To reduce the allocation of land for the construction of electric power facilities, it is possible to leverage multi-circuit overhead transmission lines (MCTLs), in which the conductors of several circuits of different voltage classes are placed on the same tower. The unique features of the arrangement of conductors on MCTL towers cause unequal inductances and capacitances of different phases. In addition, there are significant mutual electromagnetic influences on the line circuits. To account for these factors, it is advisable to model the power flow of electric power systems equipped with MCTLs using the phase frame of reference. On the basis of such models, it is possible to determine the power flows while taking into account lateral and transverse asymmetries and to analyze electromagnetic safety conditions along the routes of multi-circuit transmission lines. We proposed a technique for modeling power flows and electromagnetic fields of multi-circuit power transmission lines, in which conductors of several circuits of different voltage classes are placed on the same tower. The methodology is based on the application of phase coordinates, which are the most natural description of three-phase power systems. The method is versatile enough to be applied to solving the specified problems for MCTLs of different designs. The article presents the results of research aimed at developing a method for modeling MCTL power flows. The results of modeling power flows of an electrical network including a three-circuit power transmission line are presented. The practical use of the models developed by the authors will make it possible to make well-grounded choices regarding the options for the use of multi-circuit power lines.
The article provides results of studies aimed at implementation of power supply systems (PSS) computer-based models in conditions of inferior power quality, where the PSS include backup diesel generators. The main aim of the study was to research these generators synchronization with the PSS network. The simulation was performed in the MATLAB environment using the Simulink and SimPowerSystems software packages. Based on the results obtained, it can be concluded that the self-synchronization method can be used for turning on diesel generators for parallel operation with PSS. After the synchronization processes completion, an improvement in the quality indicators of electricity in the PSS network and at the interfaces with the power supply system in terms of asymmetry and harmonic distortions.
Current treatment of complicated calculous biliary disease typically involves a two-step procedure consisting of pre- or post-operative endoscopic retrograde cholangiopancreatography (ERCP) followed by laparoscopic cholecystectomy (LC). This practice creates drawbacks as there is the need for two anesthesia inductions and longer hospital stay. The combination of LC and ERCP (LC + ERCP) for patients with cholecysto-choledocholithiasis has shown safety advantages, reducing anesthesia inductions and bringing high efficiency. This is a retrospective case series implemented at the Department of General Surgery - Hanoi Medical University Hospital between March 2020 and July 2022. In total, 44 patients met the criteria of this study. The average age of the cohort was 55.43 ± 18.12 years. The mean operating times of ERCP and LC were 58.05 ± 20.10 min and 54.09 ± 23.80 min, respectively. There was one intra-operative adverse event and no conversion. The mean hospital stay was 3.95 ± 2.28 days, and the rate of stones clearance was 100 per cent. LC combine ERCP in a single setting is a safe, effective procedure in treating cholecysto-choledocholithiasis.
hoạch và Điều tra Tài nguyên nước miền Bắc 3 Cục Quản lý Tài nguyên nước 4 Trường Đại học Khoa học tự nhiên-Đại học Quốc gia Hà Nội 5 Trung tâm Chất lượng và Bảo vệ Tài nguyên nước
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