High-voltage fuse having a plurality of helically wound ribbon fuse links

Claim 2

A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs; c. a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of serially related points of reduced crosssectional area, said ribbons forming a plurality of helical extension-springlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch and having when in unloaded condition an axial length substantially less than said axial spacing between said axially inner end surfaces of said pair of plugs, each of said plurality of windings having axially outer overcenter ends affixed to said axially inner surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway and being axially stretched to such a degree as to be self-supporting and having an extended length approximately equal to said axial spacing between said axially inner end surfaces of plugs; and d. a body of pulverulent arc-quenching filler inside said casing submersing each of said plurality of windings, being in immediate physical engagement with each of said plurality of windings, and being the only lateral support of each of said plurality of windings.

Claim 3

A current-limiting high-voltage fuse as specified in claim 1 including at least six helical extension-springlike windings having equal angular spacings.

Claim 4

A current-limiting high-voltage fuse as specified in claim 2 wherein said windings are stretched to such an extent that the deflection per turn exceeds the diameter thereof.

Claim 5

A current-limiting high-voltage fuse as specified in claim 1 wherein the spacing between contiguous turns of said plurality of windings ranges from near zero to one thirty-secondth of an inch in the nonloaded and unstretched condition thereof.

Claim 6

A current-limiting high-voltage fuse as specified in claim 3 wherein the deflection per turn is about twice the diameter thereof.

Claim 7

A current-limiting high-voltage fuse as specified in claim 1 wherein said plurality of serially related points of reduced cross-sectional area is formed by a plurality of serially related circular perforations arranged along the centerline of said ribbons, and wherein the longitudinal edges of said ribbons are uninterrupted by notches.

Claim 8

A current-limiting high-voltage fuse as spEcified in claim 1 wherein each of said plurality of windings is formed by a pair of coaxial winding sections each having axially inner spaced overcenter ends conductively interconnected by a substantially straight fusible conductor means.

Claim 9

A current-limiting high-voltage fuse as specified in claim 8 wherein said straight fusible conductor means is formed by a length of round silver wire spotwelded at the axially outer end thereof to said axially inner spaced overcenter ends of one pair of coaxial winding sections.

Claim 10

A current-limiting fuse as specified in claim 8 wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged at each end of said length of round silver wire to form double breaks at the occurrence of overloads of inadmissible duration.

Claim 11

A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs; c. A plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of circular perforations arranged along the centerline thereof, the longitudinal edges of said ribbons being uninterrupted by notches, said ribbons forming a plurality of helical extension-springlike windings having a diameter less than one-half of an inch and having when in unloaded condition a length less than said axial spacing between said axially inner end surfaces of said pair of plugs, said plurality of windings having axially outer overcenter ends affixed to said axially inner end surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway, said plurality of windings being axially stretched to such a degree as to be self-supporting, having an extended length approximately equal to said axial spacing between said axially inner end surfaces of said pair of plugs and having a deflection per turn exceeding the diameter of each of said plurality of windings; and e. a body of quartz sand inside said casing submersing each of said plurality of windings, being in immediate physical engagement with each of said plurality of windings, being composed of particles ranging from 20 to 70 U.S. Standard Sieve Number, and being the only lateral support of each of said plurality of windings between said axially outer overcenter ends thereof.

Claim 12

A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs; c. A plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of circular perforations arranged along the centerline thereof, the longitudinal edges of said ribbons being uninterrupted by notches, said ribbons forming a plurality of helical extension-springlike windings having a diameter less than one-half of an inch and having when in unloaded condition a length less than said axial spacing between said axially inner end surfaces of said pair of plugs, said plurality of windings having axially outer overcenter ends affixed to said axially inner end surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway, said plurality of windings being axially stretched to such a degree as to be self-supporting, having an extended length approximately equal to said axial spacing between said axially inner end surfaces of said pair of plugs and having a deflection per turn exceeding the diameter of each of said plurality of windings; and e. a body of quartz sand inside said casing submersing each of said plurality of windings, being in immediate physical engagement with each of said plurality of windings, being composed of particles ranging from 20 to 70 U.S. Standard Sieve Number, and being the only lateral support of each of said plurality of windings between said axially outer overcenter ends thereof.

Claim 13

A current-limiting high-voltage fuse as specified in claim 10 including at least six extension-springlike windings having equal angular springs.

Claim 14

A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of terminal elements having a predetermined axial spacing closing the ends of said casing; c. a plurality of pairs of coaxial helically wound ribbon fuse links inside said casing forming at least six pairs of coaxial helical extension-springlike windings arranged parallel to the axis of said casing and forming a cylindrical pattern coaxial with said casing, the constituent ribbon fuse links of said pairs of windings being of relatively hard resilient sheet silver and of rectangular cross section and having circular perforations arranged along the centerlines thereof, the longitudinal edges of said ribbon fuse link being uninterrupted by notching, each of said pairs of windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch, and each of said pairs of windings having axially outer overcenter ends affixed to one of said pair of terminal elements, and each of said pairs of windings having axially inner ends, a pluRality of fusible conductor means of silver, each of said plurality of fusible conductor means conductively interconnecting said axially inner ends of one pair of said pairs of windings, and each of said plurality of fusible conductor means having a shorter axial length than each winding of said pairs of windings, each of said plurality of fusible conductor means having a sufficiently small cross-sectional area to generate when carrying current larger amount of heat per unit of length than the same unit of length of said ribbon fuse links when carrying the same current, each pair of said pairs of windings having when in unloaded condition an aggregate length less than the difference of said predetermined axial spacing between said pair of terminal elements and the axial length of each of said plurality of fusible conductor means, each of said pairs of windings being axially stretched to such an extent as to be self-supporting, to have a deflection per turn exceeding the diameter thereof and to have an extended length substantially equal to the difference of said axial spacing between said pair of terminal elements and said axial length of each of said plurality of fusible conductor means; and d. A body of pulverulent arc-quenching filler inside said casing submersing said pairs of windings and said plurality of conductor means, being in immediate physical engagement with said pairs of windings and said plurality of fusible conductor means and being the only lateral support provided for said pairs of windings and said plurality of conductor means inside all of the space bounded by said casing and said pair of terminal elements.

Claim 15

A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of terminal elements having a predetermined axial spacing closing the ends of said casing; c. a plurality of pairs of coaxial helically wound ribbon fuse links inside said casing forming at least six pairs of coaxial helical extension-springlike windings arranged parallel to the axis of said casing and forming a cylindrical pattern coaxial with said casing, the constituent ribbon fuse links of said pairs of windings being of relatively hard resilient sheet silver and of rectangular cross section and having circular perforations arranged along the centerlines thereof, the longitudinal edges of said ribbon fuse link being uninterrupted by notching, each of said pairs of windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch, and each of said pairs of windings having axially outer overcenter ends affixed to one of said pair of terminal elements, and each of said pairs of windings having axially inner ends, a pluRality of fusible conductor means of silver, each of said plurality of fusible conductor means conductively interconnecting said axially inner ends of one pair of said pairs of windings, and each of said plurality of fusible conductor means having a shorter axial length than each winding of said pairs of windings, each of said plurality of fusible conductor means having a sufficiently small cross-sectional area to generate when carrying current larger amount of heat per unit of length than the same unit of length of said ribbon fuse links when carrying the same current, each pair of said pairs of windings having when in unloaded condition an aggregate length less than the difference of said predetermined axial spacing between said pair of terminal elements and the axial length of each of said plurality of fusible conductor means, each of said pairs of windings being axially stretched to such an extent as to be self-supporting, to have a deflection per turn exceeding the diameter thereof and to have an extended length substantially equal to the difference of said axial spacing between said pair of terminal elements and said axial length of each of said plurality of fusible conductor means; and d. A body of pulverulent arc-quenching filler inside said casing submersing said pairs of windings and said plurality of conductor means, being in immediate physical engagement with said pairs of windings and said plurality of fusible conductor means and being the only lateral support provided for said pairs of windings and said plurality of conductor means inside all of the space bounded by said casing and said pair of terminal elements.

Claim 16

A current-limiting high-voltage fuse as specified in claim 12 wherein said pairs of windings have equal angular spacings.

Claim 17

A current-limiting high-voltage fuse as specified in claim 12 wherein said pair of terminal elements is formed by a pair of terminal plugs inserted into the ends of said casing, wherein each of said pair of terminal plugs is provided with an axially outer cylindrical coaxial projection of reduced diameter, and wherein one of said pair of terminal plugs and said projection thereof jointly define a passageway substantially coaxial with said cylindrical pattern.

Claim 18

A current-limiting high-voltage fuse as specified in claim 12 wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent one of the ends of each of said plurality of fusible conductor means, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes other pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

Claim 19

A current-limiting high-voltage fuse as specified in claim 12 wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the axially outer ends of each of said plurality of fusible conductor means, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

Claim 20

A current-limiting high-voltage fuse as specified in claim 12 wherein each of said plurality of fusible conductor means is formed by one of a plurality of straight lengths of round silver wire each spot-welded to said axially inner ends of one pair of said pairs of windings and arranged over the center of said one pair of said pairs of windings, wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the spot-welds attaching one of said lengths of silver wire to said axially inner ends of one pair of said pairs of windings, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

Claim 21

A current-limiting high-voltage fuse as specified in claim 12 wherein each of said plurality of fusible conductor means is formed by one of a plurality of straight lengths of round silver wire spot-welded to said axially inner ends of one pair of said pairs of windings and arranged in a common plane extending diametrically across the center of said one pair of said pairs of windings, wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the axially outer ends of each of said plurality of lengths of silver wire, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes other pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

Claim 22

A current-limiting high-voltage fuse as specified in claim 12 wherein each of said plurality of fusible conductor means is formed by one of a plurality of helically wound lengths of round silver wire mounted on an insulating core and having ends conductively connected to said axially inner ends of one pair of said pairs of windings, wherein said insulating core of each of said plurality of helically wound lengths of silver wire is affixed to said axially inner ends of one pair of said pairs of windings, wherein a silver-severing overlay of a metal having a lower fusing point than silver is arranged adjacent each of the axially outer ends of one of said plurality of helically wound lengths of round silver wire, and wherein said pulverulent arc-quenching filler is a body of quartz sand and excludes other pulverulent arc-quenching filler means having a smaller heat conductivity than quartz sand.

Claim 23

A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing, said pair of terminal plugs having axially inner end surfaces having a predetermined spacing, one of said pair of terminal plugs defining a passageway substantially parallel to the common axis of said casing and said pair of terminal plugs; c. A plurality of fusible elements inside said casing conductively interconnecting said pair of terminal plugs, each of said plurality of fusible elements including a pair of axially outer sections having serially related relatively short points of reduced cross-sectional area and an axially inner section conductively interconnecting the axially inner ends of said pair of axially outer sections and establishing a region of reduced cross-sectional area of considerable greater length than the length of each of said relatively short points of reduced cross-sectional area, said axially outer sections being formed by coaxial pairs of extension-springlike windings of ribbons of relatively hard sheet silver rectangular in cross section having circular perforations along the centerlines thereof forming said relatively short points of reduced cross-sectional area, the longitudinal edges of said ribbons being uninterrupted by notching, each of said coaxial pairs of windings having a diameter ranging from less then three-sixteenths of an inch to about one-half of an inch and being arranged in a cylindrical pattern around the axis of said passageway defined by said one of said terminal plugs, each pair of said pairs of windings having when in unloaded condition a shorter aggregate length than the difference of said spacing between said axially inner end surfaces of said pair of terminal plugs and the axial length of said axially inner section of each of said plurality of fusible elements, and each of said pairs of windings being stretched to such an extent as to be self-supporting, to cause the deflection per turn to exceed the diameter thereof and to have an aggregate length substantially equal to the difference of said spacing between said axially inner end surfaces of said pair of terminal plugs and the length of said axially inner section of each of said plurality of fusible elements; d. a plurality of pairs of silver-severing overlays of a metal having a lower fusing point than silver, each pair of overlays being arranged adjacEnt the axially inner ends of one of said pairs of windings to establish two breaks in series upon fusion of each pair of said plurality of pairs of overlays; and e. a body of pulverulent arc-quenching filler inside said casing submersing said pairs of windings and said axially inner section of each of said plurality of fusible elements and being in immediate physical engagement with said pairs of windings and said axially inner section of each of said plurality of fusible elements, and said body of pulverulent arc-quenching filler being the only lateral support provided for said pairs of windings and said axially inner section of each of said plurality of fusible elements inside of all of the space bounded by said casing and said pair of terminal plugs.

Claim 24

A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing, said pair of terminal plugs having axially inner end surfaces having a predetermined spacing, one of said pair of terminal plugs defining a passageway substantially parallel to the common axis of said casing and said pair of terminal plugs; c. A plurality of fusible elements inside said casing conductively interconnecting said pair of terminal plugs, each of said plurality of fusible elements including a pair of axially outer sections having serially related relatively short points of reduced cross-sectional area and an axially inner section conductively interconnecting the axially inner ends of said pair of axially outer sections and establishing a region of reduced cross-sectional area of considerable greater length than the length of each of said relatively short points of reduced cross-sectional area, said axially outer sections being formed by coaxial pairs of extension-springlike windings of ribbons of relatively hard sheet silver rectangular in cross section having circular perforations along the centerlines thereof forming said relatively short points of reduced cross-sectional area, the longitudinal edges of said ribbons being uninterrupted by notching, each of said coaxial pairs of windings having a diameter ranging from less then three-sixteenths of an inch to about one-half of an inch and being arranged in a cylindrical pattern around the axis of said passageway defined by said one of said terminal plugs, each pair of said pairs of windings having when in unloaded condition a shorter aggregate length than the difference of said spacing between said axially inner end surfaces of said pair of terminal plugs and the axial length of said axially inner section of each of said plurality of fusible elements, and each of said pairs of windings being stretched to such an extent as to be self-supporting, to cause the deflection per turn to exceed the diameter thereof and to have an aggregate length substantially equal to the difference of said spacing between said axially inner end surfaces of said pair of terminal plugs and the length of said axially inner section of each of said plurality of fusible elements; d. a plurality of pairs of silver-severing overlays of a metal having a lower fusing point than silver, each pair of overlays being arranged adjacEnt the axially inner ends of one of said pairs of windings to establish two breaks in series upon fusion of each pair of said plurality of pairs of overlays; and e. a body of pulverulent arc-quenching filler inside said casing submersing said pairs of windings and said axially inner section of each of said plurality of fusible elements and being in immediate physical engagement with said pairs of windings and said axially inner section of each of said plurality of fusible elements, and said body of pulverulent arc-quenching filler being the only lateral support provided for said pairs of windings and said axially inner section of each of said plurality of fusible elements inside of all of the space bounded by said casing and said pair of terminal plugs.

Claim 25

A current-limiting high-voltage fuse as specified in claim 20 including at least six coaxial pairs of windings having equal angular spacings.

Claim 26

A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing, said pair of plugs having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs; c. a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver rectangular in cross section each having a plurality of serially related points of reduced cross-sectional area, said ribbons forming helical extension-springlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch, having axially outer overcenter ends and having when in unloaded condition a length substantially less than said axial spacing between said axially inner end surfaces of said pair of fuses, said windings being arranged in a cylindrical pattern around said passageway defined by said one of said pair of plugs, and said windings being stretched to such an extent that said axially outer overcenter ends thereof are coextensive with said axially inner end surfaces of said pair of plugs; d. a plurality of screws having shanks parallel to the common axis of plugs screwed into said axially inner end surfaces of said pair of plugs to clamp said axially outer overcenter ends of said windings against said axially inner end surfaces of said pair of plugs; e. a plurality of solder joints adjacent said plurality of screws conductively connecting said axially outer overcenter ends of said windings to said axially inner end surfaces of said pair of plugs and securing said plurality of screws in the position thereof; and f. a body of pulverulent arc-quenching filler inside said casing submersing said plurality of fusible elements.

Claim 27

A current-limiting high-voltage fuse including: a. a tubular casing of insulating material; b. a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing, said pair of plugs having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs; c. a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver rectangular in cross section each having a plurality of serially related points of reduced cross-sectional area, said ribbons forming helical extension-springlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch, having axially outer overcenter ends and having when in unloaded condition a length substantially less than said axial spacing between said axially inner end surfaces of said pair of fuses, said windings being arranged in a cylindrical pattern around said passageway defined by said one of said pair of plugs, and said windings being stretched to such an extent that said axially outer overcenter ends thereof are coextensive with said axially inner end surfaces of said pair of plugs; d. a plurality of screws having shanks parallel to the common axis of plugs screwed into said axially inner end surfaces of said pair of plugs to clamp said axially outer overcenter ends of said windings against said axially inner end surfaces of said pair of plugs; e. a plurality of solder joints adjacent said plurality of screws conductively connecting said axially outer overcenter ends of said windings to said axially inner end surfaces of said pair of plugs and securing said plurality of screws in the position thereof; and f. a body of pulverulent arc-quenching filler inside said casing submersing said plurality of fusible elements.

Claim 28

A current-limiting high-voltage fuse as specified in claim 22 wherein the outer periphery of the heads of each of said plurality of screws intersects at right angles the axis of one of said helical windings.

Claim 29

An electric high-voltage fuse gear including: a. a tubular fuse-receiving structure having a predetermined inner diameter; b. a pullcover for closing one of the ends of said fuse-receiving structure, said pullover being provided with a pullhandle; c. a pair of fuse holders, one of said pair of fuse holders being arranged adjacent one of the ends of said fuse-receiving structure remote from said pullcover and affixed to said fuse-receiving structure, and the other of said pair of fuse holders being arranged inside said pullcover and affixed to said pullcover; and d. a high-voltage fuse arranged in said fuse-receiving structure, said fuse including a tubular casing of insulating material arranged in substantially coaxial relation inside of said fuse-receiving structure and having an outer diameter but slightly less than said inner diameter of said fuse-receiving structure, said high-voltage fuse further including a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs, a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of serially related points of reduced cross-sectional area, said ribbons forming helical extension-springlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch and having when in unloaded condition a length less than said axial spacing between said axially inner end surfaces of said pair of plugs, said windings have axially outer overcenter ends affixed to said axially inner end surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway defined by one of said pair of plugs and said winding being stretched to such a degree as to be self-supporting, to have an extended length approximately equal to said axial spacing between said axially inner end surfaces of said pair or plugs, and a body of pulverulent arc-quenching filler inside said casing submersing each of said windings, being in immediate physical engagement with each of said windings, and being the only lateral support of each of said windings.

Claim 30

An electric high-voltage fuse gear including: a. a tubular fuse-receiving structure having a predetermined inner diameter; b. a pullcover for closing one of the ends of said fuse-receiving structure, said pullover being provided with a pullhandle; c. a pair of fuse holders, one of said pair of fuse holders being arranged adjacent one of the ends of said fuse-receiving structure remote from said pullcover and affixed to said fuse-receiving structure, and the other of said pair of fuse holders being arranged inside said pullcover and affixed to said pullcover; and d. a high-voltage fuse arranged in said fuse-receiving structure, said fuse including a tubular casing of insulating material arranged in substantially coaxial relation inside of said fuse-receiving structure and having an outer diameter but slightly less than said inner diameter of said fuse-receiving structure, said high-voltage fuse further including a pair of cylindrical terminal plugs inserted into the ends of said casing and closing said casing and having axially inner end surfaces having a predetermined axial spacing, one of said pair of plugs defining a passageway extending substantially parallel to the common axis of said casing and said pair of plugs, a plurality of fusible elements inside said casing conductively interconnecting said pair of plugs, said plurality of fusible elements including ribbons of relatively hard resilient sheet silver of rectangular cross section each having a plurality of serially related points of reduced cross-sectional area, said ribbons forming helical extension-springlike windings having a diameter ranging from about three-sixteenths of an inch to about one-half of an inch and having when in unloaded condition a length less than said axial spacing between said axially inner end surfaces of said pair of plugs, said windings have axially outer overcenter ends affixed to said axially inner end surfaces of said pair of plugs and being arranged to form a cylindrical pattern around the axis of said passageway defined by one of said pair of plugs and said winding being stretched to such a degree as to be self-supporting, to have an extended length approximately equal to said axial spacing between said axially inner end surfaces of said pair or plugs, and a body of pulverulent arc-quenching filler inside said casing submersing each of said windings, being in immediate physical engagement with each of said windings, and being the only lateral support of each of said windings.