Abstract
This paper reports a study of the origin and propagation of the space stem when a bi-exponential voltage impulse is applied to a 1.3 m point-plane air gap. The tests are carried out by using impulse shapes ranging from 0.25/2000 to 120/2000 mu s. Among these impulse shapes, the optimum with respect to the observation of the space stem formation is the 0.3/2000 mu s one. Some detailed photographs obtained with an image converter allow one to identify the following phenomena: negative streamers, a Trichel zone, a negative corona, a cathodic zone (cathodic stem), positive streamers and space stems. The current measurements allow one to quantify some energetic thresholds. The 5/2000 mu s impulse shape leads to a quasi-continuous space stem propagation in the gap. Thus it is possible to study the role of the positive and negative streamers in the space stem's behaviour, which is defined as their zone of origin. A stem replica mechanism is explained and some associated energetic criteria are discussed.
Export citation and abstract BibTeX RIS