Research On EFT Interference Of Relay And Its Radiation Field

EFT is one of the major interference sources which cause EMC question. Therefore, it is very important to study the generation mechanism and calculate the radiation field of EFT for the systemic electromagnetic compatibility design.EFT is very typical interference sources which will appear as the relay break the inductive load circuit. In order to study its generation mechanism, incorporating the arc theory and the traditional circuit method is adopted. Establishing a double-loop circuit mode, this mode can explain the special negative voltage phenomenon in EFT transient process. Then, divide EFT into three stages to build its numerical model using the least squares method. The numerical model method proposed is demonstrated to be valid through comparing with experimental result.Secondly, to calculate the EFT radiation field around wire, deforming grids technology has been studied. Ground loop model, as an example, of which the simulation model is set up, the mesh method and case study are also provided. Meanwhile, to consider the actual environmental impact on the radiation field, the influence of grounding parameters is properly investigated with the basis of the above mentioned model, and the corresponding conclusion is presented.Finally, an equivalent circuit model of shielded cables is conducted. Then the method of simulated implementation for calculating the radiation field of shielded cables is studied systematically. The equivalent circuit model divided into two systems of inside and outside which is linked by the transfer impedance. The inner system solves the transmission line equation to obtain its distribution current, while the external system is equivalent to the wire mode. In order to implement accurate calculation of the radiation field, an improved FDTD method through fitting the frequency-dependent parameters and convolution recursive calculations is adopted, solving the problem that the traditional FDTD method can not directly deal with, hence, the relevant examples are carried out. At last, taking the coaxial cable for example, the radiation field is calculated, and the correctness of method is verified by simulations and experiments.