Transient Overvoltage Analysis in HVDC MMC Power Cables: Assessment of the Critical Points

The current scenario of continuous and increasing production of energy from renewable sources and the progressive increase of interties between different countries, gives the high voltage direct current transmission lines (HVDC) a role of present and future protagonist in the electrical power transmission. One of the main issues concerning the HVDC systems is the effect of the transient overvoltages (TOV) which occur during fault conditions on the DC side of a HVDC link. In fact, even if power cables are tested in order to withstand overvoltages with standardized characteristics, the real TOV phenomena do not have standard features. In this paper, the analysis of the TOVs of a HVDC symmetrical monopolar configuration is carried out, by studying the TOV propagation along the cable line and by defining step by step the overvoltage trend for different fault sections. Moreover, by means of a probability study, the most stressed points along the cable are identified by taking into account all the possible fault positions, so to highlight which are the more critical positions of the cable system irrespective of the fault section.