JPH0447854Y2 - - Google Patents

Description

[Detailed explanation of the idea]

[Industrial Application Field] This invention relates to a cross-linked polyethylene power cable for direct current. [Problems specific to DC cables] When cross-linked polyethylene is used as an insulating material for DC power cables, it is said that the influence of space charges is large. Although the behavior of space charge is not yet well understood, it is thought to be related to the decrease in DC breakdown voltage characteristics and polarity reversal breakdown voltage characteristics at high temperatures. [Problems to be solved by conventional techniques and ideas] - Part 1: A method of infiltrating an organic semiconducting liquid into a cable insulator has been considered (for example, Japanese Patent Laid-Open No. 52-8487).
Publication No.). However, in this case, the organic semiconducting liquid penetrates only near the semiconducting layer;
Even from the attached drawings of Publication No. 8487, it cannot be considered that the organic semiconducting liquid permeates the entire cable insulator.・Part 2: Between the cable insulator and the inner and outer semiconducting layers, the insulation resistance is smaller than the insulator and greater than the semiconducting layer due to carbon inclusion, and the insulation resistance decreases from the insulator side to the semiconducting layer side. There is also an idea to provide an extremely thin layer (for example, about 0.5 mm) having a resistance gradient as follows (Japanese Patent Publication No. 116983/1983). In this technology, space charges accumulate at and near the interface between the insulator and the semiconducting layer, and the accumulation
Based on the idea that there is a close relationship between the applied voltage and the applied time, the aim is to prevent space charge from accumulating at the interface and its vicinity, and as a result, the long-term charging characteristics are improved. That thing,
Reporting. However, there is no report that DC breakdown voltage characteristics and polarity reversal breakdown voltage characteristics are improved at high temperatures. [Means for solving the problem] Instead of making only the extremely thin layer at the interface between the cable insulator and the semiconducting layer a carbon-containing layer, as in the conventional technology "Part 2" above, The entire insulator is made of crosslinked polyethylene containing carbon particles and having a resistivity of 10 ¹² to 10 ¹⁶ Ω·cm. [Function] If the entire cable insulator is made of cross-linked polyethylene containing carbon particles and having a resistivity of 10 ¹² to 10 ¹⁶ Ωcm, how will the space charge behave? Although there are some points that are not well understood, it has been confirmed through experiments that the DC breakdown voltage characteristics and polarity reversal breakdown voltage characteristics at high temperatures are improved, resulting in an increase in DC power transmission capacity, as described below. Ta. [Example 1] In "Fig. 1", 10 is a cable conductor, and the following are in order: an inner semiconducting layer 20, an outer semiconducting layer 40,
A cable sheath 50 is provided. These are the same as the conventional ones. 30 is an insulator, which is made of crosslinked polyethylene containing carbon particles as described above. This is carbon particles with a particle size of 30 to 100 mm,
By containing 0.5 to 15% of crosslinked polyethylene, a resistivity of 10 ¹² to 10 ¹⁶ Ω·cm (at 90°C) is achieved. Note that this value is slightly lower than that of pure crosslinked polyethylene. In this way, the influence of space charges was suppressed, and the DC breakdown voltage and polarity reversal breakdown voltage, especially at high temperatures, could be improved. This is considered to be due to the following reasons. In the case of conventional cross-linked polyethylene cables, there is a large barrier to charge transfer at the interface between the semi-conducting layer and the cross-linked polyethylene insulator, resulting in DC breakdown due to charges being accumulated in the insulator near the semi-conducting layer. It is thought that the characteristics will be lost. The barrier to charge transfer is generally called the "work function," and when different types of materials, such as a semiconducting material and an insulator, come into contact, an energy barrier of a certain size exists at the interface. When charge carriers pass through that interface, energy above a certain level is required. The above-mentioned DC characteristic deterioration phenomenon will be qualitatively explained. If we call the barrier to charge transfer at the interface between the semiconducting layer and the cross-linked polyethylene insulator "interfacial resistance" and the resistance to charge transfer in the insulator "insulation resistance," then normal cross-linked polyethylene Since the cable has interfacial resistance>>insulation resistance, charges moving towards the electrode surface (semiconducting layer) in the insulator cannot easily pass through the interface between the semiconducting material and the insulating material, and the charges near the semiconducting layer. It is thought that the electric field strength in the insulator increases significantly, resulting in a loss of DC breakdown characteristics. In order to quickly dissipate the space charge in the insulator and improve DC characteristics, it is necessary to increase the insulation resistance or
It seems most desirable to create a condition where interfacial resistance ≒ insulation resistance by lowering the interfacial resistance. However, cross-linked polyethylene has one of the highest insulation resistances among the practical insulators currently being considered, and it is difficult to increase the insulation resistance even higher. Therefore, in the present invention, the semiconducting layer is made semiconductive by adding a large amount of carbon to the insulator, so if carbon is added to the insulator in the same way, the same type of homogeneous layer will be formed throughout the insulator. Carbon is added to the insulator because it is thought that the interfacial resistance will be reduced because it becomes a material. The present invention is based on the above-mentioned idea, and since the state of interfacial resistance≒insulation resistance has been established, the space charge is quickly dissipated, that is, the electrode surface is placed near the electrode surface (semiconductor layer). It is thought that space charges of opposite polarity are no longer accumulated (or the amount accumulated is significantly reduced), and as a result, the DC breakdown characteristics are improved. Examples of specific numerical values are as follows. This has a conductor cross section of 200mm and an insulation thickness of 2.5mm.
This is an example of the characteristics of a 6.6kvCV cable at high temperature (conductor temperature 90℃).

[Table] Conventional products refer to DC cables that do not contain carbon. [Example 2] The insulator 30 is multilayered and graded in the radial direction. That is, for example, as shown in Figure 2, the insulator 30 is divided into three layers 31, 32, and 33, and the resistivity is increased by increasing the carbon content of the layers 31 and 33.
10 ¹³ to 10 ¹⁴ Ω·cm, and the resistivity of the middle 32 layers is 10 ¹⁵ to 10 ¹⁶ Ω·cm. In this way, as shown in the potential and electric field distribution diagram shown in Figure 2, the distortion of the electric field due to space charges is effectively suppressed, and the DC breakdown voltage and polarity reversal breakdown voltage can be easily improved. You will be able to do this. Examples of specific numerical values are as follows. This is an example of the same cable as in "Example 1", and the conductor temperature is also as high as 90 degrees Celsius (the values for the conventional cable are the same as in "Example 1", but for reference only) )

[Table] [Effects of the invention] By forming the entire cable insulator from cross-linked polyethylene containing carbon particles and having a resistivity of 10 ¹² to 10 ¹⁶ Ωcm, direct current breakdown at high temperatures can be reduced. It was confirmed through experiments that the voltage characteristics and polarity reversal breakdown voltage characteristics were improved. As a result, the power transmission capacity of DC power can be increased.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of another embodiment together with a potential and electric field distribution diagram. DESCRIPTION OF SYMBOLS 10... Cable conductor, 20... Outer semiconducting layer, 30... Cable insulator, 40... Outer semiconducting layer.

Claims (1)

[Claims for Utility Model Registration] A DC power cable in which an inner semiconducting layer, an insulator, and an outer semiconducting layer are sequentially provided around a cable conductor, wherein the entire insulator contains carbon particles. A direct current power cable, characterized in that it is made of crosslinked polyethylene with a resistivity of 10 ¹² to ^{10 16} Ω·cm.