The advantages of cross-linked polyethylene cable with multi-core round strand structure are:

(1) The electric field is uniform over the fan conductor, which is beneficial to the cable to raise the voltage level;

(2) increase the softness or curvature of the conductor, by the stranded core of multiple wires is flexible, can be curvature larger.

Because when a single metal conductor moves along the radius, the outer part of its center line is bound to elonge, and its inner part is shortened. When multiple conductors, the wires can slide between, while the two parts inside and outside the center of the twisted round core can move each other to compensate, bending will not cause the plastic deformation of the wire, so that the softness and stability of the core greatly improved. The curvature of the cable is proportional to the square root of the number of strands, the more strands are, the more bending is easier, but the curvature of the cable is also limited by the outer protective layer. Therefore, when making conductors with different nominal cross-sections, a certain number of strands are specified. And in order to prevent the twisting phenomenon, the direction of each layer twist is left and right opposite, so that each layer of wire has a fixed position, not easy to spread. When bent, each wire has the same elongation.

The size of the conductive core is calculated by the accumulation of the horizontal, square millimeter. The standards for the interception of cores are different from country to country. China currently provides for medium and low voltage cable core stomping specifications are: 2 .5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150, 185, 240, 300, 400, 500, 630, 800, high-voltage XLPE insulated heat shrink cable, now commonly used heat shrink cable, now commonly used XLPE cable The core is cut in 300, 400, 630, 1,000 and so on, and the copper and aluminum conductor sections are produced according to the above specifications.

The wires used in XLPE insulated cables are generally tight-pressure cores, and in order to reduce the shape of the conductors, the wires are also pressed by a rolling wheel after stranding to reduce the gap between the wires. Because of the presence of these voids, the nominal cross-section of the conductor is smaller than the area contained by its outer circle, which is as tight as the pressure coefficient. The usual non-compression conductor has a compression coefficient of 0.73 to 0.77, while a compression core has a compression coefficient of 0.88-0 .93.

The pressure coefficient size of the conductor is one of the key factors that determine the quality of xlPE insulated cables. Some countries with rapid cross-linking cables, the use of compression core or solid core, the use of compression core to prevent the spread of water, the conductor moisture is one of the root causes of cable water trees and breakdown, and will seriously affect the life of the cable, several more developed countries in Europe, such as Sweden's ASEA and Sieverts, Germany's VDE, the Netherlands NEF company has a higher pressure coefficient, but also has a non-tight core standard to adapt to a variety of other power cable. IEC in order to adapt to the situation of various countries, so there is no special provisions for the compression core, China also did not cross-link cable with compression core provisions, which is not conducive to our development and use of cross-linked polyethylene cable. The tight and non-pressing structures are regulated in both Japan and the United States. The japanese JISC-3606 and the U.S. IPCEA conductor structure, with a compression coefficient of up to 0.93 and 0.94, greatly prevent the possibility of water entering the conductor in a vertical way.

为什么交联聚乙烯电缆采用多芯圆绞线结构

交联聚乙烯电缆采用多芯圆绞线结构的优点为:

(1)电场较扇形导体电场均匀，对电缆提高电压等级有利;

(2)增加导体的柔软性或可曲度，由多根导线绞合的线芯柔性好，可曲度较大。

因为单根金属导体沿半径恋曲时，其中心线圆外部必然伸长，而其圆内部分缩短。多根导体时，导线之间可滑动，同时绞合圆线芯中心线内外两部分可以互相移动补偿，弯曲时不会引起导线的塑性变形，使线芯的柔软性和稳定性大大提高。电缆的可曲性大约和绞线数目的平方根成正比，绞线愈多，弯曲愈易，但是电缆的可曲性同时也受到外面保护层的限制。因此，在制造不同标称截面的导体时，都规定了一定的绞线股数。且为了防止扭歪现象，各层扭绞的方向是左右相反的，这样可以使每层导线都有固定位置，不易散开。当受弯曲时，每层导线的伸长程度也相同。

导电线芯的大小是按横断而积来计算的，以平方毫米作单位。各国规定的线芯截而标准不同。我国目前规定中低压电缆线芯截而规格有:2 .5, 4, 6, 10, 16, 25, 35, 50, 70, 95, 120, 150,185, 240, 300, 400, 500, 630, 800等，高压XLPE绝缘热缩管电缆，现在常用的线芯截而规格有300, 400, 630, 1 000等几种，铜和铝导体截面均按上述规格生产。

XLPE绝缘电缆所用导线一般为紧压型线芯，为了缩小导体的外形尺寸，导线在绞合后还须经过轧轮紧压，以减小线间的空隙。由于这些空隙的存在，导体的标称截面要比由它的外圆所包含的面积为小，这两个面积比为紧压系数。通常的非紧压型导体的紧压系数为0.73^0.77，而紧压型线芯的紧压系数为0 .88-0 .93。

导体的紧压系数大小是决定XLPE绝缘电缆品质的关键因素之一。一些交联电缆发展较快的国家，均采用紧压线芯或实心线芯，采用紧压线芯可防止水分扩散，导体内水分是造成电缆水树和击穿的根源之一，并将严重影响电缆的寿命，欧洲几个较发达国家的公司如瑞典的ASEA和Sieverts公司，德国的VDE公司，荷兰的NEF公司均采用较高紧压系数，同时也有非紧压芯标准，以适应其他各种电力电缆用。IEC为了适应各国情况，故未对紧压线芯作特别规定，我国也未对交联电缆用紧压线芯作规定，这是不利于我们发展和使用交联聚乙烯电缆的。在日本和美国均规定了紧压和不紧压结构。日本JISC-3606和美国IPCEA的导体结构，其紧压系数可高达0.93和0.94，极大地阻止了水分沿纵向进入导体内部的可能性。