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SF6 insulated Combined Instrument Transformers

SF6 insulated combined instrument transformers are used to convert high transmission line voltages and currents (voltage up to 800kV and current up to 6000 A) to standardized low and easily measurable values, which will be used for metering, protection and control of the high voltage system. As such, the need for accurate and reliable voltage and current transformation is essential.

The reliability and security of Trench gas-insulated instrument transformers is based on over 50 years of innovation with gas-insulated units operating under a wide range of environmental conditions. Combined instrument transformers also ensure suitable electrical insulation between high voltage and low voltage measuring equipment.

Our gas-insulated combined transformers are compliant to the latest international safety standard requirements in terms of explosion-proof, insulating material multiple chopped ageing, seismic qualification and extreme temperature conditions.

Modern production and testing facilities guarentee not only short delivery times but also a reliable operation for many years.


Reduce by %

the required footprint

for instrument transformers by combining Trench CTs and VTs into one product.

Thousands of gas-insulated combined transformers installed and in service for more than 50 years all over the world and in all environmental conditions are the best guarantee of the quality and reliability of our products.


  • Complete portfolio available from 72 to 800 kV
  • Meet all lEC and ANSI metering and protection classes, including special core classes TPS, TPX, TPY and TPZ ones
  • Rated primary Voltage up to 800 kV
    Rated primary current up to 6000A
  • CT ratings:
    Rated secondary current of 1A, 2A or 5A
    Rated short time thermal currrent up to 80kA Rated short circuit withstand up to 200 kAp
  • VT ratings:
    Maximun simultaneous burden [IEC cl. 0,2] 150 VA
    Maximun simultaneous burden [ANSI] 0,3Z/0,15Y
    Thermal limiting output up to 3000 VA
  • Suitable also for Line Discharge use
  • Wide-range ferroresonance-free design without the use of an external damping device
  • Fully type tested according to international standards
  • Special tests are also available to meet specific customer requirements

Product Design

  • SF6 is the main insulation medium
  • Explosion-proof design
  • External insulation with composite insulator; porcelain insulator available on request
  • External parts made of aluminum or stainless materials
  • Bar-type primary conductor allows higher short circuit current and avoids !arge 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 lang lifetime of more than 30 years
  • Trench Management System has been certified to ISO 9001, ISO 14001 and BS OHSAS 18001

Mechanical and electrical data

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