Mechanism and Mitigation of Power Fluctuation Overvoltage for Ultrahigh Voltage Half-Wave Length Transmission System

A new type of overvoltage phenomenon in half-wave length transmission line (HWLL) is caused by power fluctuation (PF). This paper defines this phenomenon as PF overvoltage (PFO), which belongs to the temporary overvoltage category. The amplitude of PFO is generally high, the duration time is long, and the coverage on HWLLs is wide in the case of single-phase transient fault, when the transmission power is large. This will pose a new problem for ultrahigh voltage (UHV) half-wave length ac transmission (HWACT). First, we analyze the unique transmission characteristics of HWLLs with incident and reflected wave theory. Next, according to the application scenario of HWACT in China, we construct a plant-to-grid UHV half-wave length transmission system. Then, based on a large number of electromagnetic transient simulations on the system using electromagnetic program, we obtain the PF characteristics of the UHV HWLL. Furthermore, the mechanism and characteristics of PFO are described by the characteristics of transmission and PF. Finally, we propose the mitigation measures of PFO for UHV HWLL, which include configuring metal oxide arresters differentially along HWLLs, closing high-speed grounding switches during the fault period, generator tripping after a fault, and shortening the reclosing time.