LOCATION OF IMPACT POINTS IN THE IMPULSE FLASHOVER OF AIR FROM A POINTED ELECTRODE

The position of the flashover impact point on the plane electrode in a point-plane system has been investigated using both paper and alumini um foil to record the impact points. The impact points are close to th e centre at low voltages where the probability of flashover is very lo w, The spread increases as the voltage is raised through the 100% flas hover level, then closes in again towards the centre as higher overvol tages are applied. For a long gap the widest deviation of the impact p oints from the centre is produced by a negative voltage, but with a sm all gap the widest deviation is produced by a positive voltage. Althou gh the two methods of recording the impact points yield substantially the same distribution when flashover occurs, when the paper is used it considerably reduces the negative flashover voltage so that the usual polarity effect disappears. These results are discussed in terms of s pace-charge fields, which first modify the trajectory of streamers fro m the point electrode, and secondly initiate a triggering discharge be tween the plane electrode and the recording paper.