DC supplies with electronic signal amplification of signals sent over telephonic type cables to increase safety

摘要

Auxiliary and protective circuits in power systems are operated at low DC voltage compatible with solid state components rather than the 127V DC normally used. Communication is via telephonic cables rather than the heavy cables required with 127V DC supply, with local low voltage DC supplies providing power to amplify control signals. The lower signal levels and reduced cabling costs allow all signals to be brought to a central point for control, indication, or automatic test. Reduction in the level of stray pickup and induced surges is obtained by the use of twisted wires in shielded cable (14a). Electronic protection allows the earthing (45) of one side of the DC supply (31) to reduce conductor requirements. The low tension circuit is formed into two groups. One of the groups protects the lines, transformers and moving parts, against short circuits. The other group comprises the automation, command and signalling circuits.