AS EN 50069:2013 pdf free download – Welded composite enclosures of cast and wrought aluminium alloys for gas- filled high-voltage switchgear and controlgear
5.3 Design cons iderat ions
The geometr y of an enclosure can be de termined by electr ical rather than mechanical considerat Ions。This constraint can resul t in an enclosure geometry which requires an unacceptable degree 0 f calculation oI which cannot be calculated at a11. In the case of such an enclosure or an enclosure for which cal- culations are not made, a pIoof test of the individuai hous ing i s necessar y before the internal . parts are added . When designing an enclosure, account sha1l be taken of the fol1o- wang，1f applicable :
(a ) The possible evacuation of the enclosures as part 0 f the f 111ing process . For enclosures of this type it is usually necessary to evacuate the air before introducing gas pressure，this ensures purity of the gas. The evacuated condi tion i s therefore not an operat 10nal condition and in mos t cases enclosures designed f or interngl pressure 111 be suitable for the evacuated condition without buck1 ing . F oI certain 10ng lengths and large diameter busbar sections， however，it is possible that the enclosur e wi1l buckle due to external pressure . In such cases th e design should be checkedfor external pressure and the enclosure strengthened，1 f necessary . Since this 1s not an operat lonal condition, it is not a matter of safety .
5.5 Design temperature
The selection of material and the determination of the des1gn stress depend upon the highest wall temperature which can be ex- pected during service at the design pressure (p).
5.6 Design st ress basis
The nominal design strength (K) shall be selected from the mate- rial standard F or castings . the nominal design strength of the materiai without heat treatment shall be used 1n the heat affec- ted areas of the. welds. For wrought a1uminium parts the nominal design strength in the annealed condition shall be used in the de sign . of welded structures .
5.7 Calculation
The castings shall be calculated,1iany，as prescribed in EN 50 052, clause 5. The wrought alumin1um parts shall be calculated as prescribed in EN 50 064， Clause 5。It should be noted， however，that an additional wa1l thickness of the wrought aluminium parts is required to maintain the ratio 1,3/1,5 (stress . at routine pressure test against yield strength) during the Ioutine pressure test of castings with 2,0 times the design pr essur e (p),inorderto ensure that y ielding of the wroug ht aluminium par ts does not occur.
7.1 General
Each enclosure shall be inspected during construction. Suf ficient inspections shall be made to ensure, that the materials,con- struction and testing comp1y in all respects with the require- ments of thi s standard.