US3715543A

US3715543A - Rotary electrical switching contact assembly with hollow insulating arc barrier

Info

Publication number: US3715543A
Application number: US00105797A
Authority: US
Inventors: A Keto; R Manes
Original assignee: Westinghouse Electric Corp
Current assignee: ABB Inc USA
Priority date: 1971-01-12
Filing date: 1971-01-12
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06
Also published as: CA926900A

Abstract

An electrical switching contact assembly having a housing with stationary contacts mounted thereon, and a rotating shaft with movable contacts attached thereto. The rotating shaft is mounted within the housing in a manner which will permit the stationary and movable contacts to engage when the switch is closed. The housing and shaft are constructed to permit stacking of the assembly for polyphase switching operations. An insulated hollow arc barrier member is disposed around the movable contact assembly.

Description

United States Keto et al. 1 1 Feb. 6, 1973 54 ROTARY ELECTRICAL SWITCHING 3,590,183 6/1971 Leonard ..200/166 E x CONTACT ASSEMBLY H HOLLOW 954,462 4/1910 Peterson ..200/151 INSULATING ARC BARRIER 3,251,956 5/1966 Rasor et al. ..200/168 K UX [75] Inventors: August I. Keto, Sharon; Robert .11. FOREIGN PATENTS OR APPLICATIONS Manes wheatland' 35,161 11/1934 Netherlands ..200/151 [73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa. Primary Examiner-Robert K. Schaefer Assistant ExaminerRobert A. Vanderhye [22] Filed 1 1971 Att0rneyA. T. Stratton and F. E. Browder [21] Appl. No.: 105,797 1 [57] ABSTRACT [52] US. Cl ..200/l51, 200/155 R, ZOO/162 An electrical switching contact assembly having a H0111 21/54 housing with stationary contacts mounted thereon, Field of Search 166 155 and a rotating shaft with movable contacts attached ZOO/168 K thereto. The rotating shaft is mounted within the housing in a manner which will permit the stationary and References Clied movable contacts to engage when the switch is closed. 1 The housing and shaft are constructed to permit UNITED STATES PATENTS stacking of the assembly for polyphase switching 1,895,330 1/1933 Kempton ..200/151 X operations. An insulated hollow arc barrier member is 524,717 8/1894 Harris ..200/ 151 UX disposed around the movable contact assembly. 1,785,194 12/1930 l-lammerly ..200/l62 3,2l8,425 11/1965 Olenicket al ..200/168 UX 2 Claims, 7 Drawing Figures I l 1 I 35 I8 PATENTEUFEB 6 I915 SHEET 1 0F 2 7 4% AVAZ Q6 0 ROTARY ELECTRICAL SWITCHING CONTACT ASSEMBLY WITH HOLLOW INSULATING ARC BARRIER CROSS-REFERENCE TO RELATED APPLICATIONS Title, Quick-Make and Quick-Break Switch; lnventor, Merrill G. Leonard; filed July 31, I967; Ser. No. 657,1 l4 now Pat. No. 3,590,183.

BACKGROUND OF THE INVENTION 'such as power distribution transformers, and more particularly to electrical switching contact assemblies of thetype which may be stacked for polyphase switching operations.

DESCRIPTION OF THE PRIOR ART The increasing use in recent years of underground distribution systems has necessitated the development of auxiliary devices which must be a part of the distribution system. The load break switch is frequently used in underground distribution systems to electrically disconnect the load on the distribution transformer. It is mounted either within the transformer compartment with an external means for actuating the switch or in the associated switching apparatus connected withthe underground distribution system.

Initially, switching requirements as high as 200 amperes at 7,200 volts single phase were seldom exce eded, and existing equipment was able to meet these requirements. New underground distribution systems are being designed which will require load break switches capable'of'disconnecting the load of the distribution transformer at a potential of up to 23,000 volts in the grounded wye three phase connection with a current as high as 330 amperes. Tests on present load break switches have indicated thatoperation at this level is inadequate because of the arc persisting characteristic when the load is broken. During a load break operation at these high ratings, an arc develops between the stationary contacts and the movable contacts and travels from the movablecontacts to the movable contact carrier. The are persists between the movable contact carrier and the stationary contacts even when the movable contacts are in the extreme open position. Because of the arc persisting properties 'of present'load break apparatus at the high ratings required by new distribution systems, the present apparatus has been found to be inadequate and new and more efficient devices were found necessary.

"SUMMARY OF THE INVENTION the movable contact assembly. The purpose of the arcbarrier is to insulate the stationary contacts from the conducting member of the movable contact assembly. While an arc develops between the stationary contacts and the movable contacts in the disconnect operation, the arc is restricted from moving along the conductor assembly because of the insulating properties of the arc barrier. Without the arc barrier the arc would travel to the center of the movable contact assembly and persist. The insertion of the arc barrier effectively draws the arc into the shape of a segment of a circle. The magnetic field generated by this shape helps extinguish the arc. The effective length of the arc is increased by the insertion of the arc barrier, thus aiding in arc extinguishing.

The arc barrier is circularly designed so that friction from the dielectric medium adjacent the arc barrier is kept to a minimum. The arc barrier extends a sufficient distance below the movable contact assembly to prevent the are from traveling underneath the arc barrier. I

In another assembly the movable contact assembly is embedded in the rotating shaft during the molding process used in constructing the shaft. The rotating shaft is constructed of an insulating material which surrounds the movable contact assembly and insulates it in the region between the movable contacts from the adjacent medium. The insulating effect of the shaft material prevents the are from traveling along the movable contact assembly during an opening sequence of the switch. Because the effective length of the arc is increased as the contacts move apart, the arc will be extinguished when the movable contact assembly is in the open position.

The housing of the switching contact assembly is constructed in such a manner as to allow stacking of successive units for multiphase switching operations. The ends of the rotating shaft are molded into a specific geometric shape to allow attachment to adjacent shafts when the switching units are stacked.

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

FIG. 1 is an elevational view, partially in section, of the switching contact assembly of the invention showing the placement of the arc barrier around the movable contact assembly;

. FIG. 2 is a top view of the electrical switching assembly with the movable contacts in the open position;

FIG. 3 is an elevational view, partially in section, of a snap-action type contact rotator;

FIG. 4 is an elevational view, partially in section, illustrating the stacking arrangement of three switching assemblies; I

FIG. 5 is a sectional view of the top of a contact assembly showing the molded type movable contact assembly in the closed position;

FIG. 6 is an elevational view, partially in section, of a switching contact assembly with a molded type movable contact assembly shown in the closed position; and

FIG. 7 is a sectional view of the top of a switching assembly showing a molded type movable contact assembly in the open position.

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 an electrical switching contact assembly constructed according to the teachings of this. The switching assembly is mounted in a housing which is constructed from an insulating material. The housing 10 includes a base plate 12 with a circular opening 14, mounting brackets 50 and shoulder members and 22.

Stationary contacts

16 and 18 are attached to the

shoulders

20 and 22, respectively. The

contacts

16 and 18 are substantially flat and constructed of aconducting material, such as copper, and are secured to the

shoulders

20 and 22 by suitable means, such as rivets or screws. The base plate 12 has lower projecting members 50 which are used to connect two or more housings together.

Bolts

24 and 26 are used to attach the housing 10 to similar housings or to a switch actuating mechanism.

A longitudinal rotating shaft 28, with first and

second ends

30 and 32, respectively,'is disposed in the housing 10 with the lower end 32 extending through the opening 14. There is a circular opening 31 at the upper end 30 of the shaft 28. The opening 31 permits attaching the rotating shaft 28 to the shaft 33 which may be associated with another switching assembly or with an actuating mechanism. Pin 48 is inserted through

shafts

33 and 28 so that the

shafts

33 and 28 may be rotated together.

A movable contact assembly 34 is attached to the shaft 28 by screws 44 and a collar 42 which may be an integral part of the shaft 28.

Contacts

36 and 38 are atthe movable contacts with the stationary contacts when the shaft 28 is rotated to closed circuit or open circuit position. a v

I An arc barrier 46 is constructed ofan insulating material and disposed around the shaft 28 and over the movable contact assembly 34. The arc barrier 46 may be constructed in a tapered cylindrical shape and attached to the shaft 28 by pin 48. The diameter of the arc barrier is large enough to cover the conducting bar 40 and the inner parts of the

contacts

36 and 38. Slots in the arc barrier 48 permit the protrusion of the

contacts

36 and 38 from inside the arc barrier 46. The arc barrier extends a sufficient distance below the movable contact assembly 34 to prevent arcing. under the arc barrier.

FIG. 2 shows a top view of the switching assembly of FIG. 1, with the contactsjn the open position. Arrow 55 illustrated the direction of rotation of the shaft 28 and the movable contact assembly 34 during the breaking or opening sequence. An arc develops between

contacts

38 and 18 as soon as they lose mechanical contact during an opening sequence under load. A similar reaction occurs between the

contacts

16 and 36. As the distance between the contacts increases, the arc lengthens. The length of the arc is dependent on the properties of the dielectric between the contacts, the electrical loading, and the shape of the arc path. As the contact assembly 34 rotates, the end of the are which developed on contact 38 has a tendency to travel onto the conductor bar 40 and toward the rotating shaft 28. Tests have indicated that without the arc barrier 46, and operating under conditions representative of high voltage distribution systems, an arc develops during the breaking sequence and persists between the

stationary contacts

16 and 18 and the central portion of the conductor bar 40. This persisting arc is damaging to the switching assembly and the associated circuitry as well as being a safety hazard.

By inserting the arc barrier 46 around the movable contact assembly as taught by this invention the arc cannot move along the conductor bar 40 and must remain outside the arc barrier.

Arc paths

52 and 53 illustrate the circular shape of sustained arcs. Because the length of the arc path is increased, and due to the magnetic force associated with a circular arc, the arc extinguishing characteristics of the switching assembly taught by this embodiment of the invention exceeds those of the device without the arc barrier in place. Experimental results have indicated that an arc does not persist between the stationary and movable contacts when operated at typical distribution power levels with the arc barrier in place.

Although other designs and shapes for the arc barrier may be used to suppress the arc, the cylindrical shape described in this embodiment is advantageous because viscous friction with the adjacent medium is kept to a minimum. Minimizing the friction aids in reducing the opening time and are endurance.

FIG. 3 shows an elevational view of an actuating mechanism which may be connected to the switching assembly. Rotating handle 54 turns shaft 56 and engages the snap-action type assembly 58. The snap-action assembly 58 is connected to a lower shaft 33 which is coupled to the rotating shaft 28 of the switching assembly.

In FIG. 6 is shown an elevational view, partially in section, of another electrical switching assembly.

The housing 10, base plate 12, opening 14,

bolts

24 and 26, and the mounting brackets 50 are similar to the corresponding members described in the first embodiment of this invention. Housing shoulders 60 and 62 furnish means to mount

stationary contacts

64 and 66. The

stationary contacts

64 and 66 are similar to the

movable contacts

36 and 38 which are shown in FIG. 1 and described in the first embodiment of this invention. The

stationary contacts

64 and 66 are mounted to the housing 10 symmetrically about the opening 14 in the base plate 12.

A longitudinal shaft 68, having a first or upper end and a second or lower end 72, is constructed of an insulating material. A suitable material would be an epoxy compound formulated from bisphenal A" resin plus hexahydrophthalic anhydride hardner with a dispersed glass fiber filler. Another suitable material would be glass filled polyester. The shape of the shaft 68 permits it to be constructed by machining a suitable material or by a molding process. The movable contact member 74 includes

contacts

76 and 78, and a conducting member 77. The

contacts

76 and 78 are substantially flat and have dimensions which allow engaging with the

stationary contacts

64 and 66 respectively. The

movable contacts

76 and 78 may be separate members and attached to the conducting bar 77 or they may be an integral part of the conducting bar 77. The conducting bar 77 is substantiallyv longitudinal and has a cross-section shape of suitable dimensions to permit adequate current conducting properties. The movable contact assembly 74 is mounted in the rotating shaft 68 with their longitudinal axes perpendicular. The contact assembly 74 maybe embedded in the insulating material during construction of the rotating shaft 68 when the molding process is utilized. The movable contact assembly 74 is positioned along the rotating shaft 68 to allow the

movable contacts

76 and 78 to engate with the

stationary contacts

64 and 66 respectively.

The shaft 68 has a protruding boss 80 which electrically insulates the conductor bar 77 from the surrounding medium. The boss 80 protrudes from the shaft surface to a region 82 on the conducting bar 77. The region 82 is a sufficient distance from the rotating shaft to prevent arcing between the region 82 and the

stationary contacts

64 and 66.

The first or upper end 70 of the rotating shaft 68 is designed to connect the shaft 68 to an adjacent shaft or an actuating mechanism, such as that shown in FIG. 3. Although various shapes and methods may be used, FIG. 6 illustrates a method utilizing an opening 84 which has an octagonal cross section and extends to a point 83 within the rotating shaft 68. A shaft 71, which may be attached to either a contact assembly or an actuating mechanism, is inserted into the-opening 84. Rotating shaft 71 rotates shaft 68. A suitable adhesive or cement may be applied to the shafts to prevent backlash. This arrangement eliminates the necessity of any metallic connecting hardware, such as pins, from the arcing area.

A weep hole 86 connects the opening 84 with the dielectric material surrounding the shaft 68 and prevents entrapment of air between the

shafts

68 and 71.

The cross section of the second or lower end 72 of the shaft 68 has an octagonal shape permitting insertion into an adjacent shaft.

FIG. 5 is a top view, in section, of the switching contact assembly of FIG. 6 showing their contacts in the closed position.

FIG. 7 is a top view, in section, of the switching contact assembly of FIG. 6 with the contacts in the open position. Arrow 63 illustrates the direction of contact rotation during the opening sequence. Because of the insulating properties of the protruding boss 80 around the conductor bar 77, persisting arcs must maintain paths 65 between the

contacts

78 and 66 and 67 between the

contacts

76 and 64. However, due to the arc length and the cooling effects of the dielectric medium the arc is extinguished before the movable contact member 74 acquires the fully opened position.

FIG. 4 is an elevational view illustrating three

switching assemblies

94, 96 and 98 stacked for three phase switching operations. Housing members 102 and shaft 100 are associated with an actuating mechanism, such as illustrated in FIG. 3, for actuating the three phase switching assembly shown in FIG. 4. An oil level 104 is maintained which places all the metallic connecting hardware such as the

members

24, 26, 100 and 102, in the air space above the oil level 104. This, in effect, eliminates any metallic members from the arcing region except the

contact members

64, 66, 76 and 78.

We claim:

1. An electrical switching contact assembly comprising a housing member, said housing member having a base plate with a circular opening, first and second stationary contacts, means disposed on said base plate to attach said first and second stationary contacts symmetrically about said circular opening and in a plane substantially perpendicular to the longitudinal axis of said circular opening, a longitudinal shaft with first and second ends, said first end being constructed to receive rotational torque from an external means, said second end extending into said circular opening, a movable contact assembly with first and second movable contacts, means electrically connecting said first and second movable contacts to each other, means connecting said movable contact assembly to a first position on said longitudinal shaft so that a rotational movement of said longitudinal shaft will move said first and second movable contacts in the plane of said first and second stationary contacts to make or break electrical contact with said stationary contacts, a hollow cylindrical shielding member constructed of an insulating material and having first and second ends, the first end of said shielding member being attached to a second position on said longitudinal shaft, the second end of said shielding member having slots therein, the second end of said shielding member being disposed around said movable contact assembly with said movable contacts extending outwardly through the slots in said shielding member, said shielding member being rotated by said longitudinal shaft together with said movable contact assembly to place said shielding member between said stationary contacts and the portion of said movable contact assembly which is between said movablecontacts.

2. The electrical switching contact assembly of claim 1 wherein said first end of said rotating shaft is connected to an assembly to rotate said longitudinal shaft about its longitudinal axis.

Claims

1. An electrical switching contact assembly comprising a housing member, said housing member having a base plate with a circular opening, first and second stationary contacts, means disposed on said base plate to attach said first and second stationary contacts symmetrically about said circular opening and in a plane substantially perpendicular to the longitudinal axis of said circular opening, a longitudinal shaft with first and second ends, said first end being constructed to receive rotational torque from an external means, said second end extending into said circular opening, a movable contact assembly with first and second movable contacts, means electrically connecting said first and second movable contacts to each other, means connecting said movable contact assembly to a first position on said longitudinal shaft so that a rotational movement of said longitudinal shaft will move said first and second movable contacts in the plane of said first and second stationary contacts to make or break electrical contact with said stationary contacts, a hollow cylindrical shielding member constructed of an insulating material and having first and second ends, the first end of said shielding member being attached to a second position on said longitudinal shaft, the second end of said shielding member having slots therein, the second end of said shielding member being disposed around said movable contact assembly with said movable contacts extending outwardly through the slots in said shielding member, said shielding member being rotated by said longitudinal shaft together with said movable contact assembly to place said shielding member between said stationary contacts and the portion of said movable contact assembly which is between said movable contacts.