Backup protection method for half-wavelength transmission lines based on inverse-time characteristic

Abstract

The advantages of ultra-high voltage (UHV) Half-wavelength AC transmission (HWACT) technology are achieving full-line reactive power self-balancing without the need for reactive power compensation equipment along the line and avoiding the Ferranti effect. Recently, this technology has gained considerable attention worldwide. While numerous main protection methods that were tailored to the unique operational characteristics of HWACT lines have been proposed, backup protection for HWACT has been overlooked relatively. As a transmission line requires both main and backup protection for safe and reliable operation, this paper analyzes the necessity of backup protection for HWACT lines and proposes a method based on inverse-time backup protection. This method relies on the rate of change of current (RCC), determines faults by calculating the initial value of the change rate of the fault current, and applies inverse-time characteristics to remove faults. This protection method demonstrates good quick-acting properties by adopting the RCC in the initial phase of a single-end fault without the need for dual-end communication. A large number of simulation results validated that this method was smaller affected by fault distance, initial fault phase angle, transition resistance and fault type, making it an effective protection approach for main protection failures.