2.1 Introduction

The enclosure material for an enclosed Busbar System is generally Aluminium alloy sheet/extrusion or sheet steel. Stainless steel and fibreglass enclosures have also been used for very specific requirements. The enclosure contributes a significant part to the overall cost of the product and must, therefore, be optimized.

The enclosures have to be fabricated, painted, assembled with components, installed at the site, and should require minimum maintenance for the entire life of the enclosed bus. To be cost-effective, the enclosure material properties must consider:

2.1.1 Workability & Weldability

Fabrication of enclosure comprises shearing, punching, folding, and welding. The process can be manual or automated and contributes significantly to the cost and performance of the product.

2.1.2 Strength

The enclosures are expected to withstand internal forces generated by a short circuit and external forces caused by wind, snow, ice, vibrations, and seismic activity

2.1.3 Resistance to Corrosion & Erosion

Enclosures are subjected to corrosion & erosion depending upon the service conditions. Surface coats provide additional protection and enhance life. (Gas insulated bus with Aluminium enclosure may be buried below ground. Apart from providing surface protection with coats, sacrificial anodes, and cathodic protection are provided to counter the effect of corrosion.)

2.1.4 Electrical Conductivity

Enclosure material with a higher conductivity is advantageous as it will contain losses and act as an electromagnetic shield. In many designs, where enclosure also serves as an earth conductor, higher conductivity is preferable. Enclosures of isolated phase bus carry the current almost equal to that of the conductor and to limit the losses and temperature rise, they are fabricated from high conductivity Aluminium.

2.1.5 Losses

All metallic enclosures of the Busbar Systems will generate eddy current losses and those with steel will, in addition, generate hysteresis losses which contribute to a temperature rise of the enclosure. All international Standards specify a limit on the temperature rise of the bus enclosure.