Influence of a conducting body and space charge in the gap on breakdown probability

This work is the result of investigations of the influence of a conducting electrode and additional space charrge on the impulse discharge probability for positive and negative pulses (for the point to point geometry). The space charge was formed as an extension to the insulated conducting electrode, either with an alpha source or with the corrona discharge from a thin conducting electrode. In the experiment the surge generator of the Titograd's Technical Faculty was used, with the max. voltage of 800 kV, with positive and negative pulse polarity. The diameter of the thick electrode made of brass was 4mm and of thin one 0.4 mm, the length beeing changed from 5 cm to 10 cm and 13.5 cm. The isolated electrode was suspended on a thin nylon threated and moved in steps of 10 cm along the line connecting the end points of the HV electrode and the grounded LR electrode, measuring the discharge probability Psub(x). Experimental results show a very strong influence of the conducting electrode and the coresponding space charge on the discharge probability for all the three geometries of measurements. For positive HV pulses the formed space charge effectively lengthens the insulated electrode due to alpha rays for 2 cm, and due to corrona discharge for 4 cm. For negative HV pulses the formed space charge effectively shortens the insulated electrode due to alpha rays and to corona discharge for about 5 cm