Zutao Xiang

Secondary Arc Current Analysis of an Untransposed EHV/UHV Transmission Line With Controllable Unbalanced Shunt Reactor

A conventional four-legged shunt reactor serving untransposed extra-high voltage or ultra-high voltage transmission lines may cause the secondary arc difficult to extinguish and result in single-phase autoreclosing (SPAR) failure. This paper proposed an unbalanced shunt reactor (USR) scheme and focuses on the secondary current analysis with respect to untransposed extra high-voltage/ultra-high voltage transmission lines. The fundamental theory of secondary arc calculation for the untransposed transmission line with USR was provided first, followed by the formulation of USR controlling principles and strategy. To validate the effectiveness of secondary arc current suppression, untransposed 1000-kV single-circuit and double-circuit UTL with USR were simulated using the Electromagnetic Transients Program. The results show that USR is effective in suppressing secondary arc current and recovery voltage for single-circuit and double-circuit UTL, which helps increase the SPAR success probability. Furthermore, the secondary arc current and recovery voltage are not sensitive to the variation of USR neutral reactance; hence, the value of neutral reactance can be decided in a wide range. Finally, USRs role and effect in reducing the inductive electrostatic voltage in double-circuit UTL was discussed when one line is transferred to maintenance.

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.