Fault arc extinction and system re-start on HVDC transmission lines using LCC or VSC full-bridge converters with integrated arc recovery simulation models

Abstract

HVDC systems in combination with overhead lines are frequently affected by non-permanent ground faults at DC side due to arcs. To limit the impact to the DC system or the connected AC system(s) at line-to-ground faults or unsuccessful restart attempts, a reliable recovery strategy is essential. We report on the development of a physical model of the arc extinction and recovery behaviour of arcs on HVDC transmission lines. The arc model can be used to develop, test and optimize the arc extinction and recovery strategy in the control software of a bi-polar HVDC (Voltage Sourced Converter (VSC) HVDC with full-bridge converter and Line-Commuted Converters, LCC HVDC) converter station. Based on empirical arc characteristics of long arcs in air, a simplified dynamic arc model has been developed which allows calculating fault arc parameters. These arc parameters are used to calculate the energy deposited in the arc during the fault, and the converter control minimizes the fault arc energy by extracting most of the energy stored in the transmission line. Furthermore, salient arc parameters like arc resistance, arc current and current rate of decay before current zero are used to predict the status of the arc, in particular, the precise time of arc extinction. After arc extinction, the dynamic recovery behaviour of the fault arc path is predicted using empirical recovery data. The HVDC converter is then allowed to start after a deionization time which is determined by the dynamic recovery characteristics of a worst case scenario and the energy deposited in the arc during the fault interval. This allows for a save restart sequence with minimal outage time of the order of 500 ms or less from fault occurrence to full power recovery.