Busbars

Electrical Connections. Electric current is brought from the transformers by air-cooled copper busbars and close to the electrode by water-cooled bus tubes and flexible cables, connecting to water-cooled copper contact plates at the electrode. The plates are held against the electrode by hydraulic pressure. The connectors are as short and as balanced as possible to allow cancelling of magnetic fields associated with individual conductors. 

Monopolar electrodes have a direct electrical connection with an external power supply. This requites the distribution of current over the total area of one monopolar electrode, collecting the current from the other monopolar electrode for conduction to the next cell through interceU busbars. 

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. 

Each unit cost contains all the costs involved in the installation of that unit. For motors installed costs include the starter, conduit, wire, and a proportionate share of the service panelboard and busbars. The motor cost is not included since this will be part of the equipment cost. In the case of lighting, the installed cost includes the lighting fixtures, the conduit and wire, and a proportional share of the hghting panelboard and service switching costs. 

Specilleation for high voltage busbars and busbar connections... 

IS 8084, however, has opted for list II for the busbar systems for all applications. 

Maximum loading on the incoming feeder or the main busbars at any time... 

The rating of an indoor or outdoor switchgear assembly is referred to at an ambient temperature of 40°C. For a higher ambient temperature the rating of the assembly will be reduced in the same proportion as for the busbar systems and as shown in Table 28.3. 

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. 

If the short-time lating of the interrupting device is higher than the fatilt level of the system, which is the case with modern interrupting devices, the fault level of the system alone will prevail for the busbars, components and hardwaie. For example, for a system fault level of. SO kA. if the interrupter used is of 65 kA short-time rating, the bus system and all associated components w ill be designed for 50 kA onlv. 

Diversity factor this applies to column 7 of Table 13.13. Whenever a bus section has to feed a number of outlets, one can apply the diversity factor as discussed in Section 13.4.1 (4) to optimize on the size of busbars and also the size of the main incoming feeder (Example 13.1). 

Figure 13.29 illustrates a typical power distribution scheme to assign ratings to the various devices, components and busbar systems,... 

In the cubicle construction of a switchgear assembly the busbar chamber is normally located at the top of the assembly and runs through the length of it. It is usually suitable for extension, through fish joints at either end, if required at a later date. For installations having top cable entry, the busbar chamber may also be located at the bottom of the assembly or the depth of the panel increased, with an additional shroud between the top busbar chamber and cable chamber. From these main busbars are tapped the vertical buses for each vertical panel. Manufacturers may adopt different practices for horizontal and vertical busbar arrangements to economize on their cost of production. We illustrate the most common types of busbar arrangements. 

A separate control wireway may also run through the same busbar chamber, with suitable segregation or shrouding between the main bus and the control bus. This arrangement can be seen in Figures 13.2 and 13.7. The control bus system may be required for one or more auxiliary supplies for the following auxiliary services. 

Manufacturers may adopt different practices to mount the main and auxiliary busbars, depending upon the size, rating and fault level of the system. Some of the recommended and more common of these are illustrated in Figure I3.30(a)-(d) and discussed briefly below,... 

Figure 13.30 Possible arrangements for busbar mounting systems...

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. 

To obtain a strong busbar mounting system, suitable to withstand the electrodynamic forces arising out of a system fault, modern practice is to make use of thermosetting plastics, such as DMC (Dough Moulding Compounds)... 

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

Petroleum jelly is not recommended due to its low tracking lempeialure. The minimum tracking temperature is recommended to be 200°C, the same as for the busbars during a fault. Also refer to Section 28.4.1. 

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. 

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