Visual, ultraviolet and ultrasonic display of corona fields in air

Photographic techniques were devised to assist in examining flashover behaviour of insulators, and these were developed to display the electric-field pattern by photographing, in daylight, the ultraviolet portion of the corona spectrum. Later, a special television camera was used to enable the field phenomena to be observed continuously. These techniques give more information than can be obtained by normal methods of field analysis or by visual observation in darkness. The ultraviolet discharge is accompanied by ultrasonic noise, which has been detected, and the characteristic ultrasonic patterns for various gap geometries have been recorded. Both the ultraviolet and ultrasonic techniques may be used to determine corona inception in daylight, and both are more sensitive and reliable than visual observation in darkness.