Design and Analysis of a Three-Phase Rotary Transformer for Doubly Fed Induction Generators

This paper presents the design and analysis of a novel three-phase rotary transformer that can be used to replace the brushes and slip rings of doubly fed induction generators. The transformer core is designed for easy assembly and to ensure a relatively constant reluctance while the secondary of the transformer is rotating. Guidelines for the air-gap size, stator and rotor core shape, and excitation current values are derived to ensure a balanced three-phase magnetic flux in the transformer core. The expression of the magnetizing coupling coefficient is developed with the introduction of different types of flux tubes. Guidelines and references for optimum design were provided.