With altitude, the dielectric properties of air are lower, so every bushing (the part that uses air to insulate) has to be protected using a directed field plug-in.

With altitude, ambient pressure decreases, so enclosed pressure increases and deforms the enclosure and safety disk.

Moreover, with altitude, usually, temperature decreases lower than the  guaranteed temperature (-25°C)
So we have defined 3 gaps in altitude :
Lower or equal to 1000m nothing to anticipate.
Above 1000m, and up to 3000m, with directed field connections
Third gap: above 3000m we have very few examples of this kind of use. So it's better to consult us for this kind of application.

Released for: Schneider Electric India