Practical applications for aluminum alloy cables

In recent years, there have been many sounds of aluminum instead of copper and aluminum alloy cables, but in real life, what is the application of aluminum alloy cables?

Relevant data show that copper core cables are mainly used in cables, and aluminum core cables account for less than 5%.

Its China network Zhejiang company relative to the proportion of aluminum core cable is relatively large, Zhejiang power grid jurisdiction 10kV ~ 35kV cable 45684km, aluminum core cable 3649km, aluminum core cable accounted for 7.
989%
of the voltage level cable.
Most of the aluminum core cables in operation in Zhejiang Power Grid have been put into operation
since the second half of 2009.
According to the operation records of the past three years, it can be found that the aluminum core cable has failed and stopped operation 29 times
.

The fault mainly occurs in the cable accessories, especially the middle joint a total of 19 times, accounting for 65.
52% of the fault, the middle joint failure except for 1 external force failure, the remaining 18 times are joint breakdown; Others are cable termination, external damage, construction reasons, etc.
, aluminum core cable failure to 500mm2 cable fault is particularly prominent, a total of 18 times, accounting for 62.
07% of the total statistical faults, of which 14 times for cable intermediate joint insulation breakdown or explosion, accounting for 78.
8%
of cable intermediate joint failure.

It is understood that the current construction process of the middle joint of large-section aluminum core cable has not completely solved the problem
of reliable, stable and mature on-site crimping technology.
Compared with copper, aluminum alloy in the same section and equal length, the conductivity is 61.
8% of copper, the current carrying capacity is about 78% of copper, the specific gravity of copper is 8.
9 g/cm³, the specific gravity of aluminum is 2.
7g/cm³, the same cross-sectional cable, the weight of aluminum alloy cable is only more than
half of that of copper core cable.
Due to the light weight of aluminum alloy cable, it is especially suitable for large-span buildings, such as stadiums, convention and exhibition centers and other buildings of cable laying, the use of aluminum alloy cable can reduce the load on the building steel structure, save the cost
of steel structure.
In addition, the use of aluminum alloy cables for high-rise buildings 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 the fire line that requires continuous power supply in the event of a fire.

The selection of cable conductor section should not only consider the initial cost of the cable route, but also consider the cost of electrical energy loss during the life of the cable, so the cable section should be selected from the economic current density
.
The International Electrotechnical Commission standard IEC287-3-2/1995 proposes the idea that
cable size selection is optimal for conductor cross-section economy.
According to the specification distribution of the cable section, the section of the aluminum alloy cable is increased by about 1.
5 times, and the electrical parameters such as ampacity and voltage drop are comparable
to copper.
Under similar energy consumption, the cross-section of the aluminum alloy core cable is two specifications larger than the cross-section of the copper core cable, that is, the aluminum alloy cable is larger than the copper core cable two specifications to achieve similar ampacity
.
Increasing the cross-sectional area of the conductor has an impact
on cable routing, the structural size of the cable channel, and the electrical properties.

The channel resources of cable laying are also one of the
main cable construction and operating costs.
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 land occupied 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 larger than when the cable is stationary, so in various cases, the bending radius of the cable should be as large as possible
.

The choice of cable should also consider the maximum allowable temperature of the cable when normal and short circuit, the copper core and aluminum core cable lines are different when the system is normal and short circuit, the maximum allowable temperature of the cable conductor is different when the system is normal and short-circuited, and the maximum allowable temperature of aluminum alloy cable is lower than that of the copper core cable when short-circuiting, which needs to be considered
when choosing.
In addition to determining the allowable current according to the allowable temperature, the selection of the cable should also check the thermal stability
in the event of a short circuit.
When thermal stability is insufficient, increase the cable section until it
fits.
Because the use of aluminum alloy cable increases the outer diameter of the cable, there will be a decrease in the distance between the lines, an increase in the number of cables, which will reduce the correction coefficient, that is, reduce the cable ampacity, in order to meet the working current requirements, it may also be necessary to choose a larger section of the wire
.
Therefore, the selection of aluminum alloy cable should also consider the problem
of increasing the cross-section, reducing the distance between cables, and reducing the allowable flow rate.

The capacitance current of the cable increases with the increase of the cable section, and after the selection of aluminum alloy cable, the cable cross-sectional area increases by two specifications, and the capacitance value of the cable also increases
.
Most of our country is still based on arc suppression coil compensation, the determination of arc suppression coil capacity, depending on the size of the capacitor current in the power grid, the determination of capacitor current in the power grid mainly adopts two ways of actual measurement and theoretical estimation, for the power grid that has been operated, it can also be measured by capacitive current measurement, but in the design and construction stage, because the power grid has not yet formed, it is necessary to estimate by theoretical methods
.

With the development of urban distribution networks, the load density becomes 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 reduction 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 should be checked during design to ensure the safe and reliable operation
of the power grid.