Evaluation of transformer core contribution to partial discharge electromagnetic waves propagation

• Transformer core contribution to partial discharge electromagnetic waves propagation is evaluated.
• The effects of different thicknesses in windings insulation, and variation of tangent delta of oil insulation (especially for aged oil) are studied in different range of frequencies.
• The transformer contribution to PD EM waves depends on the PD occurrence location, core material and measuring frequencies.

Accurate Partial Discharge (PD) measurement requires the expansion of the measurement frequency range to Ultra High Frequency (UHF) band. For this it is needed to implement modern techniques when monitoring an important element of power system, such as power transformer. Different kind of experimental models, such as insulation defect models, and the complete transformer windings models are used to simulate the partial insulation failure situations which occur in a real transformer. However, since in these models, some kind of simplifications are employed which may result in an electromagnetic waves (EM) propagation pattern different from what exists in a real transformer and encounter errors in its PD measurement results. In this paper, the transformer core effects on PD EM wave propagation are investigated. To address this concern, different core designs are simulated. Finite Integration Time (FIT) method is used for electric field calculation through application of Microsoft CST microwave studio Software. The probes recorded electric fields are analyzed using wavelet transform (WT). A new approach based on energy scale coefficient (for each decomposition level) is used for mother wavelet selection. Results of these simulations demonstrate how existence of core and its design affect the characteristics of measured PD signal.