EFFECT OF FLOATING CONDUCTING OBJECTS ON CRITICAL SWITCHING IMPULSE BREAKDOWN OF AIR INSULATION

The paper analyses the mechanism of breakdown of phase-to-ground and p hase-to-phase air insulation in the presence of large conducting float ing objects, under critical switching impulse stress. A new physical m odelling approach Is introduced which involves determination of the po tential of the floating object by charge simulation technique, assessm ent of streamer breakdown and/or leader inception and propagation in t he partial gaps and finally predicts the critical breakdown voltage of various configurations. As to phase-to-ground insulation, the investi gation covers rod-plane, conductor-plane and conductor-tower leg confi gurations with different gap spacings as well as different shapes, dim ensions and positions of the floating object. The phase-to-phase study additionally includes the effect of negative switching impulse conten t of the applied stress. The model is in excellent agreement with expe riment and provides a novel tool for assessment of the effect of float ing objects on switching impulse breakdown of some basic air gap confi gurations relevant to live line work.