US3129305A

US3129305A - Non-arcing switch

Info

Publication number: US3129305A
Application number: US82106A
Authority: US
Inventors: Ralph L Hurtle
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1961-01-11
Filing date: 1961-01-11
Publication date: 1964-04-14
Anticipated expiration: 1981-04-14

Description

April 14, 1964 um- 3,129,305

NON-ARCING SWITCH Filed Jan. 11, 1961 2 Sheets-Sheet 1 FIG.2

FIGB

INV EN TOR.

RALPH L. HURTLE A ril 14, 1964 R. HURTLE 3, 2 ,3

NON-ARCING SWITCH Filed Jan. 11, 1961 2 Sheets-Sheet 2 260 AMPS I 260 AMPS CURRENT CURRENT T.ME A FlG.8 W

7 mrwzzvr ozav RALPH L. HURTLE A TTORNEY United States Patent 3,129,305 NON -ARCING SWITCH Ralph L. Hurtle, West Hartford, Conn., assignor to General Electric Company, a corporation of New York Filed Jan. 11, 1961, Ser. No. 82,106 2 Claims. (Cl. 200-414) My invention relates to electric switching devices and particularly to electrical switching devices including a pair of relatively movable, separable contacts operating in air.

Switching devices according to the prior art, of the type including separable contacts operating in air, are characterized by the fact that in interrupting an electric current, an arc is drawn as the contacts separate. Such arcing damages and erodes the contact surfaces detracting from the ability or" the device to carry current in its normally closed condition, and shortening the useful life of the device.

Application Serial Number 82,083, filed January 11, 1961, by R. L. Hurtle and J. E. Bayles, assigned to the same assignee as the present invention, discloses a switching device including means for eliminating arcing during current interruption. In accordance with that invention, a curret-limiting device is provided, connected in electrical parallel relation to the main contacts. When the main contacts are opened, all of the current is carried by the remaining parallel path. The current-limiting device thereupon changes its resistance to a relatively high value, and the greatly reduced current is then interrupted by auxiliary contacts.

In accordance with the above-identified application, the current-limiting device is required to carry a portion of the current flowing in the circuit, at all times. Although the portion carried by the current-limiter may be relatively small, the necessity for carrying such currents at all times during normal use of the device constitutes a requirement necessitating use of a current-limiting device larger and more expensive than would otherwise be the case. The parallel path, including the current-limiter, also constitutes a source of power loss and heat generation Which is undesirable.

It is an object of the present invention to provide nonarcing switching apparatus utilizing a current-limiting device which is not required to carry any part of the current normally flowing in the controlled circuit.

It is another object of the invention to provide a nonarcing switching device utilizing a current-limiting device which is not normally connected in the controlled circuit, but which is connected in the circuit prior to opening of the circuit, in the process of a single switch-opening movement.

In accordance with the invention in one form, a switching device is provided including a pair of separable contact members. A current-limiting device, which is normally of very low resistance, is also provided, and disposed so that when the switch is in its normal closed condition, none of the current in the circuit passes through the current-limiting device. Means is also provided, however, whereby, during an opening operation, the currentlimiting device is placed electrically in parallel with the main contacts before the contacts separate.

Upon separation of the main contacts, therefore, the current is diverted through the current-limiter which, at that instant, has a low resistance value. The nature of the current-limiter used is such that upon the flow of substantial current therethrough, its resistance rises rapidly, reducing the current to a very low value. Continued opening movement of the switch then interrupts this remaining current without arcing.

The invention will be more fully understood from the following detailed description, and its scope will be pointed out in the appended claims.

In the drawings,

FIGURE 1 is a side elevation view of a switching device embodying the invention;

FIGURE 2 is a fragmentary view of the device of FIG- URE l, in an intermediate position during opening;

FIGURE 3 is a fragmentary view of the device of FIG- URE 1 in a second intermediate position during opening;

FIGURE 4 is a top plan view of the device of FIG- URE 1;

FIGURE 5 is a sectional view, taken substantially on the line 5-5 of FIGURE 3;

FIGURE 6 is a side elevation view of another embodiment of the invention;

FIGURE 7 is a reproduction of an oscillographic record of the current conditions during opening of the switch of FIGURE 1 with the current-limiter 55 removed, and

FIGURE 8 is a reproduction of an oscillographic record of the current conditions during opening of the switch of FIGURE 1 with the current-limiter in place as shown.

In the drawings, the invention is shown in FIGURE 1 as embodied in an electrical device including a base 40 of insulating material having a line terminal block 41 and a load terminal block 42 mounted thereon in spaced relation by suitable means, not shown. The line terminal block 41 supports a line terminal connector 43 rigidly secured thereto and serving to attach a line conductor 44. The load terminal block 42 has rigidly mounted thereon a load terminal connector 45 serving to connect a load conductor 46. The line terminal block also has mounted thereon a cylindrical stationary contact post 47. The load terminal block 42 has mounted thereon a pair of spaced conductive jaw members 48. The jaw members 48 serve to pivotally support a movable contact blade 49 which is pivotally supported therebetween on a pivot pin 50. The contact blade 49 has mounted on its outward end a generally U-shaped resilient conductive portion 51 having its ends attached to the end of the blade 49 by suitable suitable means such as by rivets 52. (See FIG- URE 4.) An insulating handle 53 is rigidly attached to the bight portion of the resilient member 51 by suitable means such as by a screw and nut 54.

In the position shown in FIGURE 1, the resilient side portions of the conductive portion 51 are in electrical contact with the corresponding side portions of the stationary contact post 47, so that the circuit is complete from the line conductor 44 to the load conductor 46, the current passing through the line terminal block 41, the stationary contact post 47, the conductive portions 51, the contact blade 49, the stationary contact jaw posts 48, the load terminal block 42, to the load conductor 46.

Mounted on the top of the stationary contact posts 47 is a current-limiter 55, which in turn serves to support a stationary member 56.

It will be observed that in the condition indicated in FIGURE 1, the total current passes from the conductor 44 to the conductor 46 without any portion thereof passing through the limiter 55.

The current-limiting device 55 is preferably a device of the type disclosed and claimed in my prior application Serial No. 29,629, filed May 17, 1960, now Patent Number 3,117,203, issued January 7, 1964, and assigned to the same assignee as the present invention. As shown in FIGURE 5 particularly, the current-limiting device 55 comprises a pair of spaced

metallic members

23, 24, respectively, having a relatively thin disc of highly refractory ceramic material 25 therebetween, the parts being bonded together in hermetically sealed relation by any suitable means, such, for example, as in the manner set forth in the above-mentioned application.

Members

23 and 24 are each provided with shallow circular recesses terial, preferably mercury 30.

It will be observed, therefore, that the mercury 30 is in electrical contact with each of the

members

23, 24, and extends through the aperture 28, thereby providing a thin thread-like conductor joining the two

terminals

23, 24. It will further be observed that the entire assembly is hermetically bonded together, and that no space or expansion room as such is provided.

In accordance with the operation of the current-limiting device 55 as set forth in my above-identified application, the device conducts current therethrough in its normal condition, that is, when the material 30' is in a liquid condition. Upon the occurrence of excess electrical currents, the portion of the material 30' in the capillary 28 becomes heated and is transformed to an extremely low conductivity vapor, and reducing the current to a value very near to zero. Since the cross-section of the capillary opening 28 is extremely small, for example in the neighborhood of .020 inch, its heat storage capacity is extremely small, and the time required for a rapidly increasing current to transform it to the vapor state is also extremely small, being in the range of only a few microseconds.

The operating characteristics of the limiter 55 are such that when it is subjected to a rapidly increasing current, the current will increase for only a very short time, until the mercury therein is transformed to the vapor state, (i.e., the limiter fires), reducing the current quickly. The current is not, however, completely extinguished, but instead a power arc is created through the mercury vapor. Since the mercury vapor is under extremely high pressure, resulting from the fact that it is confined to substantially the original volume occupied by the mercury as a liquid, the resistance of the arc is such as to maintain it at an extremely low value. During this period, a fine balance is maintained between the influence of the voltage, which tends to drive the current higher, and the pressure created by any rise in the current, which tends to increase the resistance of the arc and therefore to drive the current lower. The net result is that the current remains at a substantially constant level during this period of time, until a complete disconnection of the circuit occurs.

In operation, the handle 53 is raised to interrupt the current. In the intermediate position indicated in FIG- URE 2, the resilient conductive portion 51 bridges or contacts both the stationary contact 47 and the stationary contact 56. At this time, substantially all the current is still going through the contact post 47. As soon as the contact member 51 clears the stationary contact portion 47, however, all of'the current is forced to take the path through the limiter 55 to the stationary contact 56 and thence to the contact portions 51. When this occurs, the limiter is fired, reducing the current to a very low level. Continued upward motion of the handle 53 interrupts the remaining current by separation from the stationary contact 56, this normally occuring without arcing. It will be observed therefore, that the first stationary contact, i.e. contact 47, comprises a main current carrying contact,while the second stationary contact, i.e. 56, comprises an interrupting or arcing contact.

It will be observed that the limiter 55 is not called upon to carry any current during the normal usage of the control device. Since this is so, the limiter may be designed :to perform its duties of reducing the current to a very vention disclosed herein is also extremely useful in applications where a certain degree of arcing is permissible. In such cases, the invention disclosed herein makes it possible to interrupt electric circuits of relatively high current values or voltage values or both. It will be understood that the severity of arcing in an electric circuit is a function both of the current interrupted and of the voltage of the circuit.

In order to insure that the current transfers from the main path to the path including the regulating limiter, the design and application of the device must be such that the voltage drop through the limiter following transfer of the current is not greater than about 15 volts, which may be referred to as the commutating voltage. If the resistance through the limiter is greater than that required to produce such a voltage drop, arcing will occur between i the contact portions 51 and the contact portion 47.

It will be appreciated that a certain amount of time is required for the contact portion 51 to travel across the contact member 56 and to finally break therefrom. This time will be referred to, for convenience, as transit time. In order for the current to be in a depressed condition at the time the contact members 51 separate from the contact member 56, the transit time, that is the time between the firing of the limiter 55 and the separation of the contact portions 51 from the contact portion 56, cannot be greater than the period of time during which the current can be maintained in a depressed condition by the limiter. In other words, the limiter must maintain the current in a depressed condition from the time of firing to the end of the transit time.

It will be appreciated that the design considerations set forth in my above-mentioned applicationmay be applied to select a regulating limiter having the desired characteristics for each application. Thus, once the normal current carrying ability ofthe switch is decided upon, and the amount of arcing to be tolerated is also decided upon, there will be indicated a certain amount of resistance or voltage drop which must be introduced in the circuit to provide the desired results. At the same time, it will be kept in mind that in order to achieve the diversion of the current from the main path through the regulating limiter path, a commutating voltage must be avoided.

In FIGURE 6, I have shown a form of the invention corresponding generally to the form shown in FIGURE 1, excepting that the stationary contact jaws 58 are extended upwardly beyond the pivot point 59 and are provided with a transversely extending pin 60 serving to support one end of a tension spring 61 having its other end anchored on a pin 62 carried by the contact blade 63. A stop pin 64 is also provided carried by the contact jaws 58. The contact portion 65 is provided with an insulating handle portion 66, which is releasably held under a resilient catch 67 which includes a handle portion 68.

In'operation, the switch is normally in the condition shown in FIGURE 6, in which no current passes through the regulating limiter 69. The tension spring 61 is biasing the contact blade 53 toward open circuit position, but it is held in closed circuit position by the resilient latch 67. When it is desired to open the switch, the handle portion 68 is pulled to the left, releasing the catch 67 from the member 66 and allowing the spring 61 to move the contact to the open circuit position as indicated in dotted lines, the switch blade coming to rest against the stop 64.

In this form of the invention, the transit time, that is the time for the contact portion 65 to sweep across the stationary contact portion 70 is fixed, and is determined by the strength of the spring and the inertia of the parts. Therefore the actual separation time can be more closely estimated.

While I have shown only two specific embodiments of the invention, it will be readily appreciated thatmany modifications thereof may be made. I therefore intend,

movable switch member as said movable switch member is moved from closed position to open position; (d) said first stationary contact having a pair of pposed contact surfaces extending in a direction genby the appended claims, to cover all such modifications as fall within the true spirit and scope of the invention.

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

1. An electric switching device comprising:

erally parallel to said predetermined path and dis- (a) an insulating support; posed and arranged to be slidably engaged by said (b) a first generally cylindrical stationary contact pair of resilient contact portions of said movable member supported on said support; switch member respectively; (c) a current limiting device mounted on said first (e) a current limiting device carried by said first stastationary contact member and comprising a pair tionary contact; of generally disc-shaped conductive members spaced (f) a second stationary contact member carried by said apart by a generally disc-shaped insulating spacer current limiting device and having a pair of opposed having a hfole therethfrifiugh cendtrglly thefieoftand a condtact (siurfaces aclso elinrtendmg generally parallel to quantity 0 mercury mg sai o e an m erconsai pre etermine pa meeting said conductive members; (g) said first stationary contact, said current limiting (d) a }second genterglly cyliriidrical sttaltiongry tzlontact device, alnd saidnsecond stationary contact being conmem er suppor e on sat curren 1rn1 mg evice; necte eectrica yin series; (2) said first and second stationary contact members (it) said pair of resilient contact portions of said movand said current limiting device being stacked in subable switch member being in contact with said first t t' 1 1 me t; (1) Z 1 203312 1 ch ri tact blade pivotally supported on 2?; giii eii g i it wh fi sg ic l iiir iv e t lilg s wisc ll said support on a pivot pin extending at right angles member is in said closed position; to the axis of said stationary contact members, said (i) said pair of resilient contact portions having a dimovable contact blade having at least a portion theremension in the direction of movement of said movof comprising spaced-apart side portions disposed able switch member suflicient to bridge said first and and arranged to engage opposite side portions of said second contact members as said movable switch memfirst and second stationary contacts respectively; her is moved from said closed to said open circuit (g) said movable switch blade being movable from a position, whereby during movement of said movable closed circuit position in which it is in engagement contact member, said current limiting device is iniwith said first stationary contact to an open clrcuit trally out of circuit and carriesno current and secposition in which it is electrlcally disconnected from ondly is connected electrically in parallel with sald 050$ saiddgrst fandgecolnd stationaryfcontdacts; bl first statgilnaryl fiontact, and thirdly is connected in e W1 0 sai s1 e portions 0 sai mova 6 series w1 sai rst stationary contact. contact blade being greater than the spacing between said first and second stationary contact members so References Cited m the file of this patent as to cause said movable switch blade to bridge said UNITED STATES PATENTS first and second stationary contact members in at 470,161 Wurts Mar. 1, 1892 least one position of said blade as said blade is moved 2,306,728 Heddaeus Dec. 29, 1942 from said closed to said open circuit position. 2,351,826 Lindell et a1. June 20, 1944 2. )An electric switch comprising: 2,469,203 Palme et al. May 3, 1949 a a pp r 2,621,272 Kojis Dec. 9, 1952 (b) a first stationary contact carried by said support; (0) a movable switch member pivotally supported on FOREIGN PATENTS said support at a point spaced from said first station- 1,069,255 Germany Nov. 19, 1959 ary contact and having a pair of spaced resilient con- 1,075,711 Germany Feb. 18, 1960 tact portions, said resilient contact portions being 303,242 Great Britain Jan. 3, 1929 movable along a predetermined arcuate path by said 189,487 Switzerland May 18, 1937

Claims

1. AN ELECTRIC SWITCHING DEVICE COMPRISING: (A) AN INSULATING SUPPORT; (B) A FIRST GENERALLY CYLINDRICAL STATIONARY CONTACT MEMBER SUPPORTED ON SAID SUPPORT; (C) A CURRENT LIMITING DEVICE MOUNTED ON SAID FIRST STATIONARY CONTACT MEMBER AND COMPRISING A PAIR OF GENERALLY DISC-SHAPED CONDUCTIVE MEMBERS SPACED APART BY A GENERALLY DISC-SHAPED INSULATING SPACER HAVING A HOLE THERETHROUGH CENTRALLY THEREOF AND A QUANTITY OF MERCURY FILLING SAID HOLE AND INTERCONNECTING SAID CONDUCTIVE MEMBERS; (D) A SECOND GENERALLY CYLINDRICAL STATIONARY CONTACT MEMBER SUPPORTED ON SAID CURRENT LIMITING DEVICE; (E) SAID FIRST AND SECOND STATIONARY CONTACT MEMBERS AND SAID CURRENT LIMITING DEVICE BEING STACKED IN SUBSTANTIAL AXIAL ALIGNMENT;