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Arc Suppression Coils

The most common type of failure in an electrical power distribution network is a single phase-to-earth fault. Many utilities are successfully mitigating the effects of this type of fault by the use of earth-fault compensation systems.

In this scheme the systeme neutral is earthed through a high impedence reactor, a so-called arc suppression coil (Petersen coil), which is adjusted to the earth capacitance of the network. By utilizing continously variable arc suppression coils, ideal compensation of the earth-fault current, and therefore optimal efficiency of the resonant earthing technique can be achieved.

Based on years of experience in the construction of arc suppression coils, the coil design concept was thoroughly reviewed, resulting in a new and improved series of ASCs which meet today’s requirements for earth-fault compensation. By means of modern planning and production processes the economic efficiency of plunger core coils has been increased significantly.


More than

Arc Suppression Coils from Trench

delivered since the early 1970s

The new and improved series of ASCs are based on years of experience in the construction of arc suppression coils and meet today’s requirements for earth-fault compensation.


As the topology of an electrical power distribution network is subject to dynamic changes, the inductance of an arc suppression coil (ASC) used for neutral earthing must be variable.
Two basic principles to do so exist:

  • by performing switching operations on the reactor whereby coil sections are connected or disconnected (step coil). or
  • by continuous variation of the reluctance of the magnetic circuit by means of a mechanical drive (plunger core coil).

The earth-fault protection system developed by Trench Austria favours the plunger core coil compared to a reactor which is adjustable in finite steps, as:

  • no switching operations for inductance variation are required [preferable since switching can lead to network perturbations during earth fault] and
  • plunger core coils can be tuned precisely to minimum current at the fault location due to their continuous variability.

Main features

  • Continuously variable [in on-load condition] by means of variation of the air gap
  • Adjustment accomplished by means of a motor drive unit which may be either locally or remotely controlled
  • Automatic tuning to the actual network condition via an Trench Austria earth-fault compensation controller
  • Current regulation range standard 1:10 [other ranges on request]
  • Core induction practically constant within the whole regulation range and slightly below saturation point as current regulation is not achieved by connecting or disconnecting winding segments
  • Limitation of system related overvoltages
  • Compact construction

Special Designs

  • Sliding core ASC
  • Neutral earthig agreggate
  • Fixed core ASC
  • Dry type ASC/Neutral earthig agreggate

More information about design options und special designs can be found in the attached product brochure.

Standard design

  • Iron cored, oil insulated coil with continuously variable air gap adjustment in on-load condition by means of a plunger core
  • Suitable for automatic earth-fault compensation via a Trench Austria earth-fault compensation controller (see separate leaflet]
  • Winding material: aluminium
  • Motor drive unit: Trench Austria model DMA, 230/400 V, 50 Hz, [control voltage 230 V, 50 Hz], mounted on top of the tank, with hand-crank for emergency service and potentiometer for remote position indication, with separate control cabinet mounted on the side wall of the tank at operational height, oil-filled steel tank
  • with air cushion, corrugated steel tank up to 4000 kVAr, welded steel tank from 5000 kVAr
  • Oil-filling: mineral oil on naphthenic basis, PCB-free acc. IEC 60296: 2003
  • Mobile base with bidirectional rollers
  • Porcelain bushings as per EN 50180; for Um > 36 kV condenser bushings
  • Protective cap over low voltage bushings
  • Voltage measuring winding 100 or 110 V / 3 A
  • Power auxiliary winding [500 V, 5 % of coil power, 30 s short time duty] for current injection used for the Trench Austria earth-fault protection system EPSV [see separate leaflet]
  • One additional pocket for oil temperature indicator as per DIN 42554
  • Oil gauge without indicating contacts
  • Dehydrating silicagel breather
  • Surface treatment according to DIN EN ISO 12944-5-2008, system no. A1.11, top coat colour grey as per RAL 7033


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