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Ester Insulated Instrument Transformers

The new Trench Ester Insulated Instrument Transformers Portfolio is the streamlined solution to address the increasing demand by the Energy Operators for Eco-sustainable HV Equipment as well enhanced safety requirements.


The use of Ester Insulated Instrument Transformer reduces the risk of environmental damages in case of insulating liquid leakages. The insulating fluid is classified as “readily biodegradable” according to OECD 301 biodegradability, adding an increased eco-performance during the whole product lifecycle:
• No pollution Hazard during manufacturing, testing and service;
• Recycling capabilities at the end of service life which results in much lower disposal costs.


TrenchEster Insulated Instrument Transformers are based on our conventional and proven insulation, well known worldwide since long time.
Thousands of Trench instrument transformers are installed all over the world in every ambient condition with full satisfaction of our Customers.


  • Meet all lEC and ANSI metering and protection classes, including special core classes TPS, TPX, TPV and TPZ ones
  • Rated primary Voltage up to 145 kV; rated primary current up to 5000A
  • Rated Secondary Voltages: 100 V, 100:1’3 V, 100:3 V, 110 V, 110:1’3 V, …
    Rated secondary current of 1A, 2A or 5A
  • Primary and/or secondary reconnection available. Rated short circuit withstand up to 200 kA peak
  • Fully type tested according to international standards
  • Special tests are also available to meet specific customer requirements.

Product Design

  • Ester paper internal insulation
  • External insulation with porcelain or composite insulator
  • External parts made of aluminum or stainless materials
  • CT core/windings located an the top of the equipment VT core/winding located an the bottom of the equipment
  • Bar-type primary conductor allows higher short circuit current and avoids large voltage drop across the primary winding
  • Available to withstand:
    • Effects of internal arc [according to IEC 61869 Standard]
    • Multichopped Test [according to IEC 61869 Standard]
    • Heavy seismic solicitations, according to IEC 62271, IEEE 693 and specific customers’ requests [i.e. Chile ETG A.0.20]
  • Hermetically sealed. A suitable lnox steel bellows located an the top of the Transformer allows the fluid volume variation and keep the internal pressure equal to ambient one in every service conditions

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 OHSAS 18001 standards

Mechanical and electrical data

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