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Skip to main content. Log In Sign Up. Comparative Study on Cables and Busbars Comparative study for cables and busbars Preliminary considerations. Fira Romania. Comparative study for cables and busbars Preliminary considerations To compare the prices of two categories of product as different as traditional cables and busbars, it is necessary to make some preliminary considerations based on actual cases, particularly as regards calculating the actual cost of installation. Clearly the price of cable depends on the price of the raw materials.

This comparison only takes into account cables laid in perforated ducts, which ensure good ventilation and hence good heat dissipation. At present the only tray on the market meeting these requirements are the wire type. For reasons of cost, ease in procuring materials and assembly, we decided not to use multi-pole cables greater than mm2 or single-pole cables greater than mm2.

Transformer — low-voltage switchboard connection The cost of connecting the transformer and switchboard depends mainly on two factors: Let us examine two typical situations: In the first case we have a connection between a transformer and a low-voltage switchboard that is short and straight see Figure 1. Figure 1: Straight connection between transformer and low-voltage switchboard. Sizing of the wiring system starts by calculating the power required to run the factory in question.

When the installed power has been calculated, you can select the most suitable size of transformer for the factory. Now, presuming that the link between the transformer and low-voltage switchboard is short and straight, we can prove that the cost depends only on the power of the transformer.

Figure 2. Ratio for busbar and cable connection costs. Taking the cost for cable connection as , we can see for each size of transformer that the cost of a cable connection increases with the size of transformer, and cost parity materials plus installation is reached for a kVA transformer. In the second example, let us suppose that for reasons of system reliability and flexibility the factory has decided to install three transformers and the connection between transformers and switchboard has at least two horizontal, rather than straight, angles.

Figure 3.

Complex connection between three transformers and low-voltage switchboard. In the second example here, the cost ratio between connecting with busbars and cables has a similar trend to the previous example, but cost parity is reached for smaller transformers see Figure 5.

Figure 4. Transformer- switchboard connection. The problems in connecting a bundle of cables and the transformer terminal and switch are highlighted. Ratio between the cost of a complex transformer- switchboard connection using busbars and cables.

Designing a wiring system in a storey office block Let us suppose we have to design a wiring system in a storey office block and we need to power utilities rated at 45kW.

All the floors are supplied via a single shaft. Each floor needs a control panel with a knife switch and fuse holder or a thermalmagnetic circuit breaker to protect and cut off the system for the entire floor.

In our example, the switchboard supplying the various floors via the shaft is not in the immediate vicinity of the shaft, it is about 30 metres from the base of it.

This means three different systems can be considered: The entire system can use busbars, i. Alternatively, the low-voltage switchboard and the riser power supply box can be connected using busbars with a bundle of suitably sized cables, and the riser alone using busbars.

Lastly, the entire system can be laid with power cables. This means that the same number of bundles of cables as floors in the building will have to run from the switchboard and each bundle will have to run up the shaft vertically, stopping at its own floor, so the number of bundles decreases the further up you go.

Now let us examine the advantages and disadvantages of these three solutions. Busbars A study of the power for each floor shows that the capacity of the busbar must be A.

Where the busbar leaves the low-voltage switchboard, it is protected by a thermalmagnetic circuit breaker. As the busbar runs the 30 metres to the shaft, it passes through the boiler and air-conditioning rooms and then runs up the shaft vertically to the top floor see Figure 6.

There is a tap-off at each floor to supply the utilities on that floor. Flame barriers can be situated along the shaft at the various floor levels to prevent the spread of fire, smoke and heat if a fire should break out on a lower floor. Switchboard-transformer link using A busbars powered at both ends.

This bundle of cables connects with the busbar via the switchboard at the front end. To supply the riser, the cables too need to pass through the heating, cooling and ventilation rooms, so steps must be taken to prevent toxic and corrosive gases from spreading through the building from the air conditioning plant in the event of a fire. Alternatively, cables with a low emission of gas and toxic agents must be used.

Figure 7. Cable layout Figure 8 shows the power supply to the various floors of the building with a bundle of cables each from the switchboard to its own substation at each floor.

The switchboard needs to have as many circuit breakers as the outputs 15 , or alternatively the individual cables can be fused.

Figure 8. For obvious economic reasons, this coefficient will only take into account the probability of a slight increase in load power. If the power increases excessively, the transformer supplying the building will have to be replaced or paired with another transformer.

With the use of busbars, later extensions do not involve many technical problems. The new transformer will only have to be connected to the busbar from the top of the riser top floor. Thus in this case it will only be necessary to pass one cable along the shaft to supply the busbar on the other side. This solves the problem easily and economically.

Let us now consider the more common case in which total power required by the building is constant, but division between the floors varies. In the cable solution it is necessary to check that the various cables supplying the floors of the building can withstand the new load and if necessary add another cable in parallel if the power exceeds the capacity of the cable. With the busbar solution, this will not be necessary thanks to the flexibility of the system.

At most, it will be necessary to change the protection device of the cable from the switchboard to the floor substation - only a few metres of conductor. Distribution of the loads of the riser in busbars with power supply from one or both ends.

Technical comparison between cables and busbars Apart from strictly economic reasons that increasingly favour the prefabricated solution as against the one to be wired up, there are various advantages of the busbar version in technical terms.

It has been modelled to the reflected one. If the length of the line is m, the forward If p is the tilt of the input triangular wave, that of the wave reflects itself at the end of the line doubling its surge at the end of the line is 2p. So, it reaches the magnitude. The voltage at the end of the line is This formula shows the relation between the the algebraic sum of opposite impulses with the same effective protection distance dp the length of the line tilt absolute value.

The interference is destructive and it that makes VM equal the impulse withstand voltage of results in a trapezoidal wave form with a peak value of the equipment and the impulse withstand voltage Ub. VM see figure 4. The voltage profile at the terminals of a spark gap with impulse protective level of 1 kV, obtained through simulation, is showed in figure 5.

Figure 4 Input and end-of-line voltages line length: 25 m The problem is now presented under the analytical point of view and a relation between the effective protection distance dp and the impulse withstand voltage Ub is obtained.

Figure 6 shows its V-t characteristic. Figure 10 summarizes the results obtained with an impulse withstand voltage of 1. Heidler 0. Figure 8 shows Effective protection distance [m] Figure 10 Impulse protective level versus effective protection distance with an impulse withstand voltage of 1. The effective protection distances obtained with the The voltage at the end of the line versus the line length double-exponential impulse as input only measure a is reproduced in figure 9.

As it can be seen, for short lengths, i. Then, the installation is designed by keeping into account only the first lightning stroke, the equipment could not be protected against the subsequent ones. For this purpose a comparison between simulated and calculated values is shown in figure Conclusions 80 60 As told in the introduction, this work aims at 40 providing a simple and reliable method for evaluating 20 30 40 50 60 70 80 9 the effective protection distance of an SPD. Thanks to Effective protection distance [m] the theoretical approach, an analytical formula 7 has Formula 7 Simulations been found out, but it refers to a simplified input signal.

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