Converter Transformer

One of the main differences from other types of transformers is that the load currents contain higher harmonics due to the distorted waveform. The converter to the transformer causes the distorted current waveform. This has to be considered current leads to higher losses & temperatures in the transformer. Network regulations also require reduction of harmonic distortion.
These transformers are used in applications where a variable speed is required on the motor shaft. They are used in a wide variety of applications such as rolling mill drives, ship propulsion systems, mine hoist drives, wind tunnels drives etc. The figure below shows a basic circuit diagram for a system configuration for a wind tunnel. The transformer is a 12-pulse unit that feed two 6-pulse rectifiers, which are connected to two inverters, which in turn is connected to a synchronous motor. The transformer is also equipped with a tertiary winding, which is to reduce the harmonic voltage distortion in the HV supply system as increasing the power factor of the load.