Increased bulk power transactions in competitive energy markets together with large scale integration of renewable energy sources are posing challenges to high-voltage transmission systems. Environmental constraints and energy efficiency requirements also have significant effects on future transmission infrastructure development. This paper reviews the recent development in HVDC technologies and discusses the needs of the hybrid AC/DC grid structure for future power systems with focus on VSC-HVDC applications in meshed ac grid. It has also been recognized that hybrid AC/DC transmission system together with the wide area measurement system (WAMS) could effectively manage the overall power grid operation security and efficiency under uncertain supply and demand conditions. Index Terms-Transmission expansion, security and efficiency of power delivery system, HVDC transmission, VSC-HVDC, wide area measurement system Jiuping Pan received his B.S.
4~4.simct-A C a u e r circuit model of a transformer lami n a t e is presented. It considers saturation, e d d y currents a n d hysteresis. T h e simulation results agree t o experiments with a n Epstein f r a m e in t h e 10-200 Hz range. T h e p a p e r includes a description of a computationally fast hysteresis model with few adjustable p a r a m e t e r s a n d a physical approach to derive t h e C a u e r circuit. T h e model can b e used u n d e r various time-transient conditions a n d can easily b e implemented into a larger system in a circuit simulation package, such as S a b e r , t o s t u d y a transformers interaction with switching overvoltages, for example.
Research of L1 education is recently established in the Nordic countries. Since the turn of the century we have seen the emergence of national and Nordic research networks, conference and publication series, research programs, and the designation of positions as professors and associate professors. Studies of Nordic L1 research have taken stock of the disciplinary sub fields, but empirical studies of the L1 school subject as a unitary field are still in demand. The aim of this study is to investigate the emergence of Nordic L1 research and its present profile(s) through PhD research. The present study examines the abstracts of Danish, Finnish, Norwegian and Swedish L1 PhD dissertations defended between 2000 and 2017. The results point to a growing field. A general observation is that the research focuses on reading and writing, whereas oral and aesthetical expressions are minor topics. Another result is a set of national differences which are related to governmental policy documents and school curricula. Further, the research has become more internationally oriented during recent years. The L1 research is characterized as a professionalized region (Bernstein, 2003) with strong didactization (Ongstad, 2004), and a potential for powerful disciplinary knowledge (Lambert, 2017).
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