The Similarity Between the Derivative of LEMP and Its Approximate Result for Oblique Channel in Near Area

In order to protect sensitive electronic components and electrical equipment against the influence of lightning electromagnetic pulse (LEMP) field in near area, it is necessary to determine the waveform of the lightning electromagnetic field. By using the dipole method to solve Maxwell’s equations, the analytical expressions of lightning electromagnetic fields which is generated by oblique discharge channel are presented. According to the TL model, the general approximate derivative expressions of lightning electromagnetic field are derived and the waveforms of the exact expressions as well as approximate expressions are compared in near area. The results showed that the electromagnetic field derivative waveforms of the approximate results are essentially coincident with that of the accurate results within 100 m and the deviation between the accurate result, and the approximate result increased with the increasing of the horizontal distance; the deviation between the approximate result and the exact result of magnetic field is larger than that of electric field within the same distance. From above analyses it can be concluded that there is an approximation between the lightning electromagnetic field and channel base current and from then on we can get lightning electromagnetic field more effectively.