US 2340682 A
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Description (OCR text may contain errors)
Feb. 1, 19440 A. H. POWELL 2,340,682
ELECTRIC CONTACT ELEMENT Filed May 6, 1942 Fi gl. H 4 L 5/ .T 17}! '7 ii I. T
m Illll IlIlE \F I F 18 A A Inventor": Ahr'ic H.1 0 ell, fl aAWZ His Attowng Patented Feb. 1, 1944 ELECTRIC CONTACT ELEMENT Alric H. Powell, Yeadon, Pa., assignor to General Electric Company, a corporation of New York Application May 6, 1942, Serial No. 441,894
My invention relates to electric contact elements and particularly to means for extinguishing electric arcs between circuit breaking contacts. While not limited thereto the invention is particularly applicable to the contact of manually operable or other slow moving electric switches such as electric switches, controllers, and the like.
It is quite generally agreed that to interrupt quickly an electric are it is necessary both to attenuate and to cool the arc. While magnetic means have long been used for attenuation without any special attempt to cool, and air blasts have been used for both attenuation and cooling, it is not known to provide a simple, self-centered and inexpensive magnetic structure which is effective both to attenuate and to cool an arc without the provision of special air blast means. Furthermore, prior magnetic blowout arrangements frequently permit concentration of the arc in the region of burnable insulating portions of the switch and its terminal connections.
One object of this invention is to provide new and improved magnetic means for extinguishin an are between separable contact elements.
A further object of this invention is to provide magnetic means for the above purpose which shall be of simple, durable, and inexpensive construction.
It is a still further object of the present invention to provide magnetic blowout means for the separable contacts of an electric switch which shall be relatively small in size and easily mounted within a limited space.
It is another object of the invention to arrange electric arc extinguishing magnetic blowout means in connection with electric switch contacts in such manner as to obtain an optimum effeet in lengthening and deionization of the electric are.
It is a still further object ofmy invention to provide a magnetic blowout means for an electric are which shall tend to draw the arc toward the moving contact and away from the stationary switch parts.
To the attainment of the above and other objects my invention preferably comprises a small permanent magnet of relatively high coercive force mounted upon the movable contact of a pair of separable contact members in such a manner that the engaging portion of the movable contact is interposed substantially between the pole pieces of the magnet thereby to set up a magnetic flux across the face of the movable contact. The
magnet may conveniently, though not necessarily, be of substantially U or V-shape in the nature of a horseshoe magnet, and the magnet is positioned so that its bight passes behind the movable contact while its pole faces are disposed diametrically across the face thereof. The lines of force thus set up across the face of the moving contact may be resolved into a plurality of radially displaced fiux patterns having as their center a straight line between the pole pieces of the magnet. When the contacts are separated, the interaction of a magnetic field of the pattern described with the current in the arc path will force the major portion of the arc to follow the moving contact and magnet. Thus the arc will be lengthened and forced into cooler air not only by the well known magnetic blowout effect but will be further lengthened and further cooled by being made to follow the moving contact member which is itself moving into a cooler region. The advantages of such an arrangement over one in which a blowout magnet is mounted upon the fixed contact will be obvious. Where a blowout magnet is mounted upon the fixed contact the arc will be concentrated about an immovable point and the region of this point will become excessively heated. Such conditions are not favorable for deionization of the are.
My invention will be better understood by referring now to the following detailed specification taken in conjunction with the accompanying drawing. in which Fig. 1 is a side view partly broken away of a panel-mounted multiple contact finger manually operable control switch embodying my invention; Fig. 2 is a sectional view taken along the line 22 of Fig. 1; Fig. 3 is an enlarged plan view of the stationary and movable contact members only; Fig. 4 is a cross-sectional view taken along the line 4-4 of Fig. 3, and Fig. 5 is an enlarged and exploded perspective view of the movable contact member and blowout magnet.
Referring now to the drawing and particularly to Figs. 1 and 2, I have shown a manually operable control switch generally similar in construction to that described and claimed in Patent 2,202,698, issued May 28, 1940, to Isaac R. Latta. The switch is mounted within a casing III which is attached to a support, such as the panel II, by means'of supporting bolts l2 and I3 passing through the panel. The switch itself comprises a stationary contact block l4 having a plurality of pairs of stationary contacts I 5 mounted on opposite sides thereof, each pair being provided with a terminal connector l6. Between each pair of stationary contacts I5 is arranged an insulating barrier l1 provided at its lower end with a.
net 34 pair of octagonal bosses I8 on one side thereof and a pair of aligned octagonal recesses on the opposite side thereof. The bosses l8 and aligned recesses are assembled in nesting relation to space the barriers, and the barriers are bolted firmly together and to a front supporting plate I9 by means of threaded tie rods passing through the octagonal bosses IS. A support It is recessed to receive the adjacent octagonal bosses l8 and illustrates the manner in which the remainder of the barriers H are nested together.
Between each pair of barriers II two oppositely disposed movable contact members or fingers 2| are pivotally mounted upon the octagonal bosses l8, as'illustrated at Fig. 2. Each movable contact finger 2| is formed of astrip of copper or other electrically conducting material resiliently connected to a rotatable cam lever 22, by means of a pin 23 and a wipe spring 21. Each contact finger 2| is electrically connected to a terminal block 25 by means of a flexible shunt 26. The
movement of each pair of oppositely disposed.
movable contact fingers 2| is controlled by three centrally located rotatable cams 21. 28 and". The cams are mounted on a manually rotatable operating shaft 30 extending. through the panel H and terminating in an operating handle II. The cams 21 and 29 are each suitably shaped to move one contact finger 2| to a circuit closing position by engagement with one of the cam levers 22, while the cam 28 is suitably shaped to move both oppositely disposed fingers 2| to their circuit opening positions in a desired sequence by engagement with the pins 23.
Referring now particularly to Figs. 3, 4, and 5, it will be observed that the upper end of the movable contact finger 2| is provided with a diskshaped contact button 32, the diameter of which is somewhat less than the width of the strip 2| and which is welded or otherwise suitably secured to the contact finger 2|. From the foregoing description of the switch-actuating structure it will be evident that movement of the contact button 32 from its circuit-closing to its circuitopening position is accomplished without any appreciable relative rotation of the surface of the moving contact with respect to the surface of the fixed contact. Such substantially straight line movement of the moving contact surface along a line substantially perpendicular to the fixed contact surface is accomplished in the i1- lustrated embodiment of the invention by pivoting the moving contact at such a distance from the contact surfaces that its arcuate movement is very smallcompared to the length of the contact finger 2|. The movable contact support 2| is notched, as at 33, on diametrically opposite sides of the contact button 32 to provide for the mounting of a generally U-shaped permanent magnet 34. It will be understood that the magnet 34 may have any suitable configuration such that its pole pieces will be disposed on opposite sides of, or otherwise substantially diametrically with respect to, the movable contact button thereby to establish radially displaced flux patterns across its face as previously described. It is not necessary for this purpose that the pole pieces embrace the contact, but a simple bar magnet disposed parallel to the contact surface will have the desired effect to some extent. Preferably, however, the magnet is of generally U-shape and magnetized in the manner of a horseshoe magnet. As best shown at Fig. 5, I prefer to form the magas a substantially semi-circular wafer movable contact button 32.
In order to limit the physical proportions of my As previously pointed out, th greatest concentration of lines will be on the side? 2; Elsie movable contact to engage the fixed con- 0 I wish to have it understood that it is not necry that the line of intersection of the planar magnetic flux patterns lie in the contact surface of the moving contact member, and in fact I of Ithe movable contact surface.
n operation, when any pair of contacts is separated while carrying current, an initial arc will lines in the plane AI substantially at right angles and, according to well known electromagnet theory, the arc will be forced in a direction perpendicular to both the of Fig. 4 it will is further attenuated by continuous upward displacement, it comes progressively under the influence of lines of force which are gradually approaching the position of the lines of force in the plane HI. Thus the component of force exerted upon the arc tending to move it toward the movable contact is gradually increased. It will now be evident that the arc is displaced by the ma:- net not only upward to attenuate it, but also in the direction oi the movable contact further to attenuate it. Of course it will be understood that upward displacement of the arc is aided by heating of the air in the region lying immediately between the fixed movable contacts.
From the above description of an arc-interrupting operation it will be evident that by location of the blowout magnet 34 upon the movable contact rather than upon the fixed contact, I can force the electric arc to concentrate in the region of the movable contact. Since the movable contact, in moving from its closed circuit to its open circuit position, is continually moving into cooler air, it will be evident that the major portion of the arc is more efllciently cooled than it would'be if it were permitted to concentrate in the region of the fixed contact where the surrounding air might become excessively heated. This more eillcient cooling of the arc contributes to its deionization and rapid interruption. By actual test it has been found that a sample switch, in interrupting arcs up to its capacity of '75 amperes at 250 volts, possessed approximately 15% greater interrupting capacity throughout the range when the permanent magnet 34 was attached to the movable contact than when it was attached to the fixed contact.
A further advantage of my invention lies in its particular suitability to all types of switches in which it is imperative that the are be directed away from the fixed contacts. For example, in the switch which has been shown and described. the fixed contact support I 4 is of insulating material and may be detrimentally burned if exposed to a very hot arc. Also, many insulating materials, if exposed to an arc, will carbonize on the surface so-that the surface becomes electrically conducting. v terminal connectors i6 necessitates wiring of the switch in such a manner that the lead wires to the fixed contacts lie on top or the fixed contact support. It is, of course, essential that the Furthermore, the location of thearcs be kept away from this wiring so that the wiring insulation will not be burned away. Burnin: or these insulating parts is avoided by my inand scope of my invention.
What I claim as new and desire to secure by Letters Patent 01' the United States is:
In a circuit interrupter, the combination of fixed and movable contact members, each of said contact members comprising a strip of electrically conducting material and a contact button mounted thereon, the movable contact strip being wider than the attached contact button and being slotted at diametrically opposite sides of said button,'manually operable means for actuating said movable contact member from a, circuitclosing to a circuit opening position to separate said contact buttons and establish therebetween an electric arc, and means for extinguishing said are comprising a substantially U-shaped permanent magnet mounted upon said movable contact member with its bight disposed behind the movable contact button, the pole pieces of said magnet lying in said diametrically disposed slots with the movable contact button interposed therebe- I tween thereby to establish across the engaging face of said movable contact button a plurality of lines of magnetic force forming a plurality of radially displaced planar fiux patterns intersecting on a straight line between the pole pieces of said permanent magnet, whereby the force exerted by said lines of force upon said are forces said are to assume a curved and attenuated path of a shape tending to concentrate the major portion of said are about said movable contact member.
ALRIC H. POWELL.