The Overvoltage of Hybrid Transmission Line of Long Distance Ultra-high Voltage Cable and Overhead Line

With the rapid development of urban construction, the application of long-distance ultra-high voltage cable becomes an inevitable trend. However, due to larger equivalent capacitance value per unit length of the cable line, larger charging power of the line and the obvious capacitive effect, the overvoltage generated after connecting to the system is more prominent and complex than the overhead line. In this paper, the operating overvoltage and lightning overvoltage of a hybrid line of 330kV high-voltage AC cable and overhead line in a certain region is studied by using ATP/EMTP electromagnetic transient simulation software. Besides, the simulation calculation model of overvoltage is established. The overvoltage level is calculated through the amplitude of waveform, and the overvoltage characteristics and its influencing factors are analyzed. On the basis, the corresponding suppression and lightning protection measures are proposed. As the research results show, the closing no-load line can produce the highest closing overvoltage of about 2.06p.u at the cable side. The overvoltage at the cable side can be effectively dropped to 1.53p.u after installing the closing resistor at the circuit breaker side and adjusting the closing phase Angle. In addition, when the lightning current directly strikes the overhead line, the lightning overvoltage of the cable side reaches 1028kV, and the overvoltage of the overhead line reaches the maximum of about 1320kV. Installing lightning arrester in the combination place of overhead line-cable and in the middle section of overhead line can effectively reduces the lightning overvoltage at the cable side and at the overhead line to 790kV and 1096kV, respectively. The research results offer a necessary basis for the insulation coordination in the engineering application of hybrid line of 330kV cable and overhead line.