Radio interference at television frequencies
Crown effect on overhead power lines

In very hot, very dry weather, some medium-voltage lines equipped with suspended insulators produce violent disturbances.

These are inexplicable on the basis of the considerations set out in the previous paragraph, do not normally appear in the laboratory, and present an abnormal spectrum sufficiently extended towards high frequencies to interfere with television reception.

A detailed analysis of the mechanisms at work when these phenomena occur has shown that they are due to poor contacts at the joints of metal parts belonging to different elements: joints of conductor suspension parts and ball-sockets between two cap-stem insulators (cf. articles on overhead lines in this treatise). Oxidation...