These transformers are designed for temperature class F or H to minimize the weight. The transformer's protective structure is made of H class insulation materials with built-in air channels making it possible to have very powerful cooling if the device can be equipped with forced air circulation.
It is technically same as the PU type but it is encased in IP 23 standard steel casing. Standard colour RAL 7035.
This structure can also be used for chokes for various purposes.