Inception level of partial discharges in SF6 induced with short X-ray pulses

First generation gas insulated switchgears were constructed with large safety margin. Today´s trend is to reduce the size of the switchgears to save material and costs. With increased field strength due to reduced dimensions as well as increased pressure in the compartments, the influence of surface roughness, surface damages and conducting particles is increasing. Therefore the knowledge of the exact inception level of partial discharges due to those imperfections is of interest. The goal of the present contribution is to measure the discharge inception voltage in SF₆ in a homogeneous field configuration with a small protrusion with unprecedented high accuracy. With a short pulse X-ray source first electrons are provided within the critical volume. The experimental results show for a 0.2 MPa SF₆ insulation a threshold voltage of roughly 80 kV for positive and negative polarity at the protrusion, respectively. These inception voltages match the calculated theoretical inception level. The proposed method allows determining the inception voltage in a more efficient way as the experiment time is reduced.