Quantification of transient fault let-through energy within a faulted LVDC distribution network

Abstract

LV direct current (LVDC) distribution systems have recently been considered as an alternative approach to electrical distribution system infrastructure as they possess the flexibility and controllability that is required to facilitate the integration of low carbon technologies (LCT). For example, energising existing LV AC cables by DC with higher voltages (>0.4kV) can potentially release additional power capacity on LV cables and reduce the associated thermal losses. However, converting existing AC cables for DC operation may change the cable performance under faulted conditions, resulting in a change to its lifetime. The nature of future LVDC systems can be capacitive due to the characteristic of particular customers such as battery energy storage systems (BESS) and electric vehicles (EVs). A short-circuit fault on the DC side may lead to a discharge/release of significant transient energy in LV cables which was never anticipated under traditional LVAC networks. This paper quantifies the transient DC fault let-through energy which can be imposed on existing AC cables used for DC operation, and draws conclusions on the potential impact of such phenomena on the cable performance. A detailed model of an LVDC test network with three-core LV cables is developed using PSCAD/EMTDC for simulation studies.