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The prediction and control methods of radio interference (RI) for HVdc transmission lines passing through high-altitude region are main key factors in design of the HVdc transmission lines. In order to obtain the altitude effect and correction of RI for HVdc transmission lines, four HVdc reduced-scale test lines with the same parameters were built up at 50, 1700, 3400, and 4300 m elevation, respectively. Simultaneously, two HVdc full-scale test lines with the same conductor type of 4 × JL/G1A-500/45 had been set up at altitude 50 and 4300 m as well, respectively. Using these test facilities, a lot of RI measured data were accumulated in a long time span, from Jan. 2010 to Jul. 2014. By analyzing the RI measurement data at different altitude regions, it is indicated that the altitude correction of RI has a nonlinear relation to the altitude. Meanwhile, the RI altitude correction formula for HVdc transmission lines has been proposed in this paper. Using the proposed RI altitude correction formula, the RI levels at high altitude are lower than that predicted by using the RI correction formula of ac transmission lines, which means that it could save a lot of investments at high altitudes. [ABSTRACT FROM PUBLISHER]

Based on the second-order wave equation of voltage, discrete equations for multiconductor transmission lines (MTLs) are derived by using finite-element time-domain (FETD) method and Newmark-Beta formulation. And then, the time-domain method to process lumped elements is also given based on the node admittance method of circuit analysis. Combining all the discrete equations and lumped elements, the global FETD equation is obtained based on the single iteration variable voltage. Finally, by means of the coupled equations between current and voltage, the iteration formulas of current along MTLs are derived. Compared with EMTP program by numerical examples, the proposed method in this paper is proved to be correct and effective. Furthermore, the simulation result demonstrates that the proposed method is better than the existing FETD methods in computation efficiency and convenience for the treatment of complex lumped networks. [ABSTRACT FROM AUTHOR]