Using the same design method of strand twisting and multiple twisting, the fifth and sixth soft copper conductors are twisted. For conductors of the same cross section, the DC resistance and copper consumption of the conductor can be appropriately reduced, and the conductor's DC resistance and copper consumption can be appropriately reduced. The roundness and surface quality of the stranded conductor surface, and reduce the stranded outer diameter of the conductor. A comprehensive comparative analysis of the electrical performance of ordinary stranded conductors used for high-voltage flexible cable conductors, it is believed that such conductors can make the electric field on the conductor surface uniform, which is beneficial to improve the comprehensive electrical performance of high-voltage rubber-sheathed cables. Key: Co-directional stranded soft copper conductor; DC resistance; roundness; surface quality; stranded outer diameter; uniform electric field as the conductor of the flexible cable. At present, the fifth and third types specified in GB/T 3956-2008 are mainly used in China. 6 structures. Both of these conductors are used as conductive cores for wire and cable products for mobile applications. Regardless of whether it is domestic or foreign, the stranding methods of these two conductors basically use the first stranding to twist the strands, and then the multiple strands to be twisted into conductors, but the strands are twisted in opposite directions to the multiple strands. Due to the twisting twice, the resistance value of the conductor has increased to a certain extent compared with the solid conductor (see Table 1). How to minimize the increase in resistance caused by twisting and improve the conductivity of conductors has become the key to twisting method design and production control. At the same time, as the conductor of high-voltage cable, in order to reduce the multi-wire effect and avoid the electric field concentration caused by the excessively convex core of the strand, which causes the tip discharge, the conductive core should be as compact as possible and the surface should be flat and smooth. In addition, in order to effectively control the eccentricity of the insulated core in the three-layer co-extrusion of the high-voltage cable, the roundness of the flexible conductor must be solved. Soft conductors are not easy to be pressed tightly. Therefore, the stranding gap of the conductor will be large, which will cause the electric field intensity on the surface of the conductor to be very uneven.

Table 1 Resistance comparison between the fifth conductor and solid conductor

In the GB/T 12972 and MT 818 standards, it is recommended to use the same conductor structure of the stranded wire and the twisted direction, but few manufacturers have tried it. The main reason for this situation is that if the pitch diameter ratio of the same twist is not well grasped, the twisted wire is easy to produce lanterns or burrs, and in serious cases, there will be phenomena such as vaulting horses. The key to stranding of this kind of conductor is how to control the pitch diameter ratio of the strands and twisting.

1 The design of stranded conductors in the same direction

The ultimate goal of stranded conductors in the same direction is how to eliminate the twisting pitch generated when the conductors are twisted into strands as much as possible during the twisting, so that the entire conductor looks like a one-time twisting. Everyone knows that the one-time stranded soft conductor is much more rounded than the twisted soft conductor, and there is no gap caused by the twisted strand. The conductor twisted outer diameter is smaller than the ordinary twisted twisted wire ( See Table 2). In order to achieve the effect of one-time stranding, it is first necessary to select a suitable multiple stranded pitch diameter ratio according to the different types of conductors and the different stranding levels. Then, according to the pitch diameter ratio of the outermost layer, the pitch diameter ratio of the strands is calculated. Make it in the multiple twisting process, just to eliminate the twisting coefficient of the strands as much as possible. When the cage stranding machine is used, due to the back-twisting device, the strands are twisted once in the reverse direction of the multiple twisting during the multiple twisting process of the same twisting. Therefore, the twisting pitch of the multiple twisting is exactly the strand Twice the line. Take the fifth conductor of 70mm2 as an example, the outermost pitch diameter ratio N=12 times the multiple strands, the stranded outer diameter d of the strand is 2.5mm, and the conductor stranded outer diameter D is 11.5mm, then the multiple stranded pitch Length L=N(Dd)=108mm, then if you want to completely retract the stranding pitch of the outermost layer, the stranding pitch l should be about 54mm (ie l=L/2=108/ 2=54), then the pitch diameter ratio is n=1/d=54/2.5=21.6 times.

Table 2 The outer diameter of the same direction stranded conductor and the ordinary stranded conductor Specification/mm2 The largest outer diameter of the same direction stranded conductor/mm ​​The largest outer diameter of the ordinary stranded conductor/mm ​​Comparison of the two

Note: Ordinary stranded conductor refers to the stranded conductor whose stranding direction is opposite to that of multiple stranding. If a stranding machine without a back-twisting device is used, the pitch of the strands and the twisting are the same to achieve a complete co-twisting effect. Therefore, it is not recommended to use a twisting device without a back-twisting device.

2 Comparison of the same direction stranded conductor and ordinary stranded conductor

The difference between the same direction stranded conductor and ordinary conductor is mainly manifested in the following aspects: (1) Stranded outer diameter. Due to the use of the same twisting method, the gap between the single conductor wires is relatively reduced, the twisting distance of the strands is completely retracted, the gap between the strands is basically eliminated, and the conductor outer diameter is relatively reduced by about 10% (see Table 2). (2) DC resistance. The design of the same direction twisted conductor is equivalent to the successful twisting of the entire conductor at one time. Compared with the reverse twisted conductor, since the stranding pitch of the strands is eliminated during the twisting process, the conductor twisting coefficient is reduced , The conductor of the same cross-section can save about 0.8% of copper. Since the soft conductor is a non-compressed conductor, the contact resistance between the single wires is much higher than the resistance of the conductor itself, so the conductor current mainly runs along the direction of the single wire. Compared with the common stranded conductor, the twisting coefficient of the strands does not exist due to the elimination of the twisting distance of the strands, and the conductor resistance reduction value is equivalent to the twisting coefficient value of the strands (see Table 1 ), about 0.8%. According to practice, we measured the resistance value of the two conductors and the conductor weight and compared them (see Table 3).

Table 3 Comparison of resistance value and material consumption of the fifth kind of co-directional stranded conductor and ordinary stranded conductor

(3) Stranding gap. According to practice, when squeezing insulation or conductor shielding, Table 4 shows the comparison of the gaps between the same direction and reverse twisted conductor strands. The same direction stranded conductor has almost no strand gaps, which can save a lot of gaps for filling. Materials (see Table 4).

Table 4 Comparison of the gaps between the same direction and reverse stranded conductor strands

3 Application of stranded conductors in the same direction

Co-stranded conductor technology can be applied to the 5th, 6th or softer metal-plated and non-metal-plated soft copper conductors, which can meet the special requirements of various professional-use cables. It can be widely used in flexible cables for special occasions such as mine flexible cables, marine cables, rolling stock cables, general rubber cables, and soft structure power cables. (1) Use flexible cables. The particularity of the coal mine environment requires far higher requirements on cables than ordinary cables, especially the bending performance of mobile cables. According to the GB/T 12972 and MT 818 series of standards, the bending radius of the general mobile mining rubber-sheathed flexible cable is 6 times the cable diameter, and the reinforced cable is 15 times. According to our more than ten years of actual experience in the production of shearer cables, it is consistent with the meaning of the standard, that is, the smaller the outer diameter of the cable, the smaller the bending radius of the cable, and the service life of the cable is directly related to the bending of the cable. The radius is related (see Table 5).

Table 5 Comparison of actual service life of MCP-0.66/1.14kV shearer cable using co-directional and reverse-stranded conductors

After adopting the same stranded conductor, the outer diameter of the shearer cable with MCP-0.66/1.14 power core 35mm2 can be reduced from the original standard 47.8-51.0mm to 44.2-47.5mm; MCP-0.66/1.14 power core 95mm2 The coal machine cable can be reduced from the original standard 64.9~71.4mm to 59.5~63.9mm. Therefore, the diameter of the cable is reduced by 10% when the conductor cross-section, insulation and sheath thickness are unchanged. The reduction of the cable outer diameter is equivalent to an increase in the multiple of the cable bending radius, and the actual service life of the cable is relatively improved (see Table 5). (2) Marine cables, rolling stock cables, ordinary rubber-sheathed cables, etc. The particularity of the place where marine cables are used determines strict requirements for cable outer diameter and weight. Since the stranded conductor in the same direction can reduce the outer diameter of the strand, reduce the amount of material, and increase the conductor resistance, it can improve the product quality of the cable and reduce the difficulty of process control when used in marine products. Since there are almost no strand gaps on the surface of the co-stranded conductor, part of the insulation material can be effectively saved. Adding 0.8% of the copper consumption can reduce material consumption and material cost. Used for rolling stock cables and rubber-sheathed cables, the same effect can be achieved (3) Soft structure power cables and high-voltage mining cables. Due to the higher voltage level of this part of the cable, the stranded roundness of the conductor is also required to be higher. Generally, cables of 3.6/6kV and above have a conductor shielding layer. As the conductor of high-voltage cables, the first and second types of conductors are easy to solve. The use of pressing rollers can make the surface of the conductors basically round and smooth, avoiding electric field concentration and tip discharge caused by conductor defects, and effectively reducing the eccentricity of the insulated core Spend. If Category 5 conductors are used, the design and control are not good, the strands on the conductor surface are protruding, the gap is serious, and the conductor roundness is poor. In order to prevent the conductor shield from being embedded in the conductor in large quantities, plum petals are formed, which can not play the role of homogenizing the electric field well. ), the conductor must be wrapped with a layer of semi-conductive tape, and then three layers of co-extrusion. Since the surface of the stranded conductor in the same direction is very round and there is no gap between the strands, it can be used for cables above 3.6/6kV without the semi-conductive tape and directly squeeze the semi-conductive layer to meet the specified electrical performance requirements. Therefore, stranded conductors in the same direction are more suitable for high-voltage cables than stranded conductors in the opposite direction.

4 Summary

The design and application of stranded conductors in the same direction are obtained through continuous practice and continuous learning of experience. Through comparative analysis, the following conclusions are drawn:

(1) The use of stranded conductors in the same direction can appropriately reduce the DC resistance of the conductors.

(2) The use of stranded conductors in the same direction can improve the surface quality of the conductor and the roundness of the conductor.

(3) The use of the same stranded conductor can reduce the outer diameter of the conductor, reduce the cost, and can reduce the allowable bending radius of the shearer cable, and improve the service life of the cable.

(4) The same direction twisted conductor is more suitable for high-voltage cables than the reverse twisted conductor. However, in the production process, it is necessary to strictly control the pitch of the stranded conductor bundle and the twisted twist in the same direction, and strictly control the tension of the twisted twist, otherwise phenomena such as loose strands and elliptical conductors will occur. The application of stranded conductors in the same direction gives us great advantages in improving the service life of shearer cables, the insulation performance of high-voltage cables, the outer diameter and weight of marine cables and rolling stock cables, as well as the general 5th and 6th conductors in all applications. Material cost control provides a new way. The application of stranded conductors in the same direction is promising.

Zhengzhou Hengtian Copper Industry Co., Ltd. Technology Department

2017.3