Problems of increasing cable use on high voltage and maximum voltage level


Because of the current political factors and the decreasing public acceptance of overhead lines more three-phase cables both in the 110-kV distribution network level and the 220/380-kV transmission network level will be used. This poses a problem for grid operators because the operating experience accumulated over many decades in overhead line technology does not apply. Another problem is that the electrical operating behaviour of the cables on the basis of

  • a considerably smaller characteristic impedance
  • a much greater charging capacity
  • a considerably larger R/X proportion of the positive sequence

is significantly different from that of overhead lines. Thus the electrical characteristics of the distribution and transmission networks are changed by the partial underground cabling. There are also completely different planning principles to be considered for pure 110-kV or 380-kV underground systems compared with overhead systems.

For the partial underground cabling of 110-kV networks or of the extra-high voltage grid there are, amongst others, the following considerations

  • wire and cable sizing / definition of conductor cross-sections
  • influencing of the stationary power flow and short circuit conditions in the grid
  • charging current compensation
  • influencing of the existing neutral point treatment or the single-pole fault currents
  • influencing of the grid resonances and harmonics
  • insulation coordination / protection against external and internal overvoltages
  • transient demands on switches
  • grid protection
  • handling of the cable shields

to be investigated and the corresponding conclusions with regards to planning and operation of the respective electrical energy supply grids need to be drawn.

P&M Power Consulting can draw on many years of experience of the technical and economic problems in the increasing use of cables on the HV and EHV level and offers you in this context engineering services on all the points stated above.