Owing to the specific mode of regulation and structure of the voltage source converterhigh voltage direct current (VSCHVDC) transmission system

the DC line fault current is characterized by high increasing speed and great peak value. This is extremely susceptible to destruction of converter devices and damage to insulation of equipment. VSCHVDC system cannot realize fault selfclearing by adjusting the firing angle. Therefore

higher requirements are made on protection and fault handling of DC transmission lines. For DC line faults

not only is reliable and fast protection needed for fault identification

but also corresponding control measures and circuit should be taken to limit the fault current and reduce the damage of the current to converter devices

the DC line itself and system. Based on the fault characteristics of VSCHVDC transmission lines

the state of the art of DC line protection technology and prospects for application at home and abroad are described. Protection and fault handling technologies of DC lines are summarized and analyzed with respect to fault current limiting

reducing fault impact

and protection principle. The fault handling capability of several protection circuits

converter topologies

DC transmission structures and DC breakers are focused on. Finally

several key issues about protection and fault handling of VSCHVDC transmission lines and future directions for further research demanding prompt solution are discussed. This work is supported by National Natural Science Foundation of China (No. 51377104

No. 51407115) and Postdoctoral Science Foundation of China (No. 2014M560333).