US2224611A - Electric circuit interrupter - Google Patents

Description

Dec. 10, 1940. w. F. SKEATS ELECTRIC CIRCUIT INTERRUPTER Filed June 8, 1940 Fig.1.

\ LIQUID LEVEL.

lnventnr'z Wilfr'ed F. Skeats,

b y His Attorney.

Patented Dec. I0, 1940 UNITED STATES ELECTRIC CIRCUIT INTERKUPTER Wilfred F. Skeats, Lansdowne, Pa., assignor to General Electric Company, a corporation of New York Application June 8, 1940, Serial No. 339,534

8 Claims.

My invention relates to circuit interrupters, more particularly to those of the fluid blast type 4 wherein a so-called pressure generating arc is utilized to project an arc extinguishing fluid blast through the arc to be interrupted.

The aforesaid type circuit interrupter has proved very successful in commercial practice for the interruption of heavy load and short circuit power currents, a well-known example being, the oil blast circuit breaker. This breaker in its simplest form has two breaks in series, one of which is for the pressure generating arc and the other for the interrupting arc subject to the oil blast. The breaker performs well throughout its,

' interrupting range and is highly eflicient at maximum interrupting capacity due to the high velocity of the oil blast. The principle of arc interruption here involved is also applicable to are extinguishing liquids other than oil, such as for example water which in some cases is desirable because of its non-inflammable character. However, it has been found that the vapor pressures generated in water by the arc heat may be excessive at high currents and insufficient at low currents for proper arc interrupting performance.

The principal object of the present invention is the provision of an improved electric circuit breaker of the fluid blast type particularly adapted for vaporizable arc extinguishing liquids such as water, wherein the fluid pressure for the arc extinguishing blast is within proper limits throughout the interrupting range of the breaker.

In accordance with my invention, arc'control means is associated with the pressure generating are so that the arc is automatically lengthened at small currents to provide adequate blast pressure, and is automatically shortened or short circuitedin part at heavy currents to avoid excess pressure.

My invention will be more fully set forth in the following description referring to theaccompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this invention.

Referring to the drawing, Fig. 1 is an elevational view in section of the essential parts of an electric circuit breaker embodying the present invention and Fig. 2 is a plan view in section taken along the line 2-2 of Fig. 1.

The circuit breaker illustrated by way of ex ample is of the well-known oil blast type, such as disclosed and claimed in Paul Patent 1,947,224, granted February 13, 1934, for Circuit interrupting apparatus, and comprises a strong pressure confining casing I of steel in which the arc to be interrupted is drawn between a fixed contact structure 2 and a movable contact rod 3. Interposed with respect to the fixed and movable contacts in the open circuit position shown is an insulating bafile 4 having a central opening or bore 5 for the movable contact. The lower part of the insulating baffle has mounted thereon intermediate contacts comprising a pair of conducting gate-like members 6 which are pivotally mounted on the battle structure at l and are resiliently biased by the springs 8 so as to close the lower end of the opening 5 when free of the rod contact 3. I

In this serve to divide the are drawn between the contacts 2 and 3 into two sections, namely a lower or pressure generating are between the upper or arcing surface 2' of the fixed contact and the gates 6, and the interrupting arc gates 6 and the contact rod 3. This are is formed entirely within the opening 5.

The bailie 4 is also provided with a cross-blast passage indicated at 9 traversing at right angles the arc path in the vertical passage 5. The blast passage, as in the case of the Paul patent, com municates with the lower or pressure generating chamber III at one end, and with an upper or pressure relief chamber indicated at H at the exhaust end. The opposite ends of the blast passage 9 are not shown since the blast passage extendsperpendicular to the plane of the drawing. The switch casing is suitably lined and insulated as indicated at II, the insulating baflle 4 being rigidly positioned by means of mechanically strong insulating cylinders l3 and It. The contact and baflle structure above described is immersed in the arc extinguishing liquid, which in the present case is preferably water.

The circuit interrupting operation, referring to the apparatus so far described, is essentially the same as that described in the aforesaid Paul patent. That is, when the rod contact 3 is raised to open the circuit, the are initially formed between this rod and the contact 2 vaporizes water 4 in the pressure generating chamber l0, thereby generating vapor pressure in this chamber. As the rod 3 continues to move upwards, the conducting gate members 6 close behind the contact to divide the are into serially related sections. 5 When the contact rod uncovers the cross blast passage 9, the pressure in the lower chamber projects an interrupting blast of water and-vapor through the arc to interrupt it within the central baflle opening position, the intermediate contacts 6 15 between the 20 5. The rod contact 3 is 5 isolated with respect to the "contact 2 by continued movement above the liquid level.

For the purpose of automatically-controlling the pressure generated witliin the chamber III in the manner above described, means including an arc control device generally indicated at l5 are provided in proximity to the pressure generating arc. The are control-device is so related to cooperating parts of the fixed and movablecontact structures that the pressure generating arc, which is drawn through the device is appreciably lengthened in the case of small or weak currents so as to generate an appreciable amount of vapor pressure, and is shortened or in part short circuited at heavy currents in accordance with the current magnitude so as to avoid excess pressure.

Specifically, the arrangement comprises an insulating disk I 6 in which is embedded a laminated iron core I! of the shape illustrated by Fig. 2. The insulating disk I6 is provided with a central opening l8 through which the contact 3 operates. The opening It! also communicates with narrow slot-like extensions I 8' and I!" which are appreciably offset laterally as illustrated in Fig. 2 with respect to the central axis of the opening [8. The laminated iron core I! is positioned so as substantially to surround the opening |8 l8'-.| 8", the portion IQ of the core surrounding the slot I8 being of small cross-sectional area as compared with that at 20 so that it-ls more readily saturable by magnetic fiux. A gap is provided between the core portions 2| so that this portion of the core has a moderately high magnetic reluctance. U

The are control device so far described is generally similar in structure and function to that disclosed and claimed in my Patent No. 2,085,549,

granted June 29, 1937, for Electric control device,

In other words, the magnetic field set up by the path I!) becomes saturated so that the reluctance increases. In the case of heavy short circuits, the gap path actually has less reluctancethan the path at I9,- due to the large cross section of the core, and the arc is moved through the slot [8" in the direction of the gap.

Furthermore, between the two limits of a light current are which will find its equilibrium position at the end of the slot l8, and the heavy current arc, which will find its equilibrium position some'distance down the slot l3", intermediate current arcs will find their equilibrium positions at intermediate points. This may be explained as follows. Referring to Fig. 2, let'it beassumed that an arc is drawn initiallyat the center of the opening l8, and further that the current flows upward from the plane of-the drawing through this arc. This will tend to set up flux flowing towards the bottom of the drawing in the lefthand portion. of the slot and in the saturated section l9, and, towards the upper part of-the drawing at all points to the right of the are.

Now if the current in the arc is low, the greater part of the fiux passing to the left of the current will pass through the iron section ['9 so that the flux density across the slot to the left of the current will be very low. The flux will distribute itself more or less uniformly in that part of the slot at the right'of the arc, however, and this will result in a higher density for the flux trav- "ersing the gap towards the top of the drawing at the right of the arc than for the'flux traversing the slot in the opposite direction on the left of the are. This flux will react with the arc to move it to the left. As it does so, however, more space will be available for the flow of flux at the right of the arc and less at its left so that the fiux density will tend to decrease to the right of the arc and to increase to the left of the arc. Thus eventually unless an extremely light current is flowing, a point will be reached at which the flux density is the same on both sides of the arc. Here there wili be no resultant force on they arc,

so that its lateral movement will-cease. Moreover should the arc for any reason be moved to the left of this point, the flux density at the left of the arc will be greater than the flux density at the right of the arc so that the resultant force on the arc will be to the right and the arc will tend to move in that direction.

Should the current in the are be in excess of that value which has its equilibrium position at the center of the opening IS, the flux density at its left will be higher than the flux density at its right and the arc will start to move to the right allowing more space for the flux at the left and consequently decreasing its density, and allowing less space for the flux at the right and consequently increasing its flux density until the flux densities to the left and right of the arc become equal, at which time the arc has reached its equilibrium position.

It will be noted that while the slot 18' has been made quite long inorder to allow sufllcient motion to draw out the arc to considerable length, the reduced section of the iron core has been made long also so that the amount of flux which can traverse the gap l8 while the arc is not in that gap is limited by saturation of the iron section in the region where the slot [8' joins the opening Hi. This makes possible a flux distribution such that in spite of the length of the contacts 23 which form a.cbnductin g socket for.

the rod contact in the closed circuit position. The segments 23 are biasedstogether by compression springs 23' and electrically connected by flexible conductors 24 to the conducting cylinder 2, which is in turn electrically connected as indicated to the breaker terminal 25. Accordingly, when the rod contact 3- separatesfrom the contact segments 23, the arc is automatically transferred to the arcing surface 2' of the fixed contact.

Cooperating with the above described are contion defined by the extreme end of the slot ll",

This arcing member is inclined approximately 45' so that when the are between the contact 2 and the conducting gate I is at an offset posi-' it is also of maximum length.

The pressure generated by an arc of given current is approximately proportional to the length of the arc. Therefore, in view of the' fact that a weak or predetermined minimum current are will move well into the slot l8" according to the magnetic forces established by the arc current, the extent of lateral movement being inversely related to the magnitude of the arc current, an

- l8" toward that part of the path.

For the purpose of controlling this heavy current arc in accordance with the current magnitude, an arcing runner 21 is connected to and positioned beneath one of the gates 5 so as to parallel the slot l8". This arcing member preferably comprises a fln-like conductor having a gradually tapered arcing surface 21' and is electrically and mechanically connected to the gate 6 at the right. Also paralleling the slot l" and positioned directly beneath the arc runner 21 is a horizontally positioned arcing member 28. The length of the arc can be gradated as desired in accordance with the current magnitude by proper design of the core 20 and are runner 21 and if desired the arc runners 21 and 28 can be positioned well within the slot ll".

Accordingly, when the arc strikes the member 21, it is'shortened so that its actual length is dc flned approximately by the distance between the arcing surface at 21' andthe arc runner 25. Al-

though of comparatively short length when at the end of the. slot l8", this short circuit arc-will generate ample vapor pressure by reason of its high amperage. Such an arc is diagrammatically indicated at Ia.

It will therefore be apparent that I have provided means for controlling within comparatively wide limits the arc pressure generated in a fluid or water blast type circuit breaker and that this pressure can be fairly well predicted for a given interrupting operation since the arc itself govems to a practical extent the pressure that it should generate. By way of example, the predetermined minimum value of current may be 2000 amperes whereas from 10,000 amperes through 40,000 amperes and upwards the arc will be positioned between the central position and the arc runners 21 and 20 in the slot 1"" according to the current magnitude as previously. described.

The design of this type breaker-"is therefore -greatly facilitated and improved and its range .of application extended since heretofore it has been necessary to provide long are lengths to assure clearing of the circuit satisfactorily at low currents. This has resulted in the generation of excessive pressures at high currents/Also the irterrupting performance of a fluid blast type breaker embodying my invention is more efficient, positive and predictable. This improved operation includes shorter arc length and lower mechanical stresses in the circuit breaker structure.

In the operation of an interrupter of this type it. will be observed that the arc exists in a confined location in the vertical passage and that considerable pressure may therefore be generated in this passage as well as in the blast passage 9. This pressure will have a tendency to break open the baflle l roughly on the plane of these two passages. I- have, however, devised means whereby the effect of this pressure may be substantially overcome and this breakage prevented.

In order to maintain with assurance a flow of arc extinguishing liquid through the cross blast passage 9, it is desirable to prevent flow upward around the outside of the cross'blast baille I. This may be preventedby blocking the annular passage 30, which is in communication with the arc pressure region at 29, either above or below the baille 4. Should the passage 30 be blocked below the baffle 4 as at 32, that part of the passage 50 surrounding the baffle 4 will communicate directly with the region above the baille, and its pressure will therefore be low so that the bursting force from the pressure in passages 5 and 9 will have substantially its full effect and unless the baflle is made very strong breakage is to be anticipated. It will be observed, however, that by placing blocking means above the baiile as at 3|, that 'part of the passage 30 surrounding the bafile will be at substantially the same pressure as the region below the baille, which is in turn substantially equal to the pressure in the passages 5 and 5. Thus the pressure around the battle will be substantially equal to that responsible for the bursting force inside the baflle and the internal force will be counteracted and no breakage will occur. In order to prevent breakage of the baille therefore it is desirable that the passage 30 be left open up as far as the point 3| and b blocked at that point.

It should be understood that my invention is not limited to specific details of construction and arrangement thereof herein illustrated, and that changes and modifications may occur to one skilled in the art without departing from the spirit of my invention.

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

1. An electric circuit interrupter of the fluid blast type comprising arcing members spaced a predetermined distance apart toform a pressure generating break, electro-magnetic means for causing lateral movement of the arc formed at said break in a direction and to an extent dependent upon the magnitude of the arc current, conducting means electrically connected to one of said arcing members for causing lengthening of said are when it is moved onto said conducting means, one of said arcing members also having electrically connected thereto other conducting means for causing shortening of said are as com-' pared with said predetermined break distance when it is moved in the opposite direction into contact with said conducting means.

2. An electriccircuit breaker of the fluid blast type-comprising relatively movable contacts separable to form a pressure generating break, said break being deflned by arcing members spaced a predetermined distance apart, electro-magnetic means for causing lateral movement of the arc formed at said break in .a direction .and to an' extent dependent upon the magnitude of the arc current, oflset arcing means electrically connectedto one of said arcing members for causing lengthening of said are when it is moved onto said arcing means, one of said arcing members also having electrically connected thereto other offset arcing means for causing shortening of said are as compared with said predetermined break distance when it is moved in the opposite direction.

3. An electric circuit interrupter of the fluid blast type comprising a pair of arcing structures spaced to define a pressure generating break, electro-magnetic means disposed at said break for causing lateral movement of the are formed between said arcing structures in a direction and to an extent dependent upon the magnitude of the arc current, one of said arcing structures havin an offset arcing surface for causing progressive lengthening of said are in accordance with the extent of theare movement in one direction along said surface, one of said arcing structures also having electrically connected thereto means for gradually shortening said arc when it is moved in accordance with predeter-' mined increase in amperage in the opposite direction.

4. An electric circuit breaker of the fluid blast type comprising relatively movable contacts separable to form a pressure generating break, said break being defined by spaced arcing members, electro-magnetic means for causing lateral movement of the are formed at said break in a direction and to an extent dependent upon the magnitude of the arc current, one of said arcing members having an offset inclined arcing portion for causing progressive lengthening of the are when it is moved in that direction, said arcing member also having an oilset arcing runner extending in the opposite direction, and a coacting arcing runner connected to the other arcing member having a tapered arcing surface facing said first named runner whereby the arc is correspondingly shortened when it is moved a predetermined dis-' tance in said opposite direction in accordance with predetermined increase in the arc current.

5. An electric circuit breaker of the fluid blast type comprising fixed and movable contacts separable to form a pressure generating break, intermediate arcing means arranged to form with said fixed contact an arc gap of predetermined length for the pressure generating arc after predetermined opening movement of said movable contact, electro-magnetic means for causing .lateral movement of the are formed in said gap in a direction and to an extent dependent'on the magnitude of the arc current, said fixed contact having an annular arcing portion and an oflset" arcing portion inclined approximately 45 from said intermediate arcing means for causing progressivelengthening 01' the are when it is moved laterally in a direction away from the central axis of said fixed contact, said fixed contact also having an arcing runner oflset in the opposite direction with respect to said central axis, and a coacting arcing runner depending from said intermediate arcing means and having an arcing surface gradually approaching said firstnamed arcing runner so as to form therewith a gradually shorting arc gap whereby the arc is shortenedand confined to said short gap when itis moved in said opposite direction. M

6. An electric circuit breaker of the fluid blast type including arcing members arranged to form a'gap for a pressure generating arc, means for regulating the length of said are in accordance with arc current magnitude comprising core structure defining a magnetic path substantially surrounding said pressure generating are, said path having saturable and non-saturable portions, insulating means for said core forming an elongated slot extending away from the central axis of said arcing members in opposite directions and related to said saturable and non-saturable portions for causing variable positioning of said are in said slot in accordance with the magnitude of the arc current, an arcing runner connected to one of said arcing members for causinglength ening of said arc when it is moved in said slot in one direction, and additional arcing runner,

structure coacting with said arcing members for causing gradual shortening of said are when it is moved in said slot in the opposite direction.

7. An electric circuit breaker oi the fluid blast type including spaced arcing means arrangedto form a gap for a pressure generating arc, one of said means comprising a pair of conducting gate members, means for regulating the length of said are in accordance with arc current magnitude comprising core structure defining a magnetic path substantially surrounding said pressure gensin crating arc, said path having saturable and nonsaturable portions, insulating means for said core forming an elongated slot extending away from the central axis of said arcing means in opposite directions toward said saturable and non-saturable portions respectively whereby said are is caused to assume various positions in said slot in accordance with the magnitude of the are current, an arcing runner connected to one of said arcing means for causing lengthening of said are when it is moved in said slot in one direction. a second arcing runner also connected to one oi said arcing means and extending in the opposite direction irom said first-named arcing runner along said slot, and a third arcing runner connected to one of saidconducting gates and having an arcing surface gradually approaching said second arcing runner to form a gradually shortening arc gap therebetween for said are when it is moved in said slot in the opposite direction. I

8. An electric circuit breaker of the fluid blast type comprising a chamber containing an arc extinguishing liquid, relatively movable contacts separable to form an arc in said chamber, a batfle structure through which said arc is drawn dividing said chamber into a pressure generating portion and a low pressure or exhaust portion, said baiile having a passage for directing an arc extinguishing liquid blast from said pressure portion through said baille to said exhaust portion, the interior of said baflle thereby being subjected to arc-generated bursting pressure, means for transmitting liquid pressure from said pressure portion .to exterior side walls of said baille structure, and pressure sealing means between said baiiie structure and chamber disposed closely adjacent to the exhaust portion side of

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