High frequency modelling of a transformer winding for partial discharge localization

Mohamoud Sagaale

The IEEE defines Partial Discharge (PD) as an electric discharge that only partially bridges the insulation between two conductors. In high voltage equipment such as transformers, floating components or defects in transformers can be the cause of partial discharge. Over periods of time the transformer ages and will result in faults. The materials in the transformer such as the windings can be damaged due to mechanical and electrical stresses. For this reason study of PDs is important for the prevention of faults and in maintenance of transformers. In this thesis a 3-phase 6.6kV, 1MVA high voltage transformer winding is modelled using the lumped parameter model. The transformer winding is then simulated using MATLAB/ SIMULINK along with SimPowerSystems toolbox. A simulated current pulse is injected at different positions along the winding, to simulate PDs in the winding. The responses due to the PD injection at various positions are measured from the line-end and analysed. The voltage response results indicated that PD’s along the winding have more oscillations moving away from the line-end, hence PD at disc pair 10 is the most oscillatory. It was also evident that as the PD moves away from the line-end the waveforms have a greater distortion. The frequency spectra results showed that the poles (crests) always occurred at fixed frequencies no matter the location of the PD, thus the frequency of the poles are independent of the PD location. However the zeros (troughs) altered in frequency depending on the PD location, and as the PD source moved away from the line-end, the zeros increased in frequencies.

High frequency modelling of a transformer winding for partial discharge localization

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