Overview of DC transmission line fault analytical methods and single-ended protection

DC transmission technology, which plays an important role in connecting AC grids, can transmit power asynchronously under long-distance and large-capacity conditions. Protection devices and control system of the DC transmission system are quickly put into use after the information of the first traveling wave caused by faults of DC lines having been detected. Therefore, the current HVDC transmission line mainly adopts single-ended protection based on first traveling wave information as main protection for DC lines and such protection is not affected by the control strategy. But in the fault transient stage, changes of electrical quantities of DC transmission lines will show nonlinear characteristics because of the control strategy. At present, the analytical method of fault characteristics in the transient stage is not perfect and the rapid coordination of control and protection has not been realized. This paper presents an overall introduction to the research statuses of fault analytical methods and single-ended protection principles of DC transmission lines. First, the fault characteristics of LCC- based DC transmission lines and VSC-based DC transmission lines are compared. Second, the current research statuses of HVDC transmission line analytical models and fault transient analytical methods are analyzed and the shortcomings of current analytical methods are listed. Third, the current single-ended protection principles of DC transmission lines are classified, and then the problems and valuable research directions in the process of studying single-ended protection principles based on the coordination of control and protection are listed. Finally, the outlook for the rapid coordination of control and protection of DC transmission lines is determined.