Research On Fast Time Domain Solution Of Lightning Electromagnetic Field And Lightning Location

The location of lightning strike point is of great significance to the lightning protection of power system.During the process of ground lightning,the lightning electromagnetic field near the lightning channel can spread for hundreds of kilometers or even more along the surface,so the electromagnetic wave can be collected by the sensor,and the location of lightning strike point can be realized by its waveform.Considering that Cooray-Rubinstein formula is an important method to solve the lightning electromagnetic field,this paper studies the fast solution of lightning electromagnetic field in time domain and lightning location from this formula,and the main research results are as follows:1.In this paper,a fast time-domain calculation method of lightning electromagnetic field above the earth is proposed.As the premise of Cooray-Rubinstein formula,the lightning electromagnetic field above the lossless earth is of great significance to the subsequent calculation of lightning electromagnetic field above the lossy earth.The theoretical calculation formula of electromagnetic field near lightning channel on lossless earth under dipole method is usually directly calculated by numerical method,which takes a long time.In this paper,starting from the frequency domain form of this formula,a more analytical formula is derived according to the partial integral formula and Newton Leibniz formula.Compared with the original formula,the new formula is less affected by the segment length dz’ of lightning channel,and can get accurate enough results by taking larger dz’,which significantly reduces the amount of data and calculation steps in the calculation process and greatly improves the calculation speed.In addition,this paper has done relevant simulation in matlab to verify the effectiveness of this method.2.In this paper,a fast time-domain calculation method of lightning electromagnetic field above the earth is proposed.In this method,starting from solving Cooray-Rubinstein formula in time domain with the step form kernel function Kε(t),the Talbot numerical Laplace inverse transform method is introduced,and the solving process of Laplace inverse transform is accelerated by selecting the appropriate Talbot integration path.Based on the obtained Kε(t),the method of calculating the convolution part in time domain in C-R formula by recursive convolution is derived.In this paper,the relevant simulation is also done in matlab,and the results show that the Kε(t)calculated by Talbot method is basically consistent with the results of its analytical form,and the results of subsequent recursive convolution calculation also have good calculation accuracy and speed.3.In this paper,the electromagnetic time inversion method is used to locate the lightning stroke,and the location of the lightning stroke in the lightning channel is realized.The traditional electromagnetic time inversion method can realize the location of lightning strike point only considering the point source electromagnetic field.However,the electromagnetic field of lightning channel discussed in this paper is a collection of multiple point source electromagnetic fields,among which the point radiation sources which are not in the same plane as the sensors will interfere with the positioning effect of the original method.Based on this,this paper proposes an improved method,that is,the lightning point location is realized by time inversion after the lightning electromagnetic field is guided.Derivation operation can avoid the electromagnetic field of interference source,only keep the required electromagnetic field,and restore it to the scene of point source electromagnetic field.Finally,this paper makes relevant simulations in matlab,and the results show that this method has a good positioning effect when the lightning point is located inside and outside the sensor.