DE2021977A1 - Electrical insulation of cryogenic cables - Google Patents

Description

United Wire and Cable Works

Corporation

Beilin and Duisburg

1 Berlin 44, Am Oberhafen 5 - 9

HerrmannAtz B I 69/153 Mr.

April 24, 1970

Electrical insulation of cryogenic cables

The invention relates to the electrical insulation of cables, which are operated at low temperatures. In the case of such cables, the usual ones are applied in a known manner Insulating materials for those operated at normal temperature Cable as a result of the contraction that occurs during cooling unsuitable as insulating material. For example, soaked paper, polyethylene or other polyolefin-based polymers are used as insulating materials for high-voltage cables. In the case of the impregnated paper, the large contraction of the impregnating agents used causes: At a temperature of a few tens of degrees Celsius below the freezing point, cavities are formed which, as a result of the impregnation, just become should be resolved. That's why it separates from the usual Impregnated paper as insulating material for low-temperature cables the end. ·

108847/0931

- 2 - BI 69/153 Mr.

In polyethylene, the linear thermal contraction is at a cooling of the tree temperature to temperatures below 40 K ⁰ 2.4%. With a cable length of z. B. 250 m makes the length contraction of the insulation therefore 6 m, while the length of the metallic conductor is only about 0.4%, ie shortened by about 1 m. Such a difference is intolerable. If the insulation is applied in such a way that it is firmly connected to the conductor and therefore its length cannot change independently of the conductor, there is a risk that, as a result of the mechanical stresses between the conductor and its insulation, either the insulation, the conductor or both are damaged or deformed. This danger is great because, on the one hand, the expansion modulus of the insulating materials used in cable technology increases sharply with decreasing temperature, but on the other, their elongation at break decreases sharply.

There are also known substances with insulating properties whose coefficient of linear thermal expansion is that of the conductor metals is close or smaller. However, such substances alone cannot be used for cable insulation, since they lack the electrical and mechanical properties required for this. They are hard to brittle inorganic ones Fabrics that result in flexible and compact insulation

cannot be processed.

It is therefore the object of the present invention to provide insulation for low-temperature cables, their functionality not affected at low temperatures by the thermal contraction of the insulating material during cooling will. This object is achieved according to the invention in that the insulation from a processing and laying temperature flexible insulating material and

109847/0937

SAD

■ 202 * 977

-3: - B I 69 / 1.53 Hr

another insulating material with a much smaller one linear coefficient of thermal expansion ", the resulting coefficient of thermal expansion of the insulation one of the coefficient of thermal expansion of the conductor metals substantially has closer value than that of the flexible insulating material alone. . ..

The insulation can expand the fabric with little. coefficients either in the form of powder, flakes or Contain fibers, or it can be in the form of tissue, Tape, fleece or had a component as a carrier or reinforcement of insulation. As a fabric with a small

- ^π -1
nen - under 1. 10 ^y grd lying - linear heat expansion coefficient is provided according to the invention 3iO ^ in the form of quartz powder or aerosil, or glass in the form of powder flakes, fibers, mats, fleece, fabric or tape.

According to the invention, the insulation is advantageously wrapped around the conductor in the form of tapes. In order to exclude air inclusions which are harmful in high-voltage insulation, tapes with a triangular or parallelogram-shaped profile are preferred according to the invention. Such insulation is shown in Figures 1 and 2. Here, 1 denotes the conductor, and 2 and 3 denote the wound insulation.

A voltage G breakdown occurs in wound insulation preferred to. a path leading between the belts instead, because here the dielectric strength is on lowest is. To the electrical breakdown voltage of the To increase insulation, it is desirable that the tapes assemble into compact insulation after they have been wound. This is done according to the invention by using self-adhesive tapes, tapes also cold vulcanizing Rubber or self-vulcanizing tapes, which are

109 847/09 37

- 4 - BI 0/153 Mr.

vulcanized together, reached.

The isolation of those to be operated at normal temperature. Cables for higher voltages used known flexible ones Insulating materials may also contain foreign matter, but at most in such small amounts that they do not have a significant influence on the coefficient of thermal expansion. They are here usually as unwanted contaminants consider. Larger amounts of foreign substances are added to the flexible insulating materials for normal conducting cables not added, since they generally increase the electrical properties over those in the range of the usual operating temperatures Admissible values also deteriorate and, in addition, there are larger amounts of inorganic in insulating materials such as polyethylene Substances cannot be incorporated.

In contrast, the invention makes use of the knowledge that the electrical properties, including the dielectric strength, significantly improve when cooling to low temperatures. One can therefore be considered flexible Insulating materials also use materials that are used for the insulation of cables operating in the normal temperature range are not suitable, and also. a large proportion of inorganic May contain substances such as B. vulcanizable or crosslinkable macromolecular substances, but also polytetrafluoroethylene and thermoplastics.

The insulation of cryogenic cables according to the invention offers the advantage that it has a sufficiently small coefficient of thermal expansion, which as a result of different Contraction of the insulation and the mechanical stresses occurring are largely reduced.

109847/0937

- 5 - B I 69/153 Mr.

This will damage the insulation as well as deformation of the conductor when it cools down.

5 S. Description of claims 1 sheet drawing. with 2 figures

Claims

1098A7 / 0937

Claims (13)

- 6 - BI 69 / $ 15 Patent claim before .JElektrische insulation of cryogenic cables, characterized in that the insulation arbeitimgs- of a in the locking and laying temperature flexible insulating material and another insulating material with a much smaller linear thermal expansion coefficient, wherein the resulting coefficient of thermal expansion of the insulation an the thermal expansion coefficient of the conductor metal substantially closer value has than that of the flexible insulating material alone. 2. Insulation according to claim 1, characterized in that the insulating material with the small coefficient of thermal expansion is contained in the flexible insulating material as a filler in the form of powder, flakes or fibers. 3 · Insulation according to claim 2, characterized in that SiOo ^{in the} form of quartz powder or aerosil is provided as filler. A-. Insulation according to claim 2, characterized in that the filler is glass in the form of powder, flakes or fibers. 5- insulation according to claim 1, characterized in that the flexible insulating material can be vulcanized or crosslinked is. 6. insulation according to a dex * claims 1 to 5, characterized in that that it is applied in the form of edges. 109847/0937 “AD ORfGtNAL 2821077 -7: - BI 7. Insulation according to claim 6, characterized in that the insulating material with the low coefficient of thermal expansion is contained in the flexible insulating material as a carrier or reinforcement in the form of fabric, tape, fleece or hat . 8. Insulation according to claim 7, characterized in that the tapes contain glass fabric, glass tape, glass mat or glass fleece as a carrier or reinforcement. 9 · Insulation according to claim 2, 6 and 7 »characterized in that insulating materials with the low coefficient of thermal expansion are used in the flexible insulating material as a carrier or reinforcement in the form of fabric, tape, fleece or mat and at the same time as a filler in the form of powder, flakes or fibers are included. 10. Insulation according to one of claims 6 to 9 »characterized in that the bands are triangular or parallelogram-shaped Have a profile. 11. Insulation according to one of claims 6 to 10, characterized in that that the tapes are self-adhesive. 12. Insulation according to one of claims 6 to 10, characterized in that the tapes are self-vulcanizing. 13. Insulation according to one of claims 6 to 10, characterized in that the flexible insulating material is a cold-vulcanizing rubber. 109847/0937 Blank page