The Variable Ratio Distribution Transformer (VRDT)






The VRDT offers a simple and cost-efficient alternative to conventional low-voltage grid expansion by helping release the potential of the medium voltage grid. This is done by effectively decoupling the low voltage from the medium voltage making it available separately, without having to build significant new infrastructure.



  • Develop robust and sustainable solutions for grid modernisation
  • Improve voltage quality
  • Innovatively develop the most cost-effective integration of renewable energy into the distribution grid


Main information:

With the growth in renewable energy as a distributed energy source it has become clear that new electricity production cannot be integrated into the existing German network in its status quo. Therefore, network expansion is an increasing necessity within Germany. The German low- and medium-voltage level networks, which already accommodate the majority of energy from renewable energy installations, differ in their network structure and need to adapt to handle the changing production-consumption dynamic.

With the VRDT, Avacon AG has enabled the conversion of a medium voltage bandwidth to a regulated reference voltage at the low voltage bus bar of the local secondary substation (bus bar = metallic strip that conducts a substantial current of electricity). The technology allows the decoupling of the low voltage from medium voltage. In accordance with current regulations, the complete bandwidth of +/- 10% of the nominal voltage is then available for both medium and low voltage separately. The VRDT thus helps to release potential for the medium voltage grid that was formerly reserved for the low-voltage.

This means that the VRDT is improving the voltage quality and becoming a cost-effective alternative to a conventional grid expansion (laying parallel cables and transformer replacements).


Additional information:

  • Comparisons of different scenarios show that the VRDT is a preferable economic solution if further renewables generation is implemented. Total costs of planned expansion projects with VRDT-use accumulate to 2.3 million €
  • Avacon AG is the European leading implementer of VRDT, with a total of 114 VRDTs in operation
  • Avacon AG is a German power and gas network operator as well as infrastructure service provider. Its activities are concentrated in large parts of Western and central Germany. Avacon provides energy to 16 million people. About 1,700 employees are working for Avacon AG in 15 different locations



RGI gratefully acknowledges the EU LIFE funding support:

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Funded by the European Union. Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the LIFE Programme. Neither the European Union nor the granting authority can be held responsible for them.