Metal encapsulation prevents accidental contact with live parts and provides high mechanical stability against internal arcs. In the event of overpressure, integrated bursting discs provide safe pressure relief.
The 8DN9 thrives where AIS fails:
The 8DN9 utilizes $SF_6$ gas, which has a dielectric strength significantly higher than air. This allows the physical clearances between live parts to be reduced drastically. siemens 8dn9