(1) The electrical appliances are arranged in a closed or semi-closed metal shell, the distance between each other and the ground can be reduced, and the structure is compact. (2) The electrical components have been assembled in the factory, which greatly reduces the amount of ready-made installation work, which is helpful to shorten the construction cycle. It is also convenient for expansion and relocation (3) High operation reliability and easy maintenance (4) More steel consumption and higher cost