Introduction  Low-frequency alternating current power transmission technology has attracted wide attention. Although its theoretical research continues to go deeper, there are still many problems to be solved before its engineering implementation in large-capacity long-distance offshore wind power transmission scenarios. The development and selection of offshore low-frequency main transformer is one of such problems.

  Method  Based on the detailed description of the structure and working principle of the low-frequency alternating current transmission system for offshore wind power, the low-frequency operation characteristics of the offshore main transformer were analyzed.

  Result  If the transformer is transformed by increasing the core section and winding turns, the weight, volume and total loss of the low-frequency transformer will be increased greatly, which will have a great impact on the economy of the overall transmission scheme of offshore wind power and the load and layout of offshore step-up station. It is necessary to study the miniaturization, light weight and low loss design of offshore low-frequency transformer.

  Conclusion  The key transformation technologies of offshore low-frequency transformer are discussed in detail. In the aspect of transformer core, the research and development of high-performance oriented silicon steel sheet with high magnetic density or low loss is the most concerned low-frequency transformer transformation technology. With the offshore advantages, the design of water cooling mode and intelligently monitored transformer cooling mode can also optimize the overall quality and volume of transformer. Ester high ignition point insulated oil transformer has the advantages of biodegradability, inflammability and high reliability of oil, which means that it is more suitable for offshore low-frequency transformer compared with the conventional mineral oil transformer. The future development of the above key technologies is expected to provide reference for the development and application of large-capacity and high-voltage class offshore low-frequency transformer, so as to promote the engineering practice of low-frequency technology in the field of large-capacity long-range offshore wind power transmission.