Neutral point three-phase coils (neutral point coils)


Neutral point three-phase coils (neutral point coils)

Neutral point coils (zig-zag coupling) are used to earth a neutral via high impedance..

The neutral point three-phase coils are located in the HVB/HVA source stations and connected to the MV network. Neutral point three-phase coils allow:

  • The creation of an artificial neutral point
  • The introduction of a defined impedance between this neutral point and the earth, in order to limit the current during phase-earth faults on the network.

Main characteristics

  • Isolation voltage from 7.2 kV to 36 kV.
  • Hermetic structure, in a mineral oil bath, for an exterior installation.
  • Frame supporting a crystal-oriented iron-silicon sheet single-phase magnetic circuit.
  • Copper coils.
  • Insulation made of class H metal aramid fibres.
  • ONAN cooling mode.
  • Lifting by the 2 rings located on the cover.


  • Operating reliability: Exceptional mechanical resistance in terms of electro-dynamic force due to coils bonded with epoxide resin*.
    (*Qualification tests defined by the EDF HM-24/94/021 B specification dated 17/07/95, conducted in the Renardières Electrical Engineering Laboratory).
  • Endurance of inductances against thermal shocks caused by repeated neutral currents during operation (solid insulation with a thermal index > 180°)


  • Rural environment
  • Peri-urban environment
  • Urban environment

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