## 2 Materials and Methods  
### Structure and Modeling of the RMU  
Based on the \"10 kV AC outdoor box-type switchgear\" commonly found in communities and along streets in China, a simplified model of its cable room was studied. The model has dimensions of 420 mm in length, 280 mm in width, and 830 mm in height. The dehumidifier has been simplified and is now represented by two ventilation pipes for the entry and exit of dry air. Each pipe has a length of 348 mm and a diameter of 58 mm, and they are connected to the back of the cable room. The geometric model and dimensions of the simplified cable room model with an electric heating wire are illustrated in Figure 2a. According to the configuration of the 10 kV RMU, three-phase copper core cables are chosen. In the cable room, 4.5 mm thick cross-linked polyethylene is used to create three single-phase cables, each with a radius of 11.9 mm [17]. The length of the middle cable is 565 mm, while the lengths of the left and right cables are slightly longer, approximately 570 mm. Additionally, to experimentally validate the simulation's accuracy and assess the feasibility of the experiment, a simple cable room was constructed in a 1:1 ratio. An electric heating wire was used as the heat source for thermal analysis instead of a central cable. The wire had a length of 565 mm and a radius of 0.5 mm. Corresponding simulations were conducted to validate the results. Based on the verification results, the structure and dimensions of the simulation model with cables are depicted in Figure 2b.  
Figure 1: The flowchart of research.  
Due to experimental limitations, it is difficult to directly validate the case presented in Figure 2b in the laboratory. In Figure 2b, the simulation first calculates the heating power of the cable, and then adds it to the case in Figure 2a. The further optimization of the case in Figure 2b is supported through mutual verification between experiments and the case in Figure 2a. Finally, Figure 2c depicts the model grid, which will be explained in Section 2.2, while Figure 2d illustrates the positions and coordinates of the monitoring points in the model, which will be discussed in Section 2.5.  
Optimization of pipe layout is one of the main optimization methods in this study. The layout of the left and right pipes is based on the original structure of the dehumidification equipment, and the pipes are located in the middle of the wall, which is referred to as Layout 1 in the following text. We are considering the layout of the cable room structure and attempting to improve it on the basis of the original layout to make the internal flow more uniform and sufficient, in order to improve the dehumidification. The schematic diagram of the pipeline layout is shown in Figure 3a,b, which includes Layout 2: exchanging the air supply and air outlet on the basis of Layout 1; Layout 3: vertically arranging ventilation ducts, taking into account the internal structure of the original cable room, adjusting the position appropriately, with the lower ducts supplying air and the upper ducts extracting air; and Layout 4: swapping the air supply and air outlet on the basis of Layout 3.  
Figure 2: (**a**) Geometric structure and dimensions of cable room model with electric heating wire, (**b**) geometric structure and dimensions of simulation model with cables, (**c**) schematic diagram of the main grid of the cable room and (**d**) XYZ coordinates and reference points of the main monitoring points.  
Pipes 1 and 2 are separated on the right and left sides, while pipes 3 and 4 are vertically distributed on the wall, one above the other. The layout is referred to as Layout 1, where air is supplied through Pipe 1 and extracted through Pipe 2. Layout 2 supplies air to Pipe 2 and extracts air from Pipe 1. Layouts 1 and 2 are depicted in Figure 3a. Layout 3 supplies air to Pipe 4 and extracts air from pipe 3; Layout 4 supplies air to Pipe 3 and extracts air from Pipe 4. Layouts 3 and 4 are shown in Figure 3b.