Structural Parameters Optimization Of Corona Ring Of High Power Very Low Frequency Antenna

The antenna end of tethered balloon type high power VLF communication system will be exposed to an extremely strong alternating electric field environment when it is in operation.Due to dielectric loss,abnormal temperature rise may occur at the antenna end,which may lead to antenna fracture in serious cases.It is an effective measure to install corona ring at the end of antenna to improve the electric field distribution and restrain the temperature rise.To achieve the best performance,in this paper,the simulation models were built to figure out the effect of the structural parameters of the corona ring,including ring radius,tube radius and ring depth.The relationship functions between the maximum electric field intensity and temperature to the structural parameters of corona ring were built according to the simulation results.Moreover,the structural parameters were optimized through improved whale optimization algorithm based on levy flight.The effectiveness of the optimization results is verified by simulation and experiment.The main works of the full text are as follows:(1)The theory within the very low frequency range used to calculate the electric field norm,dielectric loss power and temperature were illustrated as the basis of estimating the electric field norm and temperature rise at the antenna end.The conclusion that the dielectric loss of the antenna end is proportional to the frequency and the square of the electric field norm was drawn.The simulation models which interconnect the electric field in frequency domain and the temperature field in time domain were established.Based on the research of the effect of the excitation parameters,the condition of environment,and the material of sheath on the maximum electric field norm and temperature of the epoxy mandrel,the worst condition was determined.The worst condition was applied as the background of the optimization to ensure the safety of tethered balloon type very low frequency communication system.(2)The simulation models of the very low frequency antenna installed with the corona rings were built.The variable-controlling method was implemented to analysis the impact of tube radius,ring radius,and ring depth on minimizing the maximum electric field norm and the temperature rise of the epoxy mandrel.The functions implying the relationship between the structural parameters and the maximum electric field norm or the temperature were constructed through nonlinear regression.All the coefficients of determination reach 0.98,which illustrates that the functions meet the requirement of the engineering.(3)The whale optimization algorithm and levy flight were described.By combining the whale optimization algorithm with levy flight,the hybrid algorithm improves the ability of jumping out of the local optima.Tested by benchmarks of CEC,the hybrid one shows better performance compared with the particle swarm optimization algorithm and the traditional whale optimization algorithm.Through applying the constructed relation functions to the hybrid whale optimization algorithm with levy flight,the optimal parameters were gained separately in terms of minimizing the electric field norm and temperature.By comparing the results gained by simulated annealing algorithm,the accuracy and the efficiency of the hybrid algorithm was verified.(4)The reason why the optimal parameters gained by two relation functions are different was analyzed.As for this specific problem,the corona ring was optimized with the principal of minimizing temperature.The effectiveness and accuracy of optimization was tested by simulation and experiment.The optimized corona ring could restrain the maximum temperature less than 12℃.