Large capacity submerged arc furnace's key problems in the design of DC power supply 01

Submerged arc furnace is a necessary equipment

Submerged arc furnace is a necessary equipment for smelting ferrosilicon, ferronickel, ferrochromium and calcium carbide in ferroalloy industry. According to incomplete statistics, there are more than 30000 submerged arc furnaces in China. For a long time, domestic submerged arc furnaces mostly use AC power supply, resulting in low power factor, difficult control and balance of three-phase power grid, low efficiency and high operation cost.  In contrast, DC power supply has greater advantages, such as DC power supply can eliminate reactance voltage drop, skin effect, inter electrode interference effect and other problems, and has low operation loss and high electrical efficiency. Therefore, at present, the power supply of large capacity submerged arc furnace is developing towards DC power supply. This paper discusses several key problems in the design of DC power supply for large capacity submerged arc furnace, including the selection of main circuit topology, the optimization of current sharing coefficient, the design of monitoring system and the improvement of power factor. Then come and have a look with Me!

High current output requires the use of parallel devices to meet the operation requirements. With the increase of the number of parallel devices, the problem of low current sharing coefficient appears. Therefore, it is particularly important to optimize the topology of the parallel circuit and reduce the output coefficient of the main circuit.

Submerged arc furnace's design of controllable rectifier circuit

The basic unit is three-phase bridge and double inverse star rectifier circuit. Considering the output current only, on the premise of paralleling the same number and capacity of power electronic devices, the output current of double anti star rectifier circuit is twice that of three-phase bridge rectifier circuit. However, under the same output voltage and current, the installed capacity of the rectifier transformer of the three-phase bridge rectifier circuit is 21% lower than that of the double inverse star. At the same time, the reverse voltage borne by the rectifier is half of that of the double inverse star, and the utilization rate of the transformer winding is twice as high as that of the double inverse star. Therefore, considering comprehensively, if the output voltage is high, the three-phase bridge rectifier circuit has great advantages. Since the current of submerged arc furnace power supply reaches 40 ~ 150ka during operation, in order to meet the demand of output current and reduce electromagnetic interference, three-phase bridge in-phase inverse parallel structure and double anti star in-phase inverse parallel structure can be used. 

Compared with the first two structures, the two structures expand the output current twice and reduce the electromagnetic interference. However, this structure is difficult to meet the output current requirements of large capacity submerged arc furnace power supply exceeding 100kA. In order to further expand the output current, reduce the harmonic content and improve the power factor of the system, 12 pulse double anti star in-phase inverse parallel structure and 12 pulse three-phase bridge in-phase inverse parallel structure can be selected. The typical characteristics of 12 pulse three-phase bridge in-phase inverse parallel structure are: large output current, less harmonic content, low electromagnetic interference, high winding utilization, no need to use balanced reactor, etc.  Therefore, in the DC power supply of large capacity submerged arc furnace, the three-phase bridge in-phase inverse parallel structure with pulse number of 12 and above is more suitable.