Interim Report on the Study of Electromagnetic Inductive Interference from 11.4KV Three Phase, Four Wire, Common-Neutral Multi-Grounded Power-Distribution System to Telecommunication Circuits

The 11.4KV three-phase, four-wire, common-neutral multigrounded power distribution systems extensively adopted by Taiwan Power Company now introduces some new inductive interference on the telecommunication circuits due to the electrostatic and electromagnetic couplings, which we have never encountered before. The interference due to electrostatic coupling may be eliminated by earthing the metal sheath of communication cable. However, the interference due to the electromagnetic coupling can hardly be avoided. These power distribution systems may introduce interference on the communication circuits not only at fault condition but also at normal working state. At normal working state, the noise voltages and the longitudinal voltages induced on the telecommunication circuits will reduce the communication quality and make the telephone switching equipment misoperating. In worst condition, the dangerous voltages will appear on the telecommunication circuits and will destroy the communication equipment, or even human life. This paper presents the interim report on the study of inductive interference problems from the 11.4KV three-phase, four-wire, common-neutral multigrounded power distribution systems. It includes (I) Introduction, (II) General description of 11.4KV three-phase, four-wire, common-neutral power distribution systems, (III) Effects of such power distribution systems on the telecommunication circuits, (IV) Prediction formulae for computation of each kind of electromagnetically induced voltages, (V) Preliminary results of the study on the interference problems, (VI) Counter measures against inductive interference, (VII) Conclusion and Annex.