Simulation Research On Overvoltage Of 330kV Power Cable-Overhead Hybrid Line

With the rapid development of urban construction,the application of long-distance ultra-high voltage power cables-overhead hybrid lines is 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.Studying the overvoltage problem of the 330kV hybrid line has important theoretical and practical value for the stable operation of the power system and the insulation coordination of the transmission line.In this paper,I used ATP-EMTP electromagnetic transient simulation software,combined with engineering practice,a 330kV cable-overhead line simulation model is established,I calculated the overvoltage level through the waveform amplitude,analyzed the overvoltage characteristics and influencing factors,and proposed effective overvoltage suppression measures based on the calculation results.The thesis first analyzes the generation mechanism of lightning overvoltage,power frequency overvoltage and operating overvoltage of hybrid transmission lines.For the lightning overvoltage,I built a simulation model in ATP-EMTP to determine the lightning current,tower and insulator string flashover models.I simulated and analyzed the lightning overvoltage distribution.And the impact of lightning strike position and arrester on overvoltage.The research results show that the lightning overvoltage amplitude on the overhead line side can reach 3.3MV,and the overvoltage amplitude on the cable side is much smaller than that on the overhead line side.Affected by the location of the lightning strike,the cable head and end voltages all decrease with the increase of the lightning strike distance,and the overall cable end voltage is higher than the cable head voltage.Arrangement of lightning arresters on both sides of the cable can effectively suppress the lightning overvoltage of the transmission line to the insulation level.In view of the power frequency overvoltage,I determined the calculation model and parameters of the cable and overhead lines,and simulated the power frequency overvoltage waveform distribution caused by the capacity rise effect,asymmetric short-circuit grounding and asymmetric load dump.At the same time,I also analyzed the impact of parallel high reactance and transmission line length on power frequency overvoltage.Aiming at the operating overvoltage,I established a simulation model of the hybrid line.The results of the study found that the closing no-load line can produce a closing overvoltage of about 1.84p.u on the cable side,and the heavy breakdown caused by the opening of the circuit breaker will only occur on the line without high impedance.Choosing a lightning arrester with a relatively low voltage can suppress the operating overvoltage of the line within a safe range.