Potential of using Low Voltage Direct Current in local distribution network to improve the overall efficiency

This project reviews the potential of Low Voltage Direct Current (LVDC) to replace Low Voltage Alternative Current (LVAC) power in distribution grids. The study addresses three different problems: a comparative literature review on LVAC and LVDC systems, a study of the compatibility of the type of low voltage cables that are used in buildings with a future LVDC distribution grid and a technical comparison from transmission and conversion losses point of view. The literature review provides an overview and explanations for the understanding of the problem. Then, a special review of ageing phenomena and implementation to the case study – low voltage building cables – concludes that there is a low risk of electrical ageing in existing Alternating Current (AC) cables when used in a Direct Current (DC) system. Finally, a comparison of LVAC and LVDC is carried out at three different levels: 1) the cable resistive losses are compared in LVAC and LVDC and the difference proved not to be over 1% in standard situations because skin and proximity effects are not significant at low frequency and low voltage level, 2)a comparison of the possible home and distribution layouts – single-phase and three-phase AC versus unipolar and bipolar DC – concludes to the clear advantage of DC over AC to carry power over longer distances than AC, 3)an energy consumption comparison between households fed either with AC or DC concludes to the absence of significant loss savings as no conversions are fully removed