Research On Electromagnetic Environment Of UHV DC Transmission Lines

Based on the actual situation of our country,UHVDC transmission is widely used in China due to its unique advantages.Relevantly,the electromagnetic environment problem along with UHVDC transmission has attracted much attention.The criteria of electromagnetic environment of UHVDC transmission lines mainly include electric field,ion current,audible noise and radio interference.The main reason causing electromagnetic environment problem is DC corona.When the electric field on the conductor surface exceeds the corona inception field strength,the corona discharge will appears around the conductor.So a calculation is first made in this paper for the electric field strength on the conductor surface.The Markt-Megle method is used to calculate the surface electric field strength of conductor bundles.A detailed formula derivation is completed and the corona inception voltage calculation method as well as the integral method of electric field to the potential are given.By using the analytic method to calculate ground electric field strength and ionic current density,the calculated results and the measured results are compared,which have verified that the proposed method and program are workable and feasible.As the space-charge-free field is the important component of total electric field,the maximum space-charge-free field strength can be used as a reference index.Split conductor is equivalent to a single wire and the presence of the ground is taken account,the influence of bipolar HVDC bundle spacing,voltage,conductor height as well as the bipolar pole spacing is also inquired on the nominal electric field distribution on the ground by the image method.Meanwhile,the analysis is performed for the effect of bipolar HVDC bundle spacing,voltage,conductor height and bipolar polar distance on the total electric field at ground level and ion current density size distribution.To raise the power transmission capability of unit corridor,more efficient arrangement of transmission lines has to be adopted.The vertical bipolar HVDC transmission lines,double-circuit HVDC transmission lines in the same corridor and are the alternatives.In this paper an approach to calculate the total electric field at the ground level underneath the vertical bipolar HVDC transmission lines,double-circuit HVDC transmission lines in the same corridor is proposed.Using the proposed method,the distribution features of the total electric field at ground level underneath such transmission lines are analyzed.For calculating the DC line radio interference and audible noise,CISPR and EPRI recommended formula is adopted.