SPECTROSCOPIC MEASUREMENTS OF STREAMER FILAMENTS IN ELECTRIC BREAKDOWN IN A DIELECTRIC LIQUID

Emission spectroscopy has been utilized to provide information about t he electron density and temperature in streamers and breakdown arcs in transformer oil. Recorded spectra include strongly broadened hydrogen Balmer-alpha lines and vibration/rotation band profiles of the C-2 mo lecule. The origin of the observed broadening of hydrogen lines is dis cussed and it is concluded that it arises mainly from collisions with charged particles, so-called dynamic Stark broadening. By assuming tha t the broadening is due solely to dynamic Stark broadening, electron d ensities between 1 x 10(18) and 1 x 10(19) cm(-3) were obtained for th e rear of positive streamer filaments during the later stages of propa gation. For negative streamers we obtained an upper limit of 3 x 10(16 ) cm(-3) and for breakdown arcs electron densities up to 4 x 10(18) cm (-3). The temperature information in the C-2 emission profiles and the intensity ratio of the hydrogen Balmer lines are discussed. Rough est imations of the temperature are presented both for positive and for ne gative streamers.