The basic principles of increased safety

This type of protection covers electrical apparatus which generate  

It should be emphasized that this fact does not exclude the penetration of combustible mixtures into the enclosure s interior. Generally, all internal parts or components shall be considered to be exposed to these mixtures. The gas exchange between external and internal atmospheres is caused by operational load cycles of the apparatus and the thermal cycles derived thereby. The following calculation will demonstrate this fact a cage induction motor with internal free volume ymot is running in an external atmosphere with a temperature 

= +20°C (=293 K). In steady state (full load condition) the internal air volume is heated up to T2 = +150°C (=423K) due to the losses in the stator iron and windings, the rotor and, with a smaller contribution, the bearings due to friction. Assuming air to be an ideal gas, following the equation with  

When starting the motor at ambient temperature at full load and continuous operation until steady state, the air will follow the equation 

What is the philosophy of increased safety, or, in other words, what is the difference to normal industrial equipment  

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