Rubber-plastic insulated cables began to take the lead over oil-paper insulated cables in 1975. The proportion of paper-piezoelectric cables in rubber-plastic insulation in the United States has reached 99%, of which 95% are KV PE and XLPE, 2% are ethylene-propylene, and less than 1% are oil-paper insulated cables. German 1 kV plastic cable accounts for 90%, 10 kV XLPE for 5%, PE for 8%, PVC for 12%, oil paper for 72%, 25-35 kV XLPE for 34%, oil paper for 42%, oil paper for 20% in 1980s, XLPE for 56%. In Britain, PVC and XLPE account for 67% of 1 kV and below, and rose to 75% in the 1980s. In the late 1980s and early 1990s, XLPE insulated cables will slightly exceed oil-paper insulated cables, especially in new projects. Oil-paper insulated cables will be eliminated. In 20-30 kV, XLPE insulated cables plus other rubber-plastic cables account for 80% or more. In the field of high voltage cables, XLPE insulated cables will be eliminated. The cable has also reached the share of oil-paper insulated cable. Although XLPE insulated cables with 765 kV voltage can not compete with oil-filled cables at ultra-high voltage level, it is possible for XLPE insulated cables to catch up with or surpass oil-filled power cables in the near future from the manufacturing level of 550 kV XLPE insulated cables developed now, mainly because XLPE insulated cables have high performance. The operating temperature increases the current carrying capacity of the cable; XLPE insulated cable also has the advantages of smaller bending radius, light weight, no need for oil supply system, easy maintenance and installation.

In the manufacturing technology of heat-shrinkable pipes, the initial XLPE used steam as the pressure and heating medium of chemical reaction, so this method is called wet cross-linking. It is generally believed that XLPE insulation contains micron-sized micropore, and water vapor crosslinked by wet method is easy to penetrate into molten PE under high humidity and high pressure. Therefore, this method can increase the number of micropore and increase the size of micropore in XLPE. In the early 1970s, many countries introduced dry cross-linking, which reduced the microvoids and moisture in XLPE and improved the reliability of XLPE insulated cables. At the end of 1970s, XLPE manufacturing has made greater progress. In addition to improving the good physical and electrical properties of XLPE itself, new semi-conductive shielding materials and super-clean insulating materials have emerged, which further reduce the impurity content in insulators. Multilayer co-extrusion method has been introduced in the process, which reduces the interlayer interface and makes XLPE absolute. The partial discharge of edge cables is greatly reduced, which lays a foundation for the development of UHV cables.

In the field of semi-conductive shielding, Graphite-Coated tape was initially used in XLPE insulated cables to wrap around the insulation. This method is based on the interface problem, which makes the partial discharge of the cables very large. Once the water enters the cables, the water directly contacts with the insulation, which easily leads to water trees and electric trees. Therefore, it has been eliminated in the 1970s abroad. In China, this technology was phased out only in the 1980s. Later, the semi-conductive shield was extruded by three layers at the same time. XLPE was used as the material. Waterproof tree agent and anti-electronic transmitter were added to the material, which made the performance of the cable more excellent.

In terms of insulation manufacturing, since the 1990s, in order to reduce the problem of X LPE insulation retraction, the Finnish company's manufacturing stress relief device has been adopted, which improves the problem of cable retraction.

XLPE绝缘电缆发展历史（二）

1975年橡塑绝缘电缆已开始领先于油纸绝缘电缆。美国橡塑绝缘中纸压电缆所占比例已达99%，其中KV级PE和XLPE为95%，乙丙为2%，油纸绝缘电缆小于1%。德国1 kV塑料电缆己占90%; 10 kV XLPE占5%, PE占8%, PVC占12%,油纸占72%;25-35 k V XLP E占34%，油纸占42%,80年代油纸降为20%,XLPE为56%。英国1 kV及以下，PVC和XLPE占67%, 80年代升到75%, 80年代末、90年代初，10 kV中，XLPE绝缘电缆将略超过油纸，特别是新上项目，油纸绝缘电缆将被淘汰，20-30 kV中，XLPE绝缘电缆加上其他橡塑电缆占80%或更高，高压电缆领域，XLPE绝缘电缆也己达到油纸绝缘电缆占有率。虽然在超高压等级上，例如765 kV电压XLPE绝缘电缆还无法和充油电缆竞争，但从现在研制出的550 kV XLPE绝缘电缆制造水平来看，在不久的将来，XLPE绝缘电缆赶上或超过充油电力电缆是可能的，这主要是由于XLPE绝缘电缆具有较高的运行温度，使得电缆载流容量增加;XLPE绝缘电缆还具有弯曲半径较小，重量轻，无需供油系统，维护和安装都较容易等优点。

热缩管在制造技术方面，初期的XLPE使用水蒸气作为化学反应的加压和加热媒质，因此，此法称为湿法交联。一般认为XLPE绝缘中含有微米大小微孔，湿法交联的水蒸气在高湿高压下容易向熔融的PE中渗透，故这种方法会增加XLPE中微孔数量及增大微孔尺寸。21世纪70年代初，各国相继推出干法交联，减少了XLPE中的微孔和水分，提高了XLPE绝缘电缆运行的可靠性。70年代末，XLPE制造方面又有了更大发展，除了完善XLPE本身的良好物理和电性能外，又出现了新型的半导电屏蔽材料及超净绝缘材料，使绝缘体中的杂质含量进一步减少，在工艺上又引进了多层共挤法，减少了层间界面，使XLPE绝缘电缆局部放电量大为下降，为超高压电缆的发展奠定了基础。

在半导电屏蔽方面，最初在XLPE绝缘电缆上使用的是涂石墨层布带绕包在绝缘上，这种方法山于界面问题，使得电缆局部放电很大，这种电缆一旦进水，水分直接和绝缘接触，易引发水树和电树，因此在国外70年代就已经被淘汰，而在我国直到80年代各厂间才逐步淘汰了这一工艺，以后半导电屏蔽使用三层同时挤出工艺，材料采用XLPE,在材料中加入防水树剂和防电子发射剂，使得电缆性能更加优异。

在绝缘制造方面，90年代开始，为了减少X LPE绝缘回缩问题，采用了芬兰公司的消除制造应力装置，使得电缆回缩问题得到改善。