Difference between dense insulated busway and air insulated busway and its selection

The standard for dense insulated busbars is defined as: after the bare busbar is covered with insulating material, it is placed close to the channel housing. The standard for air-insulated busway is defined as: the busbar is supported in the casing by an insulating gasket and insulated by an air medium. The main difference between the two is that the structure is different and the insulation is different.

How to choose and apply, first we analyze the performance and characteristics of two different forms of busway:

Dense insulated busbars are more complicated in terms of processing. From the perspective of safety performance, insulation requirements are relatively high. The advantages are many, that is, the dense insulated busway has a large current carrying capacity, a specific good energy saving effect, good dynamic heat stability, small volume, good heat dissipation, low temperature rise, and is suitable for transmission of high power current.

The air insulated busway is analyzed from the processing angle, and the manufacturing process is relatively simple; in terms of safety performance, the insulation requirement is lower than that of the dense insulated busway, and the insulation method is also flexible (wrapped or unwrapped), and the tapping is convenient. The disadvantages are: poor current carrying capacity, high temperature rise, large impedance value, poor heat dissipation, and unsuitable for large current transmission. Therefore, the choice of busway type should be considered from their technical and economical.

The current carrying capacity (current carrying capacity) is an important indicator for evaluating the busway products. A large number of test data have proved that the current carrying capacity of the dense insulated busway is better than the current carrying capacity of the air insulated busway, ie: the same size of the conductor load The flow capabilities differ by one current level and even more. The main reason for the poor current carrying capacity of the air insulated busbar slot is that the impedance value is large, the loss is large, and the heat dissipation is not good, resulting in a small current allowed to be carried. This is especially true in high current air insulated busway slots. For example: 4000A busway slot uses dense insulated busbar slot, current density can be selected about 1.8A/mm2; air-insulated busway slot can only choose about 1.2A/mm2, the latter cross section (conductor) is much larger, As a result, costs increase and resources are wasted.

Reasonable selection of busway can greatly improve the safety and reliability of the transmission and distribution system. In view of the different characteristics of both dense and air type, it is recommended that the main line, the feeding part and the place with higher current level of the power distribution system be the most suitable for selecting dense insulated busway; for places with more branches and lower current levels, The air insulated busbar slot is selected, which has the advantages of large current carrying capacity, low loss, balanced reactance, convenient use and low cost.

Suggested range of specific choices: Dense insulated busbars for rated currents above 1250A; air insulated busbars or dense insulated busbars for use below 1250A (air insulated busbars are not suitable for use above 1250). The main disadvantages are: high loss and high cost. Example: Tianjin XX×X Building Project Substation low-voltage side, current class 3150A, air-insulated busway is selected in the early stage, and the cross-sectional area of ​​the conductor is in accordance with the cross-sectional area (same current level) of the dense insulated busbar conductor The selection of the temperature rise value of the on-site sampling test has reached 90K, which is 30K higher than the standard. After adjustment, the dense insulated busbar slot was selected. After the test temperature rise was only 50K, the product met the standard requirements and was well received by users. A large number of test data have proved the above viewpoints.

When selecting the busway, the user should determine the type of busway and the protection level of the busway according to different places of use, and determine the busbar current level according to the required capacity. It should be noted that the busway products provided by the factory should be compatible with the busway products that have passed the full type test. Strictly avoiding the type test is a product, and another product is provided to the user. The power transmission test on the project cannot be used as the basis for comprehensively testing the performance of the busway. The power transmission current in the project is very small and cannot reach full load operation. It cannot explain any problems. The trial operation of the busway should be a long-term, full-load operation, in order to assess whether the current carrying capacity of the busway meets the specified rating and the reliability of the insulation.

Correct selection of the current carrying capacity of the busway is related to the safety and reliability of the entire distribution system. Therefore, it should be observed that the allowable current carrying capacity of the busway must be greater than the rated current of the overcurrent protection device used, and it is also It is greater than the maximum load current that occurs.

A series of performance characteristics of dense insulated busbars make these products known as "energy-saving products." Due to the superiority of the dense insulated busway, it has decided its development space. With the development of the national economy, the rise of high-rise buildings, super high-rise buildings, and large public facilities, saving energy and reducing the voltage loss of distribution lines have become more important and priority issues. The emergence of dense insulated busway will gradually replace the air insulated busway in the entire transmission and distribution system, playing its increasingly important role.

Select the appropriate busway according to different places of use, see Table 1.

Table 1

The protection level of the busway should be determined according to different places of use, see Table 2

Table 2