| Corona loss caused by corona discharge is one of the most important factors in the design of the transmission line,and the corona loss of the bundle conductor is usually studied by UHV corona cage.At present,the measurement of corona loss based on UHV corona cage is limited,since it is difficult to guarantee the measurement quality and time cost,and some features cannot be measured by the experiment.Therefore,it is necessary to study the corona process from the point of gas discharge physics,and to establish the relationship between corona discharge and corona loss.Based on the gas discharge mechanism,this paper established a UHV corona cage bundle conductor AC ion flow field numerical calculation model,which studied time and frequency domain distribution characteristics of electric field strength near bundle conductor,and the temporal and spatial distribution of the corona current.Then,the corona loss of different conductors under different AC voltages was calculated by the method of calculating the power factor.The results of this paper are of great significance to the corona loss prediction of the transmission lines.The main work are as follows:In this paper,a three-dimensional numerical model of the AC ion flow field near UHV corona cage bundle conductor was established.Considering the influence of finite length,the inhomogeneity of electric field on surface and the corona ring on both sides of the cage,the model can calculate the emission,migration and recombination process of the space charge generated by corona under AC voltage in the three-dimensional space.According to Shockley-Ramo principle,the calculation method of corona current was put forward.In addition,the factors influencing the model were analyzed,the optimal parameters were selected.Based on the model established before,the time and space distribution characteristics of the electric field near the 8 × LGJ720 conductor and the corona current generated by the corona discharge are simulated.The electric field results showed that the electric field distribution along the conductor surface obey the rule of "the middle and end are slightly larger",the corona ring on both sides can significantly suppress the end effect;the temporal distribution of electric field on conductor surface is slightly ahead of the voltage waveform due to the influence of space charge;The distribution of space charge has an effect on the electric field within 0.5m out of the bundle conductor surface.After contracting with the results of ANSYS simulation,the results of the established model was proved to be correct.The time domain characteristics of corona current showed that the corona current was related to the charge movement in different time of AC cycle;Then FFT method was used to obtain the amplitude frequency and phase frequency curve of corona current at low frequency,the results showed that the odd harmonic components were the main component.By calculating the 50Hz component of the corona current,the corona loss under dry and rain conditions of 8 x LGJ630 conductor under different voltages were obtained.The results were consistent with the Wuhan UHV AC corona loss test results,which verified the accuracy of the method.The results showed the corona onset voltage of 8 x LGJ630 conductor under 20mm/h rain was 70kV smaller than that under dry condition,and the corona loss increased with the higher AC voltage.Then,the four factors consist of altitude,the type of bundle conductor,the number of split and the splitting distance are studied,the results showed that the increase of the altitude decreases the corona onset voltage,but make the degree of corona more severe.The corona loss of the conductor decreases with the increase of the splitting distance or the decrease of the conductor type and the number of splitting.Compared with the test results in Wuhan and Xining,the model is proved to be correct. |
PDF Full Text Request