# Quick Calculation of Magnetic Flux Density in Electrical Facilities
## 4 Case study  
The calculation of the MFD produced by a real DTS in its surroundings has been selected as an example to show the application of the developed software. This example will be studied to demonstrate the importance of considering aspects such as the wires' arrangement when executing the installation of the substation. This DTS is located on the ground floor of a building. Since a bedroom could exist on the upper floor, it is necessary to study the MFD about 20 cm above that floor. Using the program, the geometry of the room and the wiring have been introduced and the calculations have been made. The results of these calculations are shown in the following section. Then, analyzing the results, some simple modifications have been proposed to ensure the reduction in the MFDs around the substation. Figure 9 shows a picture of the studied DTS located in a building. Figure 8: Proposed method to study and minimize the impression in the surroundings of an electrical installation. The DTS (20,000 V/400 V, 630 kVA) has the following dimensions: 4 m in the direction of the X axis, 2.5 m in the direction of the Y axis and 2.5 m in height. Figure 10 shows the floor plan of the DTS and a 3D view. The high voltage line (20 kV) consists of three unipolar aluminum conductors (one for each phase) of 240 mm\({}^{2}\) with high module ethylene-propylene (HEPR) insulation, with a 16 mm\({}^{2}\) copper shield and Z1 type cover. This underground line approaches the center with a certain slope. Then, it continues parallel to the ground and arrives at the medium voltage switchgears, where it crosses them. Finally, it leaves parallel to its entry path (urban DTS in a ring main feeder). For this line, 250 A are assumed per phase. On the other hand, the low voltage line leaves the transformer terminals and goes up to a tray on the wall 2.2 m high. It is a line with three conductors per phase and an electric current of 300 A has been assumed in each conductor. After the tray with all the conductors arranged in a single layer, these go down, in contact with the wall, in groups of three (equilateral triangles with wires touching each other), passing through the low voltage panel. Then, the conductors are buried at 40 cm deep to go to the low voltage installation. The high voltage section that passes through the protection and measurement electrical cabinets and reaches the high voltage transformer terminals is not included in the study, as it has a very low current (about 20 A) and produces much lower MFD levels. The geometry data and layout of the conductors have been entered in CRMag(r)to study the MFD produced by this facility. The definition of the whole model is developed in just a few minutes. The program automatically calculates the induced currents in the high voltage insulated cable shields (these are grounded according to a solid bonding scheme) and conveniently corrects the calculation of the MFD. For some elements, such as metallic electrical cabinets or transformers, the user can select an attenuation factor, taking their dimensions into account. With a preliminary calculation, the user can find which areas have higher MFD levels, to make a detailed study of them. In order to show here the results of greatest interest and propose an alternative that has a great impact on the results,  
Figure 9: Location of the studied distribution transformer substation (DTS) in a building. the MFD will be studied on the upper floor and on the sidewalk of the main facade, where the line enters and leaves the facility. For the immission study on the upper floor, the calculation height is the plane at z=2.9 m, taking into account the 2.5 m in height of the DTS, plus 20 cm of floor thickness and calculating 20 cm above the floor. This is done because there could be a bedroom in the existing dwelling. This calculation will be carried out on the entire upper floor in a 4-m-wide square (from the coordinate x=0, y=0 to the coordinate x=4, y=4).