US2906809A

US2906809A - Coaxial cable termination

Info

Publication number: US2906809A
Application number: US626123A
Authority: US
Inventors: John W Drenning
Original assignee: Koppers Co Inc
Current assignee: Beazer East Inc
Priority date: 1956-12-04
Filing date: 1956-12-04
Publication date: 1959-09-29
Anticipated expiration: 1976-09-29

Description

Sept. 29, 1959 J. w. DRENNING COAXIAL. CABLE TERMINATION Filed Dec. 4, 1956 W l l l 1 l I l M l ll i l h o IIHHHUIIIIIIIIIIII'I 1L4 0 r kw M E wm 2 V2 0 m0 r w B M W h J Y United States Patent COAXIAL CABLE TERMINATION John W. Drenning, Baltimore, Md., assignor to Koppers Company, Inc., a corporation of Delaware Application December 4, 1956, Serial No. 626,123 6 Claims. (Cl. 174-73) This invention relates to apparatus for terminating coaxial cable transmission lines, and more particularly to apparatus for terminating solid dielectric coaxial cable transmission lines which are used to transmit high voltages to equipment such as electrostatic precipitators.

Various types of cable terminal arrangements have been used in the past in connection with transmission lines for high frequency signals. Although these arrangements have proven satisfactory in accommodating the low voltages used for high frequency signals, they have not proven entirely satisfactory in the transmission of high voltages which tend to cause large stresses in the terminals. Furthermore, past arrangements for terminating solid dielectric coaxial lines have employed some form of dielectric material in their assembly, which material has had to be heated, poured around the cable, and allowed to solidify. This procedure has required great care in its execution in order to prevent the possible occurrence of air voids which cause voltage breakdowns. As a result, the procedure has been costly in both time and labor.

The present invention provides an apparatus for terminating coaxial cable which avoids the above-mentioned disadvantages, which is economical and straightforward in its construction and maintenance, and which eliminates past difficulties in coaxial cable splicing and terminating.

More specifically, the present invention provides coaxial cable terminating apparatus which utilizes a compartment filled with an insulating fluid medium to eliminate air voids in the compartment and to prevent destructive corona discharge and spark-over between the internal high voltage parts disposed in such compartment and the grounded metal container which forms the compartment. The present invention further provides a standard porcelain through-bushing, a portion of which projects into the compartment and through which high voltage may be safely conducted to equipment destined to be energized; a mechanical fitting which serves to grasp the outer conductor of a coaxial dielectric cable to hold the cable in position and which at the same time electrically connects the outer conductor to ground; a soft metal sealing medium for the fluid insulating compartment which also serves to secure the terminal portion of the cable to the insulating compartment; and, a terminal which is apart from the insulating through-bushing and not disposed therewithin so as to necessarily require complete replacement upon the failure of such throughbushing. Further, the present invention provides a cornplete terminal assembly which is so arranged that in case of a failure of any one of the components, such defective component can be swiftly replaced by even a person without particular skill in terminal assemblies.

Various other features of the present invention will become obvious to one skilled in the art upon the reading of the disclosure set forth hereinafter.

More particularly, the present invention provides a pothead for terminating a solid dielectric coaxial cable having an inner and outer conductor comprising: an insulat- 2,906,809 Patented Sept, 29, 1959 ing compartment; a terminal arrangement in the wall of the compartment to terminate the outer conductor and to permit the inner conductor of the cable to pass therethrough into the compartment, the terminal arrangement including an outer sleeve member, first and second inner sleeve members through which the inner conductor of the cable passes into the compartment, the inner sleeve members being spaced in end-to-end relationship and movable relative each other, with the first inner sleeve member having a portion in spaced concentric relation with the outer sleeve member and having the outer wall of such portion so shaped with respect to a portion of the inner wall of the outer sleeve member to form a gripping wedge for the outer conductor of the coaxial cable, and with the second inner sleeve member having a portion of its outer wall in movable contact with a portion of the inner wall of the outer sleeve member to urge the first inner sleeve member into gripping relation with the outer conductor of the cable; and a sealing ring disposed between the first and second inner sleeve members and surrounding the inner conductor to firmly grip the inner conductor when the ring is pressure displaced between the inner sleeve members.

It is to be understood that various changes can be made, by one skilled in the art, in the arrangement, form, and construction of the apparatus disclosed herein without departing from the scope or spirit of this invention.

Referring to the drawings:

Figure l is a schematic elevational view of a portion of an electrostatic precipitator, including the coaxial cable pothead arrangement of the present invention;

Figure 2 is an enlarged detailed cross-sectional view of the coaxial cable pothead arrangement broadly disclosed in Figure 1;

Figure 3 is an enlarged detailed view of the outer conductor terminal portion of the arrangement disclosed in Figure 2;

Figure 4 is an enlarged view of a coaxial cable which has been prepared for connection to the pothead arrangement.

Referring to Figure l of the drawings, an electrical precipitator housing 2 is disclosed. Housing 2 has disposed therein a plurality of discharge electrodes 3 which cooperate with collecting electrodes (not shown) spaced therefrom in a manner well-known in the art. As is also well-known in the art, discharge electrodes 3 are supported by a frame arrangement which includes horizontal conducting bars 4 from which the discharge electrodes are suspended. Horizontal conducting bars 4 are, in turn, suspended by means of vertical conducting bars 6 and each vertical conducting bar 6 is supported from the top of the housing by having its upper threaded extremity pass through an aperture in conducting bar 7, the bar 6 being held in place on bar 7 by nut 8 fastened to the threaded extremity of bar 6. Bar 7, in turn, is supported by porcelain insulator 9 fixed to the roof of housing 2. A hood 11 serves to protect the suspension framework.

Passing through a passage in the side wall of hood 11 is a portion of a porcelain through-bushing 12, the through-bushing 12 being connected to bar 7 by means of jumper 13. The remaining portion of the porcelain through-bushing projects into coaxial cable pothead arrangement broadly designated by the reference numeral 14, the pothead arrangement being attached to the hood 11 in a manner described hereinafter. It is to be understood that the apparatus so far described is substantially conventional in the art and therefore specific details have not been set forth.

Referring to Figures 2 and 3 of the drawings, the inventive coaxial cable pothead arrangement is disclosed.

It is to be understood that the disclosed arrangement, inaddition to being useful with electrostatic precipitators,

can be used in conjunction with other electrical equipment which also might require high voltages.

The pothead includes cylindrical housing 16, welded at 17 to plate 18. Plate 18 is bolted by means of bolts 19 to plate 21, agasket 22 being provided between plate 18 and plate 21. Plate 21 is connected by nut and bolt assemblies 23 to the above described hood 11 of the precipitator housing, the plate serving to cover passage 24 in the hood. A passage 26 is provided in plate 21. This passage communicates with passage 24 and permits a portion of the porcelain through-bushing 12 to project into the insulating compartment 27, which is formed by:

the cylindrical housing 16 of the pothead. I A collar 28 surrounds the through-bushing 12 and is cemented thereto, an additional cement-like type of material being provided as at 31 to retain the through-bushing to the flange of the collar. This collar is attached to plate 21 by means of bolts 29. Bolts 29 pass through the aforementioned gasket 22, a portion of which is also positioned between the collar shoulder and plate 21.

On the top portion of cylindrical housing 16, a fluid port 32 is provided, the fluid port being surrounded by ring 33 welded to the outer Wall of the housing. Attached to the ring by means of tap bolts 34 is cover plate 36. When the cover plate is removed, an insulating fluid medium can be introduced into the insulating compartment 27. The fluid medium can be any type of electrical insulating oil I which has a high dielectric strength and which advantageously is adequate to withstand high temperatures. For example, transformer mineral oil has been found to be satisfactory. The insulating oil serves to avoid spaces of air which would otherwise exist and performs the insulating function around the inner conductor of a coaxial cable which passes into compartment 27, as will be described hereinafter. Thus, destructive corona discharge and sparkover between the inner conductor which carries high voltage and cylindrical housing 16 which is grounded (as is also described hereinafter) is prevented. To provide for possible expansion of the oils in the compartment due to temperature changes and to prevent outside dirt from entering into the compartment, a oneway ball valve 37 is located in cover plate 36 at the top of cylindrical housing 16.

Positioned at the bottom of housing 16 is a drain valve assembly 38. This drain valve serves to drain the insulating oil from compartment 27 when repairs are required or when a sampling of insulating oil is desired.

Passing through the through-bushing 12 is an electrical conductor rod 39, one end of which projects slightly beyond the bushing and into compartment 27. Washer 41 is welded at 42 to this end of the rod and a gasket 43 is provided between this washer and the corresponding end of bushing 12. The other end of conductor rod 39, which lies on the outside of compartment 27, is threaded to receive nut and washer assembly 44 to which the aforedescribed jumper 13 is attached. Assembly 44 also serves to hold rod 39 firmly in place in bushing 12. As can be seen in Figure 2 of the drawing, the inner conductor of a polyethylene insulated coaxial cable (to be described in detail hereinafter) is connected to the end of the conductor rod 39 which projects into the insulating compartment 27. This is accomplished by providing a socket 46 at this end of the rod, the inner conductor being held in place in the socket by set screw 45 passing through the side of the conductor rod and contacting the inner conductor to complete full contact between it and the rod. It is to be noted that with the rod and through-bushing arrangement disclosed, failure of the porcelain-bushing does not necessarily result in cable failure since the cable is apart from the porcelain and not contained Within it, as has been the case with graded cable potheads of the past.

In order that the inner conductor of a coaxial cable may pass into insulating compartment 27, a terminal arrangement is provided at the side wall of the cylindrical housing 16 for terminating the outer conductor and to permit the inner conductor to pass therethrough into the compartment. This terminal arrangement includes an outer sleeve member 51, one end of which is internally threaded to engage the external threads of an inner sleeve member 52. Sleeve member 52 extends through the side wall of cylinder 16 and has a portion thereof projecting into the insulating compartment with the remaining portion falling outside the compartment. The sleeve 52 is provided with an outer shoulder 53 which abuts the outer wall of the cylinder 16 and which is welded thereto at 54. It is to be noted that the passage in the. portion of the sleeve member 52 which projects into compartment 27 is flared outwardly toward the end as at 56. This serves to relieve any extreme voltage stresses on the oil in the compartment and on the polyethylene insulation of the inner conductor (to be described hereinafter).

The other end of sleeve member 52 is recessed to receive a soft lead seal ring 57.

Upon tightening of the terminal arrangement, ring 57 will be displaced by'pressure so as to grip the inner insulating polyethylene which it surrounds to form an oiltight junction between the cable and the housing and to provide additional securement of the cable to the housing. To compress and displace the seal ring 57an inner sleeve member 58 is provided on the side of ring 57 opposite the side which abuts the recess of inner sleeve member 52. Inner sleeve member 58 is in endto-end relation and movable relative sleeve member 52, sleeve member 58 being disposed within and in spaced concentric relation with outer sleeve member 51. At that end of sleeve member 58 which abuts the lead seal ring 57, there is provided a raised wedge portion 59 adapted to bite in to the soft lead seal ring and insure the displacement thereof. .In this connection, it is to be noted that the body of member 53 adjacent member 52 is of slightly larger diameter than the diameter of the recess for ring 57 in member 52. This is desirable in order to prevent too much displacement of the ring 57 when sleeve member 51 is tightened, the parts being so arranged that the ring 57 seals the unit upon displacement but does not distort the polyethylene insulation of the cable described hereinafter. The opposite end of inner sleeve member 58 is provided with a tapered outer wall portion 61, the tapered wall being adapted to cooperate with a swept back portion 62 on the inner side of the collared end 63 of outer sleeve member 51. An outer shoulder 64 is provided on inner sleeve member 58, this outer shoulder having a greater diameter than the maximum diameter of the swept back portion 62 of the collared end 63 to thus abut against the collared end when the terminal arrangement is tightened. When such terminal arrangement is tightened, the outer conductor of a coaxial cable and the outer insulation of the conductor is gripped between the swept back portion 62 of the outer sleeve member 51 and the tapered portion 61 of the inner sleeve member (as will be described in detail hereinafter). To eflect such tightening in a swift and efiicient manner, the outer sleeve member 51 is provided with apertures 66 around the outer wall to receive the tines of a spanner-type tightening wrench.

One end of a ground wire 67 is attached to the end wall of housing 16, this ground wire having its other end attached to the metallic shield of a coaxial dielectric cable as described hereinafter.

Referring to Figure 4 of the drawing, a polyethylene insulated coaxial cable broadly designated by reference numeral 71 is disclosed. This cable includes an inner copper conductor 72 surrounded by an inner polyethylene insulation 73. Surrounding the inner polyethylene insulation 73 is an outer conductor 74 in the form of copper braid, and surrounding the outer conductor is an outer polyethylene insulation76. A metallic armor shield 77 surrounds the outer insulator 76.

In a typical example wherein a coaxial cable such as disclosed in Figure 4 is prepared for installation in the pothead disclosed in Figures 1-3, the armor shield 77 is stripped back and cut off about from the end. The outer polyethylene insulation 76 and copper braid 74 are stripped back and cut oil about 8%" from the end. The inner polyethylene insulation 73 is cut olf about from the end. When this has been accomplished, the cable is ready to be connected to the pothead terminal arrangement.

The outer sleeve member 51 is slipped over the prepared end of the cable. The inner sleeve member 58 is passed over the inner polyethylene insulation 73, the tapered portion 61 of the inner sleeve member being forced under the copper braid 74. The lead seal ring 57 is slipped over the inner polyethylene insulation 73 and is pushed back until it touches the wedge 59 of the inner sleeve 58. The prepared end 73 of the coaxial cable is then passed through the inner sleeve member 52 and the inner copper conductor 72 is connected to the steel rod 39 by inserting it into socket 46 and tightening the set screw42. When this has been accomplished, the outer sleeve member 51 is then rotated so that the lead seal 57 is displaced between the two inner sleeve members 52 and 58 to form an oil-tight junction between the inner polyethylene insulation 73 and to provide additional securement of the cable to the housing. At the same time, the tightening of the terminal arrangement serves to grip the outer conductor 74 and outer insulation 76 between the tapered portion 61 of the inner sleeve member 58 and the swept back portion 62 of the collared end 63 of outer sleeve 51.

Thus, the coaxial cable is connected to the pothead in a swift and eflieient manner with a minimum of operation and a minimum of hazard. When the connection has been completed, the insulating compartment 27 is filled with an insulating oil to eliminate any air voids and to prevent spark-over between the conductor which carries high voltage and the housing 16 which is grounded.

With the above described arrangement a complete pothead assembly is obtained having components which can be replaced in case of failure in a minimum of time, and with a minimum of effort and skill by virtue of the straightforwardness of the several parts of the assembly.

The invention claimed is:

l. A pothead for terminating a solid dielectric coaxial cable having an inner conductor and insulation surrounding the same and outer conductor and sheath comprising:

an insulating compartment; a terminal arrangement in the wall of said compartment for terminating said outer conductor and to permit said inner conductor of said cable to pass therethrough into said compartment, said terminal arrangement including an outer sleeve member, first and second inner sleeve members through which said inner conductor passes into said compartment, said inner sleeve members being in end-to-end relationship and axially movable relative to each other, said first inner sleeve member having a portion in spaced concentric relation with said outer sleeve member and the outer wall of such portion shaped with respect to a portion of the inner wall of said outer sleeve member to form a gripping wedge for said outer conductor of said cable, said second inner sleeve member having a portion of its outer wall in movable contact with a portion of the inner wall of said outer sleeve member to urge said first inner sleeve member into gripping relation with said outer conductor and sheath of said cable, and a sealing ring disposed between said first and second inner sleeve members and surround ing said inner conductor and insulation to firmly grip said inner conductor insulation when pressure displaced between said inner sleeve members.

2. A pothead for terminating a solid dielectric coaxial cable having an inner conductor and insulation surrounding the same and outer conductor and sheath comprising: an insulating compartment for said inner conductor, said compartment having an insulating fluid medium disposed therein; an insulated through-bushing, at least a portion of which is disposed within said fluid medium of said compartment; a terminal arrangement in the wall of said compartment for terminating said outer conductor and to permit said inner conductor of said cable to pass therethrough into said compartment through said fluid medium and into contact with said insulated bushing, said terminal arrangement including an outer sleeve member, first and second inner sleeve members through which said inner conductor passes into said compartment, said inner sleeve members being spaced in end-to-end relationship and axially movable relative each other, said first inner sleeve member having a portion in spaced concentric relation with said outer sleeve member and the outer wall of such portion shaped with respect to a portion of the inner wall of said outer sleeve member to form a gripping wedge for said outer conductor of said cable, said second inner sleeve member having a portion of its outer wall in movable contact with a portion of the inner wall of said outer sleeve member to urge said first inner sleeve into gripping relation with said outer conductor and sheath of said cable, and a sealing ring disposed between said first and second inner sleeve members and surrounding said inner conductor and insulation to form a seal therearound when pressure displaced between said inner sleeve members.

3. A pothead for terminating a solid dielectric coaxial cable having an inner conductor and insulation surrounding the same and outer conductor and sheath comprising: an insulating compartment for said inner conductor, said compartment having an insulating fluid medium disposed therein; an insulated through-bushing, at least a portion of which is disposed within said fluid medium; a conductor rod passing through said through-bushing, a terminal arrangement in the wall of said compartment for terminating said outer conductor of said cable to pass therethrough into said compartment, through said fluid medium and into contact with said conductor rod, said terminal arrangement including an outer sleeve member, first and second inner sleeve members through which said inner conductor passes into said compartment, said inner sleeve members being spaced in end-to-end relationship and axially movable relative each other, said first inner sleeve member having a portion in spaced concentric relation with said outer sleeve member and the outer wall of such portion shaped with respect to a portion of the inner wall of said outer sleeve member to form a gripping wedge for said outer conductor of said cable, said second inner sleeve member having a portion of its outer wall in movable contact with a portion of the inner wall of said outer sleeve member to urge said first inner sleeve into gripping relation with said outer conductor and sheath of said cable, and a sealing ring disposed between said first and second inner sleeve members and surrounding said inner conductor and insulation to form a seal therearound when pressure displaced between said inner sleeve members.

4. A terminal arrangement for terminating the outer conductor of a solid dielectric coaxial cable having an inner conductor and insulation surrounding the same and outer conductor and sheath comprising: an outer sleeve member, first and second inner sleeve members through which said inner conductor passes, said inner sleeve members being positioned in end-to-end relationship and axially movable relative each other, said first inner sleeve member having a portion in spaced concentric relation with said outer sleeve member and the outer wall of such portion spaced with respect to a portion of the inner wall of said outer sleeve member to form a gripping wedge for said outer conductor of said cable, said second inner sleeve member having a portion of its outer wall in movable contact with a portion of the inner wall of said outer sleeve member to urge said first inner sleeve into gripping relation with said outer conductor and sheath of said cable, and a sealing ring disposed between said first and second inner sleeve members and surrounding said inner conductor and insulation to firmly grip said inner conductor when pressure displaced between said inner sleeve members.

5. A terminal arrangement for terminating the outer conductor of a solid dielectric coaxial cable having an inner conductor and insulation surrounding the same and outer conductor and sheath comprising: an outer sleeve member, first and second inner sleeve members through which said inner conductor passes, said inner sleeve members being spaced in end-to-end relationship and axially movable relative each other, said first inner sleeve member having a portion in spaced concentric relation with said outer sleeve member and the outer Wall of such portion shaped with respect to a portion of the inner wall of said outer sleeve member to form a gripping wedge for said outer conductor of said cable, said second inner sleeve member having a flared inner wall portion at the point where said inner conductor leaves said second sleeve, said second inner sleeve also having a portion of its outer wall in movable contact With a portion of the inner wall of said outer sleeve member to urge said first inner sleeve into gripping relation with said outer conductor and sheath of said cable and a compressible sealing ring disposed between said first and second inner sleeve members and surrounding said inner conductor and insulation to firmly grip said inner conductor insulation when pressure displaced between said inner sleeve members.

6. A pothead for terminating a solid dielectric coaxial cable having an inner conductor and insulation surrounding the same and outer conductor and sheath comprising: an insulating compartment for said inner conductor, said compartment having a fluid medium disposed therein; an insulated through-bushing, at least a portion of which is disposed within said fluid medium; a conductor rod passing through said through-bushing; a terminal arrangement in the wall of said compartment for terminating said outer conductor and to, permit said inner conductor of said cable to pass therethrough into said compartment, through said fluid medium and into contact with said conducting rod, said terminal arrangement including an outer sleeve member, first and second inner sleeve members through which said inner conductor passes into said compartment, said inner sleeve members being spaced in end-to-end relationship and movable relative each other, said first inner sleeve member having a portion in spaced concentric relation with said outer sleeve member and having the outer wall of such portion shaped with respect to a portion of the inner sleeve wall of said outer sleeve member to form a gripping wedge for said outer conductor of said dielectric cable, said second inner sleeve member having a flared inner wall at that point in which said inner conductor leaves said inner sleeve member, said second inner sleeve member also having a portion of its outer wall in threaded engagement with a portion of the inner wall of said outer sleeve member so as to be able to urge said first inner sleeve member into gripping relation with said outer conductor and sheath of said cable, and a compressible sealing ring disposed between said first and second inner sleeve members and surrounding said inner conductor and insulation to firmly grip said inner conductor insulation and form a seal therearound when pressure displaced between said inner sleeve members.

References Cited in the file of this patent UNITED STATES PATENTS 1,756,233 Austin Apr. 29, 1930 2,425,834 Salisbury Aug. 19, 1947 2,449,983 Devol Sept. 28, 1948 2,671,127 Hope Mar. 2, 1954 2,727,938 Nicholas Dec. 20, 1955 FOREIGN PATENTS 147,259 Switzerland Aug. 17, 1931 480,998 Canada Feb. 12, 1952