The low voltage DC (LVDC) distribution system is a concept of new DC based distribution system. Safety of new distribution system needs to be equal or higher than traditional AC distribution systems [1]. This paper presents protection scheme for an LVDC distribution system. The analysis approaches LVDC system as a whole-from beginning of the DC district up to the customer-end protection. The analysis consist both grounded TN and ungrounded IT grounding arrangements.

Experiences from the field setup of utility grid low voltage DC (LVDC) distribution are discussed. LVDC distribution being a novel approach to public electricity distribution, a research platform is realised to enable practical studies. The goal of the setup is to combine the requirements of the fully functional LVDC system and a flexible research platform. The scope of the paper is to discuss experiences from first six months of continuous use of the setup. The paper focuses on comparing how expected and realised results meet and how the setup has been operating in real public network. On the other hand, design flaws and challenges are covered. Finally, future research tasks and the development of the setup towards LVDC smart grid are presented.

The leading themes in the distribution network development are the cost effectiveness and system reliability. Also the requirements for reducing pollution and increasing the service quality are issues, which have led to the introduction of SmartGrids network concepts. These network solutions are mostly dependent on power electronics, applied to connection of loads, generation and storages to the independently operable low-voltage (LV) grids. One of such solutions is the low voltage DC (LVDC) distribution system, which is an interesting challenger to the AC low voltage network solutions. An often-asked question is how the shorter lifetimes of power electronics compared to the traditional network components affect on the reliability of the electricity distribution and also to its total costs. In the this paper the question about the reliability development is approached from two main points of view: The component level focusing on the reliability of power electronics based network components, and the system level concentrating on the power quality experienced by the customers and the effects of converters on the entire distribution system reliability. The question of the reliability impact of large-scale utilization of power electronics in electricity distribution is relevant, when considering the direction of the technical development in electricity distribution. This paper is especially aimed at discussing the modelling of the reliability impacts in the case of the LVDC-system.

No abstract

This article focuses on the overall system engineering aspects of low voltage DC (LVDC) electricity distribution.. The interdependencies between different parts of an LVDC distribution system are discussed emphasising the issues related with the interconnection of user-end LVDC installations and public LVDC systems. The main objective is to illustrate the importance of the total system engineering over the piecewise design approach. The aspects affecting on the selection of the DC voltage level, system structures and earthing arrangements are considered. A methodology for selecting the technoeconomic optimal voltage level within the boundary conditions set by the DC system application and the operating environment is introduced with example calculations. Presented discussions and results provide support especially for the development of the standardisation of the LVDC technology