JPH0363165B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to improvements in oil-immersed insulated lead-sheathed cables. Generally, oil-immersed insulated lead-sheathed cables are made by wrapping kraft paper or the like impregnated with synthetic oil such as dodecylbenzene or mineral oil on the conductor to form an oil-immersed insulation layer.
Further, a basic configuration in which a barrier layer and a lead-covered sheath are formed in this order on top of this is well known. By the way, when used in submarine cables, the viscosity of the insulating oil used is desired to be as low as possible because the oil supply section is extremely long. As such an insulating oil, an insulating oil having two or more benzene rings such as diallylalkane or alkylnaphthalene, which has almost the same electrical properties as the above-mentioned dodecylbenzene, has a slight swelling effect on plastics, and has a lower viscosity, has attracted attention. Applied research is being conducted. Oil-immersed insulated cables using diarylalkane or other insulating oils do not have any particular problems when the sheath is made of aluminum, but those with a lead sheath lose their insulating oil within a short period of time after use. There was a serious problem in which the tan δ and ρ deteriorated rapidly and the cable characteristics deteriorated. The inventor paid attention to this phenomenon and, as a result of diligently investigating its cause, found that the above-mentioned insulating oil having two or more benzene rings deteriorates rapidly in the presence of lead. Specifically, diallylalkane was heated in air at 115°C for 96 hours in the presence of pure lead, and the deterioration of tan δ and ρ before and after heating was as follows. tan δ 0.01% → 12% or more ρ 5 × 10 ¹⁵ Ω−cm → 2 × 10 ¹² Ω−cm When heated in nitrogen gas at 85°C for 168 hours, tan δ 0.01% → 0.7% ρ 5 × 10 ¹⁵ Ω -cm→1×10 ¹⁴ Ω−cm. As a result of further research on how to suppress this phenomenon, the inventor decided to add 0.5% tin to pure lead.
When a similar heating test was conducted at 85°C in air for 168 hours, the changes in tanδ and ρ were significantly suppressed from tanδ0.01% to 0.02 ρ 5×10 ¹⁵ Ω-cm → 4×10 ¹⁵ Ω-cm Moreover, even when a trace amount of tin (0.05%) is added, the deterioration of diallylalkane is significantly suppressed even in the presence of a trace amount of tin (tanδ0.01% → 0.5% ρ 5 × ^{10 15} Ω−cm → 2 × 10 15 Ω−cm) It has been found. The inventors have completed this invention as a result of intensive studies based on this knowledge. That is, this invention provides dielectric oil such as diallylalkane or alkylnaphthalene as an insulating oil on a conductor.
In an oil-immersed insulated lead-sheathed cable having a basic structure in which an oil-immersed insulating layer impregnated with an insulating oil having a benzene ring, a metal barrier layer, and a lead-sheathed sheath are formed in this order, tin is in contact with the insulating oil. Alternatively, it is an oil-immersed insulated lead-sheathed cable characterized by the presence of a tin compound. As mentioned above, the oil-immersed insulated lead-sheathed cable referred to in this invention has a basic structure in which an oil-immersed insulation layer, a metal shielding layer, and a lead-sheathed layer are provided in this order on a conductor, and one typical example is is as shown in FIG. In the figure, 1 is 6 made of copper.
Divided conductor, 2 is an oil passage, 3 is a conductive binder layer formed by winding together, for example, stainless steel tape and carbon paper, 4 is an oil-immersed insulating layer, and 5 is a metal formed by winding metallized paper and aluminum tape together. The shielding layer 6 is a core binder layer made of, for example, a copper wire woven cloth tape, 7 is a lead sheath, and 8 is a protective sheath made of vinyl chloride or the like. The present invention is not limited to the illustrated configuration, and various conventionally used materials for these constituent parts may be used without particular limitation. Examples of the insulating oil having two or more benzene rings used in this invention include diallylalkane and alkylnaphthalene. The method for making tin or a tin compound present in contact with this insulating oil is as follows: (i) Adding a desired amount, preferably 0.05 to 0.5%, to the lead coating material;
(ii) Using tin plating on the conductor (iii) Using tin foil or a tin compound in part of the binder layer, metal barrier layer, core binder layer, etc. of the above conductor, etc. There are methods (ii) and (iii) in particular, which are preferred since there is no risk of deterioration in mechanical properties due to compositional changes in the lead-covered sheath. As will be clear from the examples described later, this invention uses a low-loss plastic material as the insulating material, and uses conventional OF cable insulating oil (mineral oil, mineral oil, etc.) as the insulating oil.
In a low capacitance oil-immersed insulated lead-sheathed cable using diallyl alkane, etc., which is less likely to swell or dissolve plastics than DDB) and which has a high withstand voltage, tin is present in contact with the insulating oil. It can significantly improve the problem of property deterioration, especially in submarine cables, etc., because the viscosity of diallylalkane is lower than that of conventional OF oil, and it can be combined well with the above polymers. Also, because of its low capacitance (using plastic) it can be used over long distances, so it has great industrial value. The present invention will be specifically explained below with reference to Examples. EXAMPLE An oil-immersed insulated lead-sheathed cable having the structure shown in the figure was obtained by using insulating oil as shown in Table 1 and in the presence of tin as shown in Table 2 below.

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[Table] When the cables of each of the above examples were subjected to a heating test at 105°C for one month, the tan δ of the insulating oil for Examples 1 to 3 increased from the initial 0.01% to 0.03%, 0.02%, respectively.
Comparative Example 1 did not decrease much at 0.03%.
This was a significant decrease of 0.9%. In addition, in Example 4, the content of alkylnaphthalene was 0.008% → 0.02%, showing the same tendency as diallylalkane.

[Brief explanation of drawings]

The drawing is a sectional view of a cable according to the invention. DESCRIPTION OF SYMBOLS 1...Conductor, 4...Oil-immersed insulation layer, 5...Metal barrier layer,
7...Lead-covered sheath.

Claims (1)

[Claims] 1. A basic structure in which an oil-immersed insulating layer impregnated with an insulating oil having two or more benzene rings such as diallyl alkane or alkylnaphthalene, a metal barrier layer, and a lead sheath are formed in this order on a conductor. An oil-immersed insulated lead-sheathed cable having tin or a tin compound present in contact with the insulating oil. 2. The lead-sheathed cable according to item 1, wherein the conductor is formed of a tin-plated conductor. 3. The lead-sheathed cable according to item 1, characterized in that the lead-sheath is made of a lead alloy made of lead mixed with tin. 4. The lead-sheathed cable according to item 1, characterized in that tin foil or a tin compound is used as a part of the cable core material such as the shielding layer of the cable.