A Discussion on recent advances in heavy electrical plant - Switching surges and air insulation

Some thirteen years ago, a reduction was noticed in the strength of air insulation when subjected to slowly rising positive impulse voltages such as occur during switching operatons on power systems. Methods for the prediction and control of switching overvoltages have been established and empirical data collected in high voltage laboratories. Insulation against switching surges is now seen as an important factor in the feasibility of power transmission at ultra-high voltages. The strength of large air gaps depends not only on the geometry of the gap (point-plane, rod-rod, etc.), but also on the waveshape of the applied voltage. The practical diversity of gaps and waveshapes is such that a sound theoretical approach must be found if laboratory testing is to be kept within bounds. Qualitative understanding of the breakdown processes in long air-gaps has advanced rapidly in the last two years. Predictive mathematical models are now being constructed.