Variable frequency transformer - a new alternative for asynchronous power transfer

A new power transmission technology has been developed. The variable frequency transformer (VFT) is a controllable, bi-directional transmission device that can transfer power between asynchronous networks. Functionally, the VFT is similar to a back-to-back HVDC converter. The core technology of the VFT is a rotary transformer with three-phase windings on both rotor and stator. A motor and drive system are used to adjust the rotational position of the rotor relative to the stator, thereby controlling the magnitude and direction of the power flowing through the VFT. The world´s first VFT was recently installed in Hydro-Quebec´s Langlois substation, where it will be used to exchange up to 100 MW of power between the asynchronous power grids of Quebec (Canada) and New York (USA). This paper describes the VFT technology and provides an overview of the VFT equipment installed at Langlois substation. Results of commissioning tests are also included