US3580977A

US3580977A - Quick-change field coil assembly for use in an electrode having a fluid-cooled arcing surface

Info

Publication number: US3580977A
Application number: US12269A
Authority: US
Inventors: George A Kemeny; Charles B Wolf
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1970-02-18
Filing date: 1970-02-18
Publication date: 1971-05-25
Anticipated expiration: 1988-05-25
Also published as: JPS5121179B1

Abstract

An electrode has a detachable tip secured to a supporting column. The column includes fluid-channeling and electrically conducting tubes, electrically insulated from each other, extending at least a portion of the way therethrough toward the tip. Within the removable tip is a detachable magnetic field coil assembly including conduit extensions which, when the coil assembly is inserted in the electrode, are aligned with the tubes respectively. Male fittings engage contact finger assemblies and make good electrical connection. The fittings may be on the tubes and the contact finger assemblies may be on the conduit extensions, or the fittings may be on the conduit extensions and the contact finger assemblies may be secured to the ends of the tubes. Means carried by the column, or the conduit extensions including fittings or finger assemblies thereon, or both, provide fluidtight seals for the cooling fluid flow circuit through the magnetic field coil.

Description

United States Patent 1 3,580,977

[72] Inventors George A. Kemeny 3,194,941 7/1965 Baird 1. 219/121 E t; 3,369,067 2/1968 De Corso.. 13/18 Charles B. Wolf, Irwin, Pa. 3,369,068 2/ 1968 Kienast 13/18 [21] Appl. No. 12,269 3,369,069 2/1968 Kemeny et al. 13/18 [22] Filed Feb. 18, 1970 3,385,987 5/1968 Wolfet a1. 13/18 [45] Patented May 25, 1971 3,392,227 7/1968 Ostberg 13/18 [73] Ass'gnee y zgaggz g Col-Porno Primary ExaminerBernard A. Gilheany Continuation-impart of application Ser. No. jij' Emmmer Roy Ema! 777,366, Nov. 20, 1968, now abandoned. 0rneysA. T. Stratton, C. L. Mcl-lale and M. 1. Hull ABSTRACT: An electrode has a detachable tip secured to a l 54] QUICKCHANGE FIELD COIL ASSEMBLY FOR supporting column. The column includes fluid-channeling and USE IN AN ELECTRODE HAVING A FLU) electrically conducting tubes, electrically insulated from each COOLED ARCING SURFACE other, extending at least a portion of the way therethrough 19 Claims 2 Drawing Figs. toward the tip. Within the removable tip is a detachable mag- [52] U 8 Cl 15/18 netic field coil assembly including conduit extensions which,

when the coil assembly is inserted in the electrode, are aligned [S 1 Int. Cl with the tubes respectively Male fitti engage Contact fmgelassemblies and make good electrical connection. The fittings 13/ 1 may b on the tubes and the Contact fi assemblies may be 18; 219/121 (CF), 145 on the conduit extensions, or the fittings may be on the con- [56] References Cited duit extensions and the contact finger assemblies may be secured to the ends of the tubes. Means carried by the column,

[50] Field of Search UNITED STATES PATENTS or the conduit extensions including fittings or finger assem- 2,858,4l2 10/ 1958 Kane et a] 219/ 121 blies thereon, or both, provide fluidtight seals for the cooling 3,130,292 4/1964 Gage et al 2 19/12 1 (X) fluid flow circuit through the magnetic field coil.

V .%7 W & l5

V 4a l7 26 102 5a 39 27 40 I8 20 I 33 7 I 4 I3 I4 i ,2:- 4 T' Patented Miiy 25, 1971 FIG.2.

QUICK-CHANGE FIELD COIL ASSEMBLY FOR USE IN AN ELECTRODE HAVING A FLUID-COOLED ARCING SURFACE CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of application Ser. No. 777,366, filed Nov. 20, 1968, now abandoned and assigned to the assignee of the instant invention.

This application is also related to the copending application of C. B. Wolf et al. for Electrode Assembly, Ser. No. 7l5,6l9, filed Mar. 25, 1968 now Pat. No. 3,480,717 and assigned to the assignee of the instant invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to electrodes having tips with fluidcooled arcing surfaces and employing a field coil within the tip for setting up a magnetic field to cause thearc to move substantially continuously around the arcing surface, and more particularly to such a structure in which the field coil is composed of hollow conduit through which a cooling fluid flows and an energizing current flows and which may be quickly removed from a supporting electrode column and a new field coil inserted in the column in a manner to make good electricalconnection and provide fluidtight seals;

2. Description of the Prior Art Prior art electrodes having a field coil composed of hollow conduit through which a cooling fluid flows and which also carries a current to set up an arc moving magnetic field utilize a structure in which the field coil copper conductors have tubular leads brazed to the field coil copper which extend through the electrode column structure to a suitable exterior point at or near the other end of the electrode where coolant and current connections are made, as exemplified for example in U.S. Pat. No. 3,368,0l8 and U.S. Pat. No. 3,368,019. The disadvantage of the prior art arrangement is that changing the field coil is a laborious procedure which requires generally in the order of hours. Furthermore, to reducethe time required to change field coils it is necessary to storezfield coils with long lead attachments which for some electrodes result in a foot-long assembly, which is difficult -to;store and difficult to handle.

SUMMARY OF THE INVENTION In our invention the electrode tip includes inner and outer shells with peripherally spaced U-shaped tubes therebetween forming fluid passageways, the shells and tubes being brazed together to form a unit. The tip assembly may be removed simply by unscrewing the outer shell from the supporting column or an extension thereof. A fluid-channeling member threaded to the inner shell is slidably removed from a fluid carrying tube of the supporting column. The magnetic field coil within the hollow space in the innershell and consistingof turns of hollow conduit insulated from each other has a supporting structure for the housing thereof which is'maintained clamped in place in the electrode column by one or more setscrews which may be loosened. The fluid in and fluid out conduit extensions of the field coil in one embodiment have male fittings brazed to the ends thereof, which fit into spring contact finger assemblies in two tubes in the supporting column structure, the male fittings carrying O-rings which provide fluidtight seals, the spring contact fingers providing good electrical connection. The coil and the supporting structure therefor, once the setscrew or screws are loosened, may be removed, carrying with it the male fittings. A new coil. assembly may be thereafter quickly inserted, the male fittings thereof being slipped into the contact finger assemblies, the setscrews tightened, and the electrode tip assembly quickly screwed back into position, all in a matter of a few minutes at most.

In another embodiment, the spring contact finger assemblies are secured to the conduit extensions, and the male fittings are secured to the tubes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing the invention according to one embodiment; and

FIG. 2 is a fragmentary view showing a second embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, the reference numeral 10 generally indicates an electrode supporting column with an extension 11 threadably secured thereto and an electrode tip generally designated 12 threaded at 18 to the lower end of the extension 1 1. The electrode tip generally designated 12 includes inner and

outer shells

13 and 14 respectively, each of the shells being annular in shape and generally U-shaped in cross section, the inside surface of the outer shell being spaced from the outside surface of the inner shell to form a space 16 for tubes providing fluid flow passageways between the shells and extending around the entire tip. The outer shell 14 is threaded at 18 to the lower end of the extension 11, while the outer shell has an annular recess 19 around the periphery of the wall of smaller diameter thereof which closely fits the adjacent surface 20 of a support and fluid-channeling member generally designated 21 which surface has an annular groove therearound with the O- ring23 seated therein to provide fluidtight sealing engagement. The outer shell 14, tubes and inner shell 13 are brazed together to form a unit. I

As illustrated the aforementioned space 16 may have therein a plurality of generally U-shaped tubes peripherally spaced around the entire electrode tip. Those ends of tubes which lie between the wall of smaller diameter of the inner shell andthe wall of smaller diameter of the outer shell are seen at 25, 26, 27 and '28 respectively extending through an annular passageway 29 in the tip assembly and communicating with an annular passageway 30 which communicates'by way of peripherally spaced annular passageways including 31 and 32 in the support and fluid-channeling member 21, which passageways 31 and 32 communicate with the interior cavity or chamber 33 of the support member and thence with a fluid passageway 35 formed within the tubular member 36 of the supporting column. Fluid inlet passageway 35 communicates with fluid inlet means, not shown for convenience of illustration. Preferably the fluid .passageway 35 conducts cooling fluid from the electrode tip. The outside ends of tubes 25 and 28 are seen at 39 and 40 respectively communicating with an annular fluid header 41 which communicates with a fluid passageway 43 which may be in the form of drilled holes or be generally cylindrical in shape except that it does not extend around the entire. periphery of the extension 11, a certain peripheral portion of the extension 11 being solid and designated 45 and having the

bolts

46 and 47 therein for reasons to be hereinafter described. It is seen that the upper end of the fluid passageway 43 communicates with an additional annular passageway 48 near the outer wall of the electrode supporting column, the passageway 48.communicating at some point along the axis of the electrode or at the upper end of the electrode with fluid inlet means, not shown for convenience of illustration.

' The aforementioned inner shell 13 is seen to have an extended annularportion of small diameter 50 which is threaded.

at 38 to an adjacent surface of the support and fluid-channeling member generally designated 21, with an O-ring 51 in an annular groove to provide fluidtight sealing engagement between the inner shell and the wall of the fluid-channeling and support member 21. Because member 21 is threaded to extension 50 of the inner shell 13, member 21 is slidably removed from tube. 36 when the tip assembly is removed by unscrewing at 18. It is further seen that the support member 53 for the field coil generally designated 54 has an annular groove 56 extending around .the outside surface thereofiinto which extend a plurality of peripherally spaced setscrews passing through the wall of the extension generally designated 11, one of these setscrews being shown at 58, the setscrews when screwed firmly into position extending into the annular groove 56 andclamping the field coil support member .53

, housing havingan extended collar portion 65 passing through an opening 67 in the support member 53, through which collar portionof the housing passes one end of the conduit 66 which has a male fitting member 68 brazed thereto, the member 68 nestling in the spring contact fingers of a spring contact finger assembly, two of the fingers being shown at 71 and 72 and carrying current to the conduit. The contact member 68 is seen to have annular grooves therein in which are disposed O-rings 73 and 74 for providing sealing engagement with the adjacent cylindrical wall of a tubular member 76 composed of conductive material enclosed within an outer tube 77 of insulating material.

1 Individual fingers 71 and 72 may culminate in a ring which is threaded or otherwise attached at 104 to tube 76.

It will be understood that the field coil housing 63 has an additional collar portion similar to 65, not shown in the plane selected for illustration, passing through an additional opening in support member 53, the additional opening not being shown inthe plane selected for illustration, through which additional, collar'portion extends the other end of the conduit which forms the field coil, the other end of the conduit forming the field coil also having a male contact member similar to 68 but not shown in the plane selected for illustration, which also makes contact with an additional spring contact finger assembly, not shown in the plane selected for illustration, and that further conductive tube means extends from said other additional contact finger assembly through the electrode supporting column and communicates with the terminal of opposite polarity of the source of potential to which the aforementioned conductive tube 76 is operatively connected for bringing an energizing current to the field coil, and that also an additional insulating tube corresponding to insulating tube 77 insulates the conductive tube, not shown, from the remainder of the electrode assembly. In summary, a complete electrical path is provided for bringing energizing current to the field coil, and a complete fluid flow path is provided for bringing fluid to the field coil, passing said cooling fluid through the turns of the field coil, and thereafter removing the fluid and exhausting it through fluid outlet means, not shown for convenience of illustration.

More than two such disconnect assemblies would be required for some particular configuration.

The slidable relation between tube 36 and tubular portion 80 of support and fluid-channeling member 21 not only facilitates tip replacement but provides for differential thermal expansion between the outer wall surface of the electrode column formed by members 10 and 11 and the inner structure fonning the fluid flow passageway 35; it is seen that the outside wall of the aforementioned tubular member 36 is slidable with respect to the inside wall 79 of the extended annular collar portion 80 of the aforementioned support and fluid-channeling member generally designated 21. O-

rings

82 and 83 seated in annular grooves in the wall of tube 36 provide sealing engagement. It is further seen that the upper portion of the tube 36 is of generally increased wall thickness and extends into and forms sealing engagement with a tubular extension 84 which may extend up through the remainder of the electrode column and supporting structure.

As previously stated, the support member 53, the field coil housing, and the field coil are removable as a unit and can be quickly replaced in a matter of minutes at most with a new field coil'which has two conduit extensions similar to extension 66 with. male fittings similar to'fitting'68 adapted to extend into the contact finger assemblies including finger assembly generally'designated 70. The finger assemblies and their tubular structures associated therewith must be precisely positioned radially within the column assembly, and also precisely positioned peripherally within the column assembly. To this end, insulating

plates

88 and 89 are fastened to tube 76 by means of studs 91 and insulating tube 77 and insulating split ring 93. The insulating plate 89 is seen to have an annular collar 95 extending therearound which abuts against an annular shoulder 96 formed in the inside wall of the extension generally designated 11; it is also seen that the insulating plate 89 has an annular wall portion 98 which firmly abuts against the adjacent wall of the extension 11, and that the outer surface of the insulating plate 88 abuts against the inside wall 99 of the outer cylinder 15 of the column generally designated 10.

The ring member I00 seated in a groove in the outside surface of member 15 may be used for supporting an exterior cylindrical heat shield composed'of highly refractory material and preventing the heat shield from slipping down toward the bottom of the electrode.

Support member 53 for thecoil housing and the field coil may be secured to'the field coil housing in any convenient manner. For example, as illustrated in the right-hand portion of the FIG., the support member 53 has a portion extending through the annular insulating block 102 and passing through the upper wall of the coil housing 63 to form clamping means. The extended portion is designated 103. Or, member 53 may be attached to member 103 by suitable studs or bolts, not shown.

If desired, alignment pins, not shown for convenience of illustration', may be used in assisting in aligning a new field coil v assembly when the assembly is to be inserted in the electrode column. I

Particular reference is made to FIG. 2. The supporting column is generally designated 10 and has column extension 11 threaded thereto at 17. A fluid passageway is shown at 43 and another at 35, for bringing cooling fluid 'to and from the tip, or vice versa. One conductive tube is shown at 760 enclosed within insulating sleeve 77a. It will be understood that there is anothersimilar electrically insulated conductive tube extending through the column, the other tube and sleeve not being shown for'conv'enience of illustration. Male fitting 68a is secured to conductive tube 76a at 111 in any convenient manner. Male fitting 68a carries O-rings 73a and 74a in annular grooves to provide a fluidtight seal.

Conduit extension 66a extending from insulation 65 has secured thereto at 115 in any convenient manner, as by brazing, a threaded member 118 which. has contact finger assembly generally designated 70a threaded thereon at 119. Two of the spring contact fingers are shown at 71a and 72a. Thereby, good electrical connection and fluidtight seals are formed between the conduit extensions and the conductive tubes.

Alignment pins may be used if desired, as explained in connection with FIG. 1.

Whereas the quick disconnect feature has been described with reference to -a field coil used in an electrode, our invention includes means utilizing a fluid flow and a current flow, adapted to be quickly connected to and quickly disconnected from means bringing fluid to and other means conducting fluid from the utilization means, the means bringing fluid to and the other means conducting fluid from also forming electrical circuit means for bringing a current to the utilization means.

We claim as our invention:

1. An electrode having a supporting column including two contact finger assemblies and two conductive tubes terminating in the contact finger assemblies respectively, the two conductive tubes forming a fluid inlet and a fluid outlet respectively, the two conductive tubes being adapted to be connected to terminals of opposite polarity respectively of a source of potential: a field coil assembly including a coil housing, a coil support member secured to said housing, the coil support member being removably mounted in position in the supporting column, a field coil of hollow conduit with ends extending through the support member, and two male fittings on the ends of the conduit removably inserted in the contact finger assemblies of the supporting column and forming sealing engagement therewith and electrical contact therewith.

2. A field coil assembly according to claim 1 in which the supporting column is additionally characterized as having a substantially centrally located fluid-carrying tube extending therethrough, and the field coil assembly includes in addition a hollow annular electrode tip enclosing the field coil housing on the bottom and sides thereof, the tip being removably threaded to the adjacent end of the supporting column, and a fluid-channeling and support member threadedly secured to the tip and slidably inserted over the outside of the fluid-carrying tube of the supporting column.

3. A field coil assembly according to claim 2 in which the tip is additionally characterized as having a fluid flow passageway therein near the arcing surface, said fluid flow passageway communicating with the fluid-carrying tube of the supporting column while the'tip is attached thereto, said electrode supporting column being additionally characterized as having an outer cylindrical wall with a fluid passageway therein communicating with the fluid flow passageway in the tip while the tip is attached to the supporting column.

4. A quick-change field coil assembly according to claim 1 including in addition a hollow annular shell generally U- shaped in cross section having the field coil housing disposed therein, the shell being removably threaded to the column and enclosing the coil housing on the bottom and both sides thereof.

5. A quick-change field coil assembly according to claim 1 including in addition a plurality of setscrews extending through the wall of the supporting column for clamping the coil support member in position within the column and holding the field coil conduit and said male fittings aligned with the contact finger assemblies.

6. In combination, an electrode supporting column and a quick-change field coil assembly of the type in which a hollow conduit forms the turns of the coil, a housing for the coil, said turns being electrically insulated from each other, the ends of the conduit extending through the field coil housing and having connected thereto tubular male contact members detachably engaging contact finger assemblies and making sealing engagement with the inside walls of conductive tubular members electrically connected to the contact fingers, and adapted for use in an electrode having a fluid-cooled electrode tip arinular in shape and generally U-shaped in cross section in which tip the field coil and field coil housing are disposed, the electrode including a column assembly having a pair of contact finger assemblies connected to conductive tubes adapted to be electrically connected to terminals of opposite polarity of a source of potential to supply an energizing current to the coil and adapted to be connected to fluid inlet and fluid outlet means for bringing a cooling fluid to the coil, passing said fluid through the turns of the coil and thereafter exhausting the fluid from the electrode, the quick-change field coil assembly including an insulating housing and a magnetic field coil therein composed of hollow conductive conduit, the ends of the conduit extending from the housing and having male contact members secured thereto, the male contact members being removably inserted into the contact finger assemblies of the electrode column assembly and making electrical connection therewith, the male contact members while inserted in the conductive tubes of the column assembly making fluidtight sealing engagement therewith.

7. A quick-change field coil assembly according to claim 6 including in addition an annular mounting member secured to the upper end of the field coil housing, said field-coil-mounting member having a pair of passageways therethrough through which the ends of the conduit extend, the field-coilmounting member being generally annular in shape and closely fitting the inside wall of the electrode column assembly thereby being secured therein and mounting the field coil in position within the tip.

8. A quick-change field coil assembly according to claim 7 including in addition a plurality of peripherally spaced setscrews passing through the wall of the column assembly and in which the mounting member is additionally characterized as having an annular groove extending therearound for removably receiving ends of the plurality of peripherally spaced setscrews to hold the field coil securely in position.

9. A field coil assembly according to claim 6 including in addition a hollow shell of conductive material generally annular in shape and generally U-shaped in cross section having the field coil and field coil housing mounted therein, the shell having means secured thereto extending into the column as sembly with a passageway within the shell forming a fluid flow passageway for the flow of cooling fluid to cool the electrode tip.

10. A field coil assembly according to claim 8 including in addition means for clamping the electrode housing and the shell in position within the electrode column.

11. A quick-change field coil assembly according to claim 10 in which the means for securing the field coil and field coil housing within the column assembly includes an annular mounting member secured to the field coil housing, the inner cylindrical wall of the column having a portion which abuts against the member, and including in addition means for clamping the support member and the abutting portion against supporting structure of the electrode column.

12; A quick-change field coil assembly according to claim 11 in which the member is additionally characterized as having an annular groove around the outside thereof for receiving the ends of a plurality of peripherally spaced setscrews extending through the wall of the electrode column supporting structure and extending into said groove to clamp the field-coilsupporting member in position within the electrode tip.

13. In an electrode, in combination, a supporting column and removable means forming an arcing surface, the supporting column including two tubes composed of electrically conductive material extending at least a portion of the length of the column and electrically insulated from each other, a detachable field coil assembly including a fluid-cooled magnetic field coil and two coil extensions extending toward the two tubes and substantially aligned with the two tubes respectively when the coil assembly is inserted in the electrode, and means secured to each of the tubes adapted to make good electrical connection with other means secured to each of the coil extensions when the coil assembly is inserted and to form sealing engagement therewith with a fluid passage opening between tube and extension.

14. Apparatus according to claim 13 wherein the means secured to each of the tubes is a spring contact finger as sembly, and the means secured to each of the coil extensions is a fitting adapted to be engaged by the fingers of the associated contact finger assembly.

15. Apparatus according to claim 14 wherein each fitting has at least one annular groove therein, and an O-ring seated in the annular groove providing said sealing engagement.

16. Apparatus according to claim 13 wherein the means secured to each of the coil extensions is a spring contact finger assembly, and the means secured to each of the tubes is a fitting adapted to be engaged by the fingers of the associated contact finger assembly.

17. Apparatus according to claim 16 wherein each fitting has at least one annular groove therein, and a O-ring seated in the annular groove providing said sealing engagement.

18. In an electrode, in combination, a supporting column and removable means fonning an arcing surface, the supporting column including two tube means composed of electrically conductive material extending at least a portion of the length of the column and electrically insulated from each other, a detachable field coil assembly including a fluid-cooled magnetic field coil and two coil extensions extending toward the two tube means and substantially aligned with the two tube means respectively when the coil assembly is inserted in the electrode, and two spring contact finger assemblies secured to the two coil extensions respectively near the ends thereof, the last-named means and the contact finger assemblies ineach of the'two tube meal mcludmg means on the ends cludes means for forming a fluidtight seal to prevent the thereof adjacent the contact finger assemblies adapted to be firmly engaged by the fingers of the contact finger assemblies and to make good electrical connection therewith.

19. Apparatus according to claim 18 wherein at least one of escape of fluid flowing through the tube means and thecoil extensions.

Claims

3. A field coil assembly according to claim 2 in which the tip is additionally characterized as having a fluid flow passageway therein near the arcing surface, said fluid flow passageway communicating with the fluid-carrying tube of the supporting column while the tip is attached thereto, said electrode supporting column being additionally characterized as having an outer cylindrical wall with a fluid passageway therein communicating with the fluid flow passageway in the tip while the tip is attached to the supporting column.

4. A quick-change field coil assembly according to claim 1 including in addition a hollow annular shell generally U-shaped in cross section having the field coil housing disposed therein, the shell being removably threaded to the column and enclosing the coil housing on the bottom and both sides thereof.

6. In combination, an electrode supporting column and a quick-change field coil assembly of the type in which a hollow conduit forms the turns of the coil, a housing for the coil, said turns being electrically insulated from each other, the ends of the conduit extending through the field coil housing and having connected thereto tubular male contact members detachably engaging contact finger assemblies and making sealing engagement with the inside walls of conductive tubular members electrically connected to the contact fingers, and adapted for use in an electrode having a fluid-cooled electrode tip annular in shape and generally U-shaped in cross section in which tip the field coil and field coil housing are disposed, the electrode including a column assembly having a pair of contact finger assemblies connected to conductive tubes adapted to be electrically connected to terminals of opposite polarity of a source of potential to supply an energizing current to the coil and adapted to be connected to fluid inlet and fluid outlet means for bringing a cooling fluid to the coil, passing said fluid through the turns of the coil and thereafter exhausting the fluid from the electrode, the quick-change field coil assembly including an insulating housing and a magnetic field coil therein composed of hollow conductive conduit, the ends of the conduit extending from the housing and having male contact members secured thereto, the male contact members being removably inserted into the contact finger assemblies of the electrode column assembly and making electrical connection therewith, the male contact members while inserted in the conductive tubes of the column assembly making fluidtight sealing engagement therewith.

7. A quick-change field coil assembly according to claim 6 including in addition an annular mounting member secured to the upper end of the field coil housing, said field-coil-mounting member having a pair of passageways therethrough through which the ends of the conduit extend, the field-coil-mounting member being generally annular in shape and closely fitting the inside wall of the electrode column assembly thereby being secured therein and mounting the field coil in position within the tip.

9. A field coil assembly according to claim 6 including in addition a hollow shell of conductive material generally annular in shape and generally U-shaped in cross section having the field coil and field coil housing mounted therein, the shell having means secured thereto extending into the column assembly with a passageway within the shell forming a fluid flow passageway for the flow of cooling fluid to cool the electrode tip.

12. A quick-change field coil assembly according to claim 11 in which the member is additionally cHaracterized as having an annular groove around the outside thereof for receiving the ends of a plurality of peripherally spaced setscrews extending through the wall of the electrode column supporting structure and extending into said groove to clamp the field-coil-supporting member in position within the electrode tip.

14. Apparatus according to claim 13 wherein the means secured to each of the tubes is a spring contact finger assembly, and the means secured to each of the coil extensions is a fitting adapted to be engaged by the fingers of the associated contact finger assembly.

18. In an electrode, in combination, a supporting column and removable means forming an arcing surface, the supporting column including two tube means composed of electrically conductive material extending at least a portion of the length of the column and electrically insulated from each other, a detachable field coil assembly including a fluid-cooled magnetic field coil and two coil extensions extending toward the two tube means and substantially aligned with the two tube means respectively when the coil assembly is inserted in the electrode, and two spring contact finger assemblies secured to the two coil extensions respectively near the ends thereof, each of the two tube means including means on the ends thereof adjacent the contact finger assemblies adapted to be firmly engaged by the fingers of the contact finger assemblies and to make good electrical connection therewith.

19. Apparatus according to claim 18 wherein at least one of the last-named means and the contact finger assemblies includes means for forming a fluidtight seal to prevent the escape of fluid flowing through the tube means and the coil extensions.