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High-performance pressring for power transformers

The current flowing through the transformer winding generates longitudinal force. In case of short circuit this force can multiply. When a big transformer has a winding of 2000-600mm outside-inside diameters the force can come to several hundreds of tons. For this reason the transformer winding are clamped down with large rings. Because of the presence of an electrical field the pressring cannot be made of metal or any other electrical conductors. Since the invention of transformers pressrings have been made of wood, prespan paper.

A pressring with an outside diameter of two meters can be 150-200mm thick. This thickness influences the height as well as the transportability of transformers. This is one of the disadvantages of currently used pressrings. The other problems are that the wood can break in case of short circuit or under the drying process.

The above mentioned facts inspired Kompozitor Ltd. to develop composite material transformer pressrings. A glass fibre with a thermosetting composite resin coating is wound up and given heat treatment to form a homogenous material ring.


Kompozitor Kft. - Transring



External diameter: 500-2500  mm
Internal diameter: > 250  mm
Thickness: 30-150  mm

Mechanical characteristics of the material:

Density: 2  kg/dm3
Modulus of elasticity: 40.000  MPa
Compression strength (radial): 400  MPa
Bending strength (axial): 500  MPa
Operating temperature: -50-140  °C
Water absorption: ~0  %

Electrical characteristics of the material:

Electrical strength in oil: 15  kV/mm
Permittivity: 5  
Partial discharge inception voltage: 6  kV/mm

The advantages of using Transrings instead of wooden rings:

  • Higher short circuit proofness
  • Bigger compression and bending strength in case of static loading
  • Higher fatigue limits in case of dynamic loading
  • The necessary less thickness allows the usage of a lower core
  • Cost saving of steal core
  • Less oil is necessary
  • Wiring does not affect structural characteristics
  • Higher operational temperature
  • The height of transformers can be reduced


Clicking on the pictures below you can download the data sheet and a presentation of Transring.


HoneyKomp_DataSheet HoneyKomp_DataSheet



Since the launch of Transring in 1996 several rings have been mounted into the 200-320 MVA transformers of CG Electric Systems Hungary Zrt. (former Ganz Transelektro Zrt.)

The Power division of Alstrom Hungária Zrt. uses Transring products as spacers of radial clamps in their steam turbines.


Kompozitor Kft. - Transring

Brownish-red 2-meter diameter Transring.