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Optical Current Transformers

Trench Group is a pioneer in innovation, leading the shift from analog to digital technologies in high voltage switchgears.

Trench optical current transformers do not contain electronic parts and do not use oil or SF6 as insulation media. Long-term sustainability and no environmental compromises – Trench optical current transformers are tested and available for worldwide applications.


Up to kV

operation voltage

The innovative Optical CT from Trench is also suitable for highest voltage levels.

Trench Group is pioneer in developing and supplying instrument transformers for innovative digital substations. Optical current transformers are now in operation in selected projects to prove the technical reliability.

Main Features

Trench optical current transformers are based on Faraday effect principle. The output is a low power optical signal which is then transferred to a merging unit which adapts it to communication protocols such as IEC 61850-9-2.

The use of non-conventional instrument transformers in AIS switchgears enables customers to measure a wide range of grid signals which are not usually detected by conventional instrument transformers. Moreover, the communication protocols allow measuring, protection, control features and digitalized grid information.

Product Design

  • Applicable for voltage level from 72 to 800 kV
  • No environmental compromises and never subjected to gas taxation
  • Galvanic separation between primary and secondary side
  • Single fiber-optic cable instead of several copper cables with large cross-sections

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

Customer Benefits

    • No Global Warming Potential:
      GWP = 0
    • No Ozone Depletion Potential:
      ODP = 0
    Based on 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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