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S-03: Description

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The continuous filtration of tap-changers of power (main) transformers is generally focussed on the reduction of the internal contamination of its oil inventory caused by :

  • particles
  • moisture

When an on-load tap-changer works under load the dirt is always internally generated causing an increase in mechanical wear and a reduction of the dielectric strength of the oil as a consequence.

The another very unpleasant decrease of the dielectric strength of a switching oil is simultaneously caused by the moisture, because two potential sources of the water in the tap-changer always exist :

  • internal - as a by-product of the arc-induced decomposition of the oil.
  • external – due leaking of the air filter or conservator

The S-03 fitration unit was developed to handle a very new problem of recent versions of tap-changers built from non-hydroscopic (hydrofobic) insulants.

Hydrofobic insulants, on the contrary to the previously used hydroscopic materials (as e.g. boards) of „old“ tap-changers, do not have any „buffer capacity“ to the water - they are not able to bind the water from the oil.

Therefore any little amount of the water which enters into the oil inventory of a modern „hydrofobic“ tap-changer immediately increases the relative humidity and decreases the dielectric strength of the oil.

Users of „hydrofobic“ tap-changers are therefore exposed to a new and very uncomfortable operational reality.

While old „hydroscopic“ tap-changers were able to withstands the slight water contamination for relatively long time without the critical loss of the dielectric strength, the dielectric behaviour of modern tap-changers is very sensitive to any water input and the user is therefore forced to continuously remove the water and/or a dirt from his tap-changer to prevent the decrease of the dielectric strength of the oil.

The S-03 filtration unit, working continuously, satisfies both requirements by means of the external collection of the undesired substances.

The large-volume of the pre-dried cellulose insert simultaneously binds the water and dirt particles for relatively long time without negative impacts on the reliability of a tap-changer.

Basic advantages of the S-03 filter unit

  • the long-term preservation of the required dielectric strength of the oil
  • the reduction of the wear of mechanical parts
  • the reduction of costs due to prolonging of maintenance time-intervals
  • the strong reduction of the number of oil replacements = cost reduction
  • easy change of the filter insert under normal operational conditions.


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