US1792340A

US1792340A - Circuit interrupter

Info

Publication number: US1792340A
Application number: US285412A
Authority: US
Inventors: Wellman Bertram
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1928-06-14
Filing date: 1928-06-14
Publication date: 1931-02-10
Anticipated expiration: 1948-02-10
Also published as: GB313563A

Description

Feb. 10, 1931. WELLMAN 1,792,340

CIRCUIT INTERRUPTER Filed June 14, 1928 Inventor I Bertram We! [man His Attorney Patented Feb. 10, 1931 UNITED STATES PATENT OFFICE IBERTRAM WELLMAN, 0F SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK CIRCUIT INTERR'UPTER Application filed June 14,

This invention relates to circuit interrupters and the principal object is to provide improved methods and means for quickly and effectively extinguishing the are or discharge ordinarily accompanying-the interruption of the circuit. a

The present invention is particularly advantageous in connection with vacuum switches having circuit interrupting contacts separable in a highly evacuated container, although it may be employed with limited advantages in other forms of circuit interrupters. Moreover, the invention is of special advantage in interrupting direct current circuits, but may be used to obtain a quick interruption of alternating currents if desired.

\Vith the vacuum switch type of circuit interrupter in which the contacts are separated within a highly evacuated container, the interruption of alternating current circuits is most readily accomplished for the reason that the are or discharge occurring upon separation of the switch contacts tends automatically to extinguish itself when the alternating current passes through the zero point of the wave. However, in direct current circuits there is no such tendency and the ability of a vacuum switch to interrupt such circuits is correspondingly restricted.

Furthermore, the circuit interrupting ability of a vacuum switch in both alternating and direct current service depends to a considerable extent upon the particular material of which the switch contacts are formed.

' This is due to the fact that two different types of electron discharge may occur upon separation of the contacts of the vacuum switch'dependent upon the material of the contacts.

Thus a hot cathode type of emission may occur where the vacuum switch contacts are formed of a high melting point metal such as tungsten. In this case any are or spark which is formed when the contacts are initial- F ly separated or any highly localized heating of the last points of contact due to the excessive concentration of the current therein may raise the temperature of the contact material sufficiently to produce electronic emission therefrom. If the continued passing of 1928. Serial No. 285,412.

current results in the production of sufficient heat at the cathode to maintain the contact On the other hand, if the contacts of the h switch are of some low melting point material, such as copper, which vaporizes be fore the electron emission temperature is reached, arelatively cold cathode type of emission may result. In this case, the initial separation of the low melting point contacts while current is flowing may also cause arcing or result in a highly localized heating of the last points of contact such that the low melting point material is raised to the temperature where the material melts and vaporizes. At the same time, as the contacts are initially separated any appreciable potential drop therebetween may produce avery high voltage gradient. Even a relatively small absolute voltage drop be- .tween the contacts while still very close together may produce a gradient of the order of several millions of volts per centimeter. Such a voltage gradient will draw electrons from a relatively cold metal and thus produce electronic emission between the contacts even though they are not heated to a temperature sufiicient to cause electronic emission of the type referred to in connection with the high melting point contact material. The electrons drawn from the low.melting point material of the negative or cathode contact by\the high voltage gradient inevitably will collide with the molecules of metal vapor in the space between the contacts. Such. collisions will io'nize the metal vapor", thus producing additional electrons which join those already formed and travel under the influence of the impressed voltage toward the anode, or positive electrode. The positive ions travel towards the cathode, or negative electrode, and due to .meanwhile have been separated to a considerable distance.

Thus, it will be seen that when this type of electronic emission is once initiated the current in the circuit may continueindefinitely. However, in alternating current service where the current between the low melting point switch contacts .inherently passes through zero and reverses the ionized metal vapor is quickly dissipated and the emission phenomena automatically ceases substantially as soon as the current reaches the zero value. In this way even high voltage alternating current circuits are readily interrupted by vacuum switches having contacts of low melting point material. In direct current service, there is no such emission between the contacts of low melting point material and thereby interrupt the circuits.

My present invention, however, enables a vacuum switch having contacts of low melting point material quickly and eiiectlvely to interrupt direct current circuits. Briefly,

this is accomplished by providing means for reducing the direct current between the vacuum switch contacts substantially to zero value or at least below the value required to sustain the are or electron discharge after the contacts areseparated. When this oc-. curs the ionized vapor produced upon the separation of the low melting point vacuum switch contacts is quickly dissipated and thereby the electronemission phenomena is efl'ectively stopped in substantially the same manner as occurs with alternating current circuits. The reduction of the direct current to zero 'or below the are or electron discharge sustaining value preferably is obtained by connecting a charged condenser across the contacts after they have been separated sufficiently to start the electron emission phenomena so as to impress a voltage on the re sulting are or discharge between the contactsin opposition to the sustaining voltage thereof. In this way the are or discharge between the vacuum switch contacts is effectively extinguished. When once extinguished the electron emission phenomena cannot restart since the contacts are separated. Furthermore, in accordance with the present invention I provide an improved arrangement for automatically charging the condenser and connecting it to the switch contacts.

From another viewpoint, the connection of the charged condenser across the vacuum switch contacts serves to divert the current areas-ac denser in shunt with the separated switch contacts, the voltage of the charged condenser acts cumulatively with the voltage producing the current in the direct current circuit to divert the current through the shunt circuit including the condenser. Hence a large current can be quickly diverted from the are through this shunt circuit. This diversion of current quickly reverses the charge of the condenser and at the same time extinguishes the arcing or electron emission discharge between the switch contacts. Thus when the condenser is fully charged in the reverse direction, the direct current circuit is eflectively interrupted. The reversing of the charge of the condenser enables a condenser of relatively small capacity to be used to extinguish the arc or'discharge of the vacuum 4 switch. However, an uncharged condenser of reversal of current to stop the electron.

sufiicient capacity maybe used to extinguish the are or electron discharge between the vacuum switch contacts after they are separated. The im ortant feature is to connect either the charged or uncharged condenser across the vacuum switch contacts after they have been separated a sufficient distance to insure that the arc or discharge cannot recontacts a sufficient distance apart to pre- Vent re-establishment of the sparln'ng or areing requires a relatively longer time. This difficulty is overcome, however, in accordance with the present invention by connecting the condenser across the contacts only after they have been separated the required distance. In this way no matter how rapidly the condenser is charged, the arc between the contacts is effectively extinguished at the instant of connection'of the condenser thereacross.

Moreover, my present invention is not necessarily limited to the use of either a charged or uncharged condenser since other equivalent means may be employed for reducing the direct current to substantially zero value after the contacts of the vacuum switch have been separated. Thus a transformer may be connected in the direct current circuit and an alternating current superimposed upon the direct current in such a way as to reduce the current between the switch Ill contacts to zero value after the contacts have been separated to extinguish the are or electron emission therebetween. 3

In the accompanying drawing Fig. 1 is a circuit diagram schematically illustrating a preferred embodiment of the present invention wherein acharged condenser is used with a vacuum switch for interrupting direct current and Fig. 2 is a schematic circuit diagram of a modified direct current vacuum switch interrupting arrangement utilizing a transformer for extinguishing the are or electron discharge between the switch contacts.

The vacuum switch 10 illustrated diagrammatically in Fig. 1 may be of any suitable form in which the

contacts

11 and 12 are separated within a highly evacuated container 13. As shown, the contact 12 is moved into and out of engagement with the stationary contact 11 by means of the electromagnetically controlled operating mechanism ll. Relative movement of the contact 12 within the container 13 is permitted by employing a'flexible or yielding sylphon 15 for sealing the operating rod 16 upon which the movable contact 12 is carried to the easing 13. lit will be understood that the most improved technique is employed in exhaust-- ing the casing 13 to a very high degree. Moreover, the

contacts

11 and 12 and other parts within the casing should be specially treated to remove all occluded gases. This may be accomplished by heating the parts during exhaustion preferably by inductive action or by electron bombardment and the casing of the vacuum switch may be freed of gases by baking during exhaustion. The exhaustion of the casing 13 preferably is carried to a point where the vacuum is of the order of 1/100 of a micron pressure or better with all of the occluded gases removed.

The vacuum switch 10 is shown connected to control the establishment and interrupting of the circuit through which power is supplied from the direct current generator 17 to a suitable load indicated diagrammatically in the drawing, as the load resistor R1. It will be understood that means other than the vacuum switch 10 may be provided for establishing the circuit and the vacuum switch used only for interrupting the circuit if desired.

The operating mechanism 1d of the vacuum switch which may be of any suitable type is shown diagrammatically as of the type in which the toggle mechanism 18 is biased by the spring 19 to separate the

contacts

11 and 12 of the vacuum switch. The toggle mechanism is held in the position in which the vacuum switch contacts 11 and 12 are in engageinent by means of the latch 20. The releasing electromagnet 21 is connected to be energized in accordance with the current in the circpit and arranged'to release the latch 20 to effect the separation of the

vacuum switch contacts

11 and 12 upon the occurrence of an excessive overload current in the circuit.

As previously pointed out the action of the vacuum switch in interrupting the circuit depends upon the material of which the cir

cuit interrupting contacts

11 and 12 are formed. When formed of a high melting formation of a cathode spot and accompanying ionization of the vaporized metal of the contacts. With the contacts of either high nieltingor low melting point material, the discharge or are therebetween is effectively extinguished in accordance with the present invention by means of the condenser 22.

As shown in Fig. 1 one plate of the condenser 22 is permanently connected to the stationary contact 1.1 of the vacuum switch. The other plate of the condenser is connected through conductor 23 and the resistor R2 to be charged by the voltage appliedto the load represented by the resistor R1. llhe conductor 23 also is connected to the stationary switch contact 24 having a cooperating switch contact 25 illustrated as carried by the operating arm 16 of the vacuum switch 10, the circuit extending through the switch'26 having a dashpot 27 or other suitable means for delaying the opening thereof. The arrange ment is such that the time element contact 26 is maintained closed and the contact 25 is maintained out of engagement with the contact 24 when the vacuum switch 10 is in the closed position, as illustrated in the drawing. while the

contacts

24 and 25 are brought into engagement during the separation of the

vacuum switch contacts

11 and 12 and the contact 26 is released to open a time interval thereafter as determined by the time element device 27.

The operation of the invention in the form illustrated in the drawing is as follows: lVith the vacuum switch 10 closed, the direct current generator 17 supplies current to its load R1. Elie voltage of the generator 17 applied to the load R1 is also impressed upon the condenser 22 through the limiting resistor B2. In this way the condenser 22 is fully charged with the voltage and polarity of the charge corresponding to that of the generator 17, the polarities being indicated by the corresponding symbolts and l i henever the

contacts

11 and 12 of the vacuum switch are separated to interrupt the circuit either through operation of the overload releasing electromagnet 21 or by operation of the manual releasing handle 20a, an are or discharge occurs between the vacuum switch contacts of the type depending upon the material of which the contacts are formed as previously described. However, during the separation of the contacts the auxiliary contact is brought into engagement with the cooperating contact 24: while the time element contact 26 remains closed. This connects the condenser 22 so as to impress the voltage of its charge on the are or discharge between the vacuum switch contacts in opposition to the sustaining voltage of the are or discharge between the

vacuum switch contacts

11 and 12. The opposing voltage of the condenser 22 immediately neutralizes the voltage tending toniaintain the are or discharge between the

vacuum switch contacts

11 and 12. As a result, the are or discharge immediately is extinguished. Where the contacts are of low melting point material, the electron flow when once stopped cannot restart due to the immediate dissipation of the ionized metal vapor in the space between the contacts. Thus, when the current flow between thecontacts is once stopped it does not restart and the circuit is maintained interrupted. It should be noted that the engagement of the

auxiliary contacts

24 and 25 does not occur until after the contacts of the vacuum switch have been separated an appreciable distance. This insures that the discharge between the contacts is not re-established when it is once interrupted by the action of the condenser in the manner just described.

lhe limiting resistor R2 is of suficiently high resistance to maintain the current from the generator 1'? through the

auxiliary contacts

24 and 25 at a minimum or negligible value since without such a high resistance in the circuit, the contacts 24- and 25 would in efiect short circuit the generator. After the discharge between the vacuum switch contacts has ceased, the time delay contact 26 is opened thereby disconnecting the condenser 22 and the limiting resistor R2 from the negative side or" the generator 17. desired the time delay contact mechanism may be omitted and instead the contacts 2% and 25 may be arranged to make momentary sliding engagement only during the final por- 'tion of the movement of the operating rodjld and thereby temporarily connect the con denser 22 across the vacuum switch contacts only long enough to effectively stop the electron discharge therebetween and then automatically open the circuit.

/Vhile the foregoing describes the operation of my invention from one aspect, it may be also considered from another aspect. That is, with the vacuum switch contacts closed and current flowing therethrough, the separation of the contacts causes an are or electron emission discharge to occur between the contacts in the manner previously described.

Upon the engagement of the

auxiliary contacts

24 and 25 the current is diverted from the circuit including the vacuum switch connaeaaao tacts into the shunt circuit around these contacts including the charged condenser 22. lln this shunt circuit the voltage of the condenser is cumulative with respect to the voltage of the generator. Consequently a large value of current is quickly absorbed by the condenser and thus diverted from the are or discharge between the vacuum switch contacts. 'lhis diversion of current in the shunt clrcuit including the condenser 22 quickly reverses the charge of the condenser so that the polarity of the plates is changed, the positive plate being now charged negatively and the negative plate being now charged positively. In this way the capacity or the condenser 22 is utilized to the greatest advantage since it is changed from the fully charged state of one polarity to the fully charged state of the opposite polarity.

Upon the reclosure of the vaccuin switch 10 the contact 26 of the time element device is closed and the uxiliary contacts 2% and 25 are opened. Thus the condenser 22 is again charged in accordance ":r'th the voltage impressed upon the load resisto R1 preparatory to a subsequent extinguish nt oi the are or discharge between the vacuum switch contacts as just described.

In the modified arrangement diag cally shown in Fig. 2, the vacuum sw is connected to control the contin y of the circuit through which power is supp e l the direct current generator 1? to the load represented diagrammatically by th resistor R1. in this arrangement a t has itssecondary w nding 30 series with the

conta

11 and 12 of the vacuum switch and its p ary winding 31 connected to be energized from a suitable source of alternating current under the control 01' the

auxiliary contacts

24 and 25 and also the switch 32, as indicated diagrammatically in the drawing.

The operation of this modified arrange ment is as follows: Upon release of the toggle mechanism i l either manually or automatically, the contacts of the vacuum switch are separated with a resulting are or discharge established therebetween in the manner previously noted. Upon the engagement of the auxiliary contacts 24' and 25 the primary winding 31 of thetransiormer is energized from the alternating current source. This induces an alternating voltage in the secondary winding 30 01 t is transformer which is superimposed upon the voltage of the generator 1'?" in the load circuit. l Vith the superimposed alternating voltage oi a sutlicient value the current in the load circuit is thereby brought to zero value or substantially to Zero value at some point in one half wave of the alternating current. When this occurs the are or electron discharge between the vacuum switch contacts is efiectively extinguished and the direct current circuit interrupt 3d.

rveaeeo With the direct current circuit interrupted at the contacts of the vacuum switch, the load on the secondary winding of the transformer is removed and consequently only magnetizing current is supplied to the primary winding. The switch 32 then may be operated to disconnect the primary winding of the trans former from the alternating current supply source. It will be apparent that a time element switch arranged to be operated in the same manner as switch 26 of Fig. 1 may be employed instead of the switch 32 if desired. The use of the transformer for reducing the current in the direct current circuit to zero value after the separation of the vacuum switch contacts may be advantageous under certain conditions, although the condenser arrangement shown in Fig. 1 is preferred.

While I have described and illustrated preferred embodiments of the invention it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention, as set forth in the appended claims.

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

l. In combination, relatively movable switch contacts separable to interrupt a circuit, a condenser, and means for connecting the condenser across the contacts after a predetermined separation thereof to reduce the current between the contacts below the are or discharge sustaining value. I

2. In combination, a load circuit, an interrupter for the circuit having separable arcing switch contacts, a condenser connected to be charged responsively to the voltage impressed upon the load circuit when the interrupter contacts are closed, and auxiliary switch mechanism associated with the circuit interrupter for connecting the charged condenser across the arcing contacts upon a predetermined separation thereof to impress a voltage on the arc therebetween in opposition to the sustaining voltage of the arc.

3. In combination, a vacuum switch having contacts separable in an evacuated container to establish an electron discharge therebetween, and voltage impressing means eti'ective upon a predetermined separation of the contacts for impressing a voltage between the contacts independent of the sustaining voltage of the discharge to suppress the electron discharge therebetween.

4:. in combination, a vacuum switch having contacts separable in an evacuated container to interrupt the current in the circuit, a condenser, means for charging the conductor and auxiliary switch mechanism associated with the vacuum switch for connecting the charged condenser across the said contacts upon separation thereof to stop the flow of electrons between the contacts 5. In combination, a load circuit, a vacuum switch having separable contacts for interrupting the circuit, a condenser, connections between the condenser and the circuit whereby the condenser is normally charged in accordance with the voltage impressed upon the load circuit, and auxiliary switch mechanism associated with the vacuum switch and connections whereby the charged condenser is connected across the contacts of the vacuum switch with the voltage in opposition to the voltage of the discharge current therebetween upon a predetermined separation of the contacts.

6. The method of interrupting an electric circuit comprising separating conductors in the circuit to establish an are or discharge therebetween and impressing a voltage on the are or discharge independent of the are or discharge sustaining voltage to extinguish the arc or discharge between the conductors.

7. The method of interrupting an electric circuit comprising separating conductors in the circuit to establish an are or discharge therebetween and connecting a condenser between the conductors to extinguish the arc after the conductors have been separated sufficiently to prevent re-establishment of the arc.

8. In combination, a circuit interrupter having contacts separable for opening the circuit, means for separating the contacts, and means rendered effective upon a predetermined separation of the contacts for impressing a voltage on the are or discharge between the separated contacts independent of the are or discharge sustaining voltage to extinguish the are or discharge between the contacts. 1

9. In combination, a circuit interrupter having separable contacts for opening a circuit, means for separating the contacts, means for establishing a circuit in shunt with the are or discharge between the contacts upon a predetermined separation thereof, and

means for impressing a voltage on the said shunt circuit independent of the are or discharge voltage to extinguish the are or discharge between the contacts.

10. in combination, a circuit interrupter comprising separable arcing contacts. means for separatingthe contacts to open the circuit, a shunt circuit for the current between the contacts, and means effective upon a predetermined separation of the contacts for impressing a voltage on the said shunt circuit to extinguish the arc or discharge between the contacts.

11. In combination, relative movable switch contacts separable to interrupt the circuit, and means connected upon a predetermined separation of the contacts in shunt relation with the gap therebetween for impressing a voltage on the gap to counteract the tendency of current to flow between the contacts.

@ a a'eeeee 12. The method of interrupting an electric circuit comprising separating conductors in the circuit to establish an arc or discharge therebetween and impressing a voltage between the conductors-to extinguish the are or discharge after the conductors have been separated sufiiciently to prevent reestabiisb ment of the arc or discharge by the circuit voltage.

In Witness whereof l have hereunto set my hand this thirteenth day at June, 1928;,

BERTRAM WELLMAN.