The short-circuit protection of a low-power converter-fed low-voltage DC distribution network is investigated. In a public distribution network, the short-circuit protection is implemented by using fuses and circuit breakers, which may require a current that is over ten times the nominal currents of low-power DC/AC converter units to satisfy the recommendations. In the paper, the operation of the converter in a short circuit is studied, and the control scheme for the short-circuit current control and the fault ride through (FRT) operation is proposed. The operation of the short-circuit control scheme is verified by measurements. To overcome the problem of high fault current injection, alternative short-circuit protection realizations that are based on a simple low-current compact circuit breaker (but are not approved in standards) are proposed and demonstrated by measurements.

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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.

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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.