Research on 3‐D total electric field of crossing high voltage direct current transmission lines based on upstream finite element method

The ongoing large‐scale construction of ultra high voltage direct current projects in China makes the crossing of two high voltage direct current(HVDC)lines inevitable.It is critical to study the characteristics and calculation method of 3‐D total electric fields of crossing HVDC lines.The problems encountered when applying the 3‐D upstream finite element method to calculate total electric field of crossing HVDC lines and the solutions are studied in this study.In view of the surface electric field varying greatly along longitudinal direction of conductors,the calculation method adopting the Davidon‐Fletcher‐Powell optimization algorithm is introduced to realize the fast computation of 3‐D space‐charge‐free field.Considering the distinct corona intensity at different positions of conductors,a new for-mula for initializing charge density is studied to ensure the convergence of calculation process.Considering the large computation amount of total electric field,an adaptive iteration strategy is put forward to effectively speed up the calculation.The measurement of ground total electric field underneath a crossing HVDC test line is conducted to verify the validity of the proposed calculation method.The distribution characteristics of electric fields of crossing HVDC lines are calculated and analysed.The research results will provide technical support for the design and environmental impact assessment of crossing HVDC transmission lines.