US3732517A

US3732517A - Protective fuse

Info

Publication number: US3732517A
Application number: US00198791A
Authority: US
Inventors: A Keto; J Astleford
Original assignee: Westinghouse Electric Corp
Current assignee: ABB Inc USA
Priority date: 1971-11-15
Filing date: 1971-11-15
Publication date: 1973-05-08
Anticipated expiration: 1990-05-08
Also published as: CA956678A

Abstract

A load break protective fuse assembly having arc snuffing means. The arc snuffing means seals the lower contact structure of the fuse assembly, when the fuse member is withdrawn, to prevent the escape of ionized gas into the fuse assembly casing. A deionizing chamber and a gate member having a hinged door thereon may be used in conjunction with the arc snuffing means.

Description

O United States Patent 11 1 1111 3,732,517 Keto et a1. 1 1 May 8, 1973 54 PROTECTIVE FUSE 1,951,297 3 1934 Von Normann ..200/151 [75] Inventors: August I. Keto, Sharon; John J. Ast- 266889l 2/1954 Dmischcr "200/151 X leford J Monroeville both of Pa 3,265,841 8/1966 Greber ..337/278X 2,663,825 12/1953 Amundson ..317/15 [73] Assignee: Westinghouse Electric Corporation, 3.297,848 l/l967 Picard et a1 ..200/l5l X Pittsburgh, Pa.

. Primary ExaminerRoy N. Envall, Jr. [22] Flled' 1971 Attorney-A. T. Stratton et a1. [21] App1.N0.: 198,791

[57] ABSTRACT [52] [1.8. CI. ..337/278, 200/151, 317/15, A load break protective fuse assembly having are 337/282 snuffing means. The are snuffing means seals the [51] Cl. lower t t structure f th f bly h th [58] Field Of SBBICII 200/151; fuse member is withdrawn to prevent the escape of 337/273 282 317/15 ionized gas into the fuse assembly casing. A deionizing chamber and a gate member having a hinged door [56] References Cited thereon may be used in conjunction with the arc UNITED STATES PATENTS Snuffing means.-

441,933 12/1890 Cartwright 337/278 13 Claims, 5 Drawing Figures PATENT m 8197 SHEET 1 OF 2 FIG.|

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates, in general, to protective fuses for electrical apparatus and, more specifically, to protective fuse assemblies having arc snuffing means.

2. Description of the Prior Art Protective fuses are used in power transformers to protect the apparatus from the effects of excessive currents. With the recent developments in pad mounted and submersible transformers, a need has arisen for a protective fuse assembly which can be replaced easily should it be necessary. As an extra convenience, such protective fuse assemblies usually provide a switching function which may de-energize the transformer while under load.

A load break device and current limiting fuse is described in US. Pat. No. 3,628,092, issued on Dec. 14, 1971, and assigned to the same assignee as this invention. While the protective fuse described therein has many advantages, the rating at which it may be satisfactorily operated is limited. Generally, the protective fuse described in the referenced patent is suitable for use with 95 kv BIL circuits such as a 167 kva maximum single phase circuit with the voltage to ground not exceeding 8,300 volts. Since many circuits are being established at higher levels, such as 125 kv BIL with a voltage to ground of 14,400 volts, a need exists for a protective fuse assembly operatable at this level.

Using the protective fuse assembly described in the referenced patent beyond its rated operating parameters produces unsatisfactory results. When the fuse holding device is being removed from its enclosure to de-energize the transformer, an arc develops between the probe and the contact structure it is disengaged from. If the rating of the protective fuse are not exceeded, the arc is extinguished by the arc extinguishing properties of the material attached to the end of the probe. However, when the ratings are exceeded, the ionized gas formed by the arcing is sufficient to cause the arc to persist when the probe is retracted from the contact structure. The persisting arc jumps to one of the terminals of the protective fuse assembly when the probe passes by that terminal, thus the transformer is not satisfactorily de-energized.

Therefore, it is desirable, and it is an object of this invention, to provide a protective fuse assembly which may be satisfactorily operated at higher ratings than prior art protective devices.

SUMMARY OF THE INVENTION There is disclosed herein new and useful protective fuse assemblies capable of safely interrupting larger loads than prior art fuse assemblies. The ionized gas is contained below one of the terminals of the fuse assembly by an arc snuffing means. In one embodiment, the arc snuffmg means comprises coaxially positioned rods to retain the ionized gas within the probe receiver. The rods are forced together when the fuse probe is retracted. In another embodiment, the arc snuffing means comprises pivotal members which are forced together when the probe is retracted to contain the ionized gas within the probe receiver. In still another embodiment, a gate member having a hinged door thereon is placed directly above the probe receiver.

When the probe is retracted, the door is closed and the ionized gas cannot escape from the probe receiver.

A de-ionizing chamber is disclosed which may be used with the arc snuffing means. The chamber into which the ionized gas passes is formed around the lower contact structure. After tie-ionization, the gas pressure is equalized by small openings in the walls of the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS Further advantages and uses of this invention will become more apparent when considered in view of the following detailed description and drawings, in which:

FIG. 1 is an elevational view, partially in section, of a protective fuse assembly constructed according to the teachings of this invention;

FIG. 2 is a partial view of a protective fuse assembly illustrating an embodiment having multiple arc snuffing means;

FIG. 3 is a partial elevational view, shown in section, illustrating an embodiment of this invention having arc snufiing means constructed of pivotal members;

FIG. 4 is a partial elevational view, shown partly in section, illustrating an embodiment of this invention having a gate member disposed above the lower contact structure; and

FIG. 5 is a partial elevational view, shown partly in section, illustrating an embodiment of this invention having a de-ionizing chamber positioned around the lower contact structure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Throughout the following description, similar reference characters refer to similar members in all figures of the drawings.

Referring now to the drawings, and FIG. 1 in particular, there is shown a protective fuse assembly of the load break type constructed according to an embodiment of this invention. The protective fuse assembly is mounted through an opening in the transformer casing 10 and extends into the fluid coolant 12 of the transformer. A mounting coupling 14 is attached to the transformer casing 10 by the weld bead 16. A threaded adapter 18 is threaded on its outer surface and attached to the upper portion 20 of the fuse casing by a suitable adhesive. The retaining springs 22 engage with the top cap 24 and secure the removable portion of the fuse assembly in position. The eyebolt 26 provides means for pulling the removable portion of the fuse assembly from the casing structure.

A metallic terminal 28 is sealingly attached to the upper portion 20 of the fuse assembly casing and to one end of the lower portion 30 of the fuse assembly casing. The terminal 28 is connected to other electrical components of the transformer, such as a high voltage bushing, by means of the connector 32. A metallic terminal 34 is sealingly connected to the other end of the lower portion 30 of the fuse assembly casing. The terminal 34 is connected to other electrical components of the transformer, such as a high voltage winding, by means of the connector 36.

The removable portion of the protective fuse assembly includes an insulating shaft 38 which is secured to one end of the fuse 40. An upper contact 42 electrically connects one end of the fuse 40 to the terminal 28. A probe 44 is attached to the other end of the fuse may be used, such as plating the lower end of the probe 44 with the material 48.

Although described according to the arrangement shown in FIG. 1, it is within the scope of this invention that the probe 44 and the probe receiver 46 may be reversed. That is, the probe 44 would be attached to the contact 34 with its tapered portion point toward the fuse 40, and the probe receiver 46 would be attached to the lower end of the fuse 40 with its receiving and adjacent to the terminal 34.

The probe receiver 46, as illustrated, includes a housing member 49 having a first portion 50 and a second portion 52. The first portion 50 extends above the contact structure 54 and the second portion 52 is substantially concentric with the contact structure 54. The housing member 49 is constructed of an insulating material and may comprise an arc resistant material such as glass-filled polyester having an aluminum trihydrate filler, zirconia, or any other suitable material. The lower end of the housing member 49 is threaded for attachment to the threaded stud 56 of the terminal 34. The threaded stud 56 also supports the contact structure 54 and provides an electrical connection between the terminal 34 and the contact structure 54. The contact structure 54 is constructed of a suitable electrical conducting material with a resilient means, such as a garter spring 58, forcing the contact structure 54 against the probe 44 when it is inserted into the probe receiver 46.

The first portion 50 of the housing member 49 contains a substantially cone-shaped cavity 60 which guides the probe 44 when inserted. Arc snuffing means 51 is positioned between the cavity 60 and the contact structure 54. The arc snuffing means includes the

rods

62 and 64 which are coaxially aligned with each other. They extend through openings in the upper portion 50 and have tapered upper edges, such as the edge 66, which allows the probe 44 to separate the rods when it is inserted. The garter spring 68 encircles the upper portion 50 and is positioned in slots on the outside ends of the

rods

62 and 64. The garter spring 68 tends to hold the rods together when the probe is retracted.

When removing the removable portion of the protective fuse assembly to de-energize a loaded transformer, an arc develops between the arc resistant material 48 and the upper portion of the contact structure 54. The contact structure 54 may have an are resistant ring attached thereto for reducing the destructive effects of the arc. The arc persists as the probe 44 is retracted from the probe receiver 46 until it is above the arc snuffing means 51. At this point, the

rods

62 and 64 close together and snuff out the arc. Ionized gas produced by the arc is contained within the housing structure 49 and cannot flow to the terminal 28 to form an atmosphere conducive to arcing.

A small quantity of ionized gas escapes from the probe receiver 46 before the arc snuffing means 51 closes. The rating of the protective fuse assembly may be increased by adding additional arc snuffmg means. FIG. 2 illustrates an embodiment of this invention wherein two are snuflers are arranged to decrease the escape of ionized gas into the surroundings adjacent to the probe receiver 46. The first arc snuffmg means, comprising the

rods

62 and 64 and the spring 68, closes first upon removal of the probe which is attached to the fuse 40. The second arc snufiing means, comprising the rods 62' and 64' and the spring 68, closes when the probe is completely removed from the probe receiver 46. The amount of ionized gas escaping from the second arc snufiing means is substantially less than that which escapes from the first arc snuffm g means.

FIG. 3 illustrates another embodiment of this invention wherein the arc snuffing means 70 is constructed of pivotal members. The probe 44 is shown in the retracted position. In this position, the pivotal members 72 and 74 butt against each other at the joint 76. This isolates the inside area 78 of the probe receiver 80 from the area adjacent to the outside of the probe receiver 80, thus efiectively preventing the escape of ionized gas.

The pivotal members 72 and 74 may be half sections of a substantially cylindrical structure which is substantially concentric with the cylindrical housing member 82. A ridge 84 which extends around the housing member 82 engages with a channel 86 which extends around the inside of the pivotal members 72 and 74. A garter spring 88 is positioned around the pivotal members 72 and 74 to force them together. When the probe 44 is inserted into the probe receiver 80, the pivotal members 72 and 74 are pushed outwardly and remain in that position until the probe 44 is retracted. A ring 81 which is constructed of an are resistant metallic material may be positioned adjacent to the end of the contact structure 54 to reduce the destructive effects of an arc on the contact structure 54.

An arrangement is shown in FIG. 4 whereby a gate member 90 is located in the protective fuse assembly to re-strict the flow of ionized gas to the upper terminal region. The probe receiver 92 has a housing member 94 constructed according to the teachings of U. S. Pat. No. 3,628,092, filed Dec. 3, 1970, Ser. No. 94,846. The probe 44 is similarly constructed with the tip of the probe 44 constructed of an arc extinguishing material 96. It is within the contemplation of this invention that gate member 90 may be used with other probe and probe receiver constructions, such as those disclosed in other embodiments of this invention.

The gate member 90 is constructed of a suitable material and is attached to the inside wall of the lower portion 30 of the fuse assembly casing at a location directly above the probe receiver 92. The gate member 90 includes a frame member 98, a door member 100, and a hinge member 102. The frame member 98 is attached to the casing portion 30 by a suitable means, such as by the adhesive 104. The components of the gate member 90 may be constructed from different materials or they may all be constructed from the same material. The gate member 90 may be a single piece and may be formed in one molding operation from a plastic material such as nylon or polyester. The resiliency of the plastic material provides sufficient hinge action to close the door member 1(1).

FIG. 5 illustrates the lower portion of a probe receiver with a de-ionizing chamber 106 constructed therewith. The chamber 106 is concentrically disposed around the lower portion of the probe receiver and is formed by the wall section 108 and the top section 1 10. The

sections

108 and 110 are constructed of an insulating material and may be a part of the housing structure 1 12.

Ionized gas developed during arcing within the probe receiver escapes, through the openings 114, into the de-ionizing chamber 106 where the gas expands, cools, and de-ionizes. The openings 116 in the wall sections 108 allow the de-ionized gas in the chamber 106 to gradually escape therefrom to equalize the pressures.

With the embodiments illustrated and described, or any combination thereof, the problem of ionized gas escaping into the fuse assembly casing is substantially reduced in high voltage protective fuse assemblies. Since numerous changes may be made in the above described apparatus and different embodiments of the invention may be made without departing from the spirit thereof, it is intended that all of the matter contained in the foregoing description or shown in the accompanying drawings, shall be interpreted as illustrative rather than limiting.

We claim as our invention:

1. A protective fuse assembly for fluid cooled power transformers comprising a cylindrical tube sealingly mountable in an opening of a transformer casing, said cylindrical tube having an upper portion extendable through said opening to the outside of the transformer casing, a lower portion extendable into the fluid coolant of the transformer, a first terminal sealingly attached to one end of said lower portion, a second terminal sealingly attached to the other end of said lower portion and to an end of said upper portion, removable means which electrically connects a fuse between said first and second terminals when said removable means is inserted into said cylindrical tube, probe means engageable with a probe receiver, said probe receiver having contact means which contacts said probe means to form a low resistance path between said fuse and said first terminal, and arc snuffing means which blocks the path between said second terminal and said contact means when the removable means is removed, thereby preventing the flow of gases between said contact means and said second terminal.

2. The protective fuse assembly of claim 1 including a gate member having a hinged door, said gate member being attached to the inside wall of the cylindrical tube at a location which is between the probe receiver and the second terminal, said hinged door being attached to resilient means which closes said door when the probe is removed from the cylindrical tube.

3. The protective fuse assembly of claim 2 wherein the gate member is constructed from a plastic material.

4. The protective fuse assembly of claim I wherein the probe is constructed of a conducting material, the probe receiver comprises a housing member and a contact structure, said contact structure being enclosed in said housing member and adapted to receive the probe, said housing member having a first portion extending beyond the contact structure and containing openings therein, said openings having a common axis which is substantially perpendicular to the axis of the probe, arc snuffing means comprising rods inserted into said openings and resilient means forcing said rods together when the probe is withdrawn from the probe receiver.

5. The protective fuse assembly of claim 4 wherein the openings in the first portion of the housing member and the arc snuffing rods are circularly shaped, with the inner end of the rods tapered to permit the probe insertion to move the rods apart.

6. The protective fuse assembly of claim 4 wherein the resilient means comprises a garter spring disposed around the first portion of the housing member and positioned against the outer ends of the arc snuffing rods.

7. The protective fuse assembly of claim 4 wherein the first portion of the housing member supports at least one are snuffmg means which comprises two rods.

8. The protective fuse assembly of claim 4 wherein the first portion of the housing member supports a plurality of arc snuffing means.

9. The protective fuse assembly of claim 4 wherein the rods are constructed of an arc extinguishing material.

10. The protective fuse assembly of claim 1 wherein the probe receiver comprises a housing member, a contact structure enclosed in said housing member which is adapted to receive the probe, said housing member having pivot means thereon, arc snufi'mg means comprising a substantially cylindrical member which is divided into two complementary sections, one end of said cylindrical member having a substantially cylindrical cavity into which said housing member is inserted, channel means on the inside wall of said cylindrical member which engages with said pivot means on said housing member, the other end of said cylindrical member being tapered to permit the probe insertion to move the complementary sections of the cylindrical member apart, and resilient means forcing said complementary sections together when the probe is withdrawn from the probe receiver.

1 1. The protective fuse assembly of claim 10 wherein the resilient means comprises a garter spring disposed around the outside of the complementary sections.

12. The protective fuse assembly of claim 10 wherein the pivot means comprises a ridge extending from the housing member and a channel on the inside wall of the complementary sections of the arc snuffing means, said channel having a width greater than said ridge to permit relative axial movement of the housing member and the arc snuffing means when the probe moves the complementary sections apart.

13. The protective fuse assembly of claim 1 wherein the probe receiver includes a de-ionizing chamber, said de-ionizing chamber comprising a shield portion disposed adjacent to the end of said probe receiver which is connected to the firs terminal, said shield forming a chamber into which ionized gas may flow from openings leading to the inside portion of the probe receiver, said shield having openings therein for releasing the ionized gas into the cylindrical tube to equalize gas pressures.

Claims

4. The protective fuse assembly of claim 1 wherein the probe is constructed of a conducting material, the probe receiver comprises a housing member and a contact structure, said contact structure being enclosed in said housing member and adapted to receive the probe, said housing member having a first portion extending beyond the contact structure and containing openings therein, said openings having a common axis which is substantially perpendicular to the axis of the probe, arc snuffing means comprising rods inserted into said openings and resilient means forcing said rods together when the probe is withdrawn from the probe receiver.

7. The protective fuse assembly of claim 4 wherein the first portion of the housing member supports at least one arc snuffing means which comprises two rods.

10. The protective fuse assembly of claim 1 wherein the probe receiver comprises a housing member, a contact structure enclosed in said housing member which is adapted to receive the probe, said housing member having pivot means thereon, arc snuffing means comprising a substantially cylindrical member which is divided into two complementary sections, one end of said cylindrical member having a substantially cylindrical cavity into which said housing member is inserted, channel means on the inside wall of said cylindrical member which engages with said pivot means on said housing member, the other end of said cylindrical member being tapered to permit the probe insertion to move the complementary sections of the cylindrical member apart, and resilient means forcing said complementary sections together when the probe is withdrawn from the probe receiver.

11. The protective fuse assembly of claim 10 wherein the resilient means comprises a garter spring disposed around the outside of the complementary sections.