Insulation design of a medium frequency power transformer for a cost-effective series high voltage dc collection network of an offshore wind farm

Paper in proceeding, 2020

DC can be used advantageously in transmission of power from offshore wind farms, utilizing series connection of the individual turbines’ outputs. Employing individual wind turbine converters, operating at high frequency, the advantage of DC can be achieved without the need for a large central converter. This solution obviates the need of expensive, bulky and heavy 50 Hz transformer or centralized DC/DC converter platforms.

Power electronic converters are among the enabling technologies to establish a series DC intertie system. The most important advantage of a DC/DC converter using a Medium Frequency Power Transformer (MFPT) is its compact size in comparison with a normal grid frequency transformer.

The function of a MFPT is to provide voltage step up and isolation between generators and the HVDC link. The need for a compact structure dictates further design constraints. A MFPT should have a high-power transmission capability from a small volume as well as minimal internal insolation distances. Further-more, in the series DC integration circuit, DC/DC converters can        experience a very high offset DC voltage depending on the converter’s position with respect to earth (in the range of one or two hundred kilovolts), while the primary side (wind turbine generator side) is only exposed to a few kV.

Due to its promising features, many research activities have been devoted to the design and optimization of MFPTs. However, only a few activities specifically addressed the insulation requirements for them. In this article, the challenges of the high DC voltage insulation design of a MFPT are presented.