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At higher voltages, large auto-transformers are used to interconnect the 400kV-500kV systems with either the 230kV-275kV systems or 120kV-145kV systems (the exact values depend on the country being considered).

The HV and MV windings in an auto-transformer are connected together unlike in other transformers. The result is that the MV winding (common winding) is shared between the MV and HV systems. This results in a smaller and less expensive transformer than if the windings were separated as in a conventional fully rated two winding transformer.

  • constant quality because of modular design

  • large reduction of engineering time for standardised transformer designs

  • reduced engineering lead time for even the most complicated transformers

  • The windings are clamped independently from the core, so no stresses are transferred to the core steel material, resulting in improved core losses in service.

  • The coil clamping pressure is maintained by the steel tie-rods connecting the upper and lower steel clamping plates, meaning the winding pressure is maintained for the life of the transformer.


  • Max. Available Power (kVA)

  • Max. High Voltage (V)

  • Min. High Voltage (V)

  • Max. Low Voltage (V)

  • Min. Low Voltage (V)

  • Min. Available Power (kVA)