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Reply To: معمای کابل شماره 4 – کابل های قدرت آبگرد


    با عرض معذرت، سوالتان خیلی روشن نیست. کابلهای آبگرد کابلهای جریان زیادی هستند که با جریان آب خنک می شوند. کاربرد مهم آنها نیز در کوره های الکتریکی جریان بالا است که در ثانویه ترانس بین الکترودهای عظیم جرقه زن و ترانسفورماتور مخصوص کوره قرار می گیرد. نحوه اتصال سیم پیچی ترانس برای نمونه در شکل زیر آمده است. روی مدار معادل سیستم پس از شکلگیری جرقه نیز مطالعات زیادی صورت گرفته است. Figure 1 shows the physical model of the electric arc furnace. In this particular EAF model, there are three electrodes that are moved vertically up and down with hydraulic actuators. Each of these electrodes has a diameter of roughly 1.5m, weighs approximately 40 tons and is 1 to 2 stories tall. In theory, the ore is melted with a huge power surge from the electrodes. The actual product is denser than the scrap and thus falls to the bottom of the furnace creating the matte. Above the matte lies the slag where the electrode tips are dipped. The tremendous heat created by these electrodes causes the ore to liquefy and separate. Thereupon more raw materials are placed in the furnace and the process repeats itself. Arcing is a phenomenon that occurs when the electrodes are moved above the slag. As the electrode approaches the slag, current begins to jump from the electrode to the slag, creating electric arcs. Depending on the magnitude of the input voltages of the electrodes, the arcing distance can vary. Usually, arcing occurs in a region within centimeters of the slag (approximately 10- 15cm). Therefore, the EAF model must take into account the instances when x1, x2, x3 are negative (i.e. the electrodes are suspended above the slag). Figure 1 above shows the sign convention used in the project. For the EAF circuit, several assumptions were made. It must be noted that this is a three-phase circuit with a double configuration. The outer resistances (inter-electrode resistances) form a delta circuit with the three nodes. The inner resistances (slag-to-matte resistances) form a wye-connection with Vm as a virtual ground (floating neutral). Figure 2 shows the electrical model for the EAF with the chosen direction of currents. To simplify calculations, the inter-electrode resistances are equivalent and represented by R. As for the slag-to-matte resistances, tests showed that these resistances displayed inverse linear relations with respect to their position. Consequently, by taking the slag-to-matte conductances, the inverse function becomes a linear relationship, which makes for simpler calculations. The slag-to-matte conductances Gi, where i represents the electrode, can be written as: Gi=Ci . Xi +Gs where c is the conductance coefficient (in Siemens/m), xi is the immersion depth of the electrode in the slag (in m) and Gs is the total conductance of the slag (in S). In other words, Gs is the conductance of the slag when the electrodes are positioned at the surface of the slag. Using these assumptions and KCL, it is now possible to solve the EAF electrical circuit.