JPH0456009A - Improving method for semiconductive layer interface of polyolefin insulated cable - Google Patents

Abstract

PURPOSE:To enhance the dielectric breakdown strength by adding non-ion activating agent in a certain molecular weight to a semiconductive layer material, and thereby performing removal or reduction. CONSTITUTION:To a semiconductive layer material an anion activating agent is added having a molecular weight of 300-20000 such as sorbitane aliphatic acid ester, glycelin aliphatic acid ester, decagrlne aliphatic acid ester, polyglyceline aliphatic acid ester, polypropylene glycol, or pentelystor aliphatic acid ester. This additive is moved dispersively to the connection surface with an insulative substance layer 2, i.e. the interface of the semiconductive layer 3, through utilization of a hot cross-linking temp. in the process of cable manufacture. With heating, the dispersiveness of carbon particles in the semiconductive layer in the neighborhood of the interface of the layer 3, which controls in turn the crystalline structure in the insulative substance layer 2 in the neighborhood of the semiconductive layer interface, and electric irregularity of around one mum on the layer 3 interface is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for improving the interface between semiconducting layers of a polyolefin insulated cable.

(Prior art and its problems) Plastic power cables using polyolefin for insulation, such as CV cables, do not use oil unlike oil-impregnated insulated paper cables, so-called OF cables, so they are easy to install and maintain. Yes, and the transmission loss is also small. Therefore, it is beginning to be put into practical use not only for conventional power distribution but also for ultra-high voltage applications.

However, this Cv cable has a large insulation deterioration over time, so the design potential gradient for the insulator has to be smaller than that of the OF cable (therefore, it is necessary to increase the thickness of the insulating layer accordingly. As a result, OF Of course, it causes an increase in power transmission loss compared to cables, but at the same time, the outer diameter inevitably increases, so the costs for transportation and installation work are also large.For this reason, the construction cost of cable lines is There are problems such as a significant increase in

Therefore, research has been carried out to solve this problem,
Is the insulation deterioration over time, that is, V-, as mentioned above, due to the drooping of the characteristics?
As shown in the cross-sectional view shown in Figure 1, irregularities that remain on the surface of the conductive layer (1) during manufacturing, such as electric field concentration at semiconductive protrusions (3) protruding into the insulating layer (2), may occur. It has been clarified that it is a conductor ((4) in the figure is a conductor), and a method for its removal has also been proposed.

However, with conventional methods, an average interface roughness of around 1 micron remains at the interface between the semiconducting layer and the insulating layer, as shown in Figure 2, which is the starting point of dielectric breakdown (5). It has been revealed that the dielectric breakdown strength can be further improved by eliminating or reducing this electrical misalignment.

(Objective of the Invention) The present invention provides an effective method for reducing electrical irregularities at the interface of a semiconducting layer of about 1 micron, and further improves dielectric breakdown strength. This makes it possible to realize even higher performance cables.

(Means of the present invention for solving the problems) The present invention is characterized by the following points. That is, in the semiconductive layer material, a nonionic activator with a molecular weight of 300 to 20,000, such as sorbitan fatty acid ester, glycerin fatty acid ester,
Nonionic active agents such as decaglin fatty acid ester, polyglycerin fatty acid ester, polypropylene glycol, and pentaerythritol fatty acid ester are added. Then, this additive is applied to the connection surface with the insulating layer (2) in Figure 1 by utilizing the high thermal crosslinking temperature during cable manufacturing.
That is, it is characterized by being diffused and moved to the interface of the semiconductive layer (3). That is, heating controls the dispersibility of carbon particles in the semiconducting layer near the interface of the semiconducting layer (3), thereby controlling the crystal structure in the polyolefin insulating layer (2) near the interface of the semiconducting layer. , semiconducting layer (3)
The electrical irregularity of about 1 micron on the interface is reduced. Next, an experimental example of the present invention will be explained.

(Experiment example) In the experiment, an insulator layer (
2) A model cable with a thickness of 3.5 mm was used.

In order to see the effects of additives, the raw materials and manufacturing conditions were exactly the same, and on the other hand, 2 wt% of sorbitan fatty acid ester was added as an additive to a semiconductive layer material (ethylene vinyl acetate copolymer with carbon particles added). , and the other was produced without additives, and the results shown in Table 1 were obtained. Figures 3 (A) and (B) are electron micrographs of the additive and non-additive conditions used to obtain the results shown in Table 1, and Figure 4 (A) and (B)
and Figures 5(A) and 5(B) are electron micrographs (50
These are the interfacial roughness distributions with and without addition, determined by computer analysis of 00 times), and the quantitative evaluation results of the interfacial roughness.

As is clear from Table 1 and above, according to the present invention, the planar interface roughness can be significantly reduced to just over 1%.
% Weibull dielectric breakdown strength was improved by about 20%.

(Effects of the Invention) As described above, according to the present invention, it is possible to significantly suppress the occurrence of electrical irregularities at the interface of a semiconducting layer, thereby improving the dielectric breakdown strength of a polyolefin insulated cable and reducing the insulation thickness of the cable. The insulating film can be made smaller by increasing the slope of the design potential that determines the electrical potential, which improves the thermal and mechanical properties of the cable, and at the same time allows more power to be transported with the same conductor diameter.

In addition, the outer diameter of the cable can be made smaller, which not only reduces the amount of raw materials required for manufacturing (but also increases the unit length of the cable, which is determined by the cable drum), resulting in the use of very expensive cables. The amount of connection work and manhole work is reduced.

[Brief explanation of drawings]

1 and 2 are cross-sectional views of a conventional polyolefin insulated cable, and FIG. 3 is a partial cross-sectional view. FIGS. 4 and 5 are experimental results. (1)...Semiconducting layer, (2)...Insulator layer, (3)...Semiconducting protrusion, (4)...Conductor, (5)...Semiconducting layer interface Irregularities of 1 micron or less. agent

Claims (1)

[Claims] Molecular weight 3 in the semiconducting layer material of polyolefin insulated cable
A nonionic surfactant of 00 to 20,000 is mixed in, and this is diffused and moved to the contact surface with the insulating layer using the heat generated during cable manufacturing to reduce the roughness of the semiconducting layer interface. A method for improving the semiconducting layer interface of a polyolefin insulated cable.