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Some experimental results on discharge development in ultra-long air gaps (breakdown voltages, parameters of the leader stage) are presented. The obtained data are compared to available data on breakdown of long air gaps under positive switching pulses with critical time-to-crest. Existing empirical and theoretical formulae for calculation of sparkover voltage of rod-to-plane air gaps are reviewed. Electrical strength of ultra-long air gaps is considered based on general analysis of physical processes in leader stage of spark discharge. The electrical strength has been thus expressed in the given paper via some characteristic stabilization electric field for each spatial scale. As predicted here, the electrical strength along the lightning development path may decrease down to 3÷10 kV/m.

The matter to justify a choosing of the test conditions when studying the lightning stroked aircraft by the insulated scaled model is considered. The selectivity for striking points under the High Voltage (HV) pulses of different polarity and waveform was experimentally been determined. The negative polarity voltage pulses have been concluded to be preferably used. A new method for conducting such tests with the help of a physical laboratory model of the charged thunderstrom cell has been proposed. This method allows an induced both free-gained charge on the tested model objects to be modelled. A preliminary experimental study has been carried out.