Silicone Transformer Oil

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Silicone Transformer Oil
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• Mineral oil is by far the most abundant
  transformer fluid in use in Australia. There are
  however other options, which do have their place
  in specific transformer applications including
  chlorinated hydrocarbons (e.g. PCB which is
  banned), high molecular weight hydrocarbons,
  biofluids, esters, and silicone fluids.

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• Silicone fluids or more correctly
  polydimethylsiloxane (PDMS) are a type of fully
  synthetic oil and can be formulated for use as a
  dielectric fluid in high voltage transformers.
  Pure PDMS is additive-free (so no pour-point
  depressants, heat-stabilizers or halogens are
  present) and is compatible with the internal
  materials used in the construction of a
  transformer including copper, aluminium, steel,
  timber and paper. Silicone dielectric coolant is
  equally compatible with modern oil processing
  equipment (e.g. filters and drying units) and
  procedures.

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• Silicone oil is proudly man made. The chemical
  process that produces dimethylsiloxane starts
  with the production of dimethylchlorosilane from
  chloromethane and silicon. This then goes
  through a series of hydrolysis reactions to
  eventually result in cyclical siloxane.
  Manufacturers include Dow Corning, Wacker, and
  ClearCo. Although there are no manufacturers in
  Australia, Benzoil can import and does supply
  silicone transformer oil through our valued
  channel partners with stock available from our
  local warehouses.

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• Like any transformer oil, electrical grade
  silicone oil is characterized by properties
  including
• High dielectric strength
• High flash point
• Broad in service temperature band
• Low vapour pressure
• Low pour point
• Low viscosity change at high and low temperatures
• Chemical inertness

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• When selecting a transformer fluid the
  application, expected usage patterns and intended
  location of the asset are vital considerations.
  The key selling point and most prominent
  advantage a silicone fluid has over mineral oil
  has to do with thermal stability, flash point and
  fire point. Silicone transformer oil can be
  subjected to temperatures markedly above normal
  operating temperatures for a transformer, and to
  its credit will resist creating excessive vapour
  pressure, withstand dielectric break down, nor
  will it generate corrosive by-products.

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• Research indicates that insulating paper
  impregnated with silicone oil does age at a
  slower rate than in standard mineral transformer
  oil due to its capacity to draw out and absorb
  moisture.
• The fire point of a liquid is the temperature at
  which it will continue to burn after ignition for
  at least 5 seconds, while the flash point is the
  lowest temperature at which it can form an
  ignitable mixture in air. For silicone
  transformer oil the fire point tends to be around
  370 degrees C, where the flash point is around
  300 degrees C. Compare this with 160 and 175
  respectively for mineral transformer oil.

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• Although we are familiar with seeing
  transformers up poles and in various outdoor
  settings, spare a thought for the engineer who
  must design to allow for transformers in building
  basements, under city streets, in train tunnels
  and on city building roof tops. With fire
  hazards more of a concern in indoor
  installations, liquids with higher flash point
  represent less of a fire hazard. The use of
  silicone oil in transformers indoors and in
  sensitive locations does result in lower
  insurance premiums to the transformer owners.
  This financial incentive is driving transformer
  retrofills, where standard mineral oil is
  decanted and swapped out for a synthetic
  equivalent.