Busbars supports

Only high tensile (HT) fasteners must be used for busbar Jointing and their interconnections or links not only to take care of the fault level but to also maintain the recommended contact pressure over a long period of operation as noted in Table 29.1. An ordinary fastener may not be able to withstand or sustain this torque for long. Similarly, the busbar supports, which are mounted on only two or three fasteners, should also be fitted with these fasteners. 

F = maximum electrodynamic forces acting on each support, in the event of a fault, as calculated above = 514 kgf / = centre distance between two busbar supports = 40 cm M = sectional modulus of each busbar at section x - x... 

For busbar joints we have considered 8 Numbers bolts of size M-10 (diameter of bolt shank, 10 mm), as in Figure 29.4. As the size of these fasteners is greater than that of the busbar supports, their suitability is not determined separately. 

Assuming the distance between each busbar support of the same phase to be 400 mm then the force on each section of busbars, insulators and the fasteners. 

Figure 31.5(b) Cross-sectional view of an iPB with insulated (discontinuous) enclosure illustrating busbar-supporting arrangement (Courtesy Best Crompton)... 

Busbars. Fitting the tank for d-c power is usually accompHshed usiag round copper busbars, both for supporting the anodes and the work or cathodes. Size of the copper bus is determined by the amount of current flow expected 1000 amperes requires about 6.5 cm of cross-sectional area. The bus is iasulated from the tank, and any other sources of grounding, and coimected to the d-c power supply. Shorter distances from the tank as well as fewer electrical connections keeps the voltage drop to a minimum. 

The mechanical endurance of the current-carrying parts of all the equipment, bus system, deviees and components, used in a particular circuit as well as the load-bearing members and supports on which they are mounted. The electrical parts of a device (breakers and switches, etc.) are the responsibility of the component manufacturers. The manufacturer of the switchgear assembly is responsible for the busbar systems, metallic links and wires. 

It is permissible to lest just one panel of a multi panel-assembly so long as the construction of other panels is similar and busbar arrangement and supports are the same. The value of the prospective short-circuit current may be determined from a calibrated oscillogram. The test current in any phase should not vary by more than 10% of the average in the three phases and must be applied for a predetermined time of I or. 1 seconds. Unless specified otherwise, this should be considered as to be I second. 

If the busbars consist of more than one section in cross-section, or different distances between the supports or the busbars, the test may be conducted separately on each section. 

Below we analyse the adequacy and the suitability of busbars, fasteners and the insulators supporting the busbars, to withstand the above forces acting differently at different locations. 

It is possible that during the fault only one ot the insulators is subject to the transitory first peak of the fault, as there may be slight misalignment between the insulators, asymmetry in the busbars, an imperfect bolt fixing and their fastening, or a combination of such factors. To be on the safe side it is advisable to consider each support and its fasteners to be suitable to withstand the forces by themselves. We have assumed a factor of safety of 100% in all the above calculations to account for this. 

The designer must consider all the forces imposed by the busbar on its supports. The supports often are insulators, which may be ceramic. These are more likely to fail in tension or shear than in compression. Therefore, their axes should not be at right angles to the force on the buswork. 

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