GB1598371A - Puffer circuit interrupter with fluorocarbon liner - Google Patents

Description

(54) PUFFER CIRCUIT INTERRUPTER WITH FLUOROCARBON LINER (71) We, WESTINGHOUSE ELECTRIC CORPORATION, a corporation organised and existing under the laws of the state of Pennsylvania, United States of America, residing at Westinghouse Building, Gateway Center, Pittsburgh, Pennsylvania 15222, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to puffer circuit interrupter apparatus, and in particular to single barrel puffer circuit interrupters with protective linings.

The use of double or multiple barrel puffer circuit interrupters is well known as described in the specification of U.S. Patents 3,659,065 and 3,814,883, in which the first barrel is the main insulating and support barrel which generally encloses and protects the other barrel.

The other barrel is a necessary part of a piston operated puffer mechanism. Because of the presence of an electrical arc during an interrupting operation and the exposure of the electrical arc to a puffer gas such as sulfur hexafluoride, the opportunity for exposure of either of the barrels to the heat of the electrical arc, the arc products or the current of the electrical arc is relatively high. In addition, because of the presence of the sulfur hexafluoride gas within the main barrel of the circuit breaker interrupter and the presence of evolved gas during the arcing operation, the main or outer shell must be able to withstand relatively high gas pressure without rupturing. It would be advantageous if a single shell puffer circuit breaker apparatus could be provided.

According to the present invention, puffer circuit interrupter apparatus comprises separable contacts, terminal means electrically interconnected with said separable contacts so that said contacts are in electrical circuit relationship with a circuit, arc extinguishing gas, puffer means operable in conjunction with said separable contacts to control an electrical arc drawn on separation of said separable contacts during operation thereof by directing said arc extinguishing gas to the region of said arc, actuating means to actuate said separable contacts and said puffer means, and a rigid electrically insulating casing having a film of fluorocarbon synthetic resin on an interior wall portion thereof, said separable contacts and said puffer means and said actuating means and said gas being disposed within said casing, said terminal means being disposed on said casing, said puffer means cooperating with said casing during said actuation of said contacts to enable said gas to flow to said contacts, said interior wall portion being exposable to the electrical current of said arc and to the heat of said electrical arc and to said arc products and to the gas pressure of the combination of said gas and said evolved arc products, said fluorocarbon synthetic resin reducing friction between said puffer means and said interior wall, said fluorocarbon synthetic resin resisting electrical tracking therein in the presence of said heat of said arc and in the presence of said arc products and in the presence of said arc current, said casing containing the pressure of the combination of said gas and said arc products without rupturing, said fluorocarbon synthetic resin shielding the remainder of said casing from said arc products and from said arc current and from a portion of the heat of said arc.

Suitably, a rigid, electrically insulating casing having a protective film of fluorocarbon synthetic resin on an interior wall thereof, is provided. The casing withstands the pressure of the gas while the film resists electrical tracking due to the current of the arc, or the heat of the arc or the gaseous products caused by the arc. The fluorocarbon may comprise polytetrafluoroethylene (TFE). A resin may be used as an adhesive for the film and its surrounding fiberglass support body. The resin may comprise a base of bisphenol-A/ epichlorohydrin in one embodiment of the invention or may comprise cycloaliphatic dioxide in another embodiment of the invention.

einvention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure I shows a puffer circuit breaker apparatus partially in section, partially broken away, and partially in block diagram form; and Figure 2 shows a broken away section of a portion of the interior wall of the support and insulating cylinder for the circuit breaker apparatus of Figure 1.

Figure 1 shows a single tube puffer circuit interrupter 10 having a hollow cylindrical insulating support tube 12, with an electrically conducting terminal 14 on the left portion thereof and has an operating mechanism 16 on the right portion thereof. The insulating suPport tube 12 may be radially symmetrical about a centerline CL. A hollow, generally cylindrical electrical conductor 18 is shown in the left portion of circuit breaker apparatus 10. The hollow conductor 18 is interconnected electrically with the terminal 14 through a conducting cooler tube TU1. At the right end of the hollow electrical conductor 18 is an arcing contact piece 19 which may comprise any electrically conductive material which will withstand repeated arcing for a relatively long period of time for many operations. Flexible main conducting fingers 20 are also connected to terminal 14 by way of cooler tube TU1.

Interconnected with the operating mechanism 16, shown schematically to the right of Figure 1, is a movable connecting rod 22, the use of which will be described more fully hereinafter. Disposed on either side (top and bottom as viewed in Figure 1) of the electrically insulating support tube 12 may be electrically conductive terminals 24. Each electrically conductive terminal 24 may be seated and sealed in an appropriate groove or seat 25 in the insulating support member 12. A portion of the electrically conductive terminal 24 protrudes through the insulating support tube 12 and is threaded into an internal connector and support piece 26 for securing the terminal 24 against the inside wall of the insulating support tube 12 in electrically conducting relationship with the internal conductor 26. Disposed on the internal conducting member 26 may be a plurality of electrically conducting flexible fingers 28 and at least one unidirectional gas valve 30. Also disposed on the internal conducting member 26 is a neoprene seal 32. A cooler tube TU2 is interlocked against the inside wall of the support tube 12 at 26a on the support piece 26. The use of tube 12 will be described more fully hereinafter.

There is provided a movable electrical contact assembly 34 which includes a cylindrical hollow electrically conducting tube member 36. The electrically conducting tube member 36 may be radially disposed symmetrically about the previously-described centerline CL.

Disposed at the left end of the electrically conducting movable tube member 36 is a conducting flange 38 having an extended electrically conducting portion 39 which is adapted to make sliding electrical contact with the previously described main contact fingers 20 when the puffer circuit breaker 10 is closed. Also disposed on the left portion of the hollow conductive tube member 36 may be flexible contact fingers 40 which are complementary to the contact piece 19 described previously. On the right portion of the electrically conducting hollow cylindrical tube 36 is disposed a yoke 42 which is mechanically interconnected with the connecting rod 22 such that movement of the connecting rod 22 in the direction 70 in response to an appropriate action in the operating mechanism 16 will cause the entire body of the hollow conducting tube member 36 to move to the left to thus place the arcing contact fingers 40 in a disposition of overlapping electrical contact with the arcing contact 19 and to place the extended portion 39 of the conducting flange 38 in a disposition of electrical contact with the main contact fingers 20. It is to be noted that in this particular embodiment of the invention the relative longitudinal disposition of the contact fingers 20, the extended portion 39, the contact piece 19, and the contact fingers 40 is such that electrical contact is made during a circuit breaker closing operation between the contact piece 19 and the contact fingers 40 before electrical contact is made between the contact fingers 20 and the extended portion 39. Likewise, in an opening operation, the contact fingers 20 and the extended portion 39 separate before the contact piece 19 and the contact fingers 40 separate. The amount of overlap between fingers 40 and contact 19 is represented by D.

The fingers 40 are joined at the roots thereof so that the inner regions of tubes 18 and 36 are sealed off from chamber 52 when the circuit breaker 10 is in the closed state. There is provided a neoprene seal 44 on the outer portion of the contact flange 38. The seal operates against the inner surface of the insulating support tube 12 to thus locally isolate two gas pressure regions which will be described hereinafter. In a like manner, the previously described seal 32 operates against the hollow conducting tube 36 to locally isolate one of the previously described gas pressure regions from a third gas pressure region.

There may be disposed to the right of the electrically conducting cylinder 36 an opening 43 which provides communication between the internal portion of the hollow conducting tube 36 and the region surrounding the external portion of the hollow conducting tube member 36 to the right of the seal 32.

There is provided an arc nozzle 46, the right portion of which is disposed on the previously described conducting flange 38. Nozzle 46 is supported at the left portion thereof in sealed but movable relationship against the outer surface of the previously described hollow conductor 18. The seal 48 cooperates with the previously described seal 44 to provide the first two previously described regions of different gas pressure during the operation of the circuit interrupter apparatus 10. In a preferred embodiment of the invention, nozzle 46 always remains in sealed relationship with tube 18 thus providing an arc shield between the arcing contacts 19 and 40 and the inner surface of wall 12 during an arcing operation. On the internal portion of the arc nozzle 46 may be disposed a corrugated or ridged region 50 which provides high arc tracking resistance during the circuit breaker opening operation.

There is provided a first gas pressure region 52 which may exist between the seals 32 and the combined seals 44 and 48. Gas pressure is built up in the region 52 during a circuit breaker opening operation as will be described more fully hereinafter. A second gas pressure region 53 may exist between the left end of the circuit breaker apparatus 10 and the combined seals 44 and 48. Openings 51 disposed in the cooling tube TU1 provide paths of communication between the latter region 53 and the internal portion of the hollow conductor 18. A third gas pressure region may exist in the right portion of the circuit breaker apparatus between the seal 32 and the right side of the circuit breaker apparatus 10.

The previously described opening 43 provides a path of gas communication between the internal portion of the hollow conducting tube 36 and the region 54. All of the latter described gas pressure regions contain gas of relatively different pressure during certain portions of the operating cycle of the circuit breaker 10. The pressure in each case is related to the relative sizes of openings 51 and 43 for example. The relative gas pressures in the latter-named regions 52, 53 and 54 during opening and closing of the circuit breaker apparatus provide the puffer action which will be described hereinafter. There is provided in the conducting flange 38 an opening 56 which communicates with the previously described region 52 and with the internal portions of both of the hollow conducting members 18 and 36. The communicating path previously described is conveniently located such that the contact fingers 40 and the contact piece 19 are disposed therein during a circuit breaker opening or closing operation. The previously described flexible fingers 28 provide a path of electrical conduction between the movable hollow conductive tube 36 and the internal conductor 26. A source of electrical power S may be serially or otherwise connected with a load LD which is to be protected by the circuit breaker apparatus 10. Such an arrangement is shown schematically in Figure 1. The serial arrangement is intercon- nected with the terminal 14 and the terminal 24. Cooling tube TU1 encloses a cooling mesh M1 through which hot gas following path 62 may exhaust radially into region 53 by way of openings 51. Likewise, cooling tube TU2 encloses a cooling mesh M2 through which hot gas following path 60 may be diffused laterally by way of opening 43. In the latter case, a deflector 22a is positioned on rod 22 to aid in channeling a portion of the gas in path 60 into the mesh M2 for lateral diffusion therethrough.

During the closing operation of the circuit breaker apparatus 10, the connecting rod 22 forces the hollow conducting tube 36 to the left as viewed in Figure 1. Electrical continuity is maintained between the terminals 24 and the moving conducting cylinder 36 by way of the internal conductor or connector 26 and the fingers 28. As the cylinder 36 moves to the left, the flange 38, the nozzle 46 and the contact fingers 40 also move to the left. The movement of the flange 38 to the left causes the volume of the region 52 to enlarge, thus creating a local short term pressure differential between region 52 and regions 53 and 54 such that gas from region 54 moves through valve 30 by way of a channel 55 along the path 72 to region 52. Gas from regions 53 and 54 may move into region 52 by way of opening 56 until portion 41 of fingers 40 overlaps contact 19 thus closing off orifice 56 from regions 53 and 54. This charges region 52 with puffer gas (SF6 for example) during the circuit breaker closing operation, it being understood that the unidirectional valve 30 opens to pass gas only in the direction 72 and closes to prevent gas from passing therethrough in the opposite direction.

As the movable contact assembly 34 continues movement to the left, a position is reached where the contact fingers 40 make electrical contact with the contact piece 19 on the hollow conductor 18. A short time thereafter the extended contact region 39 makes electrical contact with the main contact fingers 20. In this position the circuit which includes the load LD and the source S is closed through the puffer circuit breaker 10.

In a contact opening operation the contact rod 22 moves in the direction 57, thus causing the hollow conductive tube 36 of the movable contact assembly 34 to move to the right. The main contact fingers 20 and the extended contact region 39 of the conducting flange 38 disengage first. Movement of the flange 38 and nozzle 46 in the direction 57 through the distance D forces the trapped gas in the region 52 to become pressured by the reduction in volume in region 52. The latter movement through the region D is sometimes referred to as "lost motion" movement. Eventually a point is reached during the contact opening cycle where the contact piece 19 of the generally stationary hollow conductor 18 and the contact fingers 40 of the movable contact assembly 34 disengage under load or overload current or the like, thus generating an arc A. The pressurized gas in region 52 follows path 58 through opening 56 and is puffed or forced into the region of the arc A for quenching and cooling the arc A and for blowing the arc A out from between the contact piece 19 and the contact fingers 40. The heated gas may then follow path 62 into the hollow conductor 18, radially through the cooling mesh M1, through the openings 51 of the tube TU1 and into the region 53. Alternatively or concurrently the heated gas may follow the path 60 through the internal portion of the cylinder 36 and out through the holes 43 to tbe diffused laterally of the centerline CL through the mesh M2 and into the region 54. The relation between the diameter of the orifice through the contact 19, the internal diameter of the tube 12, and the velocity of the piston 38 are chosen so that the volume of space 53 increases appreciably faster than gas can flow into the space through the central orifice of the contact piece 19.

The result is a reduction in gas pressure in the space 53 and an increase in the pressure drop across the central orifice of the contact 19, which increases interrupting ability.

After the arc A has been extinguished, the movable contact assembly 34 continues movement to the right in the direction 57 until a stable opened position is reached. The puffer circuit breaker apparatus 10 is in this position ready for a closing or reclosing operation. The pressure in the three gas regions 52, 53, 54 becomes equalized if such has not occurred earlier in the opening cycle. It is to be noted with respect to the arc A that the openings 56 in the conducting flange 38 provide a path whereby the arc current A may impinge upon the inner surface of the insulating support tube 12. In a like manner, the heat of the arc A may follow the same path and raise the temperature of the inner surface of the insulating support tube 12. Furthermore, the arc products produced by the interaction of sulfur hexafluoride gas for example and the electrical arc A may contact the inner surface of the insulating support member 12. These arc products may be carried along the path 62 or along the path 60 to the regions 53 and 54, respectively. The latter regions are adjacent to the inner surface of the insulating support tube 12. It is to be noted that direct radial exposure of the inner wall of tube 12 to arc A is prevented by the pressure of the cone 46. In a like manner, since the gases are likely to be hot, the residual heat of the arc A even after cooling by the cooling meshes M1 and M2 may raise the temperature in the regions 53 and 54. It is also to be understood that the pressure of the accumulated gas within the interior of the insulating support tube 12 may increase, at least for a short time, during the arcing process because of the presence of the arc products, for example. It is therefore desirous that the insulating support tube be relatively unaffected by the direct impingement of electrical current such as may exist in the arc A or by the presence of arc products or by the presence of the heat of the arc or by the presence of relatively high pressure gas for at least a short period of time.

Because of the unitary, i.e. single shell concept, the insulating support tube 12 must not only support most of the portions of the circuit breaker apparatus 10, but must also act as an electrical insulator between terminals 24 and 14. The tube 12 must also act as a gas containing vessel heat shield and corrosion resistive vessel. Generally, it has been found that if the inner wall of the insulating support tube 12 becomes carbonized, blistering and flaking of the inner wall surface interferes with the mechanical functions of the interrupter, which of course is undesirable. It has been found that a fiberglass tube alone will not resist carbonizing and the well-known tracking phenomenon associated therewith. It has been found that the use of a thin polytetrafluoroethylene (TFE) liner for a fiberglass main tube body resists tracking in the presence of the electrical arc, resists decomposition under the heat of the electrical arc, and resists decomposition under the influence of the arc products of the electrical arc. In addition, the substantial outer fiberglass support body resists rupture under the presence of the pressure of the various gases which are present either before or after the arcing operation.

It has been found that fluorinated polymers or fluoroplastic materials such as TFE work well in the previously described circuit breaker apparatus. TFE lined tubes are constructed by first coating a steel mandrel with either of two resin system which will be discussed hereinafter. At this point a five mil (.005 in.) TFE film, such as that sold under the trade name CHEMPLAST, may be utilized. The film is etched on both sides to permit resin bonding. A sodium based etching solution may be used for the etching purpose. The etched thin film is wound on the wet mandrel employing, for example, a 50% overlap to provide a two-ply liner. While the film is being wound, it is also being continuously coated with one of the two resin systems to be discussed hereinafter. The resin systems act as a bonding agent between the plies. In the preferred embodiment of the invention the total thickness of the completed liner is .010 inch.

By referring to Figure 2, in addition to Figure 1, it can be seen that the relatively thin layer of TFE film 64 forms the inner liner for the insulating support tube 12. The remaining portion 66 (not shown to its full dimension relative to the thin film 64 in Figure 2) may comprise type 30-E glass which is filament wound. The glass roving is wet wound using one of the previously described resins over the TFE liner. A 60 helical winding pattern may be used in a preferred embodiment of the invention. The layers of glass are built up until a wall thickness of 7/16 of an inch is achieved in a preferred embodiment of the invention. At this point the tube is gelled and cured, then after cooling, stripped from the winding mandrel.

As was mentioned previously, two resin systems have been found for use with the TFE lined, filament wound tube previously discussed. One of the resins is sold under the trade name DER 330. It is a bisphenol-A/epichlorohydrin base epoxy resin. Its desirable characteristics include hardness, toughness, and resistance to chemical attack. It also possesses high tensile and compressive strength, good chemical properties, and it adheres tenaciously to most materials including etched TFE. It is also favorably suited to structural laminates, such as filament wound pipes and vessels. The formulation and cure schedule is shown below: DER 330 - 70 parts by weight Diglycidylether of Neopentyl Glycol (DCENPG)- 30 parts by weight p,p'-Methylenedianiline (MDA) - 27 parts by weight Gel 2 hours at 175"F Cure 2 hours at 212"F plus 4 hours at 3000F Another resin system which was found to be useful is sold under the trademark CY-179.

This is a general purpose cycloaliphatic-diepoxide. When anhydride cured it features good electrical loss properties, are and track resistance, and high heat deflection temperature.

Another very desirable feature is its good resistance to weathering. Even if the puffer interrupter is to be protected from weather, in some instances dust and moisture may deposit on the outside surface of the single insulating tube 12 and electrical flashover between electrodes 24 and 14, for example, may occur. In these cases the cycloaliphatic resin is a distinct advantage because of its superior non-tracking performance. Formulation and cure schedules follow; CY 179 - 100 parts by weight Hexahydrophthalic Anhydride (HHPA) - 105 parts by weight Accelerator 065 (Ciba-Geigy) - 12 parts by weight Gel 2 hours at 1750F Cure 4 hours at 3000F The TFE lining, polytetrafluoroethylene, plays a number of important functions in the interrupter 10. The thermal stability of TFE is well known. The polymer does not melt, but rather cold flows at 6200F and can be used continuously at 5000F. Short times at temperatures higher than 700"F can be tolerated without the occurrence of carbonization.

ThE has good arc resistance qualities. Carbon tracks are not formed. The surface friction of ThE is low and its static friction is lower than its dynamic friction. This is useful because the piston, i.e. seal 44, of the puffer rides against the inner wall of the tube 12. The latter piston comprises the conducting flange 38 with its seal 44. The products of arced sulfur hexafluoride do not react with TFE.

It is to be understood with respect to the embodiments of the invention that the relative thin lining of the tube 12 may be larger or smaller than 10/1000 inch as was cited in the illustrative example. The relatively thin film is necessary as a protective coating for the inner surface of the insulating support tube 12. It is also to be understood that the cylindrical relationships of the elements is not necessary. The tube 12 may be non-cylindrical or even angular in cross-section in other embodiments of the invention. It is also to be understood that the basic operating characteristics of the circuit breaker are not limiting except to the extent that the single tube is utilized in close proximity to an arc, or to the heat of the arc, or the products or the arc, or the pressure caused by the arc in the presence of gas. It is also to be understood that the arrangement of the terminals of the apparatus is not limiting. It is to be understood that the cooling materials M1 and M2 may comprise wound copper mesh, but is not limited thereto in either material or geometry.

Advantageously, the unique properties of TFE makes possible the single tube concept for this type of circuit interrupter. With the geometry and spacing of the interrupter as now established, a TFE lined tube appears to be the only practical material which can be used.

All other materials tested have been found to be damaged by the ar energy. Damage from the arc energy could be avoided by making the tube much larger in diameter and thus removing the interior part of the tube from the region of highest arc energy, but this would result in a larger, more costly and more cumbersome device, which is undesirable.

Claims (10)

WHAT WE CLAIM IS:

1. Puffer circuit interrupter apparatus comprising separable contacts, terminal means electrically interconnected with said separable contacts so that said contacts are in electrical circuit relationship with a circuit, arc extinguishing gas, puffer means operable in conjunction with said separable contacts to control an electrical arc drawn on separation of said separable contacts during operation thereof by directing said arc extinguishing gas to the region of said arc, actuating means to actuate said separable contacts and said puffer means, and a rigid electrically insulating casing having a film of fluorocarbon synthetic resin on an interior wall portion thereof, said separable contacts and said puffer means and said actuating means and said gas being disposed within said casing, said terminal means being disposed on said casing, said puffer means cooperating with said casing during said actuation of said contacts to enable said gas to flow to said contacts, said interior wall portion being exposable to the electrical current of said arc and to the heat of said electrical arc and to said arc products and to the gas pressure of the combination of said gas and said evolved arc products, said fluorocarbon synthetic resin reducing friction between said puffer means and said interior wall, said fluorocarbon synthetic resin resisting electrical tracking therein in the presence of said heat of said arc and in the presence of said arc products and in the presence of said arc current, said casing containing the pressure of the combination of said gas and said arc products without rupturing, said fluorocarbon synthetic resin shielding the remainder of said casing from said arc products and from said arc current and from a portion of the heat of said arc.

2. Circuit interrupter as claimed in claim 1 wherein said fluorocarbon synthetic resin chemically comprises polytetrafluoroethylene (TFE).

3. Circuit interrupter as claimed in claim 2 wherein said fluorocarbon synthetic resin structurally comprises wound overlapping film.

4. Circuit interrupter as claimed in claim 3 wherein said film is etched and coated with thermosetting synthetic resin for bonding said overlapping layers together.

5. Circuit interrupter as claimed in claim 4 wherein said thermosetting synthetic resin comprises epoxy resin.

6. Circuit interrupter as claimed in claim 4 wherein said thermosetting synthetic resin comprises diepoxy resin.

7. Circuit interrupter as claimed in claim 5 wherein said epoxy resin material is bisphenol-A/epichlorohydrin based.

8. Circuit interrupter as claimed in claim 5 wherein said epoxy resin material is cycloaliphatic diepoxide.

9. A circuit interrupter as claimed in any one of claims 1 to 8, in which insulating tube means are provided having first and second spaced external electrical terminal means thereon, said external terminal means communicating with the internal portion of said tube means, said insulating tube having the thin film of protective fluorocarbon synthetic resin on the interior wall thereof to protect said tube from arc effects, the first electrical contact disposed within said tube means in electrical contact with said first external terminal means, the second movable contact disposed within said tube means in electrical contact with said second external terminal means, said second contact being movable into and out of contact with said first contact, piston means fixedly disposed upon said second control means for movement therewith to compress puffer gas in a gas compression region, said piston means having an opening therein which communicates with an arc region between said first and second contacts, said puffer gas flowing through said opening into said arc region as said contacts open to effect an arc between said first and second contacts, and nozzle means fixedly disposed upon said second contact means and movably disposed upon said first contact, said nozzle means at all times being radially interposed between said arc region and said interior wall of said insulating tube means to further protect said insulating tube means from arc effects.

10. Puffer circuit interrupter apparatus, constructed and adapted for use, substantially as hereinbefore described and illustrated with reference to the accompanying drawings.