Precautions for aluminum alloy cable application

In the choice of conductors, people have been copper, aluminum, iron, nickel, silver, gold, etc.
, but practice has proved that copper and aluminum are the most suitable materials for carrying current, and are currently the most important choice
of wires and cables in the world.
Gold, silver and silver-nickel alloys are only used in small quantities and are mainly used in the field of integrated circuit boards, relay contactors and circuit breaker contacts and aerospace
.

China's copper reserves were small, and it was used as a strategic material, and the use of aluminum as power wires was strongly advocated, and even aluminum core transformers and aluminum core motors were the mainstream choices
at that time.
After the reform and opening up, China's power industry developed rapidly, due to the high failure rate of aluminum core cables, aluminum core transformers, aluminum core motors with large losses and low efficiency, due to the high reliability and high quality requirements of power supply, as well as the requirements of energy saving and consumption reduction, aluminum core transformers and aluminum motors have been eliminated, and aluminum core cables are more used in overhead lines
.

With the development of urbanization in China, urban distribution network as the infrastructure of urban construction, the demand for power cables is increasing, and the proportion of power cables in the cost of power grid construction has increased
significantly.
At present, China's electrolytic aluminum overcapacity, aluminum alloy cable in mechanical characteristics than pure aluminum core cable has been improved, the use of aluminum alloy core cable voice once again
rise.
By analyzing and comparing the differences in the structural dimensions and electrical properties of copper core and aluminum alloy cables in engineering applications, the issues
that need to be considered when selecting aluminum alloy cable applications are proposed.

At the end of 014, the cable line length of the 6~20kV distribution line of the national company was about 400,000km, and the cableization rate was 12.
6%; Among them, the length of urban distribution network cables was 270,000km, and the cable rate was 47.
1%, an increase of 4.
1% year-on-year; The length of the county distribution network cable is 120,000 km, and the cable rate is 4.
8%.

Cable laying methods mainly include direct burial, cable trench, pipe, tunnel, bridge, underwater laying, etc
.
In the cable channel, 46.
4% of the pipe laying, 26.
3% of the direct burial laying, 14.
6% of the cable trench laying, 8.
3% of the tunnel laying, and 4.
4% of the bridge and other methods of laying
.

Compared with copper, aluminum alloy in the same section and equal length, conductivity is 61.
8% of copper, current carrying capacity is about 78% of copper, copper specific gravity is 8.
9g/cm3, aluminum specific gravity is 2.
7g/cm3, the same cross-sectional area cable, aluminum alloy cable quality is only more than
half of copper core cable.
Due to the light weight of aluminum alloy cable, it is especially suitable for long-span buildings, such as stadiums, convention centers and other buildings for cable laying
.
In addition, for high-rise buildings, the use of aluminum alloy cables can reduce the difficulty and workload of vertical cable laying, save labor costs, and also reduce the risk of
body damage due to cable construction.
Since the melting point of aluminum is 660 °C, aluminum alloy cables
must not be used for fire lines that require continuous power supply during disaster relief.

The channel resources of cable laying are also one of the main costs of
cable construction and operation.
Nearly half of the cables in the urban power grid are pipe laying, the selection of aluminum alloy cable in the pipe laying, the pipe aperture is one to two specifications larger than the aperture of the copper core cable or the use of two pipe holes, so that the selection of aluminum alloy cable increases the construction and operation cost
of the pipe.
Increasing the cross-section of other laying methods will also increase the floor space and increase the construction and operating costs
.

Power cables during
laying and installation.
In each bend, different directions of tensile force is generated, and the dynamic pressure that causes cable damage is generated, and the dynamic pressure generated by the cable when laying and installing traction is much greater than when the cable is stationary, so in various cases, the bending radius of the cable should be as large as possible
.

Under the premise of meeting the ampacity and energy loss, the direct cost of aluminum alloy cable is the cost of the cable body is lower than that of copper cable, because the weight of aluminum alloy cable is lighter than that of copper core cable, aluminum alloy cable is more suitable for long-span buildings, which can greatly reduce the load on the building steel structure and save the cost
of steel structure.
In addition, for high-rise buildings, the difficulty and workload
of laying cables vertically can be reduced.
In some low-voltage power distribution systems, the cable channel resources are abundant, and aluminum alloy power cables can be used in places where there are no multiple cables
laid in parallel.

However, with the development of urban distribution networks, the load density is getting higher and higher, and the density of the number of cables laid in the cable channel also increases
.
For the shortage of cable channel resources, the occasions with large short-circuit current can not only consider the direct cost of aluminum alloy cable when selecting aluminum alloy cable, but also consider the comprehensive cost, such as the selection of aluminum alloy cable to increase the size of the cable channel, over-dense laying makes the flow decrease with the decrease of cable spacing, the increase of capacitor current needs to increase arc suppression coil capacity and other construction and operating costs
.
In addition, the maximum allowable short-circuit temperature and thermal stability coefficient of aluminum alloy cable are lower than that of copper core cable, and thermal stability check should be carried out during design to ensure the safe and reliable operation
of the power grid.