Determination of single-pole auto-reclosing restart concept for VSC HVDC with fault current controllability

Summary

The penetration of distributed renewable energy resources leads to power trans-mission over long distances. Especially due to the nuclear phase out in the context of the German energy transition, offshore wind farms have to be connected to the loads in south-ern Germany. VSC HVDC transmission technology with fault current controllability offers a promising solution to the future grid design since it enables flexible power transmission over long distances with low conduction losses. The fully loaded transmission lines are demanding a fast and selective fault handling to ensure a reliable power supply. Since overhead line based energy transmission is vulnerable to faults from atmospheric impacts, temporary single pole to ground faults are the prevailing fault type. These faults vanish independently after the line is disconnected from the system for a short break to allow the arc to extinguish. After the arc path has become sufficiently deionized, the line can be put in operation again. This auto-reclosing concept is used in HVAC systems since the begin-ning of the 20th century as well as for HVDC. The interruption time for DC systems is esti-mated conservatively based on experiments for HVAC. This paper reports a first approach where a computer fluid dynamics (CFD) model is set up for investigating the temperature rise and the subsequent cooling in the air-insulated path due the fault arc. The calculated temperature profiles are used for the determination of the time dependent dielectric strength of the air-insulated path and to develop an auto-reclosing strategy. The influence of energy input is analysed for exemplary vertical and horizontal geometries. The results show that a worst-case scenario for the dielectric recovery of the air insulation path can be identified. This scenario is used to develop an auto-reclosing strategy covering the essen-tial fault scenarios. The results show, that the necessary interruption time is shorter than the assumptions from AC systems thus enabling a faster recovery of power flow.

Additional informations

Authors

KADOMSKAYA, JOHANSSON, YAN

Keywords

HVDC, Full-Bridge MMC VSC, Protection, Auto Reclosing