US3904815A

US3904815A - Electrically insulating feed-through for cryogenic applications

Info

Publication number: US3904815A
Application number: US506818A
Authority: US
Inventors: Joseph A Bamberger; Donald P Brown
Original assignee: US Department of Energy
Current assignee: US Department of Energy; Energy Research and Development Administration ERDA
Priority date: 1974-09-17
Filing date: 1974-09-17
Publication date: 1975-09-09
Anticipated expiration: 1992-09-09

Abstract

An electrical connector suitable for cryogenic applications of virtually all metal construction employing anodized aluminum rings to provide electrical isolation.

Description

United States Patent [191 Bamberger et a].

[ ELECTRICALLY INSULATING FEED-THROUGH FOR CRYOGENIC APPLICATIONS [451 Sept. 9, 1975 2,616,946 11/1952 Scheer....- 174/151 3,352,963 ll/1967 Homrig l74/18X FOREIGN PATENTS OR APPLICATIONS 1,161,606 1/1964 Germany 174/152 R OTHER PUBLICATIONS (S2819 0044) Maznitsa, A. M., et al., Low-Temperature Vacuum-Tight Current Input Lead, translated from Pribory i Tekhnika Eksperimenta, No. 1, p. 223, Jan.-Feb. 1972.

Primary Examiner-Laramie E. Askin Attorney, Agent, or Firm-Dean E. Carlson; Leonard Belkin An electrical connector suitable for cryogenic applications of virtually all metal construction employing anodized aluminum rings to provide electrical isolation.

ABSTRACT 9 Claims, 2 Drawing Figures Facing Surfaces Can/ed wifh E paxy or Anaerobic E. Sea/an! .iiiliilllllllll! Anodized Aluminum Rings 2 42 44d(Thirk Anodized Aluminum Ring) 440 Fig.1

PATENTEUSEP Facing Surfaces Coated with Epoxy 0r Anaerobic Anodized Aluminum Rings 44d (Thick Anodized Aluminum Ring ELECTRICALLY INSULATING FEED-THROUGH FOR CRYOGENIC APPLICATIONS BACKGROUND OF THE INVENTION This invention was made in the course of, or under a contract with the United States Atomic Energy Commission.

Electrical connections to superconducting apparatus at cryogenic temperatures present problems which are unique and heretofore have been difficult to overcome. Such connections must not only be capable of providing'adequate electrical insulation, but in addition the connection must frequently be leak tight over a period of time during numerous recyclings between ambient and liquid helium temperatures and high pressures. Filament-wound fiberglass and epoxied connectors to superconducting magnets have been tried, but after several temperature cycles, cryogen leaks into the insulating vacuum tend to develop through cracks in the plastic connectors. In addition, because of the mechanical strength requirements in situations where a high current capacity is required, a completely metal configuration is desirable, but then the electrical insulating properties are difficult to attain.

SUMMARY OF THE INVENTION The present invention overcomes the problems mentioned above by providing an electrical connector of virtually all metal parts capable of being leak tight to better than 5 X std. cc/sec leak rate at a liquid helium temperature and pressure of atm and above and remaining tight after repeated temperature cycling from room temperature to liquid helium temperature. In addition, the connector designed in accordance with the principles of this invention is capable of withstanding repeated acceleration forces of 2 gs and carrying currents of 5,000 amperes and higher, including support of the insulation housing and conductor required to carry such high currents. The connector has sufficiently high dielectric strength in the feedthrough as to isolate the incoming and outgoing leads from each other, and, also, to insulate the penetrating leads from associated plumbing and dewars.

In accordance with a preferred embodiment of this invention there is provided a first tubular member communicating at one end with the interior of the dewars, a second tubular member aligned with the first member and closed at the opposite end, anodized aluminum rings compressed between the open ends of the tubular members, and an electrical conductor passing through while contacting the closed end of the second tubular member into the dewars without touching the inner walls of the tubular members. In this arrangement, the interiors of the tubular members are open to the dewars, completely pressure sealed by the rings and the closed end of the second tubular member. The second tubular member is electrically isolated from the first tubular member and the dewars by the anodized aluminum rings.

It is therefore a principal object of this invention to provide an electrical feedthrough connector suitable for use under cryogenic temperature and pressure conditions.

Other objects and advantages of this invention will hereinafter become obvious from the following description of a preferred embodiment of this invention.

DESCRIPTION OF THE DRAWINGS;

FIG. 1 shows an elevation view in section of a preferred embodiment of this invention.

FIG. 2 shows an alternative preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT:

Referring to FIG. 1, electrical feedthrough connector 10 is provided with an electrical conductor 12 to pass into dewars 14 which may be at a pressure within which is substantially higher than the pressure outside. Typically conductor 12 would be one of the conductors to a superconducting magnet (not shown) within dewars 14 and there would be a second conductor (not shown) with its own connector (not shown) for the return electrical lead. Connector l0 and dewars 14 may be within an outer containment (not shown) so that there is a vacuum surrounding these assemblies. Another connector would be employed to penetrate the outer containment. Conductor 12 may carry currents as high as 5,000 amperes and above and the temperatures and pressures may be recycled periodically to ambient conditions in order for access to be gained to the equipment within dewars l4.

Connector 10 consists of a pair of

tubular elements

16 and 18 axially aligned and a pair of housing members consisting of the male member 22 threaded externally at 22a with a hexagonal lip 23 for gripping by a wrench and the female member 24, threaded internally at 24a, the former member being threaded into the latter, as is illustrated. A set screw 25 is employed to prevent element 22 from unscrewing from element 24 while in use.

Tubular element 16 at one end is welded or brazed to the wall of dewars 14 with an opening 26 to match that of element 16 so that there is communication between the interior of dewars 14 with that of element 16. The other end of the latter terminates in an annular lip 28 for a purpose to be later described.

Tubular element 18 has at one end an annular lip 32 facing but spaced from lip 28 while the other end of element 18 is provided with a closure cap 34 which is welded or brazed to both element 18 and conductor 12 so that there is complete sealing by all metallic parts.

Surrounding element 16 is a sleeve 36 of suitable electrically insulating deformable material such as Teflon, while surrounding element 18 is a similar sleeve 38. A third sleeve 42 of similar material encloses

annular lips

28 and 32.

A plurality of anodized aluminum rings or

washers

44a, 44b, and 44c providing electrical insulation are mounted adjacent

annular lips

28 and 32 as is illustrated. Male housing member 22 is threaded into female member 24 to an extent to place

washers

44a, 44b, and 44c under sufiicient compression and to insure as well proper confinement of the fluid within dewars l4 and

tubular members

16 and 18. A thicker anodized aluminum ring 44d may be employed in contact with male member 22. A typical load on the washers with helium within dewars l4 and a vacuum outside is 50,000 psi. By anodized aluminum is meant herein that the oxide layer on the metal is at least onehalf mil in thickness. So that the aforementioned washers 44b will provide leak tight confinement for the fluid within connector 10, a sealant would be applied to the facing surfaces of

lips

28 and 32 and to the faces of washers 44b to effect the seal. Any suitable sealant may be applied for this purpose, such as a commercially available anaerobic sealant or an epoxy, so that the sealant will set up under compression.

Sleeves 36, 38 and 42 perform the function of providing electrical insulation between

members

22 and 24 on the one hand and

tubular members

16 and 18 on the other hand.

It will be seen that in the use of connector the latter simultaneously seals against leakage of fluid within dewars 14 through the use of anodized aluminum rings 44b and that the anodized

rings

44a, 44b, and 44c isolate electrically conductor 12 and tubular member 18 from dewars l4 and tubular member 16. That is, tubular member 18 is at the electric potential of conductor 12 whereas dewars 14 and tubular member 16 are at some other potential, i.e., neutral, ground, or opposite potential. Of course, if desired, connector 10 may be utilized to perform either the electrical isolation or the pressure containment alone as well as in combination.

In the arrangement illustrated in FIG. 1, connector 10 provides for the transfer of electrical current into or out of dewars 14 as well as tight confinement of the fluid within. Connector 10 may be so employed only to permit transfer of fluid into or out of dewars 14 while at the same time electrically isolating dewars 14 from the supply pipe. As shown in FIG. 2, it is seen that in this configuration instead of a conductor 12, there is employed a transition member 52 terminating in a pipe 54 welded or brazed to the end of tubular member 18. Gas flow is shown by the arrows which may be in either direction.

It will be seen that the electrical connector described herein is highly useful in cryogenic apparatus and systems, especially where temperature cycling may take place. The construction is virtually all metal so that the destructive effects of temperature and/or pressure cycling are avoided. In addition, by selecting the metal of

tubular elements

16 and 18 to have a lower temperature coefficient of expansion than the metal selected for

members

22 and 24, as the temperature is reduced, the pressure on

rings

44a, 44b, and 440 is increased. In one typical application stainless steel was employed for

tubular elements

16 and 18 while aluminum was employed for

members

22 and 24.

What is claimed is:

1. An electrical connector for use with a dewars, comprising a. first metallic tubular means open at one end for communicating with a dewars:

b. second metallic tubular means aligned with and spaced from said first tubular means closed at the end away from said first tubular means;

0. means consisting of stacked anodized aluminum washers, adjacent washers being in contact with each other, filling the space between said first and second tubular means;

d. means compressing said washers forming a sealed chamber within said tubular means for communicating with the interior of a dewars, said anodized aluminum washers electrically isolating said tubular means from each other; and

e. means extending through and in contact with the closed end of said second tubular means, for providing communication with the interior of said connector and a dewars.

2. The connector of claim 1 in which said tubular means are each provided with an annular lip at the open end facing each other, said washers filling the space between said lips.

3. The connector of claim 2 having additional anodized aluminum washers surrounding said tubular means on the opposite sides of said annular lips, said compressing means compressing all of said washers.

4. The connector of claim 3 in which said compressing means comprises a pair of threaded male and female members surrounding said tubular means and enclosing said washers and compressing the latter, the male member being threaded into the female member.

5. The connector of claim 4 having tubular sleeves of deformable, electrically insulating material separating said male and female threaded members from the annular lips and washers, and separating the threaded members and the additional washers from the tubular means.

6. The connector of claim 4 in which the coefficient of thermal expansion of said threaded members is greater than the coefficient of thermal expansion of said tubular means.

7. The connector of claim 2 in which said washers and the annular lips facing said wahers are coated on contacting surfaces with sealant.

8. The connector of claim- 7 in which the means extending through and in contact with the closed end of said second tubular means consists of an electrical conductor passing through both of said tubular means for extending into a dewars and spaced from the inner walls of both said tubular means.

9. An electrical connector for use with a dewars, comprising a. first metallic tubular means open at one end for communication with a dewars;

0. means consisting of stacked anodized aluminum washers, adjacent washers being in contact with each other, filling the space between said first and second tubular means; and

(1. means compressing said washers forming a sealed chamber within said tubular means for communicating with the interior of a dewars, said anodized aluminum washers electrically isolating said tubular means from each other;

e. said closed end of said second tubular means having an opening therein for providing communication with the interior of said connector and a dewars.

Claims

1. An electrical connector for use with a dewars, comprising a. first metallic tubular means open at one end for communicating with a dewars: b. second metallic tubular means aligned with and spaced from said first tubular means closed at the end away from said first tubular means; c. means consisting of stacked anodized aluminum washers, adjacent washers being in contact with each other, filling the space between said first and second tubular means; d. means compressing said washers forming a sealed chamber within said tubular means for communicating with the interior of a dewars, said anodized aluminum washers electrically isolating said tubular means from each other; and e. means extending through and in contact with the closed end of said second tubular means, for providing communication with the interior of said connector and a dewars.

8. The connector of claim 7 in which the means extending through and in contact with the closed end of said second tubular means consists of an electrical conductor passing through both of said tubular means for extending into a dewars and spaced from the inner walls of both said tubular means.

9. An electrical connector for use with a dewars, comprising a. first metallic tubular means open at one end for communication with a dewars; b. second metallic tubular means aligned with and spaced from said first tubular means closed at the end away from said first tubular means; c. means consisting of stacked anodized aluminum washers, adjacent washers being in contact with each other, filling the space between said first and second tubular means; and d. means compressing said washers forming a sealed chamber within said tubular means for communicating with the interior of a dewars, said anodized aluminum washers electrically isolating said tubular means from each other; e. said closed end of said second tubular means having an opening therein for providing communication with the interior of said connector and a dewars.