US3372258A - Electric circuit interrupter of the vacuum type with arc-voltage control means for promoting arc transfer - Google Patents

Description

March 5, 1968 J. w. PORTER 3,372,258

ELECTRIC CIRCUIT INTERRUPTER OF THE VACUUM TYPE WITH ARC'VOLTAGE CONTROL MEANS FOR PROMOTING ARC TRANSFER Filed May 28, 1965 2 Sheets-Sheet 1 INVENTOR. JOSEPH W PORTER,

ATTORNEY ELECTRIC CIRCUIT INT ERRUPTER OF THE VACUUM TYPE WITH ARC-VOLTAGE CONTROL MEANS FOR PROMOTING ARC TRANSFER March 5, 1968 J w, PORTER v 3,372,258

Filed May 28, 1965 2 Sheets-Sheet 2 WW I //v VENTOR. JOSEPH W PORTER United States Patent ELECTRIC CIRCUIT INTERRUPTER OF THE VACUUM TYPE WITH ARC-VQLTAGE CON- TROL MEANS FOR PROMOTING ARC TRANS- FER Joseph W. Porter, Media, Pa., assignor to General Electric Company, a corporation of New York Filed May 28, 1965, Ser. No. 459,656 11 Claims. (Cl. 200144) ABSTRACT 0F THE DISCLQSURE A vacuum type circuit interrupter in which arc transfer to a preferred arcing region of the interrupter is promoted by forcing high cur-rent arcs located outside the preferred arcing region tob urn with a higher are voltage than when in said preferred arcing region. The lower arc voltage in the preferred arcing region is obtained by a strong magnetic field that is oriented generally parallel to the are when in the preferred arcing region but trans verse to are when outside the preferred arcing region.

This invention relates to an electric circuit interrupter of the vacuum type and, more particularly, to a vacuum type circuit interrupter with new and improved means for transferring an are from' an arc-initiation region to a preferred arcing region where the arc voltage developed by the arc is relatively low.

In application S.N. 328,656Lee, filed Dec. 6, 1963, and assigned to the assignee of the present invention, it is pointed out that the arc voltage developed by an arc during high instantaneous currents can be appreciably reduced by applying to the are an intense magnetic field that has its lines of force extending axially of the arc. The aforesaid Lee application is now abandoned but was replaced by a continuation-in-part application that issued as Patent 3,321,599.

An object of the present invention is to utilize this low arc-voltage characteristic of the vacuum arc in an axial magnetic field to produce rapid transfer of the are from an arc-initiation region into a preferred arcing region of the vacuum interrupter.

Another object is to promote arc transfer to a preferred arcing region of an interrupter by forcing high current arcs located outside the preferred arcing region to burn with a higher are voltage than when in said preferred arcing region.

Another object is to provide magnetic means which can increase the difference between the arc voltage developed when the arc is in the preferred arcing region and that developed when the arc is outside the preferred arcing region.

Still another object is to utilize the tendency of an arc to move into a position of minimum arc voltage for promoting division of the are into a plurality of series-related arcs.

In carrying out my invention in one form, I provide, within a highly evacuated envelope, a first electrode and a second electrode. The second electrode has a position during interruption spaced from the first electrode to define a primary arcing gap therebetween across which an arc is established. Means is provided for developing a magnetic field that has its lines of force extending transversely of an arc in said primary gap. Means including an auxiliary electrode electrically connected to the first electrode is provided to define a secondary arcing gap into which the arc is movable from said primary arcing gap. This secondary arcing gap is so disposed that the lines of force of said magnetic field in the region of any are in the secondary arcing gap extend generally parallel to this are. The magnetic field is controlled in such a manner that its flux density in the region of an arc in the secondary gap during instantaneous currents greater than 20,000 amperes will be high enough to substantially reduce the arc voltage as compared to the are voltage normally developed by an are burning across said secondary gap without said magnetic field. Means is also provided for substantially eliminating said magnetic field across the secondary arcing gap during the period just prior to current zero following an instantaneous current greater than 20,000 amperes.

In a preferred form of the invention, the magnetic field has a high enough flux density extending transversely of an arc in the primary gap to increase the arc voltage during high instantaneous currents to a level substantially higher than the arc voltage normally developed by an are burning across the primary gap without said magnetic field. This higher are voltage in the primary gap will increase the difference between the arc voltage developed by an arc in the primary gap and that developed by an arc in the secondary gap, thus accelerating transfer of the are from the primary to the secondary gap.

For a better understanding of the invention, reference may be had to the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a sectional view through an interrupter embodying one form of the present invention.

FIG. 1a is a sectional view taken along the line 1a1a of FIG. 1.

FIG. 2 is a side elevational view of a portion of FIG. 1.

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1.

FIG. 4 is a sectional view of an interrupter embodying a modified form of the invention.

FIG. 5 is an enlarged view of a portion of the interrupter of FIG. 4.

FIG. 6 is a sectional view of FIG. 4.

FIG. 7 is an enlarged fragmentary view of a portion of a modified interrupter.

FIG. 8 is an enlarged fragmentary view of another portion of the interrupter of FIG. 7.

Referring now to the interrupter of FIG. 1, there is shown a highly-evacuated envelope 10 comprising a tubular casing 11 of suitable insulating material and end structure 12 and 13 closing off the ends of the casing 11. Suitable seals 14 are provided between the end structures and the casing 11 to render the envelope vacuum-tight. The normal pressure within the envelope is lower than 10' mm. of mercury, so that a reasonable assurance is had that the mean free path for electrons will be longer than the potential breakdown paths in the envelope.

The upper end structure 12 comprises an end plate 15 having a centrally located opening 16 therein. Mounted atop this end plate is an inverted cup shaped part 17 having a bore 19 aligned with opening 16 in the end plate 15. The cup shaped part 17 is preferably made of a highresistivity, low-permeability metal such as stainless steel. The lower surface of the cup shaped part is suitably brazed about its entire circumference to the end plate 15.

Mounted Within the cup-shaped part 17 is a pair of relatively movable contacts or electrodes 21 and 22. The upper electrode 21 is a stationary electrode that is mounted on a rod 24 of highly conductive material. The stationary electrode 21 is suitably brazed to the lower end of the rod 24. The upper end of the rod 24 extends through the upper end wall of the cup-shaped member 17 and is joined thereto by a brazed joint 25 that forms a vacuumtight seal between the rod and the end wall.

The lower electrode 22 is a movable electrode that is suitably joined to an operating rod 26 of highly conductive material. This operating rod 26 freely extends taken along the line 6-6 in a vertical direction through a central opening in the lower end cap 13. The operating rod 26 is vertically movable and can be driven in an upward direction from its position of FIG. 1 to move the lower electrode 22 into engagement with the upper electrode 21, thereby closing the interrupter. Opening of the interrupter is produced by driving the operating rod 26 downwardly, thereby driving the lower electrode 22 out of engagement with the upper electrode and into its positon of FIG. 1.

For permitting vertical motion of the operating rod 26 without impairing the vacuum inside envelope 10, a flexible metal bellows 29 is provided about the operating rod 26. This bellows 29 is joined at its respective opposite ends to the end pate 13 and the operating rod 26 by suitable vacuum-tight joints. For protecting the bellows 29 from arcing products generating during operation of the interrupter, a shield 29a of inverted cup-form is provided about the bellows. This shield is suitably attached to the operating rod 26.

Each of the illustrated electrodes 21 and 22 is of a disk shape and has an annular portion 23 near its outer periphery projecting toward the other electrode. These annular portions are in substantial alignment with each other and are adapted to engage each other when the interrupter is in its closed position. Opening of the interrupter initiates an are 28 across a primary gap 27 between the projecting portions 23, and this are is subsequently extinguished to interrupt the circuit in a manner that will soon be explained.

Surrounding the lower electrode 22 is a ring-shaped electrode 30. This ring-shaped electrode 30 is mounted on the cup-shaped housing 17 and is electrically connected to the upper electrode structure 21, 24 through a connecting strap 32 of high conductivity material. The connecting strap 32 is suitably brazed at its upper end to the rod 24 and at its lower end to the ring shaped electrode 30. Suitable spacers 31, preferably of stainless steel, are suitably brazed between the housing 17 and the electrode 30 and strap 32 to support these parts on the housing 17 in spaced relationship thereto. There is an annular space 34 between the ring-shaped electrode 30 and the lower electrode 22 that serves as an arcing gap of annular form to which the arc is transferred after being initiated between the relatively movable electrodes 21 and 22.

In order to reduce the arc voltage developed by a high current are extending radially across the annular gap 34, I provide field-producing means 40 for developing an intense magnetic field that has its lines of force extending in a radial direction across the annular gap 34. Referring to FIG. 3, since an are, such as 28a, across this annular gap 34 will also extend radially thereof, the lines of force of the magnetic field in the region of an are positioned in the gap 34 will extend generally parallel to the axis of the arc. As explained in the aforementioned Lee application S.N. 328,656, such a parallel magnetic field will reduce the arc voltage developed by such an arc during high instantaneous currents, e.g. above 20,000 amperes. In a preferred form of the invention, the magnetic field strength is made high enough to reduce the arc voltage developed during peak currents greater than 40,000 amperes to less than half the arc voltage normally developed by an arc of corresponding peak current with no axial magnetic field present.

The field-producing means 40 comprises a pair of seriesconnected coils 42 and 44 wound about the cup-shaped housing 17. These series-connected coils 42 and 44 are connected in series with the electrodes 21 and 22 of the interrupter between a terminal 43 of the interrupter and the conductive rod 24. As illustrated in FIG. 2, these coils 42 and 44 are wound in opposite directions so that the magnetic field produced by the two coils buck or oppose each other. The field produced by each coil is referred to hereinafter as a sub-field. The sub-field produced by coil 42 is shown at 45, and the sub-field produced by coil 44 is shown at 46. The lines of force of each of these sub-fields surround the particular coil producing the field and extend radially of each coil in the region between the two coils. These sub-fields may be thought of as being of a generally toroidal shape. They surround the longitudinal axis of the electrodes 21 and 22 and are axially displaced from each other along this axis. Since both the sub-fields traverse the region between the two coils, a relatively high field strength is developed in this particular region. It will be apparent from FIGS. 1 and 3 that the magnetic field in this region extends radially of the annular gap 34 between the concentric electrodes 30 and 22 around the entire circumference of the gap 34. It will also be apparent from FIG. 1 that the magnetic field extends radially of the arc-initiating gap 27 between the two electrode portions 23.

Since the coils 42 and 44 are in series with the electrodes 21 and 22, it will be apparent that the above-described magnetic field has a high flux density or intensity when the current through the interrupter is high and a low flux density or intensity when the current through the interrupter is low. This is as desired since the high intensity of the magnetic field is used for reducing the arc voltage during high instantaneous currents, whereas the low intensity during low currents allows the interrupter to recover its dielectric strength at current zero without substantial interference from the magnetic field.

As pointed out hereinabove, downward opening movement of electrode 22 initiates an are 28 across the arcinitiating gap 27. The previously-described magnetic field 45, 46 will extend transversely of this arc. I have found that an intense magnetic field directed transversely of a high current vacuum arc will cause it to burn at a higher are voltage than it would in the absence of the transverse field. It has also been found that there is a strong tendency on the part of an arc to move into a position where it can burn with minimum arc voltage. I capitalize on this tendency by providing, immediately adjacent the gap 27, the annular gap 34 where the am can extend axially of the magnetic field 45, 46 and can thus burn at a very low arc voltage, as previously described. FIG. 3 shows the are at 28a extending radially across the annular gap 34. The immediate proximity of this annular gap 34 where the arc can burn with a low arc voltage results in the are moving rapidly from the high arc-voltage gap 27 into the low arcvoltage gap 34.

The are continues to burn in the gap 34 until a natural current zero is reached, at which time the gap quickly recovers its dielectric strength and prevents reignition of the arc.

The presence of a strong axial magnetic field between the electrodes at current zero would have a tendency to impair the gaps ability to recover its dielectric strength. My interrupter contains a number of features which prevent such impairment of the gaps ability to recover its dielectric strength. One is that the current-responsive fieldproducing means 42, 44 is connected in series with the arc. Thus, when the arcing current approaches zero, the current through the field-producing means approaches zero, and the field strength likewise approaches zero. Eddy currents induced in adjacent parts of the interrupter tend to produce a lag between flux and current which maintains flux in the gap at current zero. But I reduced this lag to a tolerable value by severely limiting the eddy currents.

For the purpose of suppressing such eddy currents, 1 form the cup-shaped member 1'7 of stainless steel, a highresistivity, low-permeability metal, in which negligible eddy currents are induced. I also provide a slot 50 (best shown in FIG. 1a) in the ring-shaped electrode 30 which substantially prevents eddy currents from finding a path extending circumferentially about the ring-shaped electrode 30. The main electrodes 21 and 22 are also provided with radially extending slots 52 that break up the eddy current paths through the electrodes. These slots 52, which are best shown in FIG. 3, are extended radially inward as far as possible so as to improve their effectiveness in breaking up the eddy current paths. Also each electrode is perforated in its central region, as shown at 55, to further reduce the eddy currents.

The slots 52 serve the additional function of producing movement of the arc in a circumferential direction about the periphery of lower electrode 22. In this connection, the slots 52 force the net current flowing through the electrode 22 to an arc terminal on the peripheral portion of the electrode 22 to follow a path that has a tangentiallyextending component. For example, note the radially extending arc 28a of FIG. 3 and the current path L extending through the electrode 22 generally tangentially with respect to the arc. As explained in US. Patent 2,949,520- Schneider, assigned to the assignee of the present invention, the magnetic effect of current flowing through such a tangentially extending path is to drive the arc circumferentially.

Additional force for driving an are such as 28a in a circumferential direction results from the presence of slot 50 in the ring-shaped electrode 30. This slot 58 forces current flowing through the elect-rode 30 .to an arc terminal at substantially any point on the ring-shaped electrode 30 to follow a portion of path L that extends circumferentially with respect to the ring electrode. The magnetic effect of current flowing through such a path is to lengthen the loop in the path L by driving the arc circumferentially. By driving the arc circumferentia-lly while maintaining its arc voltage low, I can limit the quantity of arcing products generated during interruption, thereby improving the ability of the interrupter to recover its dielectric strength at current zero.

For protecting insulating casing 11 from the deposition of arc-generated electrode vapors thereon, a suitable metal shield 57 of tubular form is provided. This shield is shown connected to end plate 15. An auxiliary shield 58 surrounds the lower end of shield 57 to provide additional protection against vapor-deposition for the tubular insulating casing 11.

FIG. 4 illustrates a modified form of the invention where the initial arc is first divided into two series-related arcs, and each of these series-related arcs is subsequently transferred to a region of low arc voltage, where there is an intense magnetic field extending axially of the are This interrupter of FIG. 4 comprises a highly-evacuated envelope comprising a tubular insulating casing 11 and end plates 12 and 13 suitably sealed to the casing 11 at its opposite ends. Mounted Within the sealed envelope 10 is a pair of relatively movable contacts, or electrodes, 78 and 72. These contacts are of a generally cup-shape, each comprising a base portion 73 and cylindrical flange 74 projecting away from the base portion 73 in a direction away from the other contact. The upper contact 74) is a stationary contact, and the lower contact 72 is a movable contact that can be moved in a vertical direction into and out of engagement with the upper contact.

The movable lower contact 72 is mounted on a conductor 77 of a high conductivity material, such as copper, that is spirally wound into a coil 78 of generally cylindrical form. This conductor 77 is suitably joined at its upper end to the base of the movable contact 72 and at its lower end to an operating rod 80 of high conductivity material that projects freely through the lower end cap 13. Suitable spacers 82 of a high resistivity material such as stainless steel are located between the turns of the coil to maintain a definite spacing therebetween. These spacers 82 are preferably held in position by suitable brazed joints. The spacers also structurally reinforce the coil and impart rigidity thereto. Since stainless steel has a very high resistivity in comparison to that of the copper used for conductor 77, very little of the current flows through the spacers. Nearly all the current is forced to follow the spiral path followed by the conductor '77.

The upper contact 70 is mounted on a coil 78a of substantially the same construction as the lower coil 78. Thus, the upper coil is formed from a conductor 77a that ex tends in a spiral path and has stainless steel spacers 82a maintaining a slight spacing between adjacent turns. For reasons which will soon appear more clearly, the upper coil is wound in an opposite direction from the lower coil. The upper coil 78:: is suitably joined at its upper end to a copper conductor 83 that extends through the upper end cap 12. A suitable brazed joint 84 is provided about the upper conductor 83 to mechanically support it and provide a vacuumtype connection between the conductor 83 and the end cap 12.

The operating rod 86 is mounted for vertical reciprocation. It can be driven in an upward direction to carry the movable contact '72 into engagement with the stationary contact 70, thereby closing the interrupter. The operating rod 88 can be driven in a downward direction to separate the movable contact '72 from the stationary contact 70, thereby opening the interrupter, as will soon be described. A flexible metallic bellows 29 provides a seal between the end cap 13 and operating rod 80 and thus permits vertical movement of the rod 80 without impairing the vacuum inside the envelope l0. Suitable operating means (not shown) is provided for effecting upward closing and downward opening movement of the rod 80.

Each of the contacts 7% and 72 has an annular portion 73a near its outer periphery projecting toward the other contact. These annular portions are in substantial alignment and are adapted to engage each other when the interrupter is in its closed position. Opening of the interrupter initiates an arc such as shown at 85 between the projecting portions 73a. This are is referred to herein after as the primary arc, and the gap between projecting portions 73a is referred to as primary gap 86.

Surrounding the primary gap 86 is a tubular arcdividing electrode 88 of a high conductivity material such as copper. This tubular arc-dividing electrode 88 is supported on casing 11 by pins 89 extending radially through the casing 11 in sealed relationship thereto. Under normal conditions, this arc-dividing electrode 88 is electrically isolated from both of the contacts 70 and 72.

At opposite ends of the arc-dividing electrode 88 are secondary electrodes 90 and 92 eiectrically connected to the contacts 7t? and 72, respectively. The upper secondary electrode 90 is an annular disk that is an extension of flange 74 of the cup-shaped contact 79 and extends generally perpendicular to the flange 74. The lower secondary electrode 92 is an annular disk that is an extension of flange 74 of cup-shaped electrode 72 that extends generally perpendicular to the flange. The annular space between the upper secondary electrode and the upper end of the arc-dividing electrode 88 is referred to as a secondary arcing gap 95, and the annular space between the lower secondary electrode 92 and the lower end of electrode 88 is referred to as a secondary arcing gap 96.

The primary are 85 that is initiated across the primary arcing gap 86 is divided by the arc-dividing electrode 88 into two series-related arcs which are respectively driven into the secondary arcing gaps 95 and 96. More specifically, the primary are 85 is initiated in a position radially spaced from the central axis of the interrupter. Accordingly, current flowing through the arc in the contacts '70 and '72 follows a loop-shaped path L that has a magnetic effect tending to lengthen the loop and drive the arc in a radially outward direction. In moving radially outward, the are 85 engages the arc-dividing electrode 88. This results in two ser'es-related arcs being formed in approximately the position and 102. The upper arc at 100 is quickly driven in an upward direction through position 103 and thence into a position 105 across the secondary gap 95. The lower are at 102 is quickly driven in a downward direction through position 107 and then into a position 199 across the secondary arcing gap 96.

In carrying out my invention in this embodiment, I utilize the magnetic field from coils 78 and 78a to accelerate the above-described arc-dividing action and the subsequent transfer of the series-related arcs to the secondary arcing gaps 95 and 96. This can best be understood by referring to FIG. which illustrates the magnetic field that is developed by the two coils. This magnetic field may be throught of as constituting two sub-fields 110 and 112, each of a generally toroidal shape. The lines of force of each toroidal shape sub-field are shown at 115 following loop-shaped paths surrounding and linked with their respective field-producing coils. The two toroidal subfields 110 and 112 surround the central longitudinal axis of the interrupter and are axially displaced from each other along this axis. The central longitudinal axis substantially coincides with the axes of coils 78 and 78a. Since the coils 78 and 78a are wound in opposite directions, and current flows in series through them, the subfields 110 and 112 are in bucking or opposing relationship to each other. In view of this opposing relationship, the sub-fields, at any given instant, extend in opposite directions to each other along the central axis of the interrupter but extend in generally the same radial direction in the region where the two sub-fields are adjacent each other.

It will therefore be apparent that the two sub-fields 110 and 112 extend radially of the primary gap 86 and radially of the primary arc 85 established thereacross. It will be further apparent that the magnetic field extends perpendicular to the series-related arcs in positions 199, 103, 102 and 197. It is only when the series-related arcs reach the immediate region of the secondary gaps 95, 96 that they enter a position Where the magnetic field is generally parallel to the arc.

The magnetic field strength in the secondary arcing gaps 95 and 96 is 'made high enough to produce a substantial reduction, preferably 50 percent or more, in the arc voltage at which each of these arcs will burn thereacross as compared to the arc voltage that would normally be developed by an arc of the same current but without the strong axial magnetic field. Since there is no position other than the secondary arcing gaps 95 and 96 where the are or arcs can extend parallel to the strong magnetic field, they burn at a higher voltage in locations outside the secondary gaps 95 and 96. Since an arc has a strong tendency to move into a position where it can burn with minimum arc voltage, the primary are 85 moves rapidly toward the secondary gaps. Such motion forces the primary arc to divide into the above-described series-related arcs, which in turn move rapidly into positions of minimum arc voltage across the gaps 95 and 96.

To further accelerate the transfer of arcing from the primary gap 86 to the secondary gaps 95 and 96, I make the field strength of the magnetic field in regions outside the secondary arcing gaps so high that the arc voltage developed is even higher than that which would normally be developed without a strong radial field. This higher-than-normal arc voltage increases the difference between the arc voltage that the arc will develop outside the secondary gap 95 or 96 as compared to inside and, thus, further encourages the arc to transfer to the secondary arcing gap 95 or 96, where the arc voltage will be low.

Since the coils 78 and 79a are in series with any are between the electrodes, it will be apparent that the magnetic field extending axially of the series-connected arcs falls to a low value at and just before current zero. For suppressing eddy currents in order to reduce the lag between flux and current to a tolerable value, thereby minimizing the field strength of any residual magnetic field remaining at current zero, I suitably slot all the high conductivity parts of the interrupter in the arcing region.

For example, referring to FIG. 6, the arc-dividing electrode 88 is shown with a longitudinally extending slot 129, and the electrode 72 is shown with a pair of longitudinally-extending slots 122. The other electrode 70 has a similar pair of longitudinally-extending slots (not shown). These longitudinally-extending slots in parts 83, 7t) and 72 break up circumferentially-extending paths for any 8 eddy currents induced in these parts by the magnetic field. Holes 124 in the base 73 of the contacts further break up eddy current paths.

By substantially eliminating the axial magnetic field at and just prior to current Zero, I prevent any substantial impairment of the dielectric strength of gaps and 96 by the axial field.

For condensing the arc-generated vapors that are projected radially outward from the gaps 95 and 96 during interruption, suitable vapor-condensing shields 139 and 132; of tubular form surrounding these gaps are provided. These shields are preferably formed of a high-resistivity, low-permeability material such as stainless steel, which allows negligible eddy currents to be induced therein. If it is desired to use a high conductivity material for the shields, the induction of eddy currents therein can be suppressed by constructing the shields as shown in application Ser. No. 454,282-Porter and Polinko, now Patent No. 3,345,484 filed May 10, 1965, and assigned to the assignee of the present invention. The upper shield is electrically isolated from the arc-dividing electrode 88 and the upper contact 70 and is preferably at a midpotential with respect to these parts when the circuit interrupter is open. The lower shield 132 is electrically isolated from the arc-dividing electrode 88 and lower contact 72 and is preferably at a mid-potential with respect to these parts when the interrupter is open.

For intercepting any arc-generated vapors that might bypass the shields 139 and 132, suitable end shields 134 of tubular form are also provided. In addition, a tubular central shield 135 surrounding the adjacent ends of shields 13d and 132 is provided.

The radial magnetic field in which the arcs are located until they reach the secondary gaps 95 and 96 serves not only to develop a high are voltage which accelerates arc transfer to the secondary gaps, but it also acts to rotate the arcs about the central axis of the interrupter. In this regard, the radially-extending magnetic field extends transversely of the arc and coacts with the magnetic field produced by current flowing through the arc to develop a magnetic pressure at one side of the arc which drives the are normal to the magnetic field. This are motion normal to the direction of the magnetic field carries the arc in a circumferential direction about the central axis of the interrupter. This circumferential arc motion is advantageous in reducing the quantity of electrode material vaporized by the arc, thus facilitating circuit interruption at a current zero.

In a modified form of the invention, I continue to rotate the series-related arcs about the central longitudinal axis of the interrupter when they are located in the secondary gaps 95 and 96. The force for effecting such arc-rotation is derived from a series of angularly-spaced skewed slots 139 provided in the tubular electrode 88 at its free ends. These slots are best illustrated in FIG. 7, where they are shown angularly overlapping their adjacent slot and dividing the end of tubular part 88 into a series of angularly-spaced fingers 149 respectively located between adjacent slots. Each of the slots 139 has a circumferentially-extending component that forces the current flowing to or from an arc terminal located on any one of the fingers 140 to follow a path that has a net component extending circumferentially 0f the tubular part. The magnetic effect of current flowing in such a circumferentially-extending path is to drive the arclet circumferentially of the tubular part about the longitudinal axis of the interrupter.

Additional force for rotating the arcs in secondary gaps 95 and 96 can be developed by providing the flanges 9i) and 92 with slots 142, each extending from the radially outer edge of the flange inwardly via a path having a circumferentially-extending component. Such slots 142 are shown in FIG. 8 defining fingers 143 therebetween in the flange 92. These slots force the current flowing through a finger 143 to an arc terminal on the finger to have a circumferenlially-extending component that acts to drive the arc circumferentially.

Another desirable feature of the interrupter of FIG. 4 is that the primary gap 86 is remote from the secondary gaps 95 and 96 and is well protected by the tubular parts 88 and 74 from being contaminated with arc-generated vapors from the secondary gaps. These vapors tend to condense on the tubular parts before they can reach the primary gap 86. Protecting the primary gap from such contamination helps it to rapidly develop a high dielectric strength at current zero.

To inhibit the vapors generated at either of the secondary gaps 95 and 96 from reaching the other secondary gap, the arc-dividing electrode 88 is preferably provided with an annular portion 145 projecting radially inwardly thereof in its central region. The presence of this radiallyinward projecting portion 145 also facilitates division of the are 85 into its series-related parts, as described hereinabove.

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, and I, therefore, intend 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:

1. An alternating current electric circuit interrupter of the vacuum type comprising:

(a) a first electrode,

(b) a second electrode having a position during interruptions spaced from said first electrode to define a primary arcing gap therebetween across which an arc is established,

(c) an evacuated envelope surrounding said electrodes,

((1) means for developing a magnetic field that has its lines of force extending transversely of an arc in said primary gap,

'(e) means including an auxiliary electrode electrically connected tosaid first electrode for defining, a secondary arcing gap into which said are is movable from said primary arcing gap,

(f) said secondary gap being so disposed that the lines of force of said magnetic field in the region of any are in said secondary arcing gap extend generally parallel to said arc,

(g) means for controlling said magnetic field in such a manner that its flux density in the region of an arc in said secondary gap during instantaneous currents greater than 20,000 amperes will be high enough to substantially reduce the arc voltage as compared to the arc voltage normally developed by an arc of equal current burning across said secondary gap without said magnetic field,

(h) and means for substantially eliminating said magnetic field across said secondary gap during the period just prior to current zero following an instantaneous arcing current greater than 20,000 amperes.

2. The interrupter of claim 1 in combination with means for maintaining said magnetic field transverse to said are from the point at which the are is established between said electrodes to the point at which it reaches the region of said secondary gap.

3. The interrupter of claim 1 in combination with means for rotating said are about a predetermined axis of said electrodes during movement between said primary gap and said secondary gap.

4. The interrupter of claim 1 in combination with means for rotating said arc about a pretedermined axis of said interrupter when said are is in said secondary gap.

5. The interrupter of claim 1 in which said magnetic field has a high enough flux density extending transversely of an arc in said primary gap to increase the are 10 voltage during high instantaneous currents to a level substantially higher than the arc voltage normally developed by an arc of corresponding current burning across said primary gap without said magnetic field.

6. An alternating current electric circuit interrupter of the vacuum type comprising:

(a) a first electrode,

(b) a second electrode having a position during interruptions spaced from said first electrode to define a primary arcing gap therebetween across which a primary are is established,

(c) an evacuated envelope surrounding said electrodes,

(d) means for developing a magnetic field that has its lines of force extending transversely of an arc in said primary gap,

(e) means for dividing said primary arc into a plurality of series-related arcs in an arc-dividing region,

(f) means defining a plurality of secondary arcing gaps for respectively receiving said series-related arcs,

(g) said secondary gaps being so disposed that the lines of force of said magnetic field in the region of any arc in said secondary arcing gaps extend generally parallel to said are in said secondary arcing gaps,

(h) means for controlling said magnetic field in such a manner that its flux density in the region of an arc in a secondary gap during instantaneous currents greater than 20,000 amperes will be high enough to substantially reduce the arc voltage as compared to the arc voltage normally developed by an arc of corresponding current burning across said secondary arcing gap without said magnetic field,

(i) and means for substantially eliminating said magnetic field across said secondary gaps during the period just prior to current zero following an instantaneous arcing current greater than 20,000 amperes.

7. The interrupter of claim 6 in which said magnetic field extends transversely of said primary arc and said series-connected arcs in said arc-dividing region.

8. The interrupter of claim 6 in which said magnetic field extends transversely of said primary arc and said series-connected arcs in said arc-dividing region and in which means is provided for maintaining said magnetic field transverse to each of said series-related arcs at all points in the travel of said series-related arcs between said arc-dividing region and the region of said secondary gaps.

9. The interrupter of claim 6 in which said magnetic field comprises two sub-fields each of generally toroidal shape, the two generally toroidal sub-fields surrounding a common axis and being displaced from each other along said axis,

(a) first field-producing means for producing and shaping one of said sub-fields in such a manner that its lines of force follow loop-shaped paths extending through said primary gap radially thereof and through one of said secondary gaps in a direction generally normal to the radial direction through said primary ('b) second field-producing means for producing and shaping the other of said sub-fields in such a manner that its lines of force follow loop shaped paths extending through said primary gap radially thereof and through the other of said secondary gaps in a direction generally normal to the radial direction through said primary gap,

(c) said two sub-fields being developed in bucking relationship to each other so as to extend, at a given instant, in opposite directions through said secondary gaps but in generally the same radial direction through said primary gap.

10. An alternating current electric circuit interrupter of the vacuum-type comprising:

(a) an evacuated envelope,

(b) means for establishing a magnetic field comprising two sub-fields, each of generally toroidal shape, the two generally toroidal sub-fields surrounding a common axis and being axially displaced from each other along said axis,

(c) said two sub-fields being developed in bucking relationship to each other so as to extend, at a given instant, in opposite directions along said axis and in generally the same radial direction in the region where the two sub-fields are adjacent each other,

((1) a primary arcing gap inside said envelope, radially spaced from said axis and located in the region where said two sub-fields are adjacent each other, said sub-fields extending transversely of said primary (e) an annular secondary arcing gap in said envelope located radially outward of said primary gap and displaced therefrom along said axis so that one of said sub-fields extends longitudinally of said secony s p,

(f) means for establishing an arc across said primary gap with the magnetic field in the immediate region of the are extending generally normal-to said are,

(g) and means for transferring at least a portion of said are to said secondary gap with the portion of said are in said secondary gap extending generally parallel to the magnetic field in said secondary gap in the region of the are, 4

(h) said magnetic field in said secondary gap being high enough to substantially reduce the arc voltage of high current arcs present in said secondary gap as compared to the are voltage normally developed by and are of equal current burning across said secondary gap without said magnetic field.

11. An alternating current electric circuit interrupter of the vacuum-type comprising:

(d) a primary arcing gap inside said envelope, radially spaced from said axis and located in the region where said two sub-fields are adjacent each other, said sub-fields extending transversely of said pri- (e) a pair of annular secondary arcing gaps inside said envelope, each located radially outward of said primary arcing gap and in a difierent one of said subfields,

(f) said annular secondary arcing gaps being located in positions axially spaced from said primary gap where the respective sub-fields extend generally parallel to said axis and across said secondary gap generally longitudinally thereof,

(g) means for establishing an arc across said primary gap with said sub-fields extending generally normal to said arc,

(h) means located between said primary and secondary gaps for dividing said are into a pair of series-related arcs,

(i) and means for respectively transferring said seriesrelated arcs to said secondary gaps with each secondary are extending generally parallel to the sub-field extending across its associated secondary gap,

(j) said magnetic field in said secondary gaps being high enough to substantially reduce the are voltage of high current arcs present in said secondary gaps as compared to the arc voltage normally developed by arcs of equal current burning across said secondary gaps without said magnetic field.

References Cited UNITED STATES PATENTS 2,027,836 1/1936 Rankin.

2,090,519 8/ 1937 Rankin.

2,949,520 8/ 1960 Schneider.

2,976,382 3/1961 Lee 200-144 3,014,107 12/1961 Cobine et a1 200-144 3,082,307 3/ 1963 Greenwood et al. 200144 3,185,797 5/1965 Porter 200 144 3,185,799 5/ 1965 Greenwood et al. 200-144 3,283,103 11/1966 Greenwood et al. 200 -l44 FOREIGN PATENTS 571,959 1/1958 Italy.

ROBERT S. MACON, Primary Examiner.

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