Comparison of the application of busway and cable in power distribution system

[Comparison of the application of busway and cable in power distribution system]: Traditional busway is being challenged by cables, especially branch cables. Years of practical experience have proved that the two have their own advantages in terms of product performance, application fields and economic costs, and cannot be simply concluded. This article makes a multi-faceted comparison of cables and busways, which can be used for reference. 1 Ordinary busway and cable...

Traditional busway is being challenged by cables, especially branch cables. Years of practical experience have proved that the two have their own advantages in terms of product performance, application fields and economic costs, and cannot be simply concluded. This article makes a multi-faceted comparison of cables and busways, which can be used for reference.

1 Performance characteristics of ordinary busway and cable:

The so-called ordinary bus duct is a transmission and distribution system with electrical continuity through a reasonable and safe structure, which wraps several conductors in a metal shell to form a whole. Ordinary busway is generally divided into two types: densely insulated and air-insulated. The air-insulated type has a simple structure and a large transmission current; The densely insulated type has a compact structure and good heat dissipation capacity. They all have the characteristics of strong overload capacity, easy tapping, and small footprint.

Cables are divided into single-core cables and multi-core cables. Single-core cables mainly use various insulating materials, and multi-strand copper wires are wrapped in an insulating layer as a conductor of current in a certain phase. A multi-core cable is a complete cable formed by twisting multiple insulated cores together and wrapping them with an outer sheath. The number of insulated cores of power cables is usually 1, 2, 3, 4, 5 and other cores, as well as 4+1 and 3+2 cores. The main advantages of cables are flexibility and adaptability to the environment, but they also have their inherent limitations. The following is a performance comparison of busway and cable from several main aspects.

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a) Busway ampacity:

The cross-sectional area of the low-voltage cable is 1000mm2 and the rated current is 1600A. Due to its large size and weight, such a large size cable is rarely used in practical engineering. Cables of 400 mm2 and below are commonly used in engineering, which requires the use of multiple cables to achieve simultaneous power supply. The rated current of the bus duct can reach 6300A, and its strong current-carrying capacity is incomparable to the cable.

b) Busway overload capacity:

Whether it is a cable or a busway, the overload capacity depends on the operating temperature of the insulating material used. The working temperature of the busway insulation material is 105°C, and the irradiated cross-linked flame retardant winding tape (PER) and the radiation-crosslinked polyhydrocarbon heat shrinkable tube with a working temperature of more than 140°C have been developed. At present, the permanent working temperature of the insulating material used in the cable is generally 90 °C and 105 °C, and the working temperature of the irradiated cross-linked cable is 125 °C. As a result, the overload capacity of the busway is much greater than that of the cable.

c) Busway installation tapping:

The busway generally adopts the plug-in installation and tapping method. The so-called plug-in bus duct is to use the plug-in mode to tap the power supply of the main line to the branch line, and there is a plug-in box every few meters, so the tap is very convenient. Cables need to be tapped, which is unreliable, and even prefabricated branch cables have their drawbacks. The obvious disadvantage of branch cables is that they need to be customized to the factory, usually with open "C" clamps. After a long time, it is also a question whether this kind of hoop can ensure the tightening force. In addition, the branch head of the branch cable is expensive, so the prefabricated branch cable is still not widely used. When installing branch cables, it is necessary to cut off the power supply on the floor, and there is no need to cut off the power when installing the busway, as long as the plug-in box of the busway is removed in the case of no load. However, it is very dangerous to cut off the branch power supply of the prefabricated branch cable, which is very dangerous to operate in a live situation. [Comparison of the application of busway and cable in power distribution system]: Traditional busway is being challenged by cables, especially branch cables. Years of practical experience have proved that the two have their own advantages in terms of product performance, application fields and economic costs, and cannot be simply concluded. This article makes a multi-faceted comparison of cables and busways, which can be used for reference. 1 Ordinary busway and cable...

d) Fire performance of busway:

The insulation and outer sheath of a normal cable will burn. Even flame-retardant cables burn when exposed to flames and only burn after the flame leaves. Fire-resistant cables do not burn, but they are expensive, and fire-resistant cables are only used in situations where power outages are not allowed, such as fire alarm circuit systems. The busway shell is metal, will not burn, even if the insulation material of the copper bar burns, the flame will not be dangerous to the outside of the busway.

e) Busway heat dissipation performance:

The insulation and outer sheath of the cable are both insulating and insulation. Therefore, in order to keep the heat dissipation of the cable, when the cable is laid in the tray, 2 layers are allowed to be laid, and the reason is mainly to consider the heat dissipation problem. The busway uses air conduction to dissipate heat and dissipates heat through the close-contact steel shell, so it has more heat dissipation performance than cables.

f) Operation and maintenance of busway:

The maintenance of the busway is relatively simple. During the daily maintenance of the busway, it is usually to measure the temperature rise of the shell and grommet, the temperature rise of the connector of the wire box, etc., if the grommet bolt is used 4.8 grade, it needs to be tightened regularly, and if the 8.8 grade high-strength bolt is used, it does not need to be strong regularly. However, cables are limited by factors such as easy wear, easy aging, and short lifespan, so they need to be regularly inspected and maintained, or even replaced.

2 Busway installation and construction:

Although the cable laying and installation is flexible and convenient in the direction of the line, the cable in the project is generally supported by the bridge, so the cable construction needs to be installed first, and then the cable is laid, step by step. The installation of the busway does require installation technology, but it only needs to be installed in accordance with the standard installation procedures of the product, and the installation can be completed at one time. In addition, the busway structure is compact, occupies a relatively small space, is easy to arrange the space of pipelines and lines, and is easy to install. Of course, for small current lines below 400A, the use of cables is more flexible because the cable cross-section is relatively small and the number of cables is smaller.

3 Busway power supply system:

The busway power supply system is usually the main line from the distribution center to scatter flexible power supply, while the cable power supply is limited by the difficulty of tapping, small current carrying capacity, difficult to disperse control and other factors, usually "point-to-point" power supply, especially in the high-rise building power supply system, the bus duct is particularly different from the cable.

In the traditional cable power supply mode, each floor needs to be paid off separately, and there are many cables. Such a dense laying method has poor heat dissipation, large space occupation, difficult accident inspection, and difficult maintenance. As long as a single central busway system is used for power supply, and a plug-in box of corresponding capacity is set on each floor for diversion, the purpose of power supply can be achieved. This makes the taps extremely flexible and each branch is protected by a plug-in box for the shunt capacity. As a result, busway is safer, simpler, and more reliable.

4 Economic cost of busway:

Compared with cables, in general, due to the high-grade materials used and the relatively complex process, the initial investment cost is generally larger than that of cables. However, in the long run, the use of busway is more common. At present, the service life of busway is generally 30 to 40 years, while the service life of ordinary cables is only about 15 years. As long as the busway system is installed and operated in accordance with the specifications, there is basically no need to replace parts, and only the surrounding environment needs to be routinely inspected. The cable often has the phenomenon of aging joints and falling off the insulation layer, and a certain section of the cable needs to be replaced. In addition, there are many powerful busway manufacturers in the market today that have launched aluminum conductor busway, and it has been widely used in large-scale buildings. The purchase price of this type of busway is much lower than that of cable trays, but the performance is higher than that of cables. For the first batch of users who are short of investment, this kind of busway can be selected

5 Concluding remarks

After a comprehensive analysis and comparison, it is obvious that there are obvious advantages in the selection of bus ducts for important trunk lines in low-voltage distribution systems. For small current branch lines, the selection of cables also has its advantages of flexibility and convenience, which requires the distribution designer to select and configure according to the actual needs.