The Potential Impact of Flexible DC Transmission and Distribution on Insulated Cables: Accelerated Aging and Premature Failure

Flexible DC transmission is becoming a promising technology for HV and MV links, where large amount of power must be transported, long distances are involved and integration of renewables is sought. The introduction of advanced power electronic converters, with fast and low loss switches, is dramatically improving reliability of DC lines and shortening the distance at which they become economically advantageous compared to AC. In the framework of Flexible DC, conversion of AC lines into DC, and/or hybrid use of the same lines under DC and AC, has been investigated and specified. However, there is no work or even mention of the effect of such procedures on fundamental components of HV and MV links, that is, insulated cables. This paper highlights the potential problems that can affect severely the reliability of HV and MV cables designed for AC when turned to DC supply or vice-versa. Indeed, the effect of an increase of the electric field in insulation on life, that of space charge and partial discharges is discussed and evaluated also quantitatively.