Wan Haojiang

Measurement of Shielding Effectiveness of Reinforcing Bar Loops and Cage to magnetic field

This paper presents the measurements of shielding effectiveness of reinforcing bar loops (RBL) and reinforcing bar cage (RBC) to magnetic field. A testing method was applied to measure the shielding effectiveness of RBL and RBC with its joints wired or welded. The signals in this experiment are continuous wave with frequency of 14 kHz, 100 kHz and 200 kHz. The variation of the shielding effectiveness is studied when the distance between every two neighboring loops of RBL or the mesh size of RBC has changed. The conclusions of this paper are helpful and of great importance in the engineering.

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.

Effect on lightning electromagnetic fields from the return-stroke parameters

Choice of the return-stroke parameters has a great influence on the calculation results of lightning electromagnetic pulse(LEMP) fields. In this paper, LEMP fields under different return-stroke parameters are calculated based on the MTLL model in which the channel-base current is described by a pulse function. And effect of different return-stroke speeds and channel heights on LEMP fields of different field regions are also discussed. The results show that the lightning channel height between 1 kilometre and a few tens of kilometres has a little influence on the LEMP fields, but the return-stroke speed has a distinct influence on the LEMP fields.

Development of the Measuring System for Lightning Current on High Tower

A kind of measuring system designed for the measurement of lightning return stroke currents under 50 kA, which is composed of current transformers, optical isolation system, data acquisition card and industrial computer, is described. Test results show that the current transformers and the optical isolation system have good stability. Moreover, primary research on remote transmission of the data is done. A wavelet-based compression arithmetic is designed, which is suitable for the data compression, greatly improving the speed of the data transmission.