2014/12/09 by Francisco de Leon, Francisco de León, Ashkan Farazmand +3 · 1 citation
Engineering · Materials Science · #Magnetic Properties and Applications #Non-Destructive Testing Techniques #Power Transformer Diagnostics and Insulation
paper · doi:10.1109/tpwrd.2014.2377199
openalex publication_date 2014/12/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/11
The purpose of core demagnetization is twofold: 1) to reduce the inrush currents when transformers are energized; and 2) to make sure that the frequency-response analysis (FRA) tests are consistent to avoid false diagnoses of damage during transportation. The significance of demagnetizing is presented on field measurements of an 80 MVA unit with FRA measurements. A new demagnetizer device with an alternating polarity dc voltage source is prototyped. Experimental verification of this prototype is presented for the demagnetization of transformers. A nearly complete demagnetization was observed in the laboratory for a small single-phase isolation transformer. The method proposed in this paper is applied to three-phase transformers with different core configurations and connections. Topologically correct modeling and numerical simulations confirm the full demagnetization of all branches of three-phase (three- and five-limb) transformer cores. Inrush current measurements and FRA plots before and after demagnetization confirm the effectiveness of the process.