US3452174A - Circuit interrupter for high-voltage d-c circuits - Google Patents

Description

June 24, 1969 J. J. CARROLL E AL 3,452,174

CIRCUIT INTERRUPTER FOR HIGH-VOLTAGE D-C CIRCUITS Filed Jan. 25, 1966 Sheet of 2 TV a INVENTORS. JAMES J. CARROLL, GERHARD F/w/vo, I BY ATTORNEY June 24, 1969 J. J. CARROLL ET AL 3,452,174 CIRCUIT INTERRUPTER FOR HIGH-VOLTAGE D-C CIRCUITS Filed Jan. 25, l966 She et & of 2 23 /a //v VEN TORS.

, ZZ JAMES J CARROLL, Z0 GER/HARD Ewva,

2; ATTORNEY United States Patent 3,452,174 CIRCUIT INTERRUPTER FOR HIGH-VOLTAGE D-C CIRCUITS James J. Carroll, Philadelphia, and Gerhard Frind, Secane, Pa., assignors to General Electric Company, a corporation of New York Filed Jan. 25, 1966, Ser. No. 522,977 Int. Cl. H0111 33/82, 33/76, 33/60 US. Cl. 200-148 4 Claims ABSTRACT OF THE DISCLOSURE A high voltage D-C circuit interrupter capable of developing exceptionally high are voltages for forcing the current in a high voltage D-C circuit to zero. An arc established in an arc-initiation reigon is driven along arc runners toward an exhaust opening and is lengthened as it moves along the runners by closely-spaced, gas evolving insulating plates that force the are into a zig-zag path of greatly increasing length. The arc-initiation region is closed oil? in such a manner that substantially all the gases evolved therein or supplied thereto are forced to flow out of the interrupter through said exhaust opening. The interrupter is normally filled with high pressure gas for retarding arc motion toward said exhaust opening.

This invention relates to a direct current electric circuit interrupter for use in high voltage D-C circuits and, more particularly, relates to an interrupter of this type which is capable of rapidly developing high are voltages for forcing the current through the high voltage circuit to zero.

'It is considerably more ditffiicult to interrupt direct current than alternating current because direct current contains no naturally-occurring current zeros. With alternating current, current zeros occur naturally, and to interrupt such currents, it is only necessary to prevent reignition of the are 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.

The general approach that we use for forcing the current to zero invloves rapidly building up a high are voltage that exceeds the circuit voltage. This we do by rapidly lengthening the are between closely-spaced insulating plates. While it has been recognized that are voltage can be increased by lengthening the arc and by cooling with closely-spaced insulating plates, the maximum arc voltages heretofore developed using this approach have been much too low to permit the interruption of high voltage D-C circuits (20 kv. or higher) with a practical size interrupter of this type.

An object of our invention is to provide an interrupter of this type which, though of a compact and practical size, can develop a high enough arc voltage to interrupt a high voltage D-C circuit.

Another object of our invention is to provide an interrupter of this type in which are erosion (i.e., erosion of the interrupter walls by the arc) is distributed over a wide area of the interrupter. By avoiding localized arc erosion, we can minimize changes in the crucial dimensions of the interrupter, resulting from interrupter operation, and thus can carry out many repeated interruptions, even of high currents.

In carrying out our invention in one form, We provide a D-C circuit interrupter comprising a chamber having an exhaust opening at one end and an arc-initiation region at an opposite end. Within this chamber a static presure of at least several atmospheres is normally maintained. Arcs initiated in the arc-initiation region are forced along arc runners toward the exhaust opening by 3,452,174 Patented June 24, 1969 arc-motivating means comprising (a) means for directing a blast of high pressure gas through the arc-initiation region toward the exhaust opening and (b) means for forcing substantially all gases generated by the arc in the arc-initiation region to flow out of the chamber via said exhaust opening. Arc-lengthening means is provided for forcing the arc to follow a zig-zag path of progressively increasing length as it moves toward the exhaust opening. This zig-zag path is constituted by a series of loops, adjacent ones of which bow in opposite directions disposed transversely of the direction of arc motion. The arc-lengthening means comprises a series of closelyspaced generally flat plates of insulating material so disposed that the transversely-extending portions of the loops extend between adjacent pairs of the flat plates.

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 partially schematic plan view of an interrupter embodying one form of our invention.

FIG. 2 is a sectional view along the line 22 of FIG. 1.

FIG. 3 is a sectional view along the line 3-3 of FIG. 2.

FIG. 4 is an exploded perspective view of some of the elements constituting the interrupter of FIG. 1.

FIG. 5 is a sectional view along the line 55 of FIG. 1.

FIG. 6 is a sectional view along the line 6-6 of FIG. 1.

Referring now to FIGS 1 and 2, the interrupter comprises an arcing chamber 10 having an exhaust opening 12 at the left hand end of the chamber and an arc-initiating region 14 located at the opposite, or right-hand end, of the chamber. The arcing chamber 10 comprises a stack of closely-spaced fiat plates 16, of an electrical insulating material of a character soon to be described.

Except for the plates at the extreme upper and lower ends of the chamber, each plate contains an elongated slot 18 or 20 that extends from the arc-initiation region '14 toward the exhaust opening 12 by a diagonally disposed path. Although the illustrated slots follow substantially straight line paths, a curved configuration can alternatively be used. As will be apparent from FIGS. 1 and 4, slots 18 and 20 in immediately adjacent plates diverge with respect to each other becoming progressively further apart as the distance from the arc-initiation region 14 increases. The slots .18 in alternate plates are in substantial registry, and the slots 20 in the remaining alternate plates are likewise in substantial registry. The slots 18 and 20 are slightly enlarged in the arc-initiation region 14. These enlargements are substantially aligned so that a vertically-extending passage of a generally cylindrical form is present in the arc-initiation region 14.

As will be apparent from the sectional views of FIGS. 3 and 6, each pair of adjacent slotted plates 16 are separated by spacers 22 positioned between the adjacent plates at their lateral edges. These spacers 22 preferably have a gradually decreasing width, as measured laterally of the arcing chamber as viewed in FIG. 3, and the edge of each spacer 22 is substantially in alignment with the outside edge of the slot 18 or 20 immediately thereadjacent. Accordingly, there is defined between a pair of spacers 22 in a given plane a passageway 23 that gradually increases in width proceeding from the arc-initiation region 14 to the exhaust opening 12. This passageway 23 is best shown in FIG. 3.

The uppermost and lowermost plates 24 and 25 are devoid of the slots 18 and 20 and constitute reinforcing end walls for the arcing chamber. Immediately beneath the uppermost end plate 24 is an insulating plate 26 that earries zan arc runner 28. This are runner 28 is a strap of conductive material, e.'g., graphite, that extends along the slot 18 in the insulating plate 16 that is located immediately 'therebeneath. This arc runner 28 fits in a registering opening provided in the insulating plate 26 for holding the arc runner in position. There is a bottom are runner 30 that is supported in a corresponding manner. That is, immediately above the lower end plate 25 there is an insulating plate 32 that has a registering opening 29 carrying the arc runner 30. This are runner extends along the length of slot 20 in the slotted insulating plate immediately thereabove. The superimposed plates of insulating material are all clamped together by a plurality of bolts 34 of insulating material, each of which extends through registering holes 35 provided in the plates.

Referring to FIG. 2, the electric terminals of the interrupter are constituted by a pair of conductive elements 40 and 42 which are connected to the arc runners 28 and 30, respectively. In the illustrated form of the invention, the arc runners 2-8 and 30 are interconnected by a fusible element v44 which is electrically connected at its opposite ends to the arc runners. This fusible element 44 extends vertically through the cylindrical passage that constitutes the arc-initiation region 14. The fusible element 44 is a current responsive element that is adapted to melt in response to high currents, thereby establishing an arc that extends through the arc-initiation region 14 between the two are runners. It is to be understood that other conventional means, such as separable contacts, may instead be used for rapidly initiating a long are in the arc-initiating region 14.

Immediately upon its establishment, this are at 14 is driven rapidly to the left toward the exhaust opening 12. The upper arc terminal runs to the left along the upper arc runner 28, and the lower arc terminal runs to the left along the lower arc runner 30. When the arc moves to the left out of the arc-initiation region 14, it is forced by the insulating plates 16 to follow a zig-zag path 50 that extends between the arc runners via the slots 18 and 20, as is best seen in FIG. 6. This zig-zag path 50 may be thought of as being constituted by a series of loops, adjacent ones of which bow in opposite directions that are disposed transversely of the direction of motion of the are as it moves toward the exhaust opening 12. As will be apparent from FIG. 6, the transversely-extending portions of the loops of the zigzag path extend between adjacent pairs of the flat plates 16. Any are following the zig-zag path 50 will therefore be in intimate engagement with the fiat plates 16, thus permitting a good exchange of heat between the arc and the plates.

As the arc moves toward exhaust opening 12 along the arc runners 28 and 30, zig-zag path 50 between the arc runners progressively but rapidly lengthens due to the divergence of slots 18 and 20. This, of course, results in a rapid lengthening of the arc, and this rapid lengthening rapidly increases the arc voltage developed by the arc. As the arc moves to the left, it is progressively exposed to relatively cool portions of the plates 16, thus providing an intense cooling action that further contributes to increasing the arc voltage.

The are reacts with the insulating material of plates 16 to generate gases, and these gases further contribute to are cooling. These gases are also utilized to provide a force for urging the arc to the left (in FIGS. 1 and 2) along the arc runners 28 and 30. To assure effective utilization of these gases for moving the arc to the left, we force substantially all of these gases to exhaust from the arcing chamber via the exhaust opening 12 at the left hand end of the interrupter. The right hand end of the interrupter contains no passages leading to the exterior, and thus the generated gases which escape from the chamber are forced to follow a path through the exhaust opening 12. This flow of the generated gases to the left provides an aerodynamic force on the are that drives it to the left.

We supplement this leftward force on the are by providing a cross-blast of high pressure gas that also acts to the left on the arc. This cross-blast is derived from a high pressure source 60 that supplies high pressure gas to a plurality of vertically-spaced passages 62 leading into the arc-initiation region 14. As shown in FIGS. 2 and 5, these passages '62 are located at vertically spaced points along the length of the arc. Each passage 62 extends transversely of the arc-initiation region 14 and directs high pressure gas through the arc-initiation region 14 toward the exhaust opening 12. A suitable manifold 63 (FIG. 1) external to the chamber 10 supplies these passages 62 with the high pressure gas, and this manifold is, in turn, supplied with high pressure gas from the source 60 through a high pressure line 64. This high pressure line 64 contains a normally-closed blast valve 65 that is of a conventional design. Suitable condition-responsive means (not shown) quickly opens this blast valve in response to an overcurrent or some other predetermined condition, thereby permitting high pressure gas to flow from the source 60 through the passages 62 to establish the previously-described cross-blast.

The cross-blast through passages 62 is relied upon particularly for low current arcs to drive the are rapidly out of the arc-initiation region 14. For high current arcs, even without the cross-blast, the are evolves enough gas from the insulating walls of the arc-initiation region to provide an effective gas blast for rapidly moving the are out of the arc-initiation region.

A significant point with respect to the construction of passages 62 is that they are located along substantially the entire length of the arc and can therefore provide a transversely-acting force on the are over a high percentage of its length. This is of importance with respect to the low current arcs that rely upon the cross-blast through passages 62 to move the are out of arc-initiation region 14. Subjecting a high percentage of the length of such low current arcs to these transversely-acting forces increases the speed at which the entire arc column is moved out of the arc-initiation region.

It is also importantjo note that the passages 62 terminate immediately adjacent the arc-initiation region rather than at a point remotely spaced from this region. This proximity of the passages 62 to the arc-initiation region results in the jets emerging from the passages 62 having substantially the same velocity when they enter the arc-initiation region as during their passage through the passages 62. We have a high enough pressure in the manifold of 63 to produce sonic velocity through passages 62 during low current interruptions. Thus, during low current interruptions the jets forming the coss-blast have a substantially sonic velocity as they enter the arc-initiation region.

The cross-blast through passages 62 not only provides a force for driving the low current are to the left but it also provides an arc-cooling action that further contributes to increased arc voltage. By way of example, the arc voltage developed by a 50 ampere arc is approximately doubled by the cross-blast.

Still another feature that contributes to the high arc voltage that we develop is the fact that the arcing chamber 10 is normally filled with gas at a high static pressure. In this connection, we surround the arcing chamber 10 with a tank 70 that is filled with a gas at a high static pressure, preferably of 5 to 20 atmospheres. This gas can be air, or it can be nitrogen or hydrogen. The source 60 for the cross-blast is at a substantially higher pressure than the gas in tank 70, preferably a pressure at least twice that of the pressure in tank 70. The high pressure gas that normally fills the arcing chamber increases the arc voltage by about twice that which is obtained with an arcing chamber at atmospheric pressure. A suitable overpressure valve (not shown) is provided in the tank to relieve any overpressures resulting from operation of the interrupter.

The following is a brief summary of the operation of the illustrated interrupter. When a high current flows through the interrupter, it melts the fuse element 44, establishing an arc in the arc-initiation region 14. The high current also causes the blast valve 65 to open, thereby establishing the previously-described cross-blast through passages 62 tranversely of the arc. The crossblast and the gases evolved from the insulating material by the arc all flow to the left toward the exhaust port 12, by moving the are rapidly to the left along the arc runners 28 and 30. As the arc moves to the left, it is forced to follow a zig-zag path 50 of rapidly increasing length. The are lengthening and cooling produced in this manner rapidly builts up an arc voltage of an unusually high value which rapidly forces the arcing current to zero. In tests conducted with the disclosed interrupter, it has been found that currents of l to 1000 amperes in a 20 kv, D-C circuit can be interrupted in milliseconds or less. The tests were conducted with air at a static pressure of 100 p.s.i. in the tank and 200 p.s.i. in the source 20. The slotted plates 16 in the tested device were made of Delrin, E. I. du Pont Companys trademark for acetal resin having a formula of (CH O) n.

As pointed out hereinabove, the arc vaporizes some of the insulating material that it contacts, this action being referred to as arc-erosion. The quantity of material vaporized is a direct functiOn of the are energy. It is important to avoid any localized arc-erosion that could prematurely produce detrimental changes in the crucial dimensions of the interrupter. In this connection,we have found that if the arc is moved too rapidly through the arcing chamher into its final position at the end of the arc runners 28, 30, then most of the arc erosion is concentrated in the region of the interrupter at the ends of the runners. This results in excessive erosion of the insulating plates 16 in this region and resultant excessive spacing developing between these plates.

To distribute the arc erosion over a greater portion of the interrupter, we limit the speed at which the arc moves to the end of the runners once it has moved out of the arc-initiation region 14. This we do by relying upon the relatively high density of the pressurized gas in the arcing chamber to limit the speed at which the gas in the chamber travels toward the exhaust opening 12. In this connection, it can be shown that with a given mass flow rate from the chamber, the velocity of the gas flowing through the chamber varies inversely with respect to density. The velocity of the arc varies directly with the gas velocity, and hence the lower gas velocity resulting from the high density of the gas results in lower arc velocity.

In addition, the progressive increase in the cross-section of passages 23, proceeding in a direction downstream from the arc-initiation region, as seen in FIG. 3, contributes to lower velocity for the arc. In this connection, this increasing cross-section reduces the velocity of the cross-blast from passages 62 at points progressively further downstream from the arc-initiation region.

To complete interruption of the D-C circuit, it is necessary not only to drive the current to zero but also to prevent arc-reignition when the circuit voltage is applied immediately following current zero. Our interrupter has a number of features which enable it to rapidly develop the dielectric strength necessary to prevent such arc-reignition. One of these features is that the insulating plates are made of a material that does not significantly carbonize along the exposed surface under the heat of the arc. The Delrin resin of which the plates 16 are made exhibits an exceptional resistance to such carbonization; and, thus, even in the arc-initiation region 14, where the surface creepage distance is lowest, there is a high dielectric strength available along the surface of the plates 16 at current zero. Another feature is that the cross-blast through passages 62 scavenges the arc-initiation region 14 of the gases generated by the are, replacing them with fresh, cool high pressure gas, thereby increasing the dielectric strength between the arc runners 28 and 30 in the arc-initiation region 14. In addition, the rapid movement of the are out of the arc-initiation region 14, as explained hereinabove, limits the exposure of the insulating plates 16 in the arc-initiation region to the arc, thus reducing the tendency for surface carbonization to occur in this crucial region.

Although the illustrated embodiment of our invention uses a fusible element 44 to initiate the are, it is to be understood that our invention can also be applied to an interrupter of the type that has relatively-movable separable contacts. Such contacts can be separated in a conventional manner to initiate an arc in the arc-initiation region 14.

While we have shown and described particular embodiments of our invention, it will be obvious to those skilled in the art that various changes and modifications may be made without departing from our invention in its broader aspects and we, therefore, intend in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

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

1. A direct current circuit interrupter for interrupting D-C circuits of 20 kv. or higher comprising:

(a) a chamber having an exhaust opening at one end and an arc-initiation region at an opposite end,

(b) means for normally maintaining within said chamber a pressurized gas having a static pressure of at least several atmospheres,

(c) means for initiating an arc in said arc-initiation region,

(d) arc-motivating means for forcing said arc to move from said arc-initiation region toward said exhaust opening comprising:

(i) are runners extending through said chamber from said arc-initiation region toward said exhaust opening,

(ii) means for directing a blast of high pressure gas through the arc-initiation region toward said exhaust opening via paths directed transversely of the are when in said arc-initiation region, and

(iii) means for forcing substantially all of the gases generated by the arc in said arc-initiation region and substantially all those gases directed into said arc-initiation region to flow out of said chamber via said exhaust opening,

(e) and arc-lengthening means for forcing said arc to follow a zig-zag path of progressively increasing length as it moves toward said exhaust opening, said zig-zag path being constituted by a series of loops, adjacent ones of which bow in opposite directions that are disposed transversely of the direction of motion of the arc as it moves toward said exhaust opening,

(f) said arc-lengthening means comprising a series of closely-spaced plates of insulating material that evolves gas when exposed to said arc, the transversely-extending portions of the loops of said zig-zag path extending between adjacent pairs of said plates.

2. The direct current circuit interrupter of claim 1 in combination With means for causing said cross-blast to have a substantially sonic velocity as it enters said arc-initiation region.

3. The direct current circuit interrupter of claim 1 in which said cross-blast comprises a plurality of jets entering said arc-initiation region along a major portion of the length of said arc.

4. The direct current circuit interrupter of claim -1 in combination with means for causing said cross-blast to enter said arc-initiation region with a high velocity and for causing the velocity of said cross-blast to decrease to 7 8 a relatively low level a short distance downstream from 2,740,021

3/1956 Frink 200-144 the arc-initiation'region. 7 2,757,261 7/1956 Lingal et a1.

' 3,133,176 5/1964 Schneider. References Cited UNITED C PATENTS 5 ROBERT S. MACON, Przmary Exammer. 2,345,724 4/1944 Baker et al. US. C1. X.R.

2,382,850 8/1945 Bennett. 200 -144, 149

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