The transformer in question is 7.5MVA,ONAN, oil filled,22/6.6KV, Dyn11, Z=8%,outdoor type with 22KV & 6.6KV air filled Cable
boxes. Due to arcing or short circuit in the cable box, inside air will expand instantly & create over pressure, there by bursting the cable box.The bursting would flew cable box cover to a distance or occupants around would be endangered. To avoid such bursting, whether any pressure relief device and/or silica gel breather should be provided. In case of over pressure, the breather would give way or even the device would operate.
Whether such requirement has been specified in NFPA,NEC,IEC,IEEE ? Please comment.