US1821814A - Circuit interrupter - Google Patents

Description

P 1931- c. A. NlcKLE 1,821,814

CIRCUIT INTERRUPTER Original Filed March 23, 1928 Inventor: CfliffordANicMe, log WWW H is Attorheg.

Patented Sept. 1, 1931 UNITED". STATES PATENT oFFIeE CLIFFORD A. N ICKLE, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK OIBcUI'r INTERRUPTER Application filed March '23, 1928, Serial No. 264,211. Renewed. June '5, 1931.

My inventionrelatesto devices for interrupting electric circuits, andmore particularly to vacuum switches for direct current circuits'in which a current is interrupted between electrodes separated within a highly evacuated envelope.

An object of my invention is to provide an improved arrangement for interrupting electric circuits. i

Another object of myinvention is to provide an improved arrangement for vacuum switches whereby arcing between the elec- -.trodes and consequent formation of sources tot deleterious thermionic emission from is either electrode may be avoided.

lVhen an electric circuit is interrupted by means of electrodes separated in a highly evacuated envelope any are or spark which is formed when the electrodes are moved into L0 spaced relation causes heating of the contact surfaces and thereby develops regions which may become sources of electronic emission.

If the contact surface is heated to the point where the electrons therein have sufiicient energy to break through the metal boundary into space one type of thermionic emission results' Another type of thermionic emission may result from the formation of what may be termed a cathode spot. If the contact material is'of some suitable low melting point material, such as copper, and separation of the contacts while current is flowing is initiated, the last point in contact will be vaporized by the current flowing. That is, as

" long as the current is spread over the entire surface no point is seriously heated. .But

just before the final separation the points in contact are so limited in area that the current brings them up to a point where the metal melts and vaporizes. At the same time that the contacts are separating but are still very close together the potential drop between the twocontac'ts although quite small is still millions of volts per centimeter. A gradient of the order of millions of volts per centimeter will draw electrons from a relatively cold metal and electronic emission takes lace even though the contacts are not heate' to a degree sufiicient to cause electronic emission of the first type referred to above. These electrons will form collisions with the vaporized metal in the space between the contacts. These collisions will ionize some of the metal vapor thus producing additional electrons which join those already formed and travel toward the anode or posltive electrode. The positive ions travel toward the cathode or negatively charged electrode and due to their much greater mass their motion is relatively slow so that positive charges accumulate in the region adjacent to the cathode. These positive charges produce a very high potential gradient at the cathode surface, thus continuing to pull out electrons even though the anode meanwhile has been withdrawn to a considerable distance. By my invention, low melting point materials, such as copper, become more suitable for the electrodes of direct current circuit interrupters of the vacuum type by suppressing the tendency to form cathode spots. With such materials a cathode spot is easily maintained for an indefinite period with a voltage of the order of 50 volts and currents as low as 50 or amperes. On the other hand, metals which do not favor the formation and maintenance of cathode spots, such as tungsten, may be chosen but it is desirable to suppress arcing or sparking in order to eliminate the formation of projections which may favor theformation of regions of electronic emission. By my invention high voltage gradients are eliminated or reduced to so low a value that the cathode spot effect is negligible, also the hot cathode. or thermionic emission of electrons is reduced to a negligible value.

In accordancewith my invention I provide an energy absorbing circuit in shunt to the electrodes of the interrupter to prevent any appreciable arcing between electrodes during separation and thereby prevent the formation of electronic emitting regions on the electrodes. My investigations have shown that in order entirely to eliminate an are between electrodes paralleled by an absorbing circuit when interrupting an electric circuit in which said electrodes are connected in series relation, the absorbing circuit must absorb all or substantially all of the stored 100 magnetic energy of the circuit which is to be interrupted, at such a rate that the voltage built up across the electrodes is not sufficiently high to cause a break-down of the dielec-' tric between the electrodes at any instant during the interrupting period. My investigations have also shown that the maximum potential gradient across the electrodes when they separate at a given velocity usually occurs at the instant of separation and isdirectly proportional to the current of the circuit to be interrupted and inversely proportional to the velocity of separation of the electrodes and the capacity of the condenser when such a device is used in the energy absorbing circuit. In accordance with my invention for a given current, the velocity of separation of the'electrodes and the size of the condenser are preferably so chosen as to make the rupturing potential gradient, that is, the maximum voltage per unit thickness which the dielectric between the electrodes can stand before it breaks down'electrically, greater at any. instant than the voltage built up across the absorbing circuit at the same instant.

My invention will be better understood from the following description taken in connection with the accompanying drawing in which the single figure diagrammatically illustrates one embodiment thereofyand its scope will be pointed out in the appended claims.

In the accompanying drawing I have shown an improved form of a vacuum switch which is described and claimed in an application of David C. Prince, Serial No. 264,116, filed March 23, 1928 and assigned to the same assignee as this application. As shown in the drawing, the switch is connected in a circuit indicated by conductors 1 and 2 and comprises the highly evacuated envelope 3 which may be formed either of glass, as shown, or of metal to enclose the circuit interrupting electrodes4 and 5. Suitable means, such as the tube extension 3 is provided to enable the envelope to be exhausted and sealed off when desired. A suitable pump of the type mentioned hereinafter or other suitable means may be permanently connected to the extension 3 to remove gases which may be evolved during operation of the interrupter. The electrode 4 is secured to a suitable insulating support 6 or insulated therefrom and extends through the tubular extension 7 of the envelope 3 into the central bulb portion of the envelope. The end of the tubular extension is sealed to the electrode 4, preferably by means of a yielding sylphon bellows 8', which prevents transmission of jars or shocks to the envelope 3. The electrode 5 is movable into and out of circuit closing engagement with the electrode 4 and extends through the lower tubular extension 9 and the sylphon bellows 10 at the end thereof. The flexibility of the sylphon bellows 10 readily rmits the electrode 5 to be moved into and out of circuit closing engagement with the electrode 4. The electrode 5 is maintained in alignment with the electrode 4 by means of a suitable guide member 11 through which the end of the electrode 5 is adapted to slide.

. Because the voltage required to break down a gap decreases as the pressure is decreased in the envelope and reaches a minimum at pressures of the order of a few microns and thereafter steadily rises until voltages of the order of millions of volts per centimeter potential gradient are required in a perfect vacuum, it is preferable to maintain the order of the vacuum extremely high. The vacuum preferably should be of the order-of a fraction of 9. micron; a vacuum of one tenth of a micron has been found suitable for commercial voltages. Suitable exhaustion'may be obtained by any well-known means,'such as a Gaede or molecular pump or a condensation pump of the Langmuir type. The contents of the envelope before assembly are to be suitably treated to remove occluded gases in accordance with well-known processes for the production of high vacuum apparatus, which for example, may consist in eating the metal parts to a suitable temperature approaching the melting point for a sufiicient time to remove the gases. After assembly the envelope and contents may be heated again in an oven in order to remove residual and occluded gases while the evacuation is taking place. Instead of placing the envelope and contacts in an oven the metallic portions may be subjected to a high frequency magnetic field in order to heat the parts and remove any residual gases during evacuation before the envelope is completely exhausted and sealed off.

The engagement and disengagement of the electrode 5 with the electrode 4 is accomplished by suitable means shown as an electroresponsive mechanism 12. This mechanism as shown diagrammatically in the drawing is of the type described and claimed in Letters Patent No. 1,560,440 of J. F. Tritle, issued November 3, 1925, and assigned to the assignee of my present invention. As shown,

this mechanism comprises a pivoted arm 13 carrying an armature 14 in attractive relation with the control electromagnet 15. The arm 13 is pivotally connected with the operatlng lever 16 which, in turn, is connected to operate the electrode 5 through the connecting link 17'. The link 17 is preferably of insulating material so as to isolate the operating mechanism from the potential impressed upon the electrode 5. A heavy biasing spring 18 is connected to operating lever 16'so as strongly to bias the electrode 5 out of engagement wlth electrode 4. The electrode 5 is operated lnto engagement with electrode 4 by means of the pivoted bell crank closing lever 19 connected to the closing electromagnet 20 which is energized by the closing push button 21. The switch is held closed by the magnetic attraction between the armature 14 and the electromagnet 15. The electromagnet is provided with a holding winding 22 which is normally energized from the supply source indicated on the drawing by plus and minus signs. A push button 22 is connected in series relation in a normally closed portion with winding 22 to provide a means for deenergizing winding 22 when it is desired manually to interrupt the circuit 1-2. An overload tripping winding 23 is associated with the magnetic extensions 24 between the poles of the electromagnet 15. The tripping winding 23 is shown connected in series relation with electrodes 4 and 5 and the conductors 1 and 2 of the circuit to be controlled.

In accordance with my invention an energy absorbing'circuit is connected in parallel relation to electrodes 4 and 5 and as shown preferably includes a condenser 25, although any other suitable capacitance device such as a polarization cell or any circuit capable of absorbing the magnetic energy of circuit 1-2, when the circuit is interrupted, may be used without departing from my invention in its broader aspects. As previously pointed out the absorbing circuit should have such characteristics as will permit an absorption of all or substantially all of the stored magnetic energy of the circuit which is to be interrupted at such a rate relative to the voltage built up across the electrodes that at any instant the built-up voltage will be less than the voltage required to break down the dielectric between the electrodes at the same instant. Thus when utilizing a condenser in the energy absorbing circuit the capacity of the condenser must be chosen with respect to the speed of separation available with the particular type of switch used. Since the maximum potential gradient occurs at the instant of separation and is directly proportional to the current to be interrupted and inversely proportional to the speed of separation and capacity of the condenser a proper arrangement maybe readily obtained in accordance with the foregoing principles.

The operation of the circuit interrupter is as follows: Closure of the switch 21 energizes the closing electromagnet 2O withthe resulting operation of the roller bell crank 19 into engagement with the operating arm 16. This magnet 20 is deenergized by opening switch 21. Thereupon, the spring 18 rotates the operating lever 16 about its pivotal connection to raise electrode 5 into engagement with the electrode 4. With electrode 5 thus brought into engagement with electrode 4 the circuit is closed and the operating lever 16 is free to be released by the controlling electromagnet 15. The electromagnet 15 will normally hold the armature 14 in the attracted position as long as the conditions in the electric circuit are normal or as long as holding coil 22 is energized.

In case an abnormal circuit condition should arise, such for instance, as an overload, the magnetic field set up by the winding 23 will cause the flux set up by the electromagnet 15 to be shunted away from the armature 14 thereby releasing the armature and permitting the switch to open. The characteristic feature of this type of switch which provides a quick release, coupled with the fact that light parts may be used when the contacts are separated in a vacuum and that a strong biasing spring may be used permits a high speed of separation of the contacts not only after the electrodes have started moving but at the first instant of separation. Thus, with an absorbing circuit of proper characteristics and in this case with a condenser of proper capacity chosen in accordance with the velocity of separation obtainable with the switch a substantially sparkless break may be effected. A similar opening cycle of operation may be effected by actuating switch 22 to its open position thereby deenergizing holding winding 22 which permits armature 14 to be released and contacts-4 and 5 to be separated in the same manneras previously described.

While my invention has been described more particularly with respect to a vacuum type of circuit interrupter it is also adapted for use and may be used in connection with r circuit interrupters of the quick release type, for example, of the type herein shown and described, in which the interruption is effected when the contacts are in air at atmospheric pressure, in air under a pressure greater than atmospheric pressure, or in an atmosphere of an inert gas.

In my copending application Serial No. 264,210 filed concurrently with this application, I have disclosed the switch disclosed in the parent application together with further modifications of my invention and have included in that application claims which are broader than any of the claims of this appiication.

While I have shown and described a particular embodiment of my invention, it will be obvious to those skilled in the art that changes and modifications may be made within the scope of my invention, and I, therefore, aim in the appended claims to cover all such changes and modifications as 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: 5 1. A circuit interrupter comprising relatively movable cooperating electrodes, means for strongly biasing one of said electrodes to a predetermined operating position, magnetic means for holding said electrodes in a position opposite to said predetermined position, flux shifting means for effecting a quickrelease of said holding means, and means for preventing arcing at the electrodes comprising a condenser connected in parallel circuit to said electrodes havinga capacity proportioned to the speed of separation of said electrodes so as to absorb substantially all of the stored magnetic energy of the circuit to be interrupted at such a rate that the voltage built up across said electrodes is at any in stant just insufiicient to cause breakdown of the dielectric between said electrodes.

2. A circuit interrupter comprising an evacuated envelope, cooperating circuit in- 2 terrupting electrodes within said envelope, quick release switching means for separating said electrodes initially at a high velocity of. separation, and means comprising a capacitance connected in parallel relation to said electrodes of such a value relative to the speed of separation of said electrodes that the potential built up across said capacitance shall be of such a value relative to the distance between the contact surfaces of said electrodes that the potential gradient therebetween shall be less than the rupturing potential gradient at any instant for preventing the formation of regions of electronic emission on the con tact surfaces of said electrodes at any instant when said contact surfaces are in'spaced relation.

3. A circuit interrupter comprising an evacuated envelope, cooperating circuit interrupting electrodes within said envelope, means for strongly biasing said contacts to an open position, magnetic means for holding the contacts in the closed position, flux shifting means for effecting a quick release of said holding means, and means comprising a condenser connected in parallel relation to'said electrodes and correlated in value with the speed of separation of said contacts such that the potential gradient between said contacts shall be less than the rupturingpotential gradient therebetween at any instant for preventing the formation of cathode spots on the contact surfaces of said electrodes during separation therebetween.

In witness whereof, I have hereunto set my hand this 13th day of March, 1928.

CLIFFORD A. NlCKLE.

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