CA1114862A - Semi-conductive stress relief shield for high voltage equipment - Google Patents
Semi-conductive stress relief shield for high voltage equipmentInfo
- Publication number
- CA1114862A CA1114862A CA319,629A CA319629A CA1114862A CA 1114862 A CA1114862 A CA 1114862A CA 319629 A CA319629 A CA 319629A CA 1114862 A CA1114862 A CA 1114862A
- Authority
- CA
- Canada
- Prior art keywords
- fuse
- semi
- coating
- housing
- shield
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 238000000576 coating method Methods 0.000 claims abstract description 43
- 239000011248 coating agent Substances 0.000 claims abstract description 41
- 239000000463 material Substances 0.000 claims abstract description 24
- 239000012212 insulator Substances 0.000 claims description 9
- 239000004020 conductor Substances 0.000 claims description 8
- 239000003989 dielectric material Substances 0.000 claims description 4
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 2
- 229910002804 graphite Inorganic materials 0.000 claims description 2
- 239000010439 graphite Substances 0.000 claims description 2
- 239000000725 suspension Substances 0.000 claims description 2
- 239000000155 melt Substances 0.000 claims 1
- 239000002184 metal Substances 0.000 abstract description 3
- 229910052751 metal Inorganic materials 0.000 abstract description 3
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 4
- 229910052802 copper Inorganic materials 0.000 description 4
- 239000010949 copper Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000007787 solid Substances 0.000 description 3
- 239000011810 insulating material Substances 0.000 description 2
- 239000003973 paint Substances 0.000 description 2
- 229910001316 Ag alloy Inorganic materials 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- KGBXLFKZBHKPEV-UHFFFAOYSA-N boric acid Chemical compound OB(O)O KGBXLFKZBHKPEV-UHFFFAOYSA-N 0.000 description 1
- 239000004327 boric acid Substances 0.000 description 1
- 230000015556 catabolic process Effects 0.000 description 1
- 239000000084 colloidal system Substances 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 230000001066 destructive effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000010891 electric arc Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 239000003822 epoxy resin Substances 0.000 description 1
- 239000011152 fibreglass Substances 0.000 description 1
- ISWSIDIOOBJBQZ-UHFFFAOYSA-N phenol group Chemical group C1(=CC=CC=C1)O ISWSIDIOOBJBQZ-UHFFFAOYSA-N 0.000 description 1
- 239000005011 phenolic resin Substances 0.000 description 1
- 229920001568 phenolic resin Polymers 0.000 description 1
- 229920000647 polyepoxide Polymers 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
Landscapes
- Fuses (AREA)
Abstract
SEMI-CONDUCTIVE STRESS RELIEF SHIELD FOR HIGH VOLTAGE EQUIPMENT Abstract: A semi-conductive coating is applied on the outside diameter of a cake of arc extinguishing material positioned within the interior of a high voltage fuse, and the semi-conductive coating is electrically connected to one end ferrule of the fuse to form an electrical stress shield. Upon operation of the fuse, dielectric stress between the end ferrule and the metal fitting at the other end of the fuse tends to be concentrated by the semi-conductive coating within the insulative material of the fuse housing. Without the semi-conductive stress shield, dielectric stress at the edge of the outside fuse fittings may cause a corona discharge external to the fuse adjacent to the external fitting, which may trigger an external flashover along the length of the entire fuse.
Description
L48~
The present invention relates to stress shields for high-voltage power fuses, and more particularly, to internal stress shielcls formed from a semi-conductive coating applied to the internfll portions of the fuse.
Internal stress shields in high-voltage interrupting equipment are well known in the art. For example, U.S. Patent No. 3,909,570-~larner, et al., assigned to the same assignee as the present invention, discloses metallic internal stress shields molded ;nto the insulating material of an interrupter switch to increase both the internal and external dielectric strength of the switch. Harner et al. also discloses the utilization of a partially-conductive coating over the inside of the operating mechanism housing of the interrupter switch to aid in shielding the internal components so that corona and ~IV no;se are eliminated. However, Harner does not show the use of a partially conductive coating as the stress shield itself. Another example of an internal stress shield is disclosed in U.S. Patent ~o. 2,567,768-Fahnoe. Fahnoe discloses the typical prior art metallic stress shield comprising a tubular copper shield within a high-voltage circuit interrupter to prevent the occurrence of external flashovers. The effect of the Fahnoe conductive shield is to cause the high-voltage stress to belocated in the solid dielectric of the fuse housing rather than in air surrounding the end of the fuse. Also, U.S. Patent Nos. 3,015,008-~habala et al. and ; 20 2,877,322-Harner (both of which are assigned to the same assignee as the present invention) disclose the utilization of a semi-conductive coated path between thetermainals of a high-voltage fuse over the internal surface of the bore in the f~
~ .
ti2 arc extinguishing material through which a movable conductor is withdrawn upon operation of the fuse for shielding the conductor from the destructive effects of corona discharge.
-It should be noted that in both Chabala et al. and Harner, 5 the semi-conductive coating is applied to the internal bore through which the conductor moves, and when the fuse operates, the conductive path is destroyed by the heat of fuse opera-tion thereby eliminating the conductive coating. Also, in Harner, the semi-conductive coated path is a water-resistant 10 material which completely covers the surface of the bore and prevents deterioration of the bore.
None of the above prlor art references disclose the utilization of a semi-conductive coating on the exterior surface of the cake of arc extinguishing material placed 15 within a fuse to achieve an internal stress shield capable of concentrating dielectric stress within the dielectric material of the fuse during fuse operation to eliminate corona and prevent flashover.
~he present invention comprises a unique stress ~20 shield for high-voltage fuses, interrupting switches, and ; the like. A stress shield in accordance with the present invention comprises a thin coating of semi~conductive mate-rial on the exterior surface of a cake of arc extinguishing material position within the interior of the fuse. The 25 coating is so arranged and electrically connected to one of the end fittings of the fuse that dielectric stress result-ing during fuse operation is concentrated by the semi-con-ductive coating within the dielectric material of the fuse rather than exte:rnally of the fuse.
Ihe present invention provides advantages over prior art stress shields because such a stress shield has a resistance many orders of magnitude greater than the prior art copper or other metallic stress shields and thus offers only a minimal increase in leakage current through the blown fuse. Thus, while 5 the voltage at the edge of the stress shield is the same as the metal end ferrule when no current is flowing, the high resistance of the coating prevents or impedes leakage currents. Also the present invention allows the cakes of arc extinguishing material to retain their full diameter thereby achieving the benefits of an internal stress shield without weakening the cakes of arc-10 extinguishing material to the extent that assernbly forces or operating shockmight cause crushing or cracking of the cakes.
Thus, it is a principal object of the present invention to provide an internal stress shield for high-voltage fuses, interrupters and the like which prevents corona discharge and external flashover while allowing the internal 15 structure of the fuse to remain substantially unchanged.
It is yet another object of the present invention to provide an internal stress shield for high-voltage fuses, interrupters and the like that does not increase the likelihood that harmful leakage currents will occur through the device after operation.
These and other object advantages and features shall hereinafter appear, and for the purposes of illustration, but not for limitation, an exemplary embodiment of the present invention is illustrated in the accompanying drawings.
~IGUR~ 1 is a side, cross-sectional, partially fragmentary view of a high-voltage fuse having the present invention incorporated therein.
G
~481~;~
FIGURE 2 is a cross-sectional view taken substan tially along line 2-2 in FIGURE 1.
FIGURE 3 is a cross-sectional, partially fragmen-tary view taken substantially along line 3-3 in FIGURE 1.
With reference to FIGURE 1, illustrated is a t~pi-cal expulsion type high-voltage fuc;e 10. Fuse 10 comprises a hollow insulator tube 12 that can be fabricated from any conventional organic insulator mate~rials such as fiberglass, phenolic, or epoxy resin. Insulator tube 12 has an exterior annular groove 14 adjacent one end thereof, and a metallic end fitting in the form of an exhaust ferrule 16 is attached to the end of the insulator tube 12 by compressing the end of the ferrule 16 into the groove 14. Two sets of threads ; 18 and 20 are provided within the end of ferrule 16. Threads 20 accomodate a contact bridge 22 which is threaded into the end of ferr~ule 16, and threads 18 may be utilized to attach a rain cap or exhaust device as appropriate or necessary.
Attached to contact bridge 22 and extending there-from in a cantilever fashion is a column-shaped element 24 which has attached to the end thereof a fusible element 26 which may be fabricated from silver alloy and a strain wire 28 which may be fabricated from nickel-chrome alloy. Fusi-ble element 26 and strain wire 28 are connected at their opposite ends to an arcing rod 30 which extends through a hollow bore 33 through the center of a stack of cakes of arc extinguishing material 32. Arc extinguishing material 32 may be made of boric acid or any other suitable material that emits an arc-quenching gas when exposed to an electric arc. An exhaust tube 34 is mounted within insulator tube 12 and retained between a flange 35 on the interior of ferrule 16 and a gasket 37 positioned against the cakes of arc extinguishing material 32.
L4~
Mounted on the other end of arcing rod 30 is a contact button assembly 36 which includes a striker pin 38 extending from a button flange 40 mounted to the end of an electrical contact 42 attached to the end of arcing rod 30.
5 A spring 44 engages the edge of flange 40 and is compressed between button flange 40 and a flange 46 mounted in the end of a metallic conducting tube 48. A contact assembly 50 is mounted on the interior of flange 46 at the end of conduct-ing tube 48. Contact assembly 50 c:omprises a plurality of 10 contact fingers 52 which are biasecl inwardly by a garter spring 54 to assure electrical contact with contact 42.
Conducting tube 48 is attached to the interior of insulator tube 12 by an expansion joint 56 and the end of conducting tube 48 extends from the end of insulator tube 12 to form a 15 metallic fitting at that end of the fuse. In typical service, conducting tube 48 is connected to one side of an electical circuit and ferrule 16 to the other side of the circuit.
When fuse 10 operates, fusible element 26 and strain wire 28 melt allowing arcing rod 30 to be accelerated by spring 44 20 through the hollow opening 33 in the cakes of arc extin-guishing material 32.
With reference to FIGURES 1, ~, and 3, stress shield means in accordance with the present invention com-prises a coating 60 on the exterior surface of a cake 62 of 25 the cakes of arc extinguishing material 32 closest to ferrule 16. Coating 60 is of a semi-conductive or partially conduc-tive material, i.e., a material that conducts electricity but has a very high resistance in the range of 0.5 megohm to - 50 megohms or more per inch across the length of the coating.
30 Semi-conductive coating 60, which is applied to the surface of cake 62 before it is installed in the fuse, is not required to conduct a significant current but does serve to establish . an equipotential surface within the body of fuse 10. Since the semi-conductive coating contacts conductive gasket 37, .. 5 which in turn contacts the end of exhaust tube 34, and exhaust tube 34 engages ferrule 16, semi-conductive coating 60 is in electrical connection with ferrule 16. Thus, coating 60 forms a semi-conductive layer within the fuse ; which has the effect of extending the electrical potential 10 of ferrule 16 a preferred distance further into the interior of the fuse. When a fuse operates and has just interrupted a current in a circuit, the circuit recovery voltage is impressed between ferrule 16 and the end of arcing rod 30.
Especially if current interruption occurs when arcing rod 30 15 has completed only a portion of its stroke, a major portion of the electrical potential difference between ferrule 16 and arcing rod 30 would exist adjacent to ferrule 16 in the air outside fuse tube 12 in the absence of a coating 60 inside the fuse. However, with the electrical extension of 20 tube 34 into fuse tube 12 by coating 60, the voltage gradient in the air adjacent to ferrule 16 is substantially reduced, and any electrical stress concentration occurs within the solid dielectric material of fuse tube 12 and arc extin-guishinq material 32. Thus, corona at the edge of ferrule 25 16, and the attendant likelihood of external electrical breakdown of the fuse, are eliminated.
Semi-conductive coating 60 of the present inven-tion provides substantial advantages over the prior art metallic stress shields extending into the fuse cavity.
30 First, since semi.-conductive coating 60 has substantial impedance as compared to copper or other metallic stress shields used in the prior art, semi-conductive coating 60 q6~
produces a minimum effect on current leakage performance of the fuse.
Further, since semi-conductive coating 60 has very little thickness, cake 62 of arc extinguishing material need not be reduced in diameter. Consequently, cake ` 62 retains it original strength. Semi-conductive coating 60 of the present 5 invention is also less expensive than metallic stress shields formed of metal such as copper. Further, placing a coating within hollow center bore 33 of arc extinguishing material 32 would provide shielding except that such coating would be destroyed by the arc during interruption and would thus not be available when needed. On the other hand, placing an arc resistant conductive material in the 10 bore would interfere with interruption by reducing the effective length of hollow center bore 33 of arc extinguishing material 32.
Accordingly, it cQn be seen that the effect of semi-conductive coating 60 extends beyond both the external and internal limits OI the metallic members of the fuse. Semi-conductive coating 60 extends within solid dielectric 15 material a selected distance into the gap between the end of the arcing rod 30 as it moves to the end of the fuse and the electrically-charged portions of ferrule 16, exhaust tube 34, and column-shaped element 24, thus reducing the internal voltage gradient adjacent to exhaust tube 34. Semi-conductive coating 60 also reduces the electrical stress on the outside of the fuse by concentrating the 20 stress inside the insulating material, which can better sustain high electrical stress, rather than permitting such stress to occur in the air at the edge of ferrule 16. Accordingly, lower, more uniform stress is experienced at the internal gap as well as along the exterior of the fuse.
4~6Z
.:
,~ Semi-conductive coating 60 can be achieved through the use of various kypes of coatings. For example, a paint comprising a colloidal suspension of graphite may be used to produce the desired results. Such a paint is sold by Acheson 5 Colloids Company as DAG Dispersion No. 35. Further, any number of other types of high resistance semi-conductive coatings would be suitable for the present invention.
It should also be expressly understood that the present invention may be used in other high voltage elec-10 trical equipment of generally elongated configuration inwhich an internal contact gap may establish external elec-trical stress concentration without departing from the spirit and scope of the present invention as set forth in the appended claims.
` 15
The present invention relates to stress shields for high-voltage power fuses, and more particularly, to internal stress shielcls formed from a semi-conductive coating applied to the internfll portions of the fuse.
Internal stress shields in high-voltage interrupting equipment are well known in the art. For example, U.S. Patent No. 3,909,570-~larner, et al., assigned to the same assignee as the present invention, discloses metallic internal stress shields molded ;nto the insulating material of an interrupter switch to increase both the internal and external dielectric strength of the switch. Harner et al. also discloses the utilization of a partially-conductive coating over the inside of the operating mechanism housing of the interrupter switch to aid in shielding the internal components so that corona and ~IV no;se are eliminated. However, Harner does not show the use of a partially conductive coating as the stress shield itself. Another example of an internal stress shield is disclosed in U.S. Patent ~o. 2,567,768-Fahnoe. Fahnoe discloses the typical prior art metallic stress shield comprising a tubular copper shield within a high-voltage circuit interrupter to prevent the occurrence of external flashovers. The effect of the Fahnoe conductive shield is to cause the high-voltage stress to belocated in the solid dielectric of the fuse housing rather than in air surrounding the end of the fuse. Also, U.S. Patent Nos. 3,015,008-~habala et al. and ; 20 2,877,322-Harner (both of which are assigned to the same assignee as the present invention) disclose the utilization of a semi-conductive coated path between thetermainals of a high-voltage fuse over the internal surface of the bore in the f~
~ .
ti2 arc extinguishing material through which a movable conductor is withdrawn upon operation of the fuse for shielding the conductor from the destructive effects of corona discharge.
-It should be noted that in both Chabala et al. and Harner, 5 the semi-conductive coating is applied to the internal bore through which the conductor moves, and when the fuse operates, the conductive path is destroyed by the heat of fuse opera-tion thereby eliminating the conductive coating. Also, in Harner, the semi-conductive coated path is a water-resistant 10 material which completely covers the surface of the bore and prevents deterioration of the bore.
None of the above prlor art references disclose the utilization of a semi-conductive coating on the exterior surface of the cake of arc extinguishing material placed 15 within a fuse to achieve an internal stress shield capable of concentrating dielectric stress within the dielectric material of the fuse during fuse operation to eliminate corona and prevent flashover.
~he present invention comprises a unique stress ~20 shield for high-voltage fuses, interrupting switches, and ; the like. A stress shield in accordance with the present invention comprises a thin coating of semi~conductive mate-rial on the exterior surface of a cake of arc extinguishing material position within the interior of the fuse. The 25 coating is so arranged and electrically connected to one of the end fittings of the fuse that dielectric stress result-ing during fuse operation is concentrated by the semi-con-ductive coating within the dielectric material of the fuse rather than exte:rnally of the fuse.
Ihe present invention provides advantages over prior art stress shields because such a stress shield has a resistance many orders of magnitude greater than the prior art copper or other metallic stress shields and thus offers only a minimal increase in leakage current through the blown fuse. Thus, while 5 the voltage at the edge of the stress shield is the same as the metal end ferrule when no current is flowing, the high resistance of the coating prevents or impedes leakage currents. Also the present invention allows the cakes of arc extinguishing material to retain their full diameter thereby achieving the benefits of an internal stress shield without weakening the cakes of arc-10 extinguishing material to the extent that assernbly forces or operating shockmight cause crushing or cracking of the cakes.
Thus, it is a principal object of the present invention to provide an internal stress shield for high-voltage fuses, interrupters and the like which prevents corona discharge and external flashover while allowing the internal 15 structure of the fuse to remain substantially unchanged.
It is yet another object of the present invention to provide an internal stress shield for high-voltage fuses, interrupters and the like that does not increase the likelihood that harmful leakage currents will occur through the device after operation.
These and other object advantages and features shall hereinafter appear, and for the purposes of illustration, but not for limitation, an exemplary embodiment of the present invention is illustrated in the accompanying drawings.
~IGUR~ 1 is a side, cross-sectional, partially fragmentary view of a high-voltage fuse having the present invention incorporated therein.
G
~481~;~
FIGURE 2 is a cross-sectional view taken substan tially along line 2-2 in FIGURE 1.
FIGURE 3 is a cross-sectional, partially fragmen-tary view taken substantially along line 3-3 in FIGURE 1.
With reference to FIGURE 1, illustrated is a t~pi-cal expulsion type high-voltage fuc;e 10. Fuse 10 comprises a hollow insulator tube 12 that can be fabricated from any conventional organic insulator mate~rials such as fiberglass, phenolic, or epoxy resin. Insulator tube 12 has an exterior annular groove 14 adjacent one end thereof, and a metallic end fitting in the form of an exhaust ferrule 16 is attached to the end of the insulator tube 12 by compressing the end of the ferrule 16 into the groove 14. Two sets of threads ; 18 and 20 are provided within the end of ferrule 16. Threads 20 accomodate a contact bridge 22 which is threaded into the end of ferr~ule 16, and threads 18 may be utilized to attach a rain cap or exhaust device as appropriate or necessary.
Attached to contact bridge 22 and extending there-from in a cantilever fashion is a column-shaped element 24 which has attached to the end thereof a fusible element 26 which may be fabricated from silver alloy and a strain wire 28 which may be fabricated from nickel-chrome alloy. Fusi-ble element 26 and strain wire 28 are connected at their opposite ends to an arcing rod 30 which extends through a hollow bore 33 through the center of a stack of cakes of arc extinguishing material 32. Arc extinguishing material 32 may be made of boric acid or any other suitable material that emits an arc-quenching gas when exposed to an electric arc. An exhaust tube 34 is mounted within insulator tube 12 and retained between a flange 35 on the interior of ferrule 16 and a gasket 37 positioned against the cakes of arc extinguishing material 32.
L4~
Mounted on the other end of arcing rod 30 is a contact button assembly 36 which includes a striker pin 38 extending from a button flange 40 mounted to the end of an electrical contact 42 attached to the end of arcing rod 30.
5 A spring 44 engages the edge of flange 40 and is compressed between button flange 40 and a flange 46 mounted in the end of a metallic conducting tube 48. A contact assembly 50 is mounted on the interior of flange 46 at the end of conduct-ing tube 48. Contact assembly 50 c:omprises a plurality of 10 contact fingers 52 which are biasecl inwardly by a garter spring 54 to assure electrical contact with contact 42.
Conducting tube 48 is attached to the interior of insulator tube 12 by an expansion joint 56 and the end of conducting tube 48 extends from the end of insulator tube 12 to form a 15 metallic fitting at that end of the fuse. In typical service, conducting tube 48 is connected to one side of an electical circuit and ferrule 16 to the other side of the circuit.
When fuse 10 operates, fusible element 26 and strain wire 28 melt allowing arcing rod 30 to be accelerated by spring 44 20 through the hollow opening 33 in the cakes of arc extin-guishing material 32.
With reference to FIGURES 1, ~, and 3, stress shield means in accordance with the present invention com-prises a coating 60 on the exterior surface of a cake 62 of 25 the cakes of arc extinguishing material 32 closest to ferrule 16. Coating 60 is of a semi-conductive or partially conduc-tive material, i.e., a material that conducts electricity but has a very high resistance in the range of 0.5 megohm to - 50 megohms or more per inch across the length of the coating.
30 Semi-conductive coating 60, which is applied to the surface of cake 62 before it is installed in the fuse, is not required to conduct a significant current but does serve to establish . an equipotential surface within the body of fuse 10. Since the semi-conductive coating contacts conductive gasket 37, .. 5 which in turn contacts the end of exhaust tube 34, and exhaust tube 34 engages ferrule 16, semi-conductive coating 60 is in electrical connection with ferrule 16. Thus, coating 60 forms a semi-conductive layer within the fuse ; which has the effect of extending the electrical potential 10 of ferrule 16 a preferred distance further into the interior of the fuse. When a fuse operates and has just interrupted a current in a circuit, the circuit recovery voltage is impressed between ferrule 16 and the end of arcing rod 30.
Especially if current interruption occurs when arcing rod 30 15 has completed only a portion of its stroke, a major portion of the electrical potential difference between ferrule 16 and arcing rod 30 would exist adjacent to ferrule 16 in the air outside fuse tube 12 in the absence of a coating 60 inside the fuse. However, with the electrical extension of 20 tube 34 into fuse tube 12 by coating 60, the voltage gradient in the air adjacent to ferrule 16 is substantially reduced, and any electrical stress concentration occurs within the solid dielectric material of fuse tube 12 and arc extin-guishinq material 32. Thus, corona at the edge of ferrule 25 16, and the attendant likelihood of external electrical breakdown of the fuse, are eliminated.
Semi-conductive coating 60 of the present inven-tion provides substantial advantages over the prior art metallic stress shields extending into the fuse cavity.
30 First, since semi.-conductive coating 60 has substantial impedance as compared to copper or other metallic stress shields used in the prior art, semi-conductive coating 60 q6~
produces a minimum effect on current leakage performance of the fuse.
Further, since semi-conductive coating 60 has very little thickness, cake 62 of arc extinguishing material need not be reduced in diameter. Consequently, cake ` 62 retains it original strength. Semi-conductive coating 60 of the present 5 invention is also less expensive than metallic stress shields formed of metal such as copper. Further, placing a coating within hollow center bore 33 of arc extinguishing material 32 would provide shielding except that such coating would be destroyed by the arc during interruption and would thus not be available when needed. On the other hand, placing an arc resistant conductive material in the 10 bore would interfere with interruption by reducing the effective length of hollow center bore 33 of arc extinguishing material 32.
Accordingly, it cQn be seen that the effect of semi-conductive coating 60 extends beyond both the external and internal limits OI the metallic members of the fuse. Semi-conductive coating 60 extends within solid dielectric 15 material a selected distance into the gap between the end of the arcing rod 30 as it moves to the end of the fuse and the electrically-charged portions of ferrule 16, exhaust tube 34, and column-shaped element 24, thus reducing the internal voltage gradient adjacent to exhaust tube 34. Semi-conductive coating 60 also reduces the electrical stress on the outside of the fuse by concentrating the 20 stress inside the insulating material, which can better sustain high electrical stress, rather than permitting such stress to occur in the air at the edge of ferrule 16. Accordingly, lower, more uniform stress is experienced at the internal gap as well as along the exterior of the fuse.
4~6Z
.:
,~ Semi-conductive coating 60 can be achieved through the use of various kypes of coatings. For example, a paint comprising a colloidal suspension of graphite may be used to produce the desired results. Such a paint is sold by Acheson 5 Colloids Company as DAG Dispersion No. 35. Further, any number of other types of high resistance semi-conductive coatings would be suitable for the present invention.
It should also be expressly understood that the present invention may be used in other high voltage elec-10 trical equipment of generally elongated configuration inwhich an internal contact gap may establish external elec-trical stress concentration without departing from the spirit and scope of the present invention as set forth in the appended claims.
` 15
Claims (5)
1. In a high voltage fuse of the type having a hollow insulator type; metallic end fittings mounted at each end of the fuse; an arcing rod movable through the fuse when a fusible element within the fuse melts; and a body of arc-extinguishing material positioned within the insulator tube and having a bore therethrough; the arcing rod traveling through the bore upon fuse operation; an improved stress shield for reducing the external voltage gradient of the fuse while and after the fuse interrupts current comprising:
a semi-conductive coating on the exterior of the body of arc-extinguishing material, the coating terminating adjacent, and being electrically connected to, one of the metallic end fittings so that the coating is at the same electrical potential as the one end fitting.
a semi-conductive coating on the exterior of the body of arc-extinguishing material, the coating terminating adjacent, and being electrically connected to, one of the metallic end fittings so that the coating is at the same electrical potential as the one end fitting.
2. An improved stress shield, as set forth in Claim 1, wherein the coating comprises a colloidal suspension of graphite.
3. An improved stress shield, as set forth in Claim 2, wherein said semi-conducive coating has a resistance of at least 500,000 ohms per linear inch therealong.
4. A stress shield for high voltage circuit interrupting equipment of the type having an elongated non-conducting housing with metallic fittings at each end thereof and a contact movable through a bore formed in a body of arc extinguishing material, the body being positioned within the housing;
the shield reducing the external voltage gradient of the equipment while and after the equipment interrupts current and comprising:
a coating of high resistance, electrically conductive material between an internal surface of the housing and an external surface of the body of arc-extinguishing material, the coating being electrically continuous with one metallic fitting extending to a position within the housing intermediate the metallic fittings which is substantially closer to the one fitting so that the electrical potential of the one fitting is impressed by the coating within dielectric material within the equipment.
the shield reducing the external voltage gradient of the equipment while and after the equipment interrupts current and comprising:
a coating of high resistance, electrically conductive material between an internal surface of the housing and an external surface of the body of arc-extinguishing material, the coating being electrically continuous with one metallic fitting extending to a position within the housing intermediate the metallic fittings which is substantially closer to the one fitting so that the electrical potential of the one fitting is impressed by the coating within dielectric material within the equipment.
5. Apparatus for reducing the external voltage gradient of a high voltage fuse after the fuse interrupts current in a high voltage circuit, the apparatus comprising: a layer of high resistance, electrically conductive material between an outer insulative housing and an inner arc-extinguishing body of the fuse, the layer extending longitudinally within the housing and being connected to a metallic end ferrule on one end of the housing, the layer terminating at a location along the housing intermediate the end ferrule and the opposite end of the fuse, but substantially closer to the end ferrule.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US87359478A | 1978-01-30 | 1978-01-30 | |
| US873,594 | 1978-01-30 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1114862A true CA1114862A (en) | 1981-12-22 |
Family
ID=25361951
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA319,629A Expired CA1114862A (en) | 1978-01-30 | 1979-01-15 | Semi-conductive stress relief shield for high voltage equipment |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1114862A (en) |
-
1979
- 1979-01-15 CA CA319,629A patent/CA1114862A/en not_active Expired
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| Date | Code | Title | Description |
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| MKEX | Expiry | ||
| MKEX | Expiry |
Effective date: 19981222 |