Trench Limited is a world leader in power engineering and the design of specialized electrical products- serving customers in the utility and industrial markets around the globe.

Their major product categories include air core reactors, instrument transformers, power quality products, earth fault protection, bushings, line traps, relay communications and protection and control equipment.

Trench's international operations provide fast and reliable support backed by a level of technical expertise and service that is unsurpassed within the industry. The Trench team of companies are dedicated to maintaining industry leadership through continuous improvement and innovation.

Voltage Transformers

Inductive voltage transformers are designed for 72.5kV to 800kV systems and are used to provide voltage for metering and protection applications

Features of Trench voltage transformers include:

  • Modern, lightweight design with high dielectric and mechanical strength.
  • Hermetically sealed construction.
  • High thermal burden capability (2500 VA or higher).
  • Power voltage transformers up to 30kVA.
  • Available in high accuracy designs.
  • Transmission line discharge capability.
  • Zero delay transient response
  • Ferroresonance suppression designs.
Voltage Transformers

Current Transformers

Current transformers are available for applications from 72.5kV to 800kV systems, for relaying cores, metering cores are offered in various combinations.

All Trench current transformer designs are based in "top core" or "heat type" construction. Features of this design and construction include:

  • Extremely high mechanical strength under short-circuit conditions.
  • Immunity to localized core saturation.
  • Negligible voltage drop across primary winding.
  • Hermetically sealed construction.
  • High seismic withstand.
  • Low partial discharge levels at test voltage.
  • Optional ground fault CT's and capacitance taps.
  • High accuracy designs (0.10%).
  • Broad range metering from maximum to less than 1% of rated current.
Current Transformers

Combined Instrument Transformers

The Trench combined instrument transformer (CIT) offers the station designer the possibility of being able to accommodate the current transformer and the potential transformer in one, free-standing unit. This allows optimum use of substation space while yielding cost savings by elimination of one set of mounting pads and support structures. In addition, installation time is greatly reduced.

As with individual current transformers and potential transformers, Trench CITs are available with either oil/paper or SF6 gas dielectric systems.

All operating and construction features are similar to those listed for the individual current transformers and potential transformers.

Trench offers an unparalleled scope of supply with the ability to provide CITs up to 800kV.

Combined Instrument Transformers

Capacitor Voltage Transformers

Capacitor voltage transformer (CVT's) are available for voltage ratings of 69kV - 800kV and are used to provide voltage for metering and protection applications. All CVT's are available with metering or relaying accuracy. Features include:

  • Highly reliable insulation system.
  • Film/synthetic fluid dielectric.
  • High stability of capacitance and accuracy.
  • Hermetically sealed construction.
  • Stainless steel expansion chamber with controlled pressure release.
  • Extra high strength porcelain for line trap mounting.
  • Composite insulator designs available.
  • Oil insulated base box for maximum reliability.
Capacitor Voltage Transformers



With 50 years of successful field experience, Trench is the recognised world leader in the design and manufacture of air core dry-type inductors for electric utility applications. The unique, custom design approach, along with fully integrated engineering and manufacturing facilities in both North America and Europe have enabled Trench to become the technical leader for high voltage inductors worldwide.

Line Traps for Power Line Carrier (PLC) communication systems represent a significant application segment for high voltage inductors.

Basic Function of Line Traps

Power Line Carrier (PLC) is a common method of Power System Communication, such as teleprotection, voice and data communication, etc. It has developed the reputation of being one of the most economical and reliable forms of communication and versatile in its application. Fig 2 shows a basic PLC system consisting of three distinct components:

  • Signal carrying medium (HV transmission line).
  • Communication apparatus (transmitters, receivers and associated components).
  • Coupling/blocking equipment such as coupling capacitors, line tuners (coupling devices) and Line Traps.

Line Traps are connected in series with HV transmission lines. The main function of the Line Trap is to present a high impedance at the carrier frequency band while introducing negligible impedance at the power frequency. The high impedance limits the attenuation of the carrier signal within the power system by preventing the carrier signal from being:

  • Dissipated in the substation.
  • Grounded in the event of a fault outside the carrier transmission path.
  • Dissipated in a tap or a branch of the main transmission path.

Manufacturers website:

For expert advice please call: 01608 662295

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