Although the use and development of XLPE insulated cable has only 30 years'history, it has many advantages, such as good mechanical performance, convenient installation and maintenance, excellent insulation performance, larger transmission capacity than oil-paper insulated cable with the same cross-section, simple production process and large-scale production, etc. Therefore, with the continuous development of material industry and related industries. XLPE insulated cable is widely used in power system.
At present, the practical voltage of XLPE insulated power cable in transmission and distribution system has reached 275 kV, and 500 kV XLPE insulated power cable has been tested and run. In developed countries, as early as the 1930s and 1940s, the medium and low voltage cross-linked polyethylene insulated power cables have been put into operation. Table 111 shows that with the increase of voltage, oil-paper insulation, PVC-PVC insulation, non-dripping paper insulation, butyl rubber insulation and other kinds of cables have been unable to adapt, so polyethylene (PE), cross-linked polyethylene (XLPE) synthetic rubber insulation materials developed rapidly in the second 1U_boundary war, and the speed is faster and faster. The pressure level is getting higher and higher. After 1972, XLPE insulated cables and high-voltage heat-shrinkable pipes of 110 kV grade and above were developed.
Figure I-1 Oil Paper and XLPE Cable Development
I-Oil-Paper Insulated Cables Abroad; 2-Oil-Paper Insulated Cables at Home; 3-Plastic Insulated Cables
Figures I-I and 1-2 are the development curves of cable voltage grade. It can be seen from the figure that plastic insulated power cables represented by XLPE insulated cables are developing rapidly. For example, the development history of the voltage level of XLPE insulated cables in Japan is as follows: first developed in 1955; 33 kV in 1961; 66 kV in 1962; 77 kV in 1965; 110 kV XLPE insulated cables can be produced in 1969.
Figure 1-2 Variation of the Maximum Operating Voltage of XLPE Cables
This speed represents the development speed of XLPE and PE insulated cables in developed industrial countries, as shown in Table 1-1, as well as the development status of heat shrinkable pipes in Shenzhen. At present, XLPE insulated cables used in Japan account for 85% of the total copper used in power cables, and 275 kV XLPE insulated cables have been put into operation, and 500 kV XLPE cables with nominal section of 2 000 m have been developed. Nordic, Eastern Europe, the former Soviet Union and other countries have also mass-produced this type of cable. Sweden began to produce XLPE cables in 1965. By 1975, 70% of XLPE cables with 12 kV grade and 100% of XLPE insulated cables with 24-84 kV grade were produced. In 1964, low-voltage oil-paper and plastic cables in the United States were used together, and PE and XLPE insulated cables with more than 15 kV grade were tried out. In Germany, PVC insulated cables are even used at 6-10 kV level. In Britain, oil-paper insulated cables without drip are mostly used, and plastic cables are limited. In 1970, in the field of 10-30 kV and low voltage cable, the use of PE and XLPE was 16% and 6%^-8% respectively. In the late 1970s, PE and XLPE insulated cables developed greatly because the United States solved the material problems of water and electricity branches of medium and low voltage power cables. Plastic cables were widely used in 15 kV class systems, while oil-paper insulation cables were widely used. Edge cables were almost eliminated, as shown in Table 1-2, representing the percentage of cable varieties used in the United States in 1971.