The influence of the coupling capacitance and the frequency of the voltage stress with respect to a partial discharge measurement

For high frequency voltage stress the insulation has a different electrical behaviour if compared with dc or impulse voltage stress. This reflects directly in a decreasing breakdown voltage if the the frequency is increased. Due to this special requirements have to be meet by the experimental setup to ensure reliable measurement results. Especially the duration of a discharge stress at higher frequencies causes tracking and therefore breakdown may occur at a decreased voltage. It has to be ensured that the measurement conditions are reproducible. To reveal the changed discharge phenomenon and the influence of the frequency, the ratio of size between coupling capacitor and the specimen capacity has to be sufficiently high. Therefore it is an requirement that the voltage source withstands the increased load if the discharge causes tracking. During the whole time of exposure the voltage amplitude has to be kept constant therefore. The test equipment being described was used to measure the breakdown voltage at a high frequency stress