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Blue Instrument Transformers

Trench is one step ahead in reducing the presence of SF6 in instrument transformers by introducing a completely SF6 free solution up to 420 kV. Long term sustainability and no environmental compromise are now available with this innovative clean air insulated portfolio.

The unique portfolio of Clean Air instrument transformers is tested and available for worldwide applications.

Clean Air instrument transformer are installed and in service with outstanding results, proving this innovative and eco-friendly product is highly reliable for the use in AIS and GIS switchgear applications.

The Clean Air portfolio is fully compliant and tested to international standards. It provides the same electrical and insulation features as traditional insulation technologies while at the same time giving all the benefits of a SF6 free solution.



Global Warming Potential

Clean Air is the only eco-friendly and innovative alternative to SF6 insulations with a GWP of 0.


  • Complete portfolio available up to 245 kV (current and combined transformers), 420 kV (inductive voltage transformers)
  • Meet all lEC and ANSI metering and protection classes, including
    special core classes TPS, TPX, TPY and TPZ ones
  • CT ratings:
    • Rated primary current up to 6000A
    • Rated secondary current of 1A. 2A or 5A
    • Rated short time thermal current up to 80 Ka
    • Rated dynamic current up to 200 kAp
  • Primary and/or secondary reconnection available
  • Fully type tested according to international standards
  • Special tests are also available to meet specific customer requirements.

Trench Group is a pioneer in developing and supplying alternative and eco-friendly instrument transformer technologies like the Blue portfolio with Clean Air insulation.

Product Design

  • Complete portfolio available from 72 to 245 kV: current transformers, voltage transformers and combined current-voltage transformers
  • No environmental compromises and never subjected to gas taxation.
  • Internal insulation is made by clean air, thus:
  • F-gas free insulation with lowest requirements on training, transport, installation, operation, reporting and recycling
  • C-gas free with no risk of C-decomposition
    No gas recycling required
  • Clean air is the main insulation medium
  • Explosion-proof design
  • External insulation with composite insulator; porcelain insulator available on request
  • Bar-type primary conductor allows higher short circuit current and avoids large voltage drop across the primary winding
  • Available to withstand:
    • Internal arc effects [according to IEC 61869 – protection stage 1)
    • Heavy seismic solicitations, according to IEC 62271, IEEE 693 and specific customers’ requests

Product Process

  • Optimized design to manufacturing
  • Lean manufacturing concept applied to the whole supply chain
  • Modular design allows the use of reduced numbers of components
  • Partial discharge free design and process Maintenance free during a long lifetime of more than 30 years
  • Trench Management System has been certified to ISO 9001, ISO 14001 and OHSAS 18001 standards
  • Testing laboratory accredited according DIN EN ISO/IEC 17025

Customer Benefits

  • Environmental Benefits
    • No Global Warming Potential: GWP = 0
    • No Ozone Depletion Potential: ODP = 0
  • Technical Benefits
    • Based an the proven SF6 instrument transformer designs
    • Suitable for low temperature applications at -50°C and below
    • Maintenance free during a long lifetime of more than 30 years
    • No reporting or emission costs during operation and recycling:
      • No SF6- or F-gas tax or future risk
      • No C02 emission compensation or future risk
      • No F-gas documentation or reporting costs
      • No risk of F-gas gas recycling costs
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