Electromagnetic transient study on single ±800kV UHVDC and double 500kV EHVAC lines on same tower

Detailed electromagnetic transient simulation on single circuit ±800 kV dc transmission line and double circuit 500 kV ac transmission lines on the same tower is performed to research the interaction between ac and dc transmission systems. The various serious faults on ac and dc transmission systems are simulated. The different positions and lengths of dc and ac lines on the same tower is considering to compare the impacts on overvoltage levels of dc and ac transmission lines, on the power frequency overvoltage and switching overvoltage of ac system, as well as on the secondary arc current and the recovery voltage of ac transmission lines. Simulation results show that the impacts on the respective overvoltage levels of UHVDC and EHVAC transmission lines is little when ac and dc lines on the same tower, thus the insulation co-ordination scheme could be same as the situation of only dc lines on the tower. There is some induction dc current and voltage in ac lines on the same tower with dc lines. The value of the induction dc current and voltage is more than IEC standard about the induction voltage and current of the grounding switch. The secondary arc current has no zero crossing for the induction dc current in ac lines when one HV reactance is installed on one terminal of ac lines without transposition, thus it is necessary to consider countermeasure during the design.