The thermal behavior of medium voltage dc cables can find useful applications for efficient and capacity enhanced operation in cities as well as compact power transmission on all electric ships. Concepts such as dynamic current and voltage rating, difference in thermal proximity in ac and dc operation, pulsed load application and thermal degradation with enhanced dc voltage; all are interlaced with the crucial temperature profile of insulated conductors. This paper develops a theoretical thermal model to highlight the possibility of dynamic current rating with pulsed loads. Further, a novel idea of imposing a thermal profile on cables for dc partial discharge testing is discussed. For this purpose a heat transfer model for a segmented cable is developed and experimentally validated.

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While the scientific community recognizes the benefits of DC power transfer, the distribution network operators point out the practical and economic constraints in refurbishing the existing AC network at a medium-voltage level. Some apprehensions like reliability, cost of ownership, and safety in adopting a universal DC distribution may merit considerable attention, particularly considering the long operational experience with the existing mature AC system. This paper introduces the novel concept of reconfigurable DC links as a flexible backbone integrated within the future AC distribution grids. Benefits such as hardware reconfiguration for a modular AC–DC cable operation to achieve fault redundancy, control reconfiguration for flexibility and grid-supporting ancillary services, network reconfiguration for system level distribution loss minimization and load redistribution, and fault reconfiguration for improving the grid availability are discussed. The vision, around which the concepts developed in this paper revolve around, is to present a viable way of gradual transition from AC to hybrid AC–DC to finally a universal DC system.@en

A scientific consensus is emerging on the benefits of direct current (DC) distribution in medium voltage (MV) power systems of ships and cities. At least 50% space savings and increased power transfer capacity are estimated with enhanced voltage DC operation of electric cables. The goal of this research is to contribute to developing the empirical knowledge on the insulation performance in order to validate the feasibility of such anticipated gains of DC versus alternating current (AC), and to determine the comparative impact of different operational conditions from a component engineering point of view. The partial discharge (PD) activity in cables is measured under AC and DC conditions as an indicator of insulation performance. Specifically, PDs in defects at the semicon-insulation interface are studied in terms of inception voltage, repetition rate and discharge magnitude. Empirical understanding is drawn for operating voltage and frequency dependence of the discharge behavior in such voids in the range of 10 to 20 kV and 0 to 0.1 Hz, respectively. The change in PD activity with void evolution post temperature-induced ageing process is explored@en

Microgrid concept has been widely adopted by power and energy community to boost the resilience and enhance the economics of the energy system. Stability control and economic control are two main factors to enable the reliable and efficient operation of microgrids. This paper presents two different control approaches for microgrids. The first control method adopts hierarchical structure. Each controllable resource is complied with a local controller and the microgrid is managed and optimized by a central supervisor controller. The second control method adopts the distributed structure. Distributed controller of each energy resource can communicate with each other to achieve global goals. This paper discusses the main features of these two methods and provides recommendations on how to choose appropriate control for different types of microgrids. A case study illustrates the performance difference of the two methods from economic point of view.

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