Power Transformer FRA Studies Using Ladder, Multi-Conductor Transmission Lines (MTL), Circular MTL, and Hybrid Winding Models

For numerous transformer studies, including impulse tests, sweep frequency response analysis, deformation diagnostics, fault localization, resonance behaviour, and voltage distributions, a suitable winding model is required. This paper examines several transformer winding modelling methodologies, including multi-conductor transmission lines based on turn-to-turn modelling, lumped ladder networks, and hybrid models based on disk-to-disk modelling. Presented are state- space and circuit-based methodologies for determining driving point impedance, frequency response analysis, and transfer function that can be utilised for transformer monitoring and diagnostics. Modelling and response computation of a continuous eight-disk transformer winding are described.