Effectiveness of electrostatic shielding in suppressing the impact of fast transients on transformer insulation

Transformers installed in wind and solar power plants require specific design considerations in order to protect them from the adverse effects of voltage distortions. A number of manufacturers practice the implementation of electrostatic shields in transformer windings to filter the transferred voltages. Although this method has shown some improvements, effectiveness of the electrostatic shielding for a broad frequency range requires further studies. Through an experimental study, the effectiveness of electrostatic shielding in alleviating the transfer of high frequency distortions from LV winding to HV winding and vice versa. To compare the internal field enhancement at different frequencies in the presence and absence of an electrostatic shield, the frequency response of the voltage distribution inside the transformer´s winding is also measured and analyzed. The results have shown that at some frequencies, the shield is beneficial in suppressing the stress, while at some other frequencies it amplifies the transferred voltages.