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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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Abstract:The idea of damming the Congo River has persisted for decades. The Grand Inga project, of up to 42 GW power generation capacity, can only be justified as part of a regional energy master plan for Africa, to bridge the energy gap on the continent. Proponents of very large dams have often exaggerated potential multiple benefits of a mega dam, marginalise environmental concerns and neglect the true risk of such projects, in particular for the fragile economies of developing countries. Studies have reported the financial risks, cost overruns and schedule spills associated with very large dams. In addition, most of the dams in the region are poorly managed. Therefore, the type and scale of Grand Inga is not the solution for millions of not yet electrified people in Sub-Saharan Africa. In this research, scenarios are defined based on announced costs and expected costs. Cost escalations in the range from 5% to 100% for the Inga project in 2030 and 2040 are considered, as average cost overruns are typically at about 70% or higher for similar mega-dams. It was found that when the cost overrun for the Grand Inga project exceeds 35% and −5% for 2030 and 2040 assumptions, respectively, the project becomes economically non-beneficial. In all scenarios, Sub-Saharan Africa can mainly be powered by solar photovoltaics to cover the electricity demand and complemented by wind energy, supported by batteries. Hydropower and biomass-based electricity can serve as complementary resources. The grid frequency stability of the power system is analysed and discussed in the paper. Benefits of the Inga hydropower project have to be increasingly questioned, in particular due to the fast cost decline of solar photovoltaics and batteries.