Single-terminal fault location in HVDC lines with accurate wave velocity estimation

•Discussion on the nature of the wave velocity during faults on HVDC lines.•A wide comparison between the proposed and the conventional fault location approaches.•The proposed estimated velocity will circumvent the actual velocity.•The proposed single-terminal fault location approach presents adequate computational effort.•Velocity function fitted by consolidated fault data improves the accuracy of the location. HVDC lines are very susceptible to faults once they are long and can operate under severe weather conditions. The main approaches for fault location in HVDC lines are based on the concept of traveling waves. Their performances depend on the times that the wavefronts reach the monitored terminals as well as the wave velocity. Despite the wave velocity depends on the line parameters and fault location, in the conventional approaches it is assumed constant regardless of the fault location impacting the obtained results. This paper presents a single-terminal fault location approach where the required wave velocity is estimated from line parameters and wavefronts traveling times. The wave velocity is represented by a mathematical function which is fitted to simulated and/or actual fault data, resulting in a more accurate wave velocity estimation for every fault location. Case studies were performed for different fault locations, fault resistances and ground resistivity, considering a 500 km bipolar HVDC transmission line modeled as a Frequency-Dependent (Phase) Model. The proposed approach is compared to the conventional approach in several scenarios. The results indicate that the proposed way to handle the wave velocity improves the accuracy of the fault location.