US3401243A

US3401243A - Circuit interrupter having dual-bore arc extinguishing means

Info

Publication number: US3401243A
Application number: US663018A
Authority: US
Inventors: Jr Chester W Upton; John A Sensue
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1967-08-24
Filing date: 1967-08-24
Publication date: 1968-09-10
Anticipated expiration: 1985-09-10
Also published as: JPS4614021B1; GB1200702A; FR1577702A; BE718704A; ES356615A1; SE344135B

Description

Sept. 10, 1968 c. w. UPTON, JR. ET AL 3,401,243 CIRCUIT INTERRUPTER HAVING DUAL-BORE ARC EXTINGUISHING MEANS Filed Aug. 24, 1967 United States Patent 3,401,243 CIRCUIT INTERRUPTER HAVING DUAL-BORE ARC EXTINGUISHING MEANS Chester W. Upton, Jr., Tratfortl, and John A. Sensue,

Wilkinsburg, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 24, 1967, Ser. No. 663,018 6 Claims. (Cl. 337221) ABSTRACT OF THE DISCLOSURE A high voltage circuit interrupter containing gas evolving, arc-extinguishing material inside a casing and includes a main bore and an auxiliary bore which extend axially through a plurality of blocks to form the respective bores. Conductors are disposed in the bores to draw an are which is interrupted in the auxiliary bore for smaller currents and in the main bore for larger currents. To prevent the escape of ionized gases from the auxiliary bore to the main bore, the meeting ends of the adjacent blocks each have a U-shaped recess which extends around the auxiliary bore to permit the filling of the recesses when the blocks are assembled with bonding material from one another and joins the successive blocks to one another.

Background of invention In the application of circuit interrupters at higher voltages, such as power fuses of the dual-bore type which in clude a relatively larger main bore and a relatively smaller auxiliary bore through a body of arc-extinguishing or gas evolving material, a problem arises in insuring that the arcing which results during an interrupting operation is always initiated in the smaller auxiliary bore of the interrupting and that such arcing remains in the smaller auxiliary bore to be finally interrupted when relatively smaller fault currents are being interrupted which the interrupter is incapable of interrupting in the larger main bore. If the body of arc-extinguishing material in such an interrupter includes a plurality of generally annular blocks each of which includes a relatively larger opening and a relatively smaller opening with the openings in the respective blocks being substantially aligned when the blocks are assembled or stacked in end-to-end relation to form the respective bores of the interrupter, ionized gases may escape from the small bore to the main here during an interrupting operation of the interrupter when the interrupter is attempting to interrupt relatively low fault currents, such as 1,000 amperes or less, to cause a restrike of the arc in the main bore in which the interrupter is incapable of interrupting such relatively low fault currents. It is therefore desirable to provide an improved high voltage circuit interrupter or power fuse construction of the dual-bore type which substantially prevents the travel of ionized gases between the main and auxiliary bores of the interrupter, particularly when the interrupter is called upon to interrupt relatively low fault currents which can only he successfully interrupted in the smaller auxiliary bore of the interrupter.

It is an object of this invention to provide a new and improved high voltage circuit interrupter construction.

Another object of this invention is to provide an improved means for preventing the escape of ionized gases from the relatively smaller bore to the relatively larger bore of a circuit interrupter having parallel large and small bores.

A further object of this invention is to provide an improved power fuse construction of the dual-bore type including means for joining a plurality of blocks of arcextinguishing material around the relatively smaller bore 3,401,243 Patented Sept. 10, 1968 of the power fuse and sealing off the auxiliary bore from the main bore of the power fuse structure.

A more specific object of this invention is to provide an improved means for joining a plurality of blocks of arc-extinguishing or gas evolving material together in a circuit interrupter of the dual-bore type which lends itself to convenient methods of manufacture and which substantially eliminates the risk of partially blocking or coating either bore of the circuit interrupter with the joining material.

Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:

FIGURE 1 is a side elevational view of a high voltage power fuse structure which embodies the principles of the present invention and which is shown in the normally closed operating condition.

FIG. 2 is an enlarged, longitudinal, sectional view of a fuse unit which forms part of the fuse structure shown in FIG. 1 with portions of the end fittings of the fuse unit omitted.

FIG. 3 is a bottom view of a generally annular block of gas evolving material which forms part of a body of arc-extinguishing material which is incorporated in the fuse unit of FIG. 2; and

FIG. 4 is an enlarged partial side elevational view of adjacent blocks of gas evolving material which form part of the fuse unit shown in FIG. 2 illustrating the manner in which the adjacent blocks of gas evolving material may be joined together in accordance with the invention.

Referring now to the drawings and FIG. 1 in particular, the structure shown comprises a power fuse structure of the high voltage, drop-out type, the general arrangement of which is set forth more fully in copending application Ser. No. 663,020 filed Aug. 24, 1967, by R. E. Frink and C. T. Walker, which is assigned to the same assignee as the present application.

As illustrated in FIG. 1, the fuse structure 10 includes a base (not shown) formed of sheet metal and a pair of outwardly extending insulator supports 272 and 282. The upper insulator support 272 fixedly supports in position a latching assembly 250 which includes a break contact 252, as described in greater detail in the copending application just mentioned. A lower insulator support 282 supports a hinge assembly 260 which pivotally supports a fuse unit and which includes a hinge contact 262, as described in the copending application just mentioned. As illustrated in FIG. 1, the fuse unit 100 serves to electrically bridge the break contact 252 and the hinge con. tact 262 so that electric current will normally pass there between by way of terminal pads (not shown) to which an external electrical circuit may be connected.

The fuse unit 100 includes a generally tubular fuse holder 32 which is formed from a suitable weatherproof, electrically insulating material, such as a filament wound glass epoxy material or the like, and a pair of upper and lower end fittings or

terminals

34 and 36, respectively, which are disposed at the opposite ends of the holder 32 and which are formed from an electrically conducting material. The upper and lower end fittings or

terminals

34 and 36, respectively, are securely fastened to the opposite ends of the associated holder or tube 32 by suitable means, such as cement, and a plurality of pins which pass transversely through both the end fittings and the associated holder 32. As illustrated, the fuse unit 100 also includes a hook eye 274 which is pivotally mounted on a laterally projecting port-ion 34A of the upper end fitting 34 and which may be utilized for efiecting opening and closing movements of the fuse unit 100 by means an inwardly projecting flange portion 36B against which the lower end of the holder 32 bears, as shown in FIG. 2.

The fuse unit 100 further includes a renewable or refillable unit 20 which is mounted within the holder structure and includes the outer tube 32 and the upper and lower end fittings or

terminals

34 and 36, respec tively. The renewable unit 100 includes its own supporting tube or insulating casing 108 which is formed from a suitable electrically insulating material having sufficient strength to withstand the internal gas pressures and intense heat which result during an interrupting operation of the fuse unit 100, such as a filament wound glass epoxy material. A body of gas evolving material, such as boric acid, which may include a plurality of generally

annular blocks

122, 124, 126 and 128 is disposed inside the tube 108 and spaced from the ends thereof. Each of the

blocks

122, 124, 126 and 128 includes a relatively larger central opening, as indicated at 125 for the block 126 in FIG. 3 and a relatively smaller opening at one side thereof, as indicated at 127 for the block 126 in FIG. 3, both of which extend axially through the individual blocks. When the

blocks

122, 124, 126 and 128 are axially stacked in end-to-end relation as shown in FIG. 2, with the respective larger and smaller openings thereof substantially aligned, a main bore 130 is formed through the body of gas evolving or arc-extinguishing material which includes said blocks and a relatively smaller auxiliary bore 192 is formed through the body of gas evolving material.

In order to prevent the travel of ionized gases between the main bore 130 and the auxiliary bore 192 during an interrupting operation of the fuse unit 100 and, more specifically, to prevent the escape of ionized gases from the auxiliary bore 192 into the main bore 130 during an interrupting operation of the fuse unit 100, the meeting surfaces of the

blocks

122, 124, 126 and 128 are structurally joined to one another around the relatively smaller openings of said blocks which form the auxiliary bore 192 by an electrically insulating, thermosetting, sealing and bonding material having a relatively high dielectric strength, such as an epoxy resin. More specifically, the meeting surfaces of the

blocks

122, 124, 126 and 128 at each end thereof include a groove or recess, as indicated at 126B for the block 126 in FIG. 3, which extends substantially around and is spaced from the relatively smaller opening in each of said blocks as indicated at 127 for the block 126 in FIG. 3. As shown in FIG. 3, the recess or groove 126B is spaced from the relatively smaller opening 127 and the block 126 by a generally tubular portion of the block 126, as indicated at 1260. When the

blocks

122, 124, 126 and 128 are assembled in end-to-end relation as shown in FIG. 2, the recesses or grooves in the meeting surfaces of the adjacent blocks are disposed in substantially congruent relation so that each groove or recess, as indicated at 126B, for the block 126 in FIG. 3 forms with the recess in the adjacent block a larger passageway which extends substantially around the auxiliary bore 192 and the smaller openings of the successive blocks which make up the auxiliary bore 192 with the ends of the recesses being open at the outer periphery of the respective blocks, as shown in FIG. 4, for the

blocks

126 and 128. The passageway which is formed by each pair of adjacent grooves or recesses in the meeting surfaces of each pair of blocks is substantially filled with a thermosetting, electrically insulating sealing and bonding material, as indicated at 132, in FIG. 2. It is to be noted that in FIG. 3 the tubular portion 126C which is disposed inside the recess 126B is also spaced from the outer periphery of the block 126 to permit the application of the sealing and bonding material 132 completely around the entire periphery of the joint between the successive blocks to prevent the escape of ionized gases from the auxiliary bore 192 into the main bore 130 of the fuse unit 100.

After the

blocks

122, 124, 126 and 123 are stacked in end-to-end relation, but before the blocks are assembled inside the tube 108, the sealing and bonding material or cement 132 can be forced or inserted into the passageways formcd around the auxiliary bore 192 between each pair of meeting surfaces of said blocks by the use of a pressure gun to thereby seal and join the successive blocks to one another around the auxiliary bore 192. It should be noted that because of the spacing of the recess 126B from the relatively smaller opening 127 in the block 126, the sealing and bonding material is prevented from entering either the small bore 192 or the main bore 130 which might adversely affect the arc-extinguishing characteristics of the

blocks

122, 124, 126 and 128 while still permitting a visual inspection of the ends of the joint to insure that a seal and joint is formed around the entire periphery of the blocks adjacent to the auxiliary bore 192. A relatively high dielectric ring seal is thus provided around the joint between each pair of successive blocks with a dielectric strength equal to or greater than the dielectric strength of the material from which the blocks are formed. It will be noted that the disclosed construetion also provides mechanical reenforcement of the blocks at the joints between the successive blocks around the auxiliary bore 192. It is important to note that since the passageways or recesses provided in the meeting surfaces of the

blocks

122, 124, 126 and 128 extend around the smaller openings provided in the respective blocks which form part of the auxiliary bore 192 with the ends of each passageway or recess exposed at the outer periphery of the respective blocks, the complete filling of each recess or passageway may be observed when the sealing and bonding material is flowed into the recess or passageway at one side of the smaller opening of each block when the material flows out the other end of the passageway at the other side of the smaller opening in each block.

In order to limit the gas pressures which result during an interrupting operation of the fuse unit 100 inside the tube 108 to a value within the rupture strength of the tube 108 as disclosed in greated detail in copending application Ser. No. 663,126 filed Aug. 24, 1967, by C. C. Patterson which is assigned to the same assignee as the present application, each of the

blocks

126 and 128 includes a generally C-shaped recess as indicated at 129 in FIGS. 2 and 3 which extends axially from one end of each of said blocks to a point which is adjacent to and axially spaced from the other end of the respective blocks with each of the recesses terminating peripherally short of the portion of said blocks which includes the relatively smaller opening which forms part of the auxiliary bore 192. Each of the

blocks

126 and 128 therefore includes around the major portion of its inner periphery an integral frangible inner wall, as indicated at 126A for the block 126 in FIG. 3. The inner walls 126A and 128A are arranged to disintegrate when the fuse unit 100 is called upon to interrupt relatively large current and when intense heat results within the main bore 136 and the gas pressure within the main bore 130 exceeds a predetermined value. During such an interrupting operation, the size of the main bore 130 through the

blocks

126 and 128 is effectively increased by the disintegration of the inner Walls 126A and 128A of the

blocks

126 and 128 respectively to thereby increase the size of the gas passageway in the main bore 130 and decrease or limit the gas pressure that would otherwise result.

In order to retain the

blocks

122, 124, 126 and 128 in assembled relationship with the associated tube 1G8, as shown in FIG, 2, the outer surfaces of said blocks may be coated with a suitable cement or bonding material, such as an epoxy bonding material, prior to assembly of the blocks inside the tube 108. In addition, a generally tubular or annular retaining member or plug 189 may be disposed at the upper end of the

blocks

122, 124, 126 and 128 with the major portion of the retaining member 189 extending axially inside the tube 108. The retaining member 189 may be formed or molded from a suitable electrically insulating material having sufficient strength to assist in retaining the

blocks

122, 124, 126 and 128 in assembled relationship with the tube 108 during an interrupting operation of the fuse unit 100, such as a glass polyester material. A washer 183 formed from similar material may be disposed between the retaining member 189 and the block 122 and may be employed during the preassembly and bonding of the

blocks

122, 124, 126 and 128 together prior to the assembly of said blocks inside the tube 108. It is to be noted that the retaining member 189 as well as the washer 183 includes a relatively larger central opening which forms an extension of the main bore 130 and a relatively smaller opening which forms an extension of the auxiliary bore 192.

In order to assist in retaining the member 189 in assembled relation with the associated tube 108 during an interrupting operation of the fuse tube 100, the outer surface of the retaining member 189 and the inner surface of the tube 108 at the upper end of the tube 108 include adjacent helical grooves which together form a passageway in which a helical wire 191 is disposed to firmly secure the retaining member in assembled relation with the tube 108. The retaining member 189 may be assembled with the upper end of the tube 108 by first assembling the helical wire 181 in the helical groove around the outer surface of the retaining member 189 and then screwing the retaining member 189 into the upper end of the tube 108 to the final position shown in FIG. 2. It is to be noted that the outer surface of the retaining member 189 may also be coated with a suitable cement or bonding material, such as an epoxy bonding material, to additionally secure the retaining member 189 to the tube 108.

In order to substantially prevent the escape of ionized gases from the upper end of the refillable or renewable unit 20 around the elongated conducting member 83 which extends through the main bore 130, a generally tubular member 185 is disposed in concentric or nested relation with the retaining member 189, as shown in FIG. 2, and is preferably formed from an electrically insulating material having a relatively low coefiicient of friction, such as polytetrafluoroethylene which is sold under the trademark Teflon. A shoulder portion 185A is provided at the upper end of the tubular member 185 and includes an opening of reduced cross-section or size through which the conducting member 83 passes and which forms a substantially gas-tight seal with the conducting member 83 during an interrupting operation of the fuse unit 100 when the conducting member is ac tuated to move axially upwardly, as viewed in FIG. 2. The tubular member 185 also acts as a bearing to guide the axial movement of the conducting member 83. In order to prevent the tubular member 185 from being blown out of the upper end of the tube 108 during an interrupting operation of the fuse unit 100, the retaining member 189 includes an inner shoulder portion against which the upper end of the tubular member 185 bears, as shown in FIG. 2. The escape of ionized gases from the upper end of the renewable unit 20 from the auxiliary bore 192 may be adequately prevented by reducing the size of the relatively smaller opening through the retaining member 189 through which the auxiliary conductor 182 passes so that the cross-section of the auxiliary conductor 182 substantially fills the relatively smaller opening through the retaining member 189,

In order to further assist in retaining the

blocks

122, 124, 126 and 128 in assembled relationship with the tube 108 during an interrupting operation of the fuse unit 100,

a generally tubular or annular retaining member 142 is disposed inside the tube 108 at the lower end of the

blocks

122, 124, 126 and 128, as shown in FIG. 2, and is formed or molded from an electrically insulating material having suflicient strength to assist in retaining the blocks 122 through 128 inside the tube 108 during such an interrupting operation, such as a glass polyester material. The outer surface of the retaining member 142 is preferably coated with a suitable cement or bonding material, such as an epoxy bonding material, prior to the assembly of the retaining member 142 inside the tube 108. This bonding material serves to bond the retaining member 142 to the inside of the tube 108. The retaining member 142 includes a relatively larger opening which extends axially therethrough, as indicated at 142A, into which the lower end of the main bore 130 opens and which may serve as an exhaust passageway for high pressure gases which result during the operation of the fuse unit 100. The opening 142A also serves as a chamber in which the fusible means 160 is disposed. The retaining member 142 also includes a relatively smaller opening 142B which extends axially therethrough. The lower end of the auxiliary bore 192 opens into the opening 142B and the lower end of the auxiliary conductor 182 projects in the same openin g. The insulating wall or partition 142 which is formed integrally with the retaining member 142 around the relatively smaller opening 1 42B through the retaining member 142 assists in preventing certain are products which may result during the operation of the fuse unit in a relatively smaller opening 142B of the retaining member 142 from being deflected into the relatively larger opening 142A of the retaining member 142 and impinging on parts of the fusible means 160. The retaining member 142 also includes an upwardly projecting tubular portion 142]) adjacent to the relatively smaller opening 142B through the retaining member 142 with the projecting portion 142D being joined to the adjacent block 128 around a recess in the block 128 which is adapted to receive the projecting portion 142D by a flexible bonding material, such as silicone rubber. This joint between the retaining member 142 and the block 128 around the auxiliary bore 192 assists in preventing the travel or escape of ionized gases between the auxiliary bore 192 and the main bore and between the auxiliary bore 192 and the relatively larger opening 142 through the retaining member 142 during an interrupting operation of the fuse unit 100.

The elongated conducting member or rod 83 of the refillable unit 20 is normally disposed, as shown in FIG. 2, to extend through the main bore 130 with the upper end of the conducting rod 83 projecting axially beyond the upper end of the tube 108 and with the upper portion of the conducting rod being externally threaded, as indicated at 83A. The conducting rod 83 is normally held in the position shown in FIG. 2 by a connection through the fusible means 160 to the generally annular or tubular lower conducting member or contact More specifically, the fusible means comprises a strain element 162 and a fusible element or link 164. The upper end of the strain element 162 is secured by suitable means, such as brazing, to the lower end of the conducting rod 83, while the other end of the strain element 162 is secured by suitable means, such as brazing to the connecting conductor or terminal 156 which is of the flat strip type. The connecting conductor 156 is secured in turn to the lower contact 150 adjacent to the upper end of the lower contact 150 by suitable means, such as brazing. Similarly, the upper end of the fusible element or link 164 is secured to the lower end of the conducting rod 83 by suitable means, such as brazing, while the low er end of the fusible element or link is secured to the lower contact 150 adjacent to the upper end of the lower contact 150 by suitable means, such as brazing. It is to be noted that the strain element 162 and the fusible element 164 are electrically connected in parallel between I the lower end of the conducting rod 83 and the lower contact 150 of the renewable unit 20.

Similarly, the auxiliary conductor 182 which is of a relatively smaller cross-section or size than the conducting rod 83 normally extends through the auxiliary bore 192 with the upper end of the auxiliary conductor extending axially beyond the upper end of the auxiliary bore 192 and being both mechanically and electrically connected to the upper portion of the conducting rod 82 by a transversely extending spring pin 184. The pin 184 is disposed in a transversely extending recess or opening provided at the upper end of the retaining member 189 to prevent rotation of the conducting rod 83 after assembly of the rod 83 in the renewable unit 20. The upper end of the auxiliary conductor 18?. may be formed as a loop which is assembled over the conducting spring pin 184 and retained thereon by the head 186 of the spring pin 184. The lower end of the auxiliary conductor 182 extends or projects into the relatively smaller opening 142B of the retaining member 142, as shown in FlG. 2, and is electrically connected through a helical conducting wire of reduced cross-section, as indicated at 194, to an angle-shaped auxiliary stationary terminal 157 which is secured to the tubular conducting member 150 adjacent to the upper end of the member 150 by suitable means, such as brazing. The upper end of the helical wire 194 which is disposed inside the relatively smaller opening 142B of the retaining member 142r is secured to the lower end of the auxiliary conductor 182 by suitable means, such as brazing, and the lower end of the helical wire 194 is secured to the auxiliary terminal 157 by suitable means, such as crimping or brazing, as disclosed in greater detail in copending application Ser. No. 663,127, filed Aug. 24, 1967, by C. W. Upton, C. C. Patterson and F. L. Cameron which is assigned to the same assignee as the present application.

The lower contact or conducting member 150 also includes an elongated arcing terminal 158, as disclosed in the copending application just mentioned, which projects upwardly from the upper end of the contact 150 into the relatively smaller opening 142B of the retaining member 142 to axially overlap the lower end of the auxiliary conducting member 182 with the lower portion of the arcing terminal 158 being disposed adjacent to and generally parallel to the axis of the helical wire 194. The arcing terminal 158 is electrically insulated along its length by a coating or film of electrical insulating material, such as an insulating enamel, which is provided on the arcing terminal 158 to prevent the electrical shorting out of the helical wire 194. The arcing terminal 158 which is formed from an electrically conducting material may be structurally secured to the upper end of the lower contact 150 at the inner periphery thereof by suitable means, such as brazing, or may be formed integrally therewith in a particular application. It is to be noted that the auxiliary current path which extends from the upper portion of the Conducting rod 83, through the cross pin 184, the auxiliary conductor 182 and the helical wire 194 to the auxiliary terminal 157 on the lower contact 150 is also electrically connected in parallel with the conducting paths which include, respectively, the strain element 162 and the fusible element 164.

In order to assist in retaining the

blocks

122 and 128 and the retaining member 142 in assembled relationship inside the tube 108, as well as for another important purpose during the interrupting operation of the fuse unit 100, the lower tubular conducting member or contact 150 includes a main portion 152 which extends axially inwardly from the lower end of the tube 108 to bear against the lower end of the retaining member 142. The lower contact 150 also includes a flange portion 154 at the lower end thereof against which the lower end of the tube 108 bears when the conducting member 150 is assembled with the fuse tube 108.

In order to retain the lower contact 150, as well as Cir other parts of the renewable unit 20, in assembled relationship with the tube 108 during an interrupting operation of the fuse unit 100, a generally tubular external terminal member or ferrule 172 is disposed to telescope over the lower end of the tube 108. In order to firmly secure the external terminal member 172 to the lower end of the tube 108, the internal surface of the external terminal member 172 and the external surface of the portion of the tube 108 adjacent to the members 172 include adjacent helical grooves which, when the parts are assembled, form a helical passageway in which a helical Wire 1'73 is disposed. In the assembly of the external terminal member 172 on the lower end of the tube 108, the helical wire 173 may be first assembled in the helical groove on the lower end of the tube 108 and the external terminal member 172 may then be screwed onto the lower end of the tube 108 until the parts reach their final positions, as shown in FIG. 2. In order to addltionally assist in retaining the external terminal member 172 on the lower end of the tube 108, the outer surface of the tube 108 and the inner surface of the external terminal member 1721 may be coated with a cement or bonding material, such as an epoxy bonding material, prior to the assembly of the external terminal member 172 on the lower end of the tube 108. It is to be noted that the external terminal member 172 also includes an inwardly projecting flange portion 172A around a central opening 17213 which bears against the adjacent flange portion 154 of the tubular conducting member 150 to assist in retaining the tubular conducting member 150 in assembled relation with the other parts of the renewable unit In order to form a current conducting path which extends between the lower end fitting 36 and the lower contact 150 of the renewable unit 20, the external terminal member 172 also includes an external flange portion 172C which bears against the inwardly projecting flange portion 36B of the lower end fitting 3 6. The electrically conducting path thus formed extends from the lower contact 150 through the inwardly projecting flange portion 172A of the external terminal 172 and through the externally projecting flange portion 172C to the inwardly projecting flange portion 36C of the lower end fitting 36. The area of the current transfer path between the external terminal member 172 of the renewable unit 20 and the lower end fitting may also be augmented by the contact ring 195 which may be formed of electrically conducting material and which is disposed to threadedly engage the internally threaded opening at the lower end of the end fitting .36 and bear against the external terminal member 172 of the renewal unit 20, as shown in FIG. 2.

It is important to note that in order to prevent the concentration of relatively high potential stresses adjacent to the external terminal member 172 during an interrupting operation of the fuse unit at relatively high voltages, the upper end of the lower contact extends axially beyond the upper end of the external terminal member 172 toward the other end of the tube 108 a minimum distance to prevent such a concentration of relatively high potential stresses externally of the tube 108 adjacent to the external terminal member 172, as disclosed in greater detail in copending application Ser. No. 663,029, filed Aug. 24, 1967, by F. L. Cameron.

In order to actuate the axial movement of the conducting rod 83 as well as that of the auxiliary conductor 182 during an interrupting operation of the fuse unit 100 and to electrically connect the renewable or refillable unit 20 just described to the upper end fitting or terminal 34, a spring and cable assembly 30* is disposed inside the outer tube 32 between the renewal unit 20 and the upper end fitting 34, as disclosed and claimed in copending application Ser. No. 663,021, filed Aug. 24, 1967 by C. C. Patterson which is assigned to the same assignee as the present application. The spring and cable assembly 30 includes at its lower end a generally tubular con ducting member or socket 84 having an internally threaded central opening, as indicated at 84A, to receive the upper threaded end 83A of the conducting rod 83. A lower spring seat member 86 is fixedly mounted on the socket 84 for movement therewith by assembling the spring seat 86 over the outer periphery of the socket 84 with the lower end of the spring seat 86 bearing against a shoulder provided on the outer periphery of the socket 84 and with the upper end of the spring seat 86 being engaged by a plurality of portions of the socket 84 at the upper end of the socket 84 which serve to stake or secure the spring seat 86 on the socket 84. The spring and cable assembly 30 also includes an upper spring seat 74 which is slidably disposed over the lower portion 60A of a generally cylindrical conducting member 60 whose integral upper portion 60B extends axially through an opening 34B in the upper end fitting 34 and is externally threaded at the upper end thereof, as indicated at 60C. As illustrated, the generally cylindrical conducting member 60 may be secured to the upper end fitting 34 by an internally threaded end cap 44 which may be screwed down on the upper threaded portion 60C of the conducting member 60 until the flange portion 44A of the end cap 44 bears against the upper end fitting 34 around a flange or shoulder portion, as indicated at 34C in FIG. 2. A helical tension spring 76 is secured at its upper end to the external, helically threaded portion of the upper spring seat 74, while the lower end of the spring 76 is secured to the external, helically threaded portion of the lower spring seat 86 to bias the conducting rod 83, as well as the auxiliary conductor 182, in a generally upward direction, as viewed in FIG. 2, away from the lower contact 150. It is important to note that the turns of the spring 76 are generally rectangular or square in cross-section to substantially prevent any overlapping of the turns 76 and the consequent damage of the spring 76 that might otherwise result during an interrupting operation of the fuse unit 100 as explained in greater detail in copending application Ser. No. 663,021, just mentioned.

In order to electrically connect the renewable unit and more specifically the conducting rod 83 to the upper end fitting 34 both prior to and during an interrupting operation of the fuse unit 100, a plurality of helically coiled flexible cables or conductors 82 are electrically and structurally connected at the bottom ends thereof to the conducting socket 84 into separate openings (not shown) provided in the socket 84 by suitable means, such as brazing or by staking, and at the upper ends thereof are secured to the conducting member 60 in separate openings provided in the conducting member 60 by suitable means, such as brazing or staking. In order to increase the effective current transfer area between the conducting member 60 and the upper end fitting 34, a washer 54 formed of electrically conducting material may be disposed between the shoulder which is formed at the intersection of the upper and lower portions 60A and 60B, respectively, of the conducting member 60 and the shoulder which is formed inside the upper end fitting 34, as indicated at 34D around the central opening 34B.

In order to facilitate the assembly of the renewal unit 20 and the associated spring and cable assembly inside the outer holder 32 as will be explained hereinafter, a pair of spring pins 58 may be disposed in associated openings provided at the opposite sides of the upper portion 60B of the conducting member 60 to be positioned finally within an enlarged central opening or recess 34E in the upper end fitting 34, as shown in FIG. 2.

In order to actuate the release of the latching assembly 250 shown in FIG. 1 following an interrupting operation by the fuse unit 100, as disclosed and claimed in copending application Ser. No. 663,021, previously mentioned, a tripping rod or member 52 is slidably disposed inside a central opening or passageway 72 which is provided in the conducting member 60 with the upper end of the tripping rod 52 being normally positioned below the top of the end cap 44, as shown in FIG. 2. The lower end of the tripping rod 52 is fixedly coupled to the upper spring seat 74 for axial movement therewith by the cross pin 56 which passes laterally through aligned transverse openings in the tripping rod 52 and the upper spring seat 74 and through a pair of elongated slots 62 provided at the opposite sides of the conducting member 60 with the cross pin 56 being normally positioned at the lower end of the slots 62, as shown in FIG. 2. In order to permit the axial movement of the tripping rod 52 upwardly through the end cap 44 following an interrupting operation of the fuse unit 100, the top of the end cap 44 includes a central opening 46 through which the tripping rod 52 may pass to actuate the release of the latching assembly 250 shown in FIG. 1. When the latching assembly 250 is released by the movement of the tripping rod 52, the upper end of the fuse unit will be actuated to rotate in a clockwise direction, as Viewed in FIG. 1, about the lower hinge assembly 260 to thereby provide an electrically insulating gap between the upper break contact 252 and the lower stationary hinge contact 62 by such drop-out action.

In order to assemble the renewable unit 20 and the associated spring and cable assembly 30 into the outer holder 32, the threaded end of the conducting rod 83 is first screwed into the socket 84 at the lower end of the spring and cable assembly 30-. A refill fusing tool (not shown) is then screwed into the internally threaded central opening or passageway 72 at the other end of the spring and cable assembly 30. The spring and cable assembly 30 is then inserted into the outer holder 32 with the upper end of the spring and cable assembly 30 being inserted first into the lower end of the outer holder 32, as viewed in FIG. 2, until the refill tool (not shown) passes through the central opening 34B of the upper end fitting 34. By use of the refill tool, the spring 76 is stretched and placed in tension until the cross pins 58 mounted at the sides of the conducting member 60 are drawn upwardly through a pair of radial slots (not shown) provided in the upper end fitting 34 around the central opening 34B. The upper conducting member 60 and the spring and cable assembly 30 are then rotated until the pins 58 rest on the shoulder provided at the bottom of the enlarged opening 34E in the upper end fitting 34. The end cap 44 may then be screwed down on the upper threaded portion 68C of the conducting member 63 to further stretch the spring 76 to the final condition or position shown in FIG. 2 in which the cross pins 58 are drawn upwardly away from the shoulder in the upper end fitting 34 at the bottom of the enlarged opening 34E. It is to be noted that when the spring and cable assembly 36 and the renewable unit 26 are assembled inside the outer holder 32, as just described, the cross pin 56 which couples the upper spring seat 74 to th tripping rod 52 is disposed at the bottom of the slots 62 at the op posite sides of the conducting member 60 to permit limited upward travel of the upper spring seat 74 along with the cross pin 56 and the tripping rod 52 to a final position of the tripping rod 52 in which the tripping rod 52 projects beyond the end cap 44 axially to release the latching assembly 250 as previously mentioned. The washer 54 also acts as a stop surface against which the upper end of the spring seat 74 bears to limit the upward travel of the tripping rod 52, the cross pin 56 and the spring seat 74.

In considering the operation of the fuse unit 100, it is to be noted first that the current paths which include, respectively, the strain element 162, the fusible element 164 and the helical wire 194, which are connected in series with the auxiliary conductor 182, are all electrically connected in parallel between the upper end of the conducting rod 83 and the lower contact at the lower end of the renewable unit 20. The resistance of the current path which includes the fusible element 164 and which is calibrated to have predetermined time-current characteristics is arranged to be relatively much less than the resistance of either the path which includes the strain element 162 or the path which includes the helical wire 194 so that normally most of the current which fiows through the fuse unit 100 is carried by the fusible element 164. Although the resistance of the current path which includes the strain element 162 is relatively greater than the resistance of the path which includes the fusible member 164, the resistance of the path which includes the strain element 162 is relatively less than that of the path which includes the helical wire 194 so that when the fusible element 164 melts or blows, most of the current which was formerly carried by the fusible element 164 is then transferred to the strain element 162. In other words, when the current which is flowing through the unit 100 increases to a value which is of sufiicient magnitude and duration to melt or blow the fuse element 164, most of the current which is flowing through the fuse unit 100 then transfers to the strain element 162. When the current which is transferred to the strain element 162 after the melting of the fusible element 164 is :sufiicient to melt or blow the strain element 162, the current which was previously carried by the strain element 162 is finally transferred to the current path through the auxiliary bore 192 which includes the auxiliary conductor 182 and the helical wire 194. No arcing occurs as these elements melt because of the parallel electrical path through the helical wire. When the strain element 162 melts or blows, the conducting rod 83 is no longer restrained from upward movement under the influence of the biasing spring 76 and the conducting rod 83 and the auxiliary conductor 182 will start to move upwardly under the influence of the spring 76 to thereby stretch the helical wire .194 which is electrically connected to the bottom of the auxiliary conductor 182. It is to be noted that the stretching of the [helical wire 194 permits limited travel of both the conducting rod 83 and the auxiliary conductor 182 while maintaining a continuous electrical circuit through the auxiliary bore 192 and that as long as the current path which includes the auxiliary conductor 182 and the helical wire 194 is intact, no arcing will take place in either the main bore 130 or in the auxiliary bore 192. In other words, the stretching of the helical wire 194 during the initial movement of the conducting rod 83 and the auxiliary conductor 182 following the melting or blowing of the fusible element 164 and the strain element 162 will permit the formation of an electrically insulating gap in the main bore 130, while initially maintaining a conducting path and delaying the formation of an insulating gap in the auxiliary bore 192.

After the strain element 162 melts or blows as just described, and the conducting rod 83 and the auxiliary conductor 182 begin to move upwardly to thereby stretch the helical wire 194, the helical wire 194 will either fracture mechanically when stretched to its limit or the current transferred to the current path which includes the auxiliary conductor 182 and the helical wire 194 will be sufficient to melt or blow the helical wire 194 which is of reduced cross-section compared with that of the auxiliary conductor or rod 182. After the helical wire 194 is melted or otherwise broken, an arc will be initiated between the retreating end of either the broken helical wire 194 or the auxiliary conductor 182 and the arcing terminal .158 which axially overlaps the lower end of the auxiliary conductor 182 to thereby burn through the electrical insulation on the arcing terminal 158. Even after the wire 194 melts or is broken, the formation of the significant electrically insulating gap in the auxiliary bore 192 is further delayed by the overlapping of the auxiliary conductor 182 by the arcing terminal 158 until the retreating free end of either the wire 194 or the conductor 182 passes the upper end of the arcing terminal 158 whose insulation will have burned through by this time. It is important to note that the insulating gap in the main bore 130 between the separated ends of the conducting parts will increase at a faster rate than the formation of an insulating gap in the auxiliary bore 192 due to both the delay in the formation of an arc in the auxiliary bore 192 because of the presence of the helical wire 194 and due'to the overlapping of the auxiliary conductor 182 by the arcing terminal 158. It is also important to note that the arcing which takes place in the fuse unit during an interrupting operation will always take place initially in the auxiliary bore 192, as just explained. When the retreating end of either the helical wire 194 or the auxiliary conductor 182 passes the upper end of the arcing terminal 158, the arcing which takes place initially in the auxiliary bore 192 will cause gases to be evolved from the gas evolving material around the auxiliary bore 192 which will be un-ionized.

When the current to be interrupted by the fuse unit 100 is relatively low, such as 1000 amperes or less, and when the gas pressure of the evolved gases in the auxiliary bore 19 2 increases to thereby increase the dielectric strength in the auxiliary bore .192, the insulating gap which is formed in the auxiliary bore 192, along with the corresponding increased dielectric strength, will be sufficient to interrupt the alternating current following a particular current zero in the auxiliary bore 192. The insulating gap which is formed simultaneously in the main gap 132 of the fuse unit 100 at a relatively faster rate will have sufficient dielectric strength considering the instantaneous potential dilference between the separating conducting parts in the main bore of the fuse unit 100 to prevent a restrike of the arc in the main bore 130 for such relatively low fault currents. In other words, when any fault current is interrupted by the fuse unit 100, as just described, arcing will always be initiated in the auxiliary bore 192 and for relatively small fault currents, the arcing which results will be finally interrupted in the auxiliary bore 192. One important reason for this is that the relative dielectric strength of the main bore 130 at the time that the arc is finally interrupted in the auxiliary bore 192 will be relatively higher than that in the auxiliary bore 192 to prevent a restrike or breakdown of the main bore 130 due to the potential difference which results between the separated conducting parts in the main bore 130.

For relatively higher fault currents, the arcing which is initiated in the fuse unit 100 will still be initiated in the auxiliary bore 192 in the manner just described. For such relatively higher current faults however, the gas pressure which builds up in the auxiliary bore 192 during an interrupting operation and the burning back of the separated conducting parts in the auxiliary bore 192 will result in a relatively higher dielectric strength in the auxiliary bore 192 compared with that in the main bore 130 between the separated conducting parts in the main bore 130. If the instantaneous potential difference between the separated ends of the conducting parts in the main bore 130 is sufficient when the dielectric strength of the main bore 130 becomes relatively less than that of the auxiliary bore 192, the arc will restrike in the main bore 130 to thereby cause the evolution of un-ionized gases in the main bore 130 to thereby increase the gas pressure in the main bore 130, as well as the corresponding dielectric strength in the main bore 130. The are which restrikes in the main bore 130 will be elongated both by the upward movement of the conducting rod 83 and by the burning back of the separated conducting parts in the main bore to thereby increase the quantity of un-ionized gases evolved from the gas evolving material around the main bore 130. The are in the main bore 130 will be finally interrupted following a particular current zero in the alternating current which is being interrupted when the insulating gap and the corresponding dielectric strength in the main bore 130 is sufiicient to withstand the instantaneous potential difference between the separated conducting parts in the main bore 130. If the fault current which is being interrupted is of a relatively still higher magnitude, the gas pressure in the main bore 130 along with the intense heat which results may be sufficient to disintegrate the innerwalls of the blocks 126 and-128 to thereby limit the gas pressure of the evolved gases to a value within the rupture strength of the tube 108,- as previously explained. It is to be noted that when the arc is interrupted in the main bore 130, as just described, to thereby cause the evolution of gas from the gas evolving material in the

blocks

122, 124, 126 and 128 which surround the main'bore 130, the upward movement of the conducting rod 83 along with the upward movement of the auxiliary conductor 182 will be additionally accelerated by the force of the gas pressure of such evolved gases in the main bore 130 along with the force exerted on the conducting rod 83 by the biasing force of the spring 76.

During an interrupting operation of the fuse unit 100 as just described, when the conducting rod 83 is released and moved upwardly under the influence of the spring 76 or under the influence of both the spring 76 and the gas pressure of the evolved gases inside the renewable unit 20, the turns of the spring 76 which are normally held in tension will partially collapse toward a compressed condition but after the turns of the spring 76 collapse to a certain extent, the upper spring seat 74 will slide axially on the lower portion of the conducting member 60 until the upper end of the spring seat 74 impacts or bears against the washer 54 to thereby drive or actuate the tripping rod 52 in an upward direction, as viewed in FIG. 2. The tripping rod 52 will be actuated from the position shown in FIG. 2 until the upper end of the tripping rod actuates the release of the latching means 250, as described in the copending application previously mentioned in US. Patent No. 2,403,121 which issued July 2, 1946 to H. L. Rawlins et a1. It is to be noted that the upward movement of the conducting rod 83 and the auxiliary conductor 182 will establish the insulating gaps previously described between the separated ends of the conducting parts inside the renewable unit 20 following an interrupting operation. In addition, the fuse unit 100 will be actuated by the release of the latching means 250 by the tripping rod '52 to rotate in a clockwise direction about the lower hinge assembly 260 in a drop-out movement to establish a larger insulating gap between the break contact 252 and the lower stationary hinge contact 262 of the fuse structure 10.

It is important to note that during an interrupting operation of the fuse unit, as previously described, for either relatively low fault currents or for relatively high currents, the gas seal and joint structure between the

successive blocks

122, 124, 126 and 128 as previously disclosed substantially prevents the escape of ionized gas from the auxiliary bore 192 in which all arcing initially takes place to the main bore 130 along the meeting surfaces of the successive blocks in the renewable unit 20. As previously mentioned, if such ionized gases were permitted to escape into the main bore 130, a restrike might result when the fuse unit 100 is called upon to interrupt relatively low fault currents and the restrike of an arc in the main bore would result in an arcing condition which the fuse unit 100 is incapable of interrupting for relatively low fault currents. This is because for relatively low fault currents, the quantity of gas evolved in the main bore 130 is not sufficient to establish a dielectric strength in the main bore 130 which will be great enough to interrupt the are which results in the main bore 130.

It is to be understood that the teachings of the applicants invention may be applied to power fuses for high voltage applications which are not of the drop-out type as disclosed in copending application Ser. No. 663,021, filed Aug. 24, 1967 by C. C. Patterson which is assigned to the same assignee as the present application. It is also to be understood that the teachings of the applicants invention may be applied to power fuses for high voltage applications which do not include a tubular conducting member or shield, such as the lower contact shown in FIG. 2, but which instead employ a lower contact ring of the type disclosed in copending application Ser. No. 663,127, previously mentioned.

The apparatus embodying the teachings of this invention have several advantages. For example, the joints between the plurality of blocks which make up the body of arc-extinguishing or gas-evolving material in a circuit interrupter as disclosed are sealed to prevent the escape or travel of ionized gases from the auxiliary bore to the main bore which might cause a restrike of the arc in the main bore which the circuit interrupter is incapable of interrupting. In addition, the disclosed construction provides mechanical reenforcement of the gas evolving blocks at the joints around the auxiliary bore which extends through said blocks. A further advantage of the disclosed joint construction is that the joint provides improved dielectric strength between the adjacent blocks of gas evolving mate rial around the auxiliary bore even though the edges of the blocks may be chipped or damaged during the assembly of the blocks in the manufacture of the overall circuit interrupter. A final advantage of the disclosed construction is that a positive seal is provided in the joints between the adjacent blocks and a circuit interrupter is disclosed while preventing the sealing and bonding material from entering either the main bore or the auxiliary bore which might adversely affect the gas evolving properties of the blocks during an interrupting operation of the circuit interrupter.

Since numerous changes may be made in the above described apparatus, dilferent embodiments of the invention may be made without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim as our invention:

1. A circuit interrupter comprising a tubular insulating casing, a body of gas evolving, arc-extinguishing material disposed inside of and spaced from the ends of the casing and including a plurality of generally cylindrical blocks stacked axially in end-to-end relation, each of said blocks having a relatively larger opening and a relatively smaller opening extending axially therethrough with the larger openings and the smaller openings, respectively, of the successive blocks being substantially aligned to form a large bore and a small bore, respectively, through the body of arc extinguishing material, separable conducting means between which an arc is drawn during an interrupting operation of the circuit interrupter and interrupted in the small bore for smaller currents and in the large bore for larger currents, the meeting ends of each of said blocks each including a recess extending around and spaced from the smaller opening of each block with the ends of each recess extending to openings at the outer periphery of the associated block and with the recesses in the meeting ends of adjacent blocks being substantially congruent, and an electrically insulating, thermosetting, bonding material substantially filling the passageway formed by each pair of recesses at the meeting ends of adjacent blocks to substantially prevent the travel of gases between the main bore and the auxiliary bore.

2. The combination as claimed in claim 1 wherein the electrically insulating, thermosetting bonding material includes an epoxy resin.

3. The combination as claimed in claim 1 wherein one or more of the blocks includes a generally C-shaped recess which extends axially from one of the blocks to a point which is spaced axially from the other end of the block with the smaller opening of the block being disposed between the peripheral ends of the recess.

4. The combination as claimed in claim 3 wherein the electrically insulating, thermosetting bonding material includes an epoxy resin.

5. The combination as claimed in claim 1 wherein the separable conducting means between which an arc is drawn includes a fusible conducting member and additional means is provided for actuating the separable conducting means to separate upon the fusing of the fusible conducting means.

6. The combination as claimed in claim 5 wherein the electrically insulating, thermosetting bonding material includes an epoxy resin.

. 1 16 References Cited UNITED STATES PATENTS 2,077,276 4/1937 Slepian 200-120 XR' 2,183,728 12/ 1939 Triplett 200-120 XR 2,976,381 3/ 1961 Lindell 200-120 2,599,186 6/1952 Lindell 200120 XR BERNARD A. GILHEANY, Primary Examiner.

H. B. GILSON, Assistant Examiner.