T&D World Magazine

Cable/Telecom Interference

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Q: What are the forces in play when a HVDC cable link interferes with a telecoms line within its route?
Anon (UK)

A: The potential for interference between a DC link and telecommunication circuits depends on several factors:

  • DC converter harmonic generation, i.e. magnitude, frequency spectrum and degree of balance
  • Effectiveness of any dc side harmonic filtering deployed
  • Mutual electromagnetic coupling between the DC link and the telecommunications circuits, i.e. circuit proximity and length of exposure. Close proximity with long parallel exposure gives high coupling.
  • Type of communications circuit, i.e. audible frequency range telephone wire circuit
  • Harmonic cancellation, i.e. degree of harmonic balance on DC circuit (pole mode or ground mode), DC cable proximity (close laying versus spaced laying), use of twisted pair telephone circuits
  • Electromagnetic shielding of cable circuit or telephone circuit, i.e. use of conductor screen or metallic conduit.
  • The proper construction of the telephone circuit is very important for interference mitigation, e.g. use of twisted pairs and screening.

Michael Bahrman
HVDC Business Development

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