A statistical analysis of the AC dielectric strength of liquid nitrogen with IEC spherical electrodes under controlled conditions

In this paper an analysis of the breakdown strength of liquid nitrogen with IEC spherical electrodes and adjustable gap setting under as controlled as possible conditions is presented. The analysis is performed on commercial quality liquid nitrogen in the millimetre gap range, to collect data on the reduction of performances with respect to the technically pure liquids in a range of gaps not too far from those of practical applications, and with normalized electrodes to simplify technical comparison with other dielectric liquids. With a specially developed apparatus several series of tests are performed, to get additional informations on the gap effect in the millimetre gap range, and a thorough investigation on the influence of stirring between tests is carried out. Finally, a statistical analysis of the obtained results is performed to get further hints also on the conditioning effect as well as on the influence of sample size, and all the obtained results are compared and discussed.