# Thermal and Acoustic Design of a Shelter for High-Voltage Electrical Equipment
## 5 Acoustic Aspects
### Results of the Noise Simulation  
The objective set is that the Class II limits given by the Italian legislation are not exceeded for any of the receivers. The limits are defined by an Italian Regulation DPCM 14/11/1997, which lays out values depending on six Classes, assigned as a function of the destination of the area where the receiver is located. The limits are expressed in terms of emission, immission, and differential values. Emission is defined as the A-weighted equivalent sound pressure level (\(L_{\text{Aeq}}\)) at a receiver generated by the considered source alone. Immission is the A-weighted equivalent sound pressure level at the receiver considering the energetic sum of the noise emitted by the source and the background noise. These two parameters must be evaluated over the reference period (day, from 6:00 to 22:00 and night from 22:00 to 6:00). All the evaluations must be carried out in the 20-20 kHz frequency span. The differential criterium is based on the algebraic difference of  
Figure 14: Orientations of the schematic shelter in blue, aesthetic panels and point receivers in red and cross-section line dashed in red colour (top view). Figure 13: Positions of the noise sources with respect to the shelter. The noise sources are represented as red spheres and are placed in the position where the switchgears are emitting most of the noise (spring system). the impression levels and background noise levels and it is evaluated during the \"period of maximum annoyance\". Since the limits are lower during the nighttime, this is the period considered for the following evaluations. The impression limit for the nighttime is 45 dB(A), the emission limit is 45 dB(A) and the differential limit is 3 dB(A). For the SoundPLAN(r) model, the noise maps inside and outside the shelter can be generated separately. After the in-out module carries out the first computation, an equivalent sound power level is assigned to each surface and opening of the shelter. The noise map inside the shelter is given in the left of Figure 15. The surfaces and openings of the shelter can be considered as equivalent noise sources. The right of Figure 15 illustrates their sound power levels. It is also possible to compute the distribution of the sound pressure levels outside the shelter. The horizontal noise map in Figure 16 (left) has a resolution of 1 m and is computed 2 m above the ground, while Figure 16 (right) represents the cross-section map computed up to a height of 20 m above the ground. It must be noted that in the simulations the ground was considered flat without any building or any other discontinuity. To compare the values with the limits given by the Italian legislation, it is important to compute the noise levels at the 24 receiver positions. Depending on the side of the shelter on which they are located, the distance from the shelter and the height from the ground, they are named with the following notation:  
1. The receivers closer to the inlets contain I, outlets contain O in their labels, and those along the lateral sides contain L in their labels. 2. The labels of the receivers contain the distance from the shelter, be it 15 m or 30 m.
3. The labels of the receivers contain an underscore followed by the height from the ground. As an example, for the receiver closer to the outlet of the shelter, located 15 m from it and at a height of 8 m from the ground, the tag is O15_8. Keeping these notations in mind,  
Figure 16: Emission noise map (**left**), and emission cross-section noise map along the lateral side (**right**). Figure 15: Noise map inside the shelter (**left**) and equivalent A-weighted sound power levels of every surface and opening of the shelter (**right**). the A-weighted emission levels (\(L_{\rm{Aeq}}\)) at various receivers, together with the legislation limits, are given in Figure 17.  
Immission levels are the sound pressure levels (\(L_{\rm{A,eq}}\)) at the same receivers with background noise also taken into consideration.