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Description
Superconducting wind generators provide significant advantages in terms of power density over conventional wind generators, resulting in reduced weights and volumes, which contribute to significant cost reduction in the installation and maintenance of offshore wind turbines. An efficient cryogenic cooling system is crucial to ensure the safe and stable operation of low-temperature superconducting (LTS) excitation coils. To enhance the maintainability and economic efficiency of the superconducting wind generator, especially given the significant cost of liquid helium, the cryogenic cooling system of the 20 MW LTS excitation wind generator adopts a modular cryostat structure and utilizes a helium pipe cooling technology. The generator design includes a stationary armature and rotating LTS excitation windings supplied by rotary transformers, thereby eliminating the use of brushes and slip rings and reducing operational fault rates. Additionally, the wind generator experiences frequent start-ups and shutdowns throughout its operation. Achieving efficient and stable cryogenic cooling for both rotating LTS coils and those stationary at any angle using pipe cooling technology presents a novel and challenging task.
This paper presents the detailed structural design of the modular cryostats and the pipe cooling system for a 20 MW LTS wind generator, along with an analysis of the effectiveness and heat transfer performance of the cryogenic system. The structure of helium pipes has been optimized with the aim of enhancing the thermal efficiency between the LTS coils and the cryocooler cold head. Considering the influence of gravity, the analysis investigates the flow characteristics of helium gas and liquid helium, as well as the overall heat transfer efficiency, in pipes under both rotating conditions and stationary conditions at various angles. By incorporating the calculated thermal loads on the LTS coils, such as conductive heat leakage, radiative heat leakage, and current lead heat leakage, the analysis determines the temperature differences between the coils and the cold head during both rotating and stationary conditions. This analysis validates the effectiveness of the pipe cooling system.
