CAN CSA C50069-99:2016 pdf download.Welded composite enclosures of cast and wrought aluminium alloys for gas-filled highvoltage switchgear and controlgear
4 Materials
Any suitable aluminium or aluminium alloy is permissible; a list of examples of cast materials is given in table 1 and a list of examples for wrought aluminium is given in table 2. The properties of the materials should be taken from the applicable standards.
NOTE 1. Contact with more noble metals, particularly copper and its alloys, can lead to heavy galvanic corrosion. Austenitic stainless steel is an exception to this rule because of its protective oxide film and can often be used in contact with aluminium.
Aluminium enclosures should be protected externally where, for example, they come into contact with mild steel supports. Bitumen, thin zinc sheet (which gives sacrificial protection) or a combination of these are useful in this respect. Alternatively, the mild steel supports can be galvanized or zinc or aluminium sprayed.
5 Design
5.1 General
The rules for the design of enclosures of gas- insulated switchgear and controlgear prescribed in this clause are solely for the purpose of determining the dimensions and the minimum thickness to ensure safety of the enclosures.
The rules take into account that these enclosures are subjected to particular operating conditions (see clause 1) which distinguish them from conventional compressed air receivers and similar storage vessels.
The thicknesses determined by the various equations are minima and therefore the specific nominal thickness shall be increased by the amount of any negative tolerance permitted by the material specification.
NOTE. There are designs of enclosures which differ in geometry from those for which equations are given. These designs are permitted provided the calculation is justified or proof tests are carried out as prescribed in 7.5.3.
5.2 Corrosion allowance
The enclosures are filled in service with a non- corrosive thoroughly dried gas, therefore, no internal corrosion allowance is necessary.
5.3 Design considerations
The geometry of an enclosure can be determined by electrical rather than mechanical considerations. This constraint can result in an enclosure geometry which requires an unacceptable degree of calculation or which cannot be calculated at all. In the case of such an enclosure or an enclosure for which calculations are not made, a proof test of the individual housing is necessary before the internal parts are added.CAN CSA C50069-99 pdf download.