US3489950A

US3489950A - Circuit interrupting means for a high voltage d-c circuit

Info

Publication number: US3489950A
Application number: US652473A
Authority: US
Inventors: Victor Mishkovsky
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1967-07-11
Filing date: 1967-07-11
Publication date: 1970-01-13
Anticipated expiration: 1987-01-13

Description

Jan. 13, 1970 v.- MlSHKO VSKY CIRCUIT INTERRUPTING MEANS FOR A HIGH VOLTAGE D-C CIRCUIT 2 Sheets-Sheet 1 Filed July 11, 196'? INVE/VTOR. V/CTOR M/SHKOVS/f),

ATTORNEY Jan. 13, 1970 v. MISHKOVSKY 9,950

CIRCUIT INTERRUPTING MEANS FOR A' HIGH VOLTAGE D-C CIRCUIT Filed July 11, 196'? 2 Sheets-Sheet 2 MI MN TOR. We 70/? MASH/f0 vs/ry,

BY 721mm ATTORNEY United States Patent 3,480,950 CIRCUIT INTERRUPTING MEANS FOR A HIGH VOLTAGE D-C CIRCUIT Victor Mishkovsky, Ashland, N.J., assignor to General Electric Company, a corporation of New York Filed July 11, 1967, Ser. No. 652,473 Int. Cl. H02h 3/00, 7/00; H01h 33/ US. Cl. 317-11 7 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to means for interrupting a high-voltage direct-current circuit and relates, more particularly, to circuit interrupting means of the type in which a current zero is created by discharging a commutating capacitor through a circuit interrupting device.

In the particular circuit interrupting means that I am concerned with, a circuit interrupting device, hereinafter referred to as an interrupter, is connected in series with a high-voltage direct-current line that supplies current through the interrupter. When the circuit is to be interrupted, the normally-closed contacts of the interrupter are separated to establish an arc across the gap developed between the contacts. Connected across this gap is a normally-open switching circuit that includes a precharged commutating capacitor. When the above-described arc is established across the interrupter gap, the capacitor is discharged through the quenching circuit and the interrupter, thereby forcing the arcing current to zero. By the time the current zero point is reached, the gap between the contacts has attained a substantial length. This relatively long gap, particularly if it is a vacuum gap, is usually able to withstand the recovery voltage that builds up thereacross immediately after the current zero point is reached, thus enabling the circuit interruption to be successfully completed.

Prior interrupting arrangements of this type have employed an auxiliary switch, separate from the interrupting device, for initiating discharge of the capacitor through the quenching circuit. This separate switch can constitute a rather expensive element of the interrupting arrangement, particularly since it must have its own operating mechanism. To obviate the need for such a separate operating mechanism, it has been proposed that a triggered gap device, instead of a mechanically operated device, he used as the auxiliary switch. But this too is expensive inasmuch as it also requires a separate switching device, and moreover requires a trigger and a triggering voltage source.

SUMMARY An object of my invention is to provide simple and inexpensive means constituting a part of the interrupting device which can be used for initiating discharge of the commutating capacitor at the desired instant.

Another object is to provide circuit-closing means for initiating discharge of the commutating capacitor which can be mechanically-operated by the same operator that separates the contacts of the interrupting device.

In carrying out the invention in one form, I provide a highly evacuated envelope and a pair of separable normally-closed main contacts located within the envelope for carrying load current therethrough. Also located within the evacuated envelope is an auxiliary contact that is connected in circuit with the above-mentioned commutating capacitor. During an interrupting operation, a movable one of the main contacts is separated from the other main contact and driven into engagement with the auxiliary contact to initiate discharge of the commutating capacitor. Thereafter, the movable main contact is driven into an intermediate position where it is spaced from both the auxiliary contact and the other main contact.

BRIEF DESCRIPTION OF DRAWINGS For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawing, wherein:

FIG. 1 is a schematic representation of a circuit interrupting arrangement embodying one form of my invention.

FIG. 2 is a schematic representation of a modified form of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1, there is schematically shown a high voltage D-C circuit comprising a source 12, a load 14, and a power line 16 for delivering power to the load from the source. It will be assumed that the normal load current flows in the direction indicated by the arrow 17, returning to the source through a return conductor 19. The source 12 is schematically depicted as comprising a transformer 20 and a rectifier 21 connected in series with the secondary winding of the transformer. Connected in the power line 16 and in series with the source 12 and the load 14 is the usual smoothing reactor 18 which acts to smooth the current output from the source.

For controlling the flow of current through the load 14, a circuit interrupter 25 is connected in the power line 16 in series with the load 14 and the smoothing reactor 18. In a preferred embodiment of my invention, the circuit interrupter 25 is a vacuum-type circuit interrupte As such, it comprises a highly evacuated envelope 26 comprising a casing 27 of a suitable insulating material, such as glass, and a pair of

metallic end caps

28 and 29 closing off the ends of the casing. Suitable seals 30 render the envelope 26 vacuum tight. The normal pressure Within the envelope under static conditions is lower than 10* mm. of mercury.

The internal insulating surfaces of casing 27 are protected from the condensation of arc-generated metal vapors thereon by means of a tubular metallic shield 31 suitably supported on casing 27 and preferably electrically isolated from both

end caps

28 and 29. This shield acts in a well known manner to intercept arc-generated metallic vapors before they can reach casing 27.

Located within envelope 26 is a pair of

separable contacts

37 and 38, shown in their engaged or closed-circuit position. The upper contact 37 is a stationary contact suitably attached to a conductive rod 37a, which at its upper end is united to the upper end cap 28. The lower contact 38 is a movable contact joined to a conductive operating rod 38a which is suitably mounted for vertical movement. Downward motion of the contact 38 separates the contacts and opens the interrupter, whereas return movement of contact 38 reengages the contacts and thus closes the interrupter. The operating rod 38a projects through an opening in the lower end cap 29, and a flexible metallic bellows 40 provides a seal about the rod 28a to allow for vertical movement of the rod without impairing the vacuum inside the envelope 26. As shown in FIG. 1, the bellows 40 is secured in sealed relationship at its respective opposite ends to the operating rod 38a and the lower end cap 29.

All of the internal parts of the interrupter are substantially free of surface contaminants. These clean surfaces are obtained by suitably processing the interrupter, and by baking it out during its evacuation. In addition, the

contacts

37 and 38 are effectively freed of gases absorbed internally of the contact body so as to preclude evolution of these gases during high current arcing.

Although the invention is applicable to many different contact configurations, I prefer to use the contact configuration disclosed and claimed in US. Patent 2,949,- 520Schneider, assigned to the assignee of the present invention. Accordingly, each contact is of a disk shape and has one of its major surfaces facing the other contact. The central region of each contact is formed with a recess 49 in this major surface and an annular contact-making area 50 surrounding this recess. These an nular contact-making areas 50 abut against each other when the contacts are in their closed position of FIG. 1, and are of such a diameter that the current flowing through the closed contacts follows a loop-shaped path L, as is indicated by the dot-dash lines of the drawing. Current flowing through this loop-shaped path has a magnetic effect which acts in a well-known manner to lengthen the loop. As a result, when the contacts are separated to form an arc between the areas 30, the magnetic effect of the current flowing through the path L will impel the arc radially outward.

As the arc terminals move toward the outer periphery of

disks

37 and 38 the arc is subjected to a circumferentially-acting magnetic force that tends to cause the arc to move circumferentially about the central axes of the disks. This circumferentially-acting magnetic force is preferably produced by a series of slots (not shown) provided in the disks and extending from the outer periphery of the disks radially inward by generally spiral paths. These slots correspond to slots designated 32 in the aforementioned Schneider patent and thus force the arc to revolve about the central longitudinal axis of the disks.

It is considerably more diflicult to interrupt direct current than alternating current because direct current contains no naturally-occurring current zeros. With alternating currents, current zeros occur naturally, and to interrupt such currents, it is only necessary to prevent reignition of the arc after a natural current zero. But with direct current, it is necessary first to force the current to zero and then to prevent arc-reignition.

One way of forcing the current to zero is by forcing a locally-controlled current through the interrupter in opposition to the load current flowing therethrough. This is the general approach used in the illustrated interrupting arrangement, where the opposing current is derived from a commutating capacitor 55 that is precharged with the polarity shown in the drawing. This commutating capacitor 55 is located in a normally-open arc-quenching circuit 56 that is connected through conductors 56a and 56b across the

contacts

37, 38 of the interrupter 25.

The arc-quenching circuit 56 includes normally-open circuit-closing means 60, 38 comprising an auxiliary contact 60 and the movable main contact 38, both of which are located within the evacuated envelope 26. When the interrupting device is in its closed position of FIG. 1,

contacts

60 and 38 are spaced apart and insulated from each other by the evacuated space therebetween. The auxiliary contact 60 is preferably of an annular form and is suitably joined to the upper end of a metal tube 62. The annular auxiliary contact 60 and the metal tube 62 surround contact rod 38a in spaced relationship thereto. The metal tube 62 is supported on the lower end cap 29 by a tubular insulator 63, which normally serves to electrically insulate the

parts

60 and 62 from the lower end cap.

For connecting the auxiliary contact 60 into the arequenching circuit 56, there is provided a conductive lead 64 extending in spaced relationship through an opening in lower end cap 29. This conductive lead 64 is supported on lower end cap 29 by means of a tubular insulator 65 which normally electrically isolates lead 64 from end cap 29. Tubular insulator 65 is suitably hermetically sealed at one end to the end cap 29 and at its opposite end to lead 64. Lead 64 is suitably electrically connected at its upper end to tubular conductor 62 and at its lower end to the external conductor 56a in arc-quenching circuit 56.

When the power circuit 16 is to be opened, the movable main contact 38 is driven downwardly from its solid line position into a position where its lower surface engages the auxiliary contact 60. This effectively closes the circuitclosing means 60, 38, thereby completing the arc-quenching circuit 56 through the series combination of circuit closing means 60, 38 and the arc that is then present between

main contacts

37 and 38. The arc-quenching circuit thus extends from one terminal of capacitor 55 through

conductors

56a, 64, 62,

contacts

60, 38, the are between

main contacts

38 and 37, contact 37, conductors 37a, 16, and 56b to the opposite terminal of capacitor 55.

When the circuit-closing means 60, 38 is thus closed to complete the arc-quenching circuit, precharged commutating capacitor 55 discharges in the direction of arrow 67 forcing commutating current through interrupter 25 in a direction opposite to the normal load current therethrough. The commutating current is made considerably larger than the maximum anticipated value of the load current and thus the load current is rapidly driven to zero, thus extinguishing the arc across the then-existing gap between

main contacts

37 and 38.

This gap is ordinarily capable of withstanding the usual recovery voltage that is built up between the contacts when the current zero point is reached. The fact that the gap is a high vacuum gap contributes to its high rate of dielectric recovery, thus increasing the likelihood that the gap will be capable of successfully withstanding the recovery voltage.

The movable main contact 38 remains in engagement with the auxiliary contact 60 for only a brief period, after which it is returned to an intermediate position part way between the main contact 37 and auxiliary contact 60. This intermediate position is indicated by dotted lines 38b in the drawing. If the commutating capacitor 55 is not able to completely discharge while the movable contact 38 is in engagement with the auxiliary contact 60, then an arc is drawn between

contacts

60 and 38 when movable contact 38 moves into its intermediate position. This are is, however, extinguished when the current therethrough reaches zero upon complete discharge of the commutating capacitor 55.

For controlling the motion of main movable contact 38 in the above-described manner, I provide an opening spring 70 that biases movable contact 38 in a downward opening direction. The movable contact is noramlly maintained in its solid-line closed position of FIG. 1 by means of a releasable trip-latch 72 controlled by a tripping solenoid 73. When solenoid 73 is operated, it releases the trip latch 72 and allows opening spring 70 to drive movable contact 38 downwardly through its dotted-line posit6ion and into engagement with annular auxiliary contact For returning the movable contact 38 in an upward direction to its dotted line position 38b, a reset spring 75 is relied upon. This reset spring forms a part of a dashpot assembly 76, which comprises a plunger 77 and a cylinder 78 in which the plunger is slidably mounted. The plunger can move in a downward direction impeded only by reset spring 75. During such downward movement, air is freely admitted into the space above plunger 77 by check valve 80. Spring 75 returns the plunger to its normal position of the drawing at a rate determined by the size of the orifice opening 79 above piston 77.

During an opening operation, opening spring 70 drives movable main contact 38 downwardly into the dotted line position 3812, and thereafter the momentum of the moving

contact structure

38, 38a continues this downward motion until movable main contact 38 engages auxiliary contact 60. When the downwardly moving main contact 38 enters the dotted-line position 38b, the lower end of operating rod 38a engages plunger 77. The opening spring 70 is so selected that at this point, it has substantially fully discharged. Further downward movement of the movable main contact 38 drives plunger 77 downwardly, compressing reset spring 75. After the main movable contact 38 engages auxiliary contact 60, reset Spring 75 can expand, and, in doing so, slowly returns movable main contact 38 to its dotted-line position 38b at a speed governed by the metering orifice 79.

Subsequent closing of the interrupting device is accomplished by driving the movable main contact 38 back into engagement with the stationary main contact 37. This action is performed by a suitable closing mechanism (not shown).

Prior interrupting arrangements of this general overall type have employed an auxiliary switch separate from the interrupting device as the circuit-closing means for initiating discharge of the commutating capacitor. This separate switch can constitute a rather expensive element of the interrupting arrangement, particularly since it requires a separate operating mechanism.

It will be apparent that employing the interrupting device described hereinabove obviates the need for this separate auxiliary switch and separating operating mechanism. In the disclosed interrupting arrangement, the auxiliary switch is incorporated in the interrupter device itself and the same operating mechanism is used for the auxiliary switch as for the main contacts of the interrupting device. The same evacuated envelope encloses both the main interrupting elements and the elements of the auxiliary switch. It will be further noted that the movable contact 38 serves as the movable contact of both the main interrupting device and the auxiliary switch.

The precharging circuit for the commutating capacitor 55 may be of any suitable conventional form. It is schematically shown in the drawing as comprising a source having opposed

terminals

90 and 91 and a switch 92 that can be closed to connect the commutating capacitor across

terminals

90 and 91. Upon closing of switch 92, the capacitor 55 is charged through a current limiting resistor 94 to a voltage that will be determined by the voltage of the source 91 and with the polarity shown in FIG. 1. This voltage is high enough to insure a sufiiciently high commutating current upon capacitor to discharge to interrupt the maximum expected load currents.

Although I prefer to use a vacuum-type interrupting device in practicing my invention, the invention in its broader aspects is intended to comprehend interrupters of the fluid-blast type, where a fluid-blast is relied upon to assist in interruption.

Although I prefer to incorporate the circuit-closing means in the same envelope as the interrupting elements, as is shown in FIG. 1, my invention in its broader aspects comprehends an arrangement in which these parts are housed in separate evacuated envelopes. In both arrangements, however, the parts of the two devices are mechanically coupled together so that they can be operated by a single operating mechanism. The modified form of my invention is shown in FIG. 2, where the same reference numerals are used as in FIG. 1 to designate corresponding parts of the two arrangements. In FIG. 2, the main interrupting elements are shown within and envelope 26. The circuit-closing means is shown within a separate envelope 126. The parts associated with separate envelope 126 that correspond to similar parts associated with-envelope 26 have been assigned similar reference numerals but differing in that the numeral 1 precedes each reference numeral. The movable contact 138 of the circuit-closing means is mechanically connected to the movable contact 38 of the main interrupter, as for example, through the integral rod 38a. Spring means 70 urges the movable main contact downwardly but is restrained by trip latch 72. When trip latch 72 is released, the main movable contact 38 separates from the main stationary contact 37, and the movable contact 138 of the circuit-closing means moves into engagement with auxiliary contact 60. Separation of

contacts

37 and 38 establishes an arc therebetween; and when the movable contact 138 of the circuit-closing means engages auxiliary contact 60, an arc-quenching circuit 56 is completed. This initiates discharge of the commutating capacitor 55 through the arc-quenching circuit via a path that extends through

parts

56a, 62, 60, 138, 38a, 38, the are 37, 37a, 16, and 56b. This extinguishes the arc in the same manner as pointed out in connection with FIG. 1.

Although not shown in FIG. 2, it is to be understood that suitable means, such as 75-79 in FIG. 1, is used for moving the

movable contacts

38 and 138 of FIG. 2 into a neutral position after discharge of the commutating capacitor 55 has been initiated.

While I have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from my invention in its broader aspects.

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

1. In an interrupting arrangement for a DC circuit comprising:

(a) an envelope,

(b) first and second main contacts within said envelope adapted to be connected in series with said D-C circuit,

(c) said second main contact being engageable with said first main contact to enable load current to flow therethrough and being movable out of engagement with said first main contact to draw an arc therebetween,

(d) means for forcing the current through said are to zero comprising a normally-open arc-quenching circuit connected across said cotacts and comprising a commutating capacitor and circuit-closing means in series with said capacitor for closing said arcquenching circuit upon establishment of said arc, thereby discharging said capacitor through said quenching circuit and through said arc,

(e) said circuit-closing means comprising an auxiliary contact within said envelope which is located to be engaged by said second main contact when said second main contact is moved out of engagement with said first main contact,

(f) and means for insulating said auxiliary contact from said main contacts when said main contacts are in engagement.

2. The interrupting arrangement of claim 1 in which said envelope is a highly evacuated envelope in which all of said contacts are located.

3. The apparatus of claim 1 in which said second main contact has a neutral position wherein it is physically spaced from and electrically isolated from both said first main contact and said auxiliary contact, and in which means is provided for moving said second main contact into said neutral position following its engagement with said auxiliary contact during a circuit-interrupting operation.

4. The apparatus of claim 3 in which said envelope is a highly evacuated envelope in which all of said contacts are located.

5. The apparatus of claim 2 in which (a) said second main contact is mounted on a rod projecting into said envelope,

(b) said auxiliary contact is of a generally annular form surrounding said rod,

(0) said second main contact is located between said first main contact and said auxiliary contact and has one surface for engaging said first main contact and an opposite surface for engaging said auxiliary contact.

6. The apparatus of claim 2 in which said second main contact is located between said first main contact and said auxiliary contact and has one surface for engaging said first main contact and an opposite surface for engaging said auxiliary contact.

7. In an interrupting arrangement for a D-C circuit comprising:

(a) a highly evacuated envelope,

(c) said second main contact being engageable with said first main contact to enable load current to flow therethrough and being movable out of engagement with said first main contact to draw an are therebetween,

(d) means for forcing the current through said arc to zero comprising a normally-open arc-quenching circuit connected across said contacts and comprising a commutating capacitor and circuit-closing means in series with said capacitor for closing said arcquenching circuit upon establishment of said arc, thereby discharging said capacitor through said quenching circuit and through said arc,

5 (f) means for maintaining said auxiliary contacts separated while said main contacts are engaged, (g) and actuating means common to said second main contact and said movable auxiliary contact for simultaneously driving (i) said movable auxiliary con-v tact toward engagement with said first auxiliary contact and (ii) said second main contact out of engagement with said first main contact. References Cited UNITED STATES PATENTS 2,292,174 8/1942 Suits et al. 317-11 X 2,789,253 4/1957 Vang 317-11 3,411,038 11/1968 Lee 31711 LEE T. HIX, Primary Examiner J. D. TRAMMELL, Assistant Examiner US. Cl. X.R.

(c) said circuit-closing means comprising an additional evacuated envelope, a first auxiliary contact within said additional envelope; and movable auxiliary contact structure mechanically coupled to said second main contact,