Electrical cabinets’ design intended for high altitudes requires particular attention due to the progressive reduction of the dielectric strength and the density of the air.
Standard EN 61439-1:2012-02 defines the general rules for low voltage enclosures and sets a reference limit at 2000 m above sea level. However, there are many plants installed at higher altitudes, above all in Asia, Central and South America and sometimes also in Europe.
In all these cases, it is necessary to ensure that the loads on the power circuits are sized within the limits established by the distances between the electrical connections and the tracks on the printed circuits of the electronic devices. Unless otherwise indicated, the component manufacturers indicate values up to 2000 m on the rating plates and, if currents close to the maximum declared levels are estimated, it is always preferable to introduce some precautions.
Climatic control of the panel and altitude
For Fandis, the focus is above all on the design of climate control. If cooling of internal components by ventilation is applied, great care is required. On this type of cabinet, in fact, the internal air mixes with fresher air coming from the outside and the optimal volumetric flow rate of air must take into account the altitude.
So let’s see how to proceed for sizing taking into account the altitude. Once the thermal power produced by the components during operation has been calculated and the reasonably highest temperature that we could have in the surrounding environment has been identified, the optimal working point is determined as a function of the desired temperature difference, as described in the following formula:
As we have already seen in a previous article of this blog, the work point indicates the volumetric flow rate [m3/h] but since the purpose of ventilation is to remove heat, we should refer to the mass flow rate [kg/s] and it is necessary to correlate them through coefficients determined by the specific heat of the vector fluid (air), the pressure (CEI EN 60721-2-3) and the humidity.
The normal value of atmospheric pressure at mean sea level is 101.3 kPa while 2000 m is 79.5 kPa, a difference sufficient to make us move from one size of ventilation system to the next. The Kst value as a function of the installation altitude has a rather linear trend, as can be seen in the figure.
The truthfulness and completeness of the flow rate data declared by the manufacturer is essential, if only doubts arise, it is better to ask for a test report from a certified laboratory.
We always suggest using the thermotechnical calculation software (available free on the Fandis website), a support that allows not only to consider the aspects just described, but also the dissipation of the walls according to the transmittance of the material with which they are built, the effect of the winds or solar radiation in outdoor applications.