US1733904A - Circuit-interrupting system - Google Patents

Description

Oct. 29, 1929. D. c. PRINCE 1 ,733,904

\ CIRCUIT INTERRUPTINGV SYSTEM 7 Fild My 19. 1928 y His AtiToTh 'ey.

Patented Oct. 29, 1929 UNITED STATES PATENT OFFICE DAVID C. PRINCE, OE SGHENECTAIJ-Y, NEW YORK, ASSIGNOR T GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK CIRCUI'IIJNTERRUPTING, SYSTEM Application filed May 19,

My invention relates to the interruption of electric circuits particularly by means of vacuum switches having contacts separable in a highly evacuated container, and the principal object of the invention is to insure successful interruption of the circuit in the event that the vacuum of the switch should fail or become impaired.

For controlling high potentialelectric circuits, such as used in present day power transmission systems, a vacuum switch possesses Y certain inherent advantages over the various forms of oil switches ordinarily used in such service. In particular the vacuum switch is both cheaper and simpler in construction and furthermore is capable of interrupting the circuit with practically no inductive disturbance and with much less energy loss due to arcing than an oil switch of comparable capacity. Howeventhe loss or impairment ofv the high degree of vacuum required torsuc:

the circuit when the switches are in normal operating condition, so that in case the vacuum of any one switch should at any time fail, theremaining switches are capable of successfully interrupting the circuit. For example, two vacuum switches may be connected in see ries relation in the circuit and arranged to be operated simultaneously tointerrupt the cir- I cuit as long as the vacuum in each switch is unimpaired. "With such a series connection of the vacuum switches in the circuit each switch is effective independently to interrupt the circuit whenever the other switch :becomes ineffective due to failure or impairment of its vacuum.

In addition to the series connection of the plurality of vacuum switches in the circuit to 1928. Serial No. 279,156.

be controlled, my present invention contemplates the provision of a protective arrangement for positively preventing operation of the particular switch in which the vacuum fails or becomes impaired. This is accomplished by providing each vacuum switch with a suitable vacuum gauge or device which operates responsively to failure or impairment of the vacuum therein together with means operable under control of the vacuum responsive device for disabling the operating mechanism of the switch having improper vacuum conditions. Thus in case the vacuum in any one of the series connected switches fails, the operation of this particular switch to interrupt the circuit is effectively prevented while the vacuum switches having unimpairedvacuum remain available for successfully interrupting the circuit. In this way certainty of interrupting the circuit is obtained and-all damage which might result from operation of the vacuum switch having the impaired vacuum to interrupt the circuit is effectively prevented.

In the preferred form of vacuum gauge protective arrangement embodying the present invention, each'ot' the vacuum switches which are connected inseries relation in the circuit are controlled through the agency of an operating or tripping winding. Inorder to effectively prevent operation of the vacuum switch to interrupt the circuit in case the vacuum thereof should become impaired an electrorcsponsive relay operable under the control of the vacuum gauge associated with the faulty switch is arranged to short circuit or otherwise disable the operating or tripping winding of the switch. The arrangement is such, however, that the operating or tripping windings of the remaining switches in the circuit having the vacuum thereof uninipaired are effective to produce operation of the corresponding switch'to interrupt the cir-.

cuit.

The single figure of the accompanying drawing, illustrates diagrammatically a vacuum switch circuit interrupting system em- 10 and 11 are shown connected in series relation in the circuit of the supplylines L L The supply lines L L may be assumed to extend between a high voltage source of supply and a load circuit and as illustrated are intended to carry alternating current although the present invention is in no way limited to alternating current circuits.

Each of the vacuum switches 10 and 11 is shown as of the type described and claimed in my co-pending application. Serial No. 264,114, filed March 23, 1928 and assigned to the assignees of my present invention.

I Briefly this form of vacuum switch comprises an evacuated casing or tank 12 which preferably is formed of metal, and encloses the relatively movable contacts 13, 14 of the switch mechanism. Each of the spaced apart contacts 13 is fixedly mounted on a suitable high potential insulator 15, while the contact 14 is mounted for movement into and out of bridging engagement with the stationary contacts 13. This is accomplished by con necting the operating rod 16 upon which the movable bridging contact 14 is carried to the casing 12 by means of a yielding sylphon 17. The sylphon 17 is sealed at one end to the rod 16 and at the other end to the casing 12 and expands and contracts when the operating rod 16 is lowered and raised to carry the contact 14 out of and into engagement with the stationary contacts 13 and at the same time provides an air tight connection. Each of the stationary contacts 13 is provided with suitable lead-in conductors 18 which extend through the casing or tank 12 with an air-tight insulating seal 19 therebetween as described in my previously men tioned application.

As brought out in my previously men tioned application, the tank 12 is exhausted to an extremely low pressure preferably of the order of one hundredth of a micron. In

addition the parts of the switch within the vacuum tank are treated to remove all reside gases in order to prevent im-- ual and occluded pairment of the vacuum during operation of the switch. This is accomplished preferably by heating the contacts and other parts to a high temperature either before or during the exhaustion of the tank 12 byliigh frequency inductive action or by electron bombardment, an auxiliary electron emitting filament not shown in the drawing being employed for this latter purpose. The release of occluded gases may also be accomplished bybaking out the entire switch structure in an oven while it is' being exhausted.

The operation of the vacuum switch 10 is controlled by means of a high speed operating mechanism of the type referred to in my previously mentioned application. Briefly this mechanism comprises a biasing spring 30 which serves to strongl bias the movable contact 14 to the circuit opening position as indicated in the drawing. The electromagnetic closing mechanism 31 functionsto operate the contact 14 against the bias of spring 30 to the circuit closing position.

The holding electromagnet 32 maintains the contact 14 in the circuit closing position upon the deenergization of the closing electromagnet 31, and is provided with a holding Winding 33 and a tripping winding 34. The lever mechanism 35 carries the armature 36 of magnetic material into attractive relation with the holding magnet 32 and is operatively connected with the switch operating rod 16. This controlling arrangement for the vacuum switch is constructed in accordance with the Tritle Reissue Patent No. 15,441 dated August 29, 1922 and provides for releasin the movable contact 14 with the utmost spee upon the energization of the tripping winding 34 with a curentin the proper direction. The particular form of lever mechanism 35 is constructed in accordance with the Tritle Patent N 0. 1,560,440, dated Nov. 3, 1925 and permits free tripping of the vacuum switch in case the tripping winding 34 is energized upon closure of the switch as will be described more fully hereinafter.

It will be observed that the controlling mechanism of the vacuum switch 11 is identical with that of switch 10 as just described.

, The tripping windings 34 and 34 of the vacuum switches 10 and 11 respectively are connected in series circuit and are arranged normally to be energized simultaneously with current in the proper direction to effect operation of both vacuum switches. This is accomplished by connecting the series circuit including the tripping winding 34 and 34' to be energized from the secondaries of the two current transformers T T which are inserted in the supply line L. The transformers T T are normally magnetized from the direct 1 current supply source indicated as plus and minus in the drawing in order to provide a tripping current in the series crcuit including i the tripping winding 34 and 34' in the proper .direction to effect operation of the vacuum magnetic structures of-the transformer T T and the interconnection of the secondary windings with the trip coil circuit in the manof the transformers is effective to supply a tripping current in the proper direction to eflect release of the vacuum switch movable ner illustrated insures that one or the other 1 contacts upon a rapid increase of the alternating current in the supply line L in either direction. v

. With the Vacuum switches thus constructed and connected in series relation in the circuit to be controlled thereby in case the vacuum of one of the switches should become impaired; nevertheless, the remaining switch is always available for successfully interrupting the circuit.

suitable forms of vacuum gauges may be used if desire-d. The thermo-couple type of vacuum gauge illustrated comprises a filament 41 which is heated from a suitable source of supply such as, for example, as the potential transformer T and is enclosed within an envelope 42, which is connected with the tank 12 of the vacuum switch so as to be subjected to the degree of vacuum obtaining therein. The heat may be dissipated from the filament 41 by radiation and by convection due to the gases within the casing. Thus with a high degree of vacuum there will be very little gas present and the convection losses from the filament 41.will be practically negligible. If

-'- the vacuum fails or becomes impaired due to a leak in the casing or -from-any other cause, the convection currents set up in the gases within .the casing quickly reduce the temperature of the filament 41. In order to ascertain the temperature of the filament 41 a thermocouple 43 is located in close proximity thereto and connected to an electroresponsive relay 44. The electroresponsive relay 44 preferably is of the tapalogue type, in order to operate readily with the relatively small current obtained from the thermo-couple. The electroresponsive relay 44 is arranged to maintain its contact 45 in the open position as shown so long as the filament 41 is at a high temperature and a correspondingly high current is generated by the thermo-couple 42. Whenever the filament temperature decreas s a corresponding decrease in the current output of the thermocouple is produced and the relay contact 45 is operated to the circuit closing position. The construction and arrangement of the vacuum gauge 40 and the relay 44 for the vacuum switch 11 are identical with that as just described.

In accordance with the preferred form of the present invention the relays 44 and 44' are connected to render the tripping windings 34 and 34 ineffective whenever. the vacuum in the corresponding vacuum switches 10 and 11 fails or becomes impaired. This is accomplished by connecting the contacts of the relay 44 to short circuit the tripping winding 34 of the vacuum switch 10 and likewise connecting the relay 44 to short circuit the, tripping winding 34 of the vacuum switch 11. It will be understood, however, that in case the disabling of the operating mechanism of the vacuum switches is to be accomplished by openingthe circuit of a tripping or controlling win ding, the vacuum responsive relay associated with the corresponding switch in that case may be arranged to open the circuit of the operating or tripping winding instead of short circuiting the winding as illustrated.

The operation of the vacuum switch circuit interrupting system illustrated in the drawing is as follows:

With the supply lines L L energized from a suitable source the potential transformer T serves to energize the filaments 41 and 41 of the vacuum gauges. Thus with the vacuum of each switch unimpaired the corresponding vacuum responsive relays 44 and 44 maintain their contacts in the open posi tion as illustrated in the drawing. To opert ate the vacuum switches to the circuit closing position it is necessary first to close the switches and 50 in order to energize the holding windings 33 and 33 from the direct current source indicated as plus and minus in the drawing. Suitable variable resistors R and R are provided in order to regulate the magnetizing current of the holding windlugs and thereby calibrate the value of current in the tripping winding 34 and 34 required to eifect release of the corresponding vacuum switches 10 and 11. With the hold- 7 ing windings 33 and 33 thus energized, thevacuum switch'lO may be operated to the circuit closing position by closing the normally open puslrbutton 51. This results in energizing the operating electromagnet of the closing mechanism 31 which rotates thebellcrank lever arm 52 to raise the magnetic armature 36 into attractive relation with the holding electromagnet 32. The lever mechanism 35, however, is arranged to maintain the movable contact 14 slightly out of engagement with the stationary contacts 13 as long as the closing mechanism 31 is energized. Upon the release of the push-button 51 and the resulting deenergization of the closing mechanism 31, the biasing spring 30 becomes eflfective to rotate the lower lever arm which is connected to the operating rod 16 about its pivotal connection with the upper lever arm and thereby operate the movable contact 14 into circuit closing engagement with the 00-- operating stationary cont-acts. The magnetic attraction of the armature 36 of the holding electromagnet 32 maintains the contact 14 in circuit closing engagement with the cooperating contacts against the strain of the biasing spring 30 which now tends to operate the entire levermechanism together with the\ 7 increase of current in the alternating current supply lines L and L irrespective of the direction of current. Thus in case the supply lines-L L should be short-circuited or an extremely heavy overload be imposed thereupon due to any other cause, the tripping windings 34 and 34' are energized to effect the quick release of the corresponding movable contacts 14 and 14 of the vacuum switches 10 and 11. Under such conditions both of the vacuum switches are operated subs'tantially simultaneously to jointly interrupt the circuit.

As set forth in my previously mentioned co-pending application the interruption of the circuit by separation of the contacts in the vacuum within the tanks is accomplished by the formation of a cathode spot when the contacts are formed of soft metal such as copper, or the like. This cathode spot phenomenon results from vaporization of the last point of contact occurring upon separation of the contacts. That is, just before the final separation, the current is concentrated in a very limited area of'contact which is thereby brought up to the temperature where the soft metal of the contacts .melts and vaporizes. At the same time that the contacts are separating, but are still very close together, the potential drop between the contacts, although quite small in the aggregate nevertheless provides a voltage gradient 0 the order of millions of volts per centimeter. This is due to the fact that even a small drop in potential between the contacts divided by the extremely small separation thereof, gives an exceedingly high potential gradient. Since a voltage gradient of the order of mil lions of volts per centimeter will readily draw electrons from a relatively cold metal, an electronfiow is produced from the contact which is of negative potential at the time of separation. The resulting collisions of these electrons with the vaporized metal in the space will ionize some of the metal vapor, thus producing additional electrons as well as positive ions. The positive ions travel towards the negative contact at a very much slower rate than the electrons travel to the positive contact. As a result, the positive ions maintain a very high potential gradient at the negative contact surface, thus continuing to draw out electrons from the negative contact even though the positive contained. Consequently, with the contacts conions heats the surface thereof to the point where the metal is vaporized, thus maintaining a supply of metal vapor to be ionized in the manner previously pointed out. Thus the process once initiated continues as long as the voltage between the contacts is main nected in an alternating current circuit as illustrated in the drawing, the current con tinues until the alternating current passes thru the zero value. When the current is thus momentarily withdrawn, the positive ions immediately disappear and the metal vapor diffuses so that when the alternating current voltage is again applied between the electrodes, the con itions required for the formation of a cathode spot are no longer present and no current is carried. The circuit is thus interrupted at the zero point of the alternating current wave by the vacuum switch with practically no inductive disturbance or voltage surge in the alternating current circuit. Moreover the voltage between the contacts required to maintain the current flow is of the order of only 50 or 60 volts. Consequentl only a very small v amount of energy is released in the vacuum switch including the practically negligible vaporization of the contact material required to maintain. the electron flow therein'to the zero point of the alternating voltage.

\Vhile the Vacuum switch with soft metal electrodes is particularly adapted for alternating current service as just pointed out, it is desirable .to use a higher melting point metal for the contacts when the vacuum switches are used in direct current service.

For example, tungsten metal contacts are particularly adapted for direct current service, since it is extremely difiicult to produce sufiicient metal vapor therefrom to maintain a cathode spot due to the extremely high melting point thereof. With such high melting point contacts, a thermionic emission is produced by the heating of the last point of contacts. The heat howev'er,is rapidly dissipated as the contactsare separated and the electron emission quickly ceases, with a resulting interruption of the circuit.

In case the vacuum within the tank 12 should fail or become impaired from any cause, the temperature of the correspondingvacuum gauge filament decreases thereby correspondingly decreasing the current output of the thermo-couple to .permit the vacuum gauge relay 44 to operate its contacts to the circuit closing position. Closure of the 1:5 vacuum gauge relay contacts short circuits the tripping winding 34, thereby effectively rendering the vacuum switch 10 ineffective to interrupt the circuit. However, the vacuum switch 11 having its vacuum unim- 13 paired remains efiective to interrupt the circuit upon the occurrence of short circuit or heavy overload conditions. ping winding 34 of vacuum switch 10 short circuited the amount of increase in the current of the supply lines L' L required to effect operation of the vacuum switch 11 to interrupt the circuit is materially .smaller than that required to effect simultaneousoperation of both switches. 1 This is due'to the fact that the load or burden upon the secondary windings of the current transformer T T has been materially reduced by the short tween successive half cvclesis necessary to supply the required value of current to the tripping winding of the remaining vacuum switch. Thus the short circuiting of the tripping-winding of the defective vacuum switchat the same time materiallv decreases the circuit interrupting dutv imposed upon the unimpaired vacuum switches. The is a verv desirable feature since'the entire dutv of interrupting the circuit is irnposed upon only one of the vacuum switches.

l'twill he obvious that in case of failure or impairment of the vacuumwithin the casing 12' of the vacuum switch 11. the vacuum re- 7 sponsive arran ement including the thermocouple 42' and the relay 44' will function automaticallv to short circuit the tripping winding-34' of switch 11 in exactlv the same manner as previouslv described. in connection w th switch 10. Likewise the circuit interruptin dutv imposed upon the unimpaired switch 10 will be decreased as previouslv described.

It will be apparent that operation of the relays 44 and 44' upon impairment of the vacuum in the corresponding switches '10 and 11 may be emploved to o erate an alarm signal to indicate the fact that the vacuum of either switch is im aired to a station attendant or operator. Either a visual signal connected with the operating mechanism for the contacts 45 and 45 may be employed or auxiliary contacts may be arranged to close an alarm circuit.

Manual operation of the vacuum switches to the circuit opening position may be accomplished at any time independently of the electrical conditions obtaining in the supply lines L L by moving the manual control switches 50 and 50' to the circuit opening position in which they are shown in the drawing. Thls With the tripresults in deenergizing the holding windings of the holding electromagnets 32 and 32, thereby releasing the movable contact for operation by the biasing springs 30 and 30'. In case the alarm signal or circuit of either of the vacuum switches is operated in the manner previously indicated, the station at tendant or operator having knowledge of this fact would interrupt the holding magnet circuit only of the unimpaired switch in order to avoid interrupting the circuit at the switch having the impaired vacuum.

Thus it will be seen that my present invention effectively provides for any likely contingency due to, the failure of vacuum in the vacuum switches, as there is only a remote possibility that the vacuum in both of the switches would fail at the same time. .Moreover, the failure of vacuum in any one of the switches is compensated for automatically by the electroresponsive vacuum gauge arrangement described and, in this way, maintains at least one of the switches always ready to respond to an excessive increase in the current in the supply lines WVhat I claim as new and desire to secure by Letters Patent ofthe United States, is

1. In a circuit cont olling device the combination of an evacuated casing, relatively.

movable contacts operable in the vacuum within the casing, means for operating said contacts, means responsive to variations in the vacuum within the casing, and means 0perable under the control of said vacuum responsive means for rendering said operating means ineffective to operate the contacts to interrupt current when the vacuum within the casing is impaired beyond a predetermined value. I

2. The combination of a vacuum switch,

electro-responsive means for operating the switch, and means operable in response to impairment of the vacuum of the switch for pre venting operation of said electroresponsive operatinguneans to operate the switch to interrupt current.

3. In a circuit controlling device the combination of an evacuated casing, relatively movable contacts separable in the vacuum in the casing to interrupt the circuit, electroresponsive means connected to be energized responsive to predetermined electrical conditions in the circuit for effecting the separation of the contacts, and electroresponsive circuit controlling means operable in re-- sponse to an impairment of the vacuum within the casing beyond a predetermined value for controlling the energizing connections of said first electroresponsive means to prevent separation of the contacts.

4:. In a circuit controlling device, the combination of an evacuated casing, cooperating circuit controlling contacts separable in the vacuum within the casing to interrupt the circuit, one of said contacts being biased out of engagement with the other contacts, means for holding said one contact in circuit closing engagement with the other contacts, said means having an electrical winding associated therewith for effecting the releasing of said one contact for operation in accordance with its bias, and circuit controlling 'means operable in response to an impairment of the vacuum within the casing beyond a certain value for controlling the energizing circuit of said electrical winding to prevent release of said one contact.

5. In a circuit controlling device, the combination of an evacuated casing, cooperating circuit controlling contacts separable in the vacuum within the casing to interrupt the circuit, one of said contacts being biased out of engagement with the other contacts, an electromagnet for holding said one contact in circuit closing engagement with the other contacts, a' winding associated with said electromagnet for controlling the holding action thereof to effect the release of said one contact for operation in accordance with its bias, a vacuum gauge having electrical means associated therewith for providing a current variable in accordance with the degree of vacuum within the casing, and an electroresponsive circuit controlling relay connected to the electrical means of said vacuum gauge and operable to short circuit the winding associated with 'said holding electromagnet when the vacuum within the casing is impaired beyond a predetermined value.

6. A c1rcu1t controlling system comprising a plurality of vacuum switches connected to jo ntly control the circuit when the vacuum conditions of all the switches are normal and each vacuum switch being operable independently to interrupt the circuit in the event of failure of the vacuum in the other switches.

7 A circuit controlling system comprising i a plurality of vacuumswitches connected in series relation inthe circuit and arranged to operate automatically in response to abnormal circuit conditions to jointly interrupt the circuit and each operable independently to interrupt the circuit in case the other switches become ineflective due to impairment of the vacuum thereof.

8. A circuit protective system comprising in combination a vacuum switch operable automatically in response to predtermined circuit conditions to interrupt the circuit, and a second vacuum switch cooperating therewith and arranged to operate automatically in response to said predetermined circuit conditions for interrupting the circuit in the event of impairment of the vacuum of the first switch.

9. A circuit controlling system comprising a plurality of vacuum switches connected in series relation in the circuit and each operable automatically in response to abnormal circuit conditions to interrupt the circuit and means associated with each vacuum switch for preventing automatic operation thereof in response to impairment of the vacuum thereof tothereby place the'interruption of the circuit exclusively under the control of the remaining vacuum switch.

10. A circuit protective system comprising a plurality of vacuum switches connected in series relation in a circuit and each having electroresponsive means for effecting operation of the corresponding switch to interrupt the circuit, said electroresponsive means normally being connected to be energized simultaneously in response to predetermined electrical conditions in the ClIClllt controlled by said vacuum switches, and means associated with each of said vacuum switches for rendering the corresponding electroresponsive operating means thereof inefiective in response to impairment of the vacuum in the corresponding vacuum switch.

11 A circuit controlling system comprisreleasing means are energized in series circuit in response to abnormal circuit conditions in the circuit controlled by the vacuum switch, and a vacuum gauge associated with each vacuum switch and having a circuit controlling switch associated therewith and operable to short circuit the corresponding releasing winding when the vacuum of the corresponding switch is impaired beyond a predetermined value.

12. An alternating current circuit protective system comprising a plurality of vacuum switches connected in series relation in the circuit and each having electroresponsive means associated therewith for effecting operation thereof to interrupt the circuit upon a predetermined increase of the current in the circuit, and vacuum responsive means associated with each vacuum switch for rendering the electroresponsive operating means thereof inefi'ective when the vacuum thereof becomes impaired and for varying the amount of increase of the current in the alternating current-circuit required to eflect operation of the electroresponsive means of the remaining switches.

13. An alternating current circuit protective system comprising a pair of: vacuumwhen the vacuum thereof termined increase of the current in the circuit, said operating winding normally being connected to be energized in series circuit relation, and vacuum responsive means associated with each Vacuum switch for short circuiting the corresponding operating winding becomes impaired and thereby varying the amount of increase of current in the circuit required to eflectively energize the operating winding of the other switch.

In witness whereof, I have hereunto set my Hand this th day of May, 1928.

DAVTD C. PRINCE.

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