Busbars configuration

We have drawn a comparison of these forces for the other busbar configurations in Table 28.8 for more clarity. 

Busbars are mounted one below the other, horizontally but in a vertical disposition. The cooling is better and requires less derating. The short-circuit withstand capacity is high due to high sectional modulus but occupies more vertical space. This configuration is also adopted by some manufacturers. 

This is similar to (a) above but each busbar now is mounted horizontally. Due to obstruction in heat dissipation, this arrangement requires a higher derating. It is also prone to collecting dust and provides a habitable surface for lizards and rodents etc. Therefore this is not a recommended configuration. 

Figure 13.31(a) Insulators to hold busbars in flat configuration (Courtesy J.K. Plastics)... 

If the temperature rise, as determined above, exceeds permissible limits it will be desirable to provide extra louvres, a forced cooling arrangement, larger busbars or a change in their configuration whichever is more convenient and easy to implement. 

Figure 28.14 Ratio of a.c. current ratings for different configurations of busbars of the same cross-sectional area (Courtesy The Copper Development Association, U.K.)...

But when other configurations are adopted as shown in Figure 28.34, this concept may not hold true. In other configurations, however, the sectional modulus will only rise and reduce the bending stress on the busbars. 

Depending on the rating and length of the bus system, a flexible-end joint may be necessary at the panel end also to absorb expansion of the busbars and also to assist in making the end connections when the configurations of the bus sections in the equipment are different or have a mismatch, although there are no vibrations at the panel end. 

The cables and busbars connecting the transformers to the switchboards are very short in comparison with the length of the transmission lines and the transformer reactances and so their impedances may be ignored. Consider the fault being applied to the busbars of the T4 switchboard. The fault circuit for the switching configuration shown is through T2 and T4. 

Busbars can be cut, welded, bent, punched, drilled, plated, and insulated to meet specifications. They are most practical when configurations must be precise, terminal points inflexible, and installation locations confined. 

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