US2584711A

US2584711A - Circuit breaker

Info

Publication number: US2584711A
Application number: US747193A
Authority: US
Inventors: Benjamin W Jones
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1947-05-10
Filing date: 1947-05-10
Publication date: 1952-02-05
Anticipated expiration: 1969-02-05
Also published as: GB658274A

Description

Filed May 10, 1947 Inventor; Benj amh'w .W. Jorfies,

H is Attorney Patented Feb. 5, 1952 CIRCUIT BREAKER Benjamin W. Jones, Schenectady, N. Y., assignor to General Electric Company, a corporation oi 'New York Application May 10, 1947, Serial No. 747,193

1 7 Claims.

My invention relates to electric circuit breakers. and more particularly to power circuit contactors. or line switches, and has for its principal object the provision of a new and improved contactor of this type having a greatly improved contact life.

Contactors of the subject type are commonly used with blowout coils to interrupt currents having a value up to several times continuous current rating of the contactors. It has been generally understood for a number of years, that the life of the engaging contact tips in such a contactor is dependent upon a number of factors. For example, the area and shape of the contact faces, and the mechanical hardness or toughness of the contact material are known to affect contact life. Also, the strength of the blowout field may affect the contact life. Moreover, it has been recognized, in a general way, that it is de-- sirable to separate the contacts as rapidly as possible. On the other hand, the fact that the effect of these factors and their relative importance has not been clearly understood'in the past, is demonstrated by the fact that existing contactors of various manufacture operating under identical load conditions are found to have a contact tip life varying over a range of ten to one.

I have discovered that the initial opening speed of the contacts over approximately the first forty mils of opening movement is the principal controlling factor in contact tip life. Through experiment with a number of different contactors under various operating conditions, I have discovered that if the initial opening speed of the moving contact is at least thirty inches per second over at least the first forty mils of opening movement, contact tip life approaches a maximum, and the remaining factors mentioned above are of relatively minor importance. More specifically, I have discovered that an are drawn between the contacts when they separate is always drawn between the spots on the contact which separate last, and that the arc will impinge on these same two spots until the contacts separate by approximately forty mils, whether the blowout field is strong or weak. As soon as the contacts are separated by this amount, the arc will begin to move, whether the blowout field be weak or strong and whether the current be large or small.

While I have stated several times in the foregoing paragraph that the contacts must be separated by at least forty mils before an arc begins to move from the points of initial striking, I do not wish to be limited to precisely this figure.

This distance is not in any sense critical, but is a good average figure under most conditions. Actually, the minimum necessary distance for initiation of arc movement was found to be between twenty-five and forty mils, depending upon the conditions under which the arc was drawn.

With the foregoing characteristics in mind, I have devised a new and improved contactor making optimum use of the momentum and moment of inertia of the various parts of the apparatus in order most effectively to separate the contacts the necessary minimum distance within approximately one millisecond. Specifically, I have found that where a moving contact structure is struck by another movable member, such as an armature, to open the contacts, the mass of the moving contact structure should be approximately'equal to or slightly less than the mass of the armature, if the parts are movable rectilinearly; while if the moving parts are pivoted, the moment of inertia of the contact structure should be approximately equal to or slightly less than the moment of inertia of the armature. The reason for this is, of course, that if the mass or moment of inertia of the armature is too great, it will be difficult to accelerate the armature, so that the armature will not be moving as fast as desired at the instant of impact; while if the armature is too light, the momentum of the armature will be too small to impart to the moving contact structure the desired speed of initial movement, and will be unable to prevent an initial chatter at the contacts. If, however, the

mass or moment of inertia of the contact struc-- ture is the same as or slightly less than that of the armature, then a given force 'will cause the armature to attain a combination of its most useful speed and energy, so that the impact will suddenly bring the armature approximately to rest and impress its speed upon the moving contact structure.

I have discovered also that when the moving contact structure is resilient, as it frequently is, the resiliency prevents rapid acceleration of the contact tip itself, unless care is exercised in selecting the point at which impact between the armature and contact structure occurs. Specifically, I have found that the effect of resilience in retarding acceleration of the contact tip is minimized in a pivoted contact structure if the armature strikes the contact structure at or near its center of percussion corresponding to its pivot point.

My invention will be more fully understood and its various objects and advantages further appreciated by referring now to the following de- 3 tailed specification taken in conjunction with the accompanying drawing, the single figure of which is an elevational view partly in section, of a direct current contactor embodying my invention.

Referring now to the drawing, I have shown a contactor comprising a base I, having mounted thereon a stationary contact 2 positioned adjacent a blowout coil 3 and electrically connected to a terminal connector 4. Mounted upon the base beneath the fixed contact 2, is an energizing magnet comprising a magnetizable frame 5, a

coil 6 and a movable armature 1. The armature 1 is pivotally connected at its lower end to a fixed bracket 8 attached to the magnet frame 15 and depending from the lower end thereof. Pivotal connection of the armature 1 to the depending bracket 8 is made by a pair of rubber grommets 9 and a bolt 10, in the manner described and claimed in United States Patent No. 2,419,071 granted on April 15, 1947 to Chester I. Hall and assigned to the same assignee as the instant application. The armature I is provided with a laterally extending arm H disposed beneath the lower leg of the magnet frame and in engagement with a biasing spring 12. The spring 12 is a compression spring having its lower seat fixed and its upper seat on the arm ll, so that the armature 1 is biased to an unattracted or 011- cuit-opening position.

Pivotally mounted near the lower end of the armature 1, I provide a movable switch member comprising a cantilever leaf spring l3 connected at its lower end to the armature and a movable contact tip it mounted upon and carried by the free end of the spring IS. The movable contact tip I! is provided with an arcing horn l5 and is connected by a conducting cable or jumper IE to a lower terminal connector I! mounted upon the base I. Circuit-opening movement of the movable contact structure 13, l4, l5, and the armature 1 is limited by a stop l8 (shown in section) which is mounted upon a pair of studs 19 protruding in parallel spaced relation from the base i between the coil 6 and fixed contact 2. The fixed and moving contacts 2 and i4, respectively, and the blowout coil 3 are enclosed within an arc chute 20 of any desired, well-known form.

The movable contact tip 14 is connected to the upper end of the leaf spring l3 and to the jumper [6 by a rivet 2|, one head of which serves as a seat for the movable contact structure where it rests against the stop [8. t may now be observed that the movable armature l is slightly longer than the leaf spring l3, so that when the armature l is released by the coil 6 and moved to its unattracted position under the influence of the spring i2, and the leaf spring [3 it strikes the movable switch member upon the adjacent head of the rivet 2!. This point is approximately at the center of the percussion of the movable switch member corresponding to its point of pivotal attachment to the lower end of the armature I, so that there is very little tendency for the switch member to flex under impact of the armature. Sluggishness of the contact tip due to resiliency of the switch member is thus practically eliminated. Moreover, the armature I has approximately the same moment of inertia as the movable switch structure I3, ll, [5, so that upon impact of the armature with the movable switch structure in contact-opening operation, substantially the entire momentum of the armature is imparted to the switch member.

In operation, when the coil 6 is energized, the

armature 1 moves toward the coil to an attracted position and carries with it the movable switch member l3, l4, IS. The switch member moves until the contact ll engages the contact 2. Thereafter, the armature continues to move a small distance after such contact engagement to provide wiping or wear allowance action of the contacts.

As soon as energization is removed from the coil 6, the armature 1 moves toward its unattracted position under the influence of the springs l2 and B. The springs l2 and II are sufficiently strong to accelerate the armature I to a speed of at least thirty inches per second at the moment that it strikes the head of the rivet 2|. Since the armature and the movable switch member II, N, l5 have substantially equal moments of inertia, practically all of the vomentum of the armature is substantially instantaneously transferred to the movable switch member. This momentum is such that the initial velocity of the movable switch member, at least over the first forty mils of the contact tip movement, is at least thirty inches per second.

To illustrate the improved operation of a contactor embodying my invention, I compared the operation or the contactor described above and illustrated at Fig. 1 with a contactor having a shorter armature arranged to strike the leaf spring I! at a point near the free end, but somewhat below the rivet 2I. I found that in the contactor having the shorter armature, the arc remained on the initial arcing points for 3 to 8 milliseconds before it began to move. I found also that the life of the contact tips was not greater than one-hundred and fifty-thousand operations. On the other hand, with a contactor built in accordance with Fig. 1, where the moments of inertia of the armature and the movable contact structure were substantially equal and the armature struck the movable contact structure substantially at its center of percussion, as illustrated, I found that the are stuck on the initial arcing points for only 0.9 millisecond before it began to move, and that the contact tips operated satisfactorily more than two million times.

While I have described and illustrated only a preferred embodiment of my invention, many modifications will occur to those skilled in the art and I, therefore, wish to have it understood that I intend in the appended claims to cover all such modifications which fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A circuit breaker comprising, a fixed contact, a blowout coil positioned adjacent said fixed contact, a movable switch member including a movable contact engageable with said fixed contact, a movable striker member movable relative to said switch member and arranged to strike said switch member to open said contacts, said striker member and said switch member having approximately equal masses, and means for moving said striker member in a contact-opening direction with a velocity sufllcient to impart to said movable contact by impact an average initial velocity of at least thirty inches per second ov'er approximately the first 25 to 40 mils of contact opening movement whereby said blowout coil within an interval not exceeding approximately 1 milliseconds after the parting 01 said contacts initiates movement of an arc formed between said contacts.

2. A circuit breaker comprising a fixed contact,

a blowout coil positioned adjacent said fixed contact, a pivotally mounted switch member including a movable contact engageable with said fixed contact, a pivotally mounted striker movable relative to said switch member and arranged to strike said switch member to separate said contacts, said striker and said switch member having substantially equal moments of inertia, and means for moving said striker in a contactopening direction with a velocity sufficient to impart to said movable contact by impact an average initial velocity of at least thirty inches per second over approximately the first 25 to 40 mils of contact opening movement whereby said blowout coil within a time not exceeding approximately 1 /3 milliseconds after the parting of said contacts initiates movement of an are drawn between said contacts.

3. A circuit breaker comprising a fixed contact, a blowout coil positioned adjacent said fixed contact, a pivotally mounted switch member including a movable contact'engageable with said fixed contact, a pivotally mounted striker movable relative to said switch member and arranged to strike said switch member to separate said contacts, said striker and said switch member having substantially equal moments of inertia, and means for moving said striker in a contactopening direction with a velocity sufilcient to impart to said movable contact by impact an initial velocity great enough to separate said fixed and movable contacts by approximately forty mils in approximately one millisecond whereby said blowout coil initiates lateral movement of an are formed by the parting of said contacts within said approximately one millisecond.

4. A circuit breaker comprising a fixed contact, a blowout coil positioned adjacent said fixed contact, a pivotally mountedmesilient switch member including a movable contact engageable with said fixed contact, a pivotally mounted striker movable relative to said switch member and arranged to strike said switch member approximately at its center of percussion to separate said contacts, said striker and said switch member having substantially equal moments of inertia, and means for moving said striker in a contact-opening direction with a velocity sufficient to impart to said movable contact by impact an initial velocity great enough to separate said contacts by approximately forty mils in less than 1 /3 milli- "seconds whereby said blowout coil initiates a movement of an are formed by the parting of said contacts in less than said 1% milliseconds.

5. A circuit breaker comprising a fixed contact, a blowout coil positioned adJacent said fixed contact, a pivotally mounted resilient switch member including a movable contact engageable with said fixed contact, a pivotally mounted striker movable relative to said switch member and arranged to strike said switch member approximately at its center of percussion to separate said contacts, said striker and said switch member having substantially equal moments of inertia, and means for moving said striker in a contact-opening direction with a velocity sufilcient to impart to said movable contact by impact an average initial velocity of at least thirty inches per second over approximately the first forty mils of contact-opening movement whereby said blowout coil within a period of time not exceeding approximately lfi; milliseconds after the parting of said contacts initiates a lateral movement of an are formed between said contacts.

6. An electromagnetic contactor comprising a fixed contact, a blowout coil positioned adjacent said fixed contact, a movable switch member comprising a cantilever leaf spring carrying at its free end a movable contact engageable with said fixed contact, a pivotally mounted armature member movable relative to said switch member and arranged to strike said switch member approximately at itslcenter of percussion to separate said contacts, said armature and said switch member having substantially equal moments of inertia, and means for biasing said armature to its open-circuit position, the force of said biasing means being sufficient to build-up in said armature upon circuit-opening movement a momentum such that said armature imparts to said switch member by impact an average initial velocity of at least thirty inches per second over approximately the first forty mils of contactopening movement whereby said blowout coil within a period of time not exceeding approximately 1 /3 milliseconds after the parting of said contacts initiates a lateral movement of an are formed between said contacts.

'7. An electromagnetic contactor comprising a fixed contact, a blowout coil positioned adjacent said fixed contact, an energizing magnet including a movable armature pivotally mounted at one end, a movable switch member comprising a cantilever leaf spring mounted upon said armature near the pivoted end of said armature and carrying at its free end a movable contact engageable with said fixed contact, said armature and said switch member having approximately equal moments of inertia and being arranged for striking engagement at a point near the center of percussion of said switch member, and means, for biasing said armature to an open circuit position, the combined forces of said biasing means and said cantilever spring being sufilcient to cause said armature to strike said switch member with a momentum sufilcient to impart to said switch member by impact an average initial velocity of at least thirty inches per second over approximately the first forty mils of contact-opening movement whereby said blowout coil within a period of time not exceeding approximately 1 /3 milliseconds after the parting of said contacts initiates a, lateral movement of an are formed between said contacts as they part.

BENJAMIN W. JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,155,626 Steen Oct. 5, 1915 1,327,951 Haas Jan. 13, 1920 1,503,980 Carichoff Aug. 5, 1924 1,531,347 Rhodes Mar. 31, 1925 1,890,838 Whittingham Dec. 13, 1932 2,037,662 Kurz Apr. 14, 1936 2,125,149 Bruns July 26, 1938 2,200,070 Armstrong et a1 May 7, 1940 2,231 973 Van Valkenburg et al. Feb. 18, 1941 2,231,974 Van Valkenburg et al. Feb. 18, 1941 2,397,113 Iglehart Mar. 26, 1946