# Thermal and Acoustic Design of a Shelter for High-Voltage Electrical Equipment
## 1 Introduction  
Different transmission system operators are actively contributing to the smart grid evolution and are developing high-voltage electrical devices that aim to distribute and regulate electric power and its flow to various classes of consumers--industrial, commercial or residential. The device described in this article consists of a set of switchgears and other side components. When installed in urban contexts, these components are segregated through solid panels with sound insulation/absorption capabilities. These panels contain a few doors and hatches to guarantee access and maintenance. For aesthetic reasons, a second set of panels surrounds the shelter on the four vertical sides. The electrical devices inside the shelter generate heat that needs to be extracted from the shelter since an excessive temperature can lead to malfunctioning and, in extreme cases, damage. In case of failures, an additional waste of money comes from the interruption in the delivery of the electric service. For this reason, it is necessary to avoid overheating by accurately designing the openings' dimensions and positions. Since, during their operation, the switches emit an impulsive noise, the openings must be designed also from an acoustic insulation point of view. The presence of large openings in the shelter promotes the propagation of noise, instead of attenuating it. Hence, a necessary trade-off is to be reached in the design phase of the shelter. For heat dissipation, large openings on the shelter sides are needed, while to reach the acoustical objectives, the openings must be as small as possible. This article details the computational and experimental studies performed to find a suitable trade-off. For the thermal aspects, thearticle contains the implementation of the theory in a Finite Element (FE) model, followed by an experimental validation made on a downscaled structure. The acoustic aspects contain the steps needed for characterising an impulsive sound source, followed by the results of field experiments and the modelling of the sources, shelter and aesthetic panels. Studies have investigated various encased heat-emitting devices, some of the preliminary ones being a DC power supply [1], DC-DC converters for PC boards [2], and an AC/DC notebook power adapter [3]. A widely used example of an encased electrical structure that emits heat is a power transformer, on which numerous studies exist about its thermal modelling and heat dissipation. Studies such as the one carried out by [PERSON] et al. [4] presented the equivalent thermal circuit out of the governing heat transfer equations. The study by [PERSON] and [PERSON] [5] improved this lumped parameter model by refining the nonlinear thermal resistances and equivalent thermal capacitances of the transformer oil, and the effect of oil viscosity changes is introduced. The aesthetic panels also act as sun shields, protecting the electrical device from solar radiation. Studies by [PERSON] and [PERSON] [6] suggested that, through a focused design, an oil temperature reduction of 7 \({}^{\circ}\)C is possible, depending on loads. [PERSON] et al. [7] worked with the lumped parameter model refined by contributions from solar irradiation. [PERSON] [8] showed how solar irradiation affects transformer winding paper insulation by influencing its degree of polymerisation, hence significantly reducing the lifetime. Further work on refining the equivalent thermal circuit using the lumped parameter analogy, transient as well as steady-state temperatures of the main parts of a power transformer, was performed by [PERSON] et al. [9] and [PERSON] and [PERSON] [10], with validation from experimental data. Other studies on the validation from experimental data on this subject were proposed by [PERSON] et al. [11] and [PERSON] and [PERSON] [12], the latter of which has obtained very good agreement in validating the temperature distribution on a transformer's surfaces. Most of these works involve natural convection on the external surface and oil as the internal cooling medium.