US2298859A - Alternating current electric circuit breaker - Google Patents

Description

Oct. 13, 1942.y

A. ALLAN ETAL ALTERNATING CURRENT ELECTRIC CIRCUIT BREAKER Filed Nav. 12, 1940 6 Sheets-Sheet 1 Oct. 13, 1942. l A, ALLANA ETAL 2,298,859

ALTERATING CURRENT ELECTRIC CIRCUIT BREAKR Filed Nov. 12, 1940 6 Sheets-Sheet 3 Oct. 1.3, 1942. A. ALLAN :TAL 2,298,859

ALTERNATIG CHENT ELECTRIC CIRCUIT BREAKER Filed Nov. 12, 1940 GKSheets-Sheet 5 Fig. 9.

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ALTERNATING CURRENT 'LECTRIC CIRCUIT BREAKER Filed Nov. 12, 1940 e sheets-sheet Fig. 9A.

Patented Oct. 13 1942 UNITED STATES PATENT OFFICE ALTERNATING CURRENT ELECTRIC CIRCUIT BREAKER Application November 12, 1940, Serial No. 365,368 In Great Britain November 13, 1939 8 Claims.

This invention relates to A. C. electric circuitbreakers of the air-break or gas-break type, in which a blast of deionising gas is forced through the arc path to assist in extinguishing the arc, and has for its main object to provide an improved construction of this kind wherein more rapid and more efficient rupturing of the arc is ensured.

Another object of the invention is to provide a circuit-breaker comprising relatively movable contacts so mounted within an enclosing casing that the arc formed yon separating the contacts extends between arcing tips close to the throat of a lateral vent in the wall of the casing, and means whereby gas under pressure within the casing causes a deionising gas-blast to ow not only across the gap between the arcing tips but also around one or both thereof and out from the casing through the vent, thereby cooling and deionising the arc path.

Yet a further object of the invention is to provide a circuit-breaker comprising relatively movable contacts so mounted within an enclosing casing that the arc formed on separating the contacts extends between arcing tips close to the throat of a lateral vent through the wall of the casing, and means whereby a deionising gas blast is caused to ow through the arc path and out from the casing through the vent, the throat of the vent having a narrow central portion and at least one of its ends relatively broad. The width of the broad end or of each broad end is preferably greater than the width of the arcing tip adjacent thereto.

It is already known that in gas-blast circuitbreakers more efficient rupturing of the arc is obtained if the gap across which the arc extends is maintained at a predetermined short length during the period necessary for arc extinction, the predetermined length being such that its breakdown voltage is greater than the normal working voltage of the system, but less than the surge voltage which would be produced by extinction of the arc at a point in the A. C. Wave away from a current zero. The separating movement of the contacts and the arrangement of the arcing tips are preferably such as to give this short gap. This may be effected by employing two fixed contacts respectively carrying the arcing tips and a movable bridging contact, the arc being transferred from such contacts to the arcing tips during the opening movement. Alternatively one of the arcing tips may be carried by and movable with one of the main relatively movable contacts, the separating movement being 55 such as to give the desired short gap. An isolating switch is preferably provided in the circuit in series with the main circuit-breaker in order to prevent risk of subsequent breakdown owing to a sustained high voltage across the gap after extinction of the arc. Such isolating switch is preferably operated sequentially with the main circuit-breaker, so that following opening of the main circuit-breaker it opens automatically after an interval sufcient for arc extinction at the main contacts. The arrangement is conveniently such that the main circuit-breaker closes automatically after the isolating switch has opened, circuit make being effected, when desired, by closing the isolating switch.

The pressure vfor the gas-blast is preferably derived from a source external to the enclosing casing, for example from a reservoir in which gas is stored under pressure, and such gas pressure may also be utilised for effecting the separating movement of the contacts.

When the lateral vent is so arranged that the vent throat has a narrow central portion (adjacent to the gap between the arcing tips) and at least one of its ends (adjacent to an arcing tip) relatively broad, the arcing tip width may be less than that of such broad end in order to provide a flow passage around the arcing tip.

The invention may be carried into practice in various ways land one convenient arrangement together with several modifications thereof will now be described by way of example, with reference to the accompanying drawings, in which Figure 1 is a side elevation, partly in section, of a circuit-breaker unit,

Figure 2 is a view from below of part of the unit shown in Figure 1,

Figure 3 is a sectional side elevation of part of a modified form of the unit shown in Figure 1,

Figure 4 is a view from below of part of the unit shown in Figure 3,

Figures 5 to 8 are views similar to Figure 3 of further modifications of part of the unit shown in Figure 1, and

' Figures 9 and 9A are views in sectional side elevation of a circuit-breaker generally similar to that shown in Figure 1 embodied in a threephase metal-clad switchgear of the horizontal draw-out type.

In the drawings the same reference letters are used for corresponding parts.

In the arrangement shown in Figure 1 the circuit-breaker has two fixed contacts A and B and a movable bridging contact C' disposed Within an insulating casing D of generally cylindrical shape mounted horizontally and surrounded by an earthed metal enclosure which is not shown in Figure l. The rear end of the insulating casing, which is on the left hand side in Figure 1, is closed by means of a plate D1 which is bolted to the end of the casing D, whilst the front end (at the right hand side in Figure 1) opens into a metal chamber E. The fixed contact A is supported within the casing D by a metal rod A1 passing through the rear plat-e D1, the contact A being generally cup-shaped with a cylindrical flange A2 directed towards the front end of the casing. Spaced apart from the cylindrical flange A2 and in line therewith is the second fixed contact B constituted by a metalcylinder suitably supported within the casing D by means of a metal tube B1 extending through the/open front end of the casing into the frontY Chamber E.

The tube Bl serves to house and support the moving contact rod C1, which is pressed by a spring C 2 towards` the fixed contact A and carriesgapiston C3 sliding within the metal cylinder contact B, Therrd C1 carries at the end adjacent tothe contact A a number of contact fingers C4 pressed outwardly by springs C5j and serving, in the closed position of the circuitbreakento bridge the gap between the two fixed contacts A and B and, duringnthe opening movement, to remain in contact with theflxed contact B;

On'` their undersides the two fixed contacts A and B carryarcing tips A3 and B2 respectively, which are'spaced apart from one another by -a suitable short distance d which is chosen to suit the best conditions forv arc extinction by the gasblast.l This optimum distance is found to be such that, its breakdown voltage is somewhat greater than thehnormal working voltage but less than the surge voltage which would beset up by .suppression of the arc at a point 1n the A. C. wave well away from the current zero point. contact rod C1 is somewhat greater than the gap between the fixed contacts A and Bso that during opening the arc is initially formed between the fixed contact A and the movable bridging contact ngers C'4 and is then transferred to the two arcing tips A3 and B2 where it is in the most favourable position for arc extinction by the gas-blast, as will now be described.

Immediately beneath thev arcing tips A3 and B2 is a nozzle-shaped vent F of insulating material projecting downwardly through the wall of.

the casing D, the arcing tips being disposed Vclose to the throat of such vent. The gas for the blast is fed under pressure, preferably from a reservoir which is not shown in Figure 1, into the insulating casing D through a conduit El on the front chamberV E, around the tube housing B1 into an annular spaceB3 around the fixed contact B and thence into the space between the contacts so that it passes into the space C6 and acts'on the rear surface of the piston C3 thus causing the moving contact C to open against the pressure of the spring C2. It will beat once clear that, when the circuit-breaker is open, the main body of the blast will ow across the open gap between the two fixed contacts Arand B, across the arc path between the arcing tips A3 and.,B2 and thenceY out through the nozzle F. The arcing tips A3 and B2 are spaced slightly away from the wall Flofl the nozzlethroat, so that s ome of the'gas flows into the nozzle from behindwthe arcing Vtips and around the sides thereof.`

ForV an V ordinary high ,n voltageA circuit-breaker` The opening movement of the moving '2,298,859 Y such as shown in Figure 1 the width of the nozzle throat is, as shown in Figure 2, made somewhat greater than the widths of the arcing tips A3 and B2 and thus of the ionised column constituting the arc, so that the gas flows not only through the arc path and around the outsides of the arcing tips, but also past the sides of the arc. In this way, the direct flow against the arc itself causes the arc to bow out into the nozzle into a U-shape, this action preferably being assisted by the electrodynamic forces exerted by the current iiowing through the neighbouring parts of the circuit. The remaining partsV oflthelgas-blast, by flowing more or less along the length of the limbs of the U-shaped arc will exert a cooling and scavenging action on the arc and will tend to wear away the arc thread, the ions being rapidly dispersed from the arc path when the arc goes out, thereby minimising the chances of restriking of the arc after the current zero period. At the same time the ow of` gases all around the arcing tips A3 and B2 tends to keep them cool and thereby to reduce thermal ionisation and thus again Vto minimise risk of restriking. V In the case ofextra high voltage circuitbreakers, it is preferable to concentrate the gasblast somewhat more on to the arc path itself, and in this case the central portion of the nozzle thread (adjacent to the actual gap between the arcing tips) is made narrow as shown in Figures 3 and 4, so that substantially the Whole of that portion of the blast which flows between the arcing tips will. flow through the arc path itself. As shown most clearly in Figure 4 the nozzle throat has Va narrow central part F3 and ends F4 and F5 which are however still kept larger than the'arcing tips A3 Vand B2, so that the other portion of the blast still flows from behind and around the arcing tips to exert its scavenging and cooling action on the arc and on Vthe arcing tips. It isV desirable, especially in the case of an extra high voltage circuit-breaker such as is shown in Figures 3 and 4, to make the gas flow channels as smooth as possible, in order to obtain as effective a blast as possible with due economyin the use of compressed gas and for this purpose the end Clvof the moving contact member C is preferably made generally iiat and its travel is limited to leave little,` if any, projection of the surrounding cylinder wall B in the open position ofthe contact. For the same purpose, the fixed contact A may consist ofa springloaded iiat plate'A4 which follows the moving contact memberto a position in whichrit is more `or less flush with the front end of the cylindrical flange A2. It will benoticed that the ,earthed metal casing (D2) surrounding the insulating casing D is shown in Figure 3.

Although in the arrangements described above two fixed contacts A, B and a movable bridging contact C are employed, this is not essential to the invention, and the arrangement may be modified by dispensingaltogether with the secondiixed contact and mounting the second arcing tip on the movable contact member. Such modiiiedconstructions are shown in Figures 5 and 6, in which the same reference letters are againused for corresponding parts, Figure. 5 showing an arrangement with aV wide nozzle throat. like that of Figure 2 and Figure 6 anarrangement withca narrow nozzle throat like that of Figure k4. In each of these,` constructions the moving Contact C8 has one of its contact lingers C4 .longerv than the others, the travel ofthe moving contact inember being such as to leave the desired optimum gap between the two arcing tips A3 and C9 in the open position. Again, irrespective of whether there are two fixed arcing tips or one fixed and one moving arcing tip, the fixed and moving contacts may, as shown in Figures '7 and 8 comprise cooperating springy at blade contacts A5-C10 instead of the ring of contact fingers used in the arrangements shown in Figures 1 to 6. The constructions shown in these two gures diier from those shown in the previous figures in that the pressure gas is fed through an annular space A6 surrounding the fixed contact A5 and acts on the end of the moving contact C10 to cause opening of the circuitbreaker.

In all cases the arrangement is preferably such that the arcing tips are disposed close to that part of the gas flow passage at which the greatest mass of gas per unit area is displaced, in order to obtain the most effective action on the arc.

Figure 9 illustrates one convenient construction of three-phase metal-clad switchgear incorporating a circuit-breaker unit such as is shown in Figure 1. In this construction the gear is of the horizontal draw-out type, the three phases of the switchgear being arranged side-byside, only one phase thus being shown in Figure 9. In this gure the parts of the circuitbreaker unit are given the same reference letters as corresponding parts in Figure 1. The xed portion of the gear contained within a casing G has two horizontal rows of socket contacts G1, G2 each containing three sockets one for each phase. The contacts in the upper row G1 are respectively connected to the three busbars H, H1, H2 whilst those in the lower row are connected by conductcrs H3 to the feeder or other apparatus (not shown) to be connected to the busbars through the circuit-breaker.

The withdrawable portion of the gear comprises a metal casing D3 which can be racked out in the usual manner and of which the metal casings around the circuit-breakers in the three phases form part. This casing carries on its rear wall two rows of plug contacts J, J1 for cooperation with the socket contacts G1, G2 on the fixed portion of the gear. The plug contacts of the lower row J1 are directly connected respectively to the three xed contacts A of the circuit-breakers in the three phases, whilst those of the upper row J are correspondingly connected directly to the fixed contacts L ofk isolating switches respectively in series with the circuitbreakers.

Each isolating switch consists of a fixed contact L in the form of a ring or inwardly springpressed contact ngers L1 and a longitudinally movable contact rod L2 which in the closed position engages with such contact fingers. This contact rod is engaged near its front end by contact springs L3 in a metal housing L4 which is directly connected by a conducting bar L5 to the metal tube B1 surrounding the moving contact rod C1 of the main circuit-breaker. The main circuit-breaker and the isolating switch thus form part of a U-shaped circuit directly connecting the two plug contacts J, J1 in each phase. This arrangement provides for an electro-dynamic action assisting the action of the gas-blast in bowing out the arc in the manner above mentioned.

The main circuit-breakers and the isolating switches are operated pneumatically by the pressure of the gas utilised for the gas-blast. 'I'he operating mechanism may be of any convenient form and in the arrangement shown in Figure 9 each isolating switch moving contact rod L2 is pivoted to one end of a floating operating lever M whose other end is pivoted to the end of a crank arm M1, whilst an intermediate point is pivoted to one end of -a link M2 pivoted at its other end to one arm of a bell-crank lever M3 mounted on a horizontal spindle M4. The other arm of the lever M3 is operated through suitable link M5 and lever M6 by the piston M7 of a pneumatic operating motor M8.

In order to obtain the desired automatic sequential operation of the main circuit-breakers and isolating switches, a hook-shaped pivoted latch N is arranged to engage with the end of one arm of the bell-crank lever M3 when the isolating switches are closed. Three projections of which only the projection N1 is shown in Figure 9, on the latch N respectively engage with the surfaces of the moving contact rods C1 of the three main circuit-breakers and thereby prevent release of the latch to open the isolating switches until all three circuit-breakers have reached the fully open position. The main contact rods C1 are normally locked in the closed position by means of pivoted latches N2 normally held in their operative position by pivoted arms N3.

When the circuit-breaker trip gear or other mechanism (not shown) for opening the circuitbreakers is operated, the latches N2 are released and compressed air is supplied from a reservoir P to the space P1 above the cylinder P2 of an operating motor P3 for a main valve P4 controlling the supply of compressed air to the main circuitbreakers. The valve P1 is thus opened and compressed gas flows into the space P5 and thence through the ducts P6 to the main circuit-breakers to cause opening of the contacts and extinction of the arc between the arcing tips A3-B2 in the manner described above with reference to Figure 1. Operation of th'e trip gear also causes compressed gas from the reservoir P to be supplied to the space M9 above the piston M7 of the pneumatic operating motor M8 for the isolating switches but this motor, although subjected to gas pressure, cannot actually operate, owing to the engagement of the latch N, until the three circuit-breakers have all fully opened. The projections N1 on the latch N drop into notches N4 in the main circuit-breaker contact rods C1, when these rods reach their fully open positions and thus release the latch N, whereupon the piston Ml of the motor M8 moves downwardly to effect opening of th'e three isolating switches. The opening of the three isolating switches in turn operates a control valve (not shown) for the operating motor P3 so that this motor operates to close the valve P1 thus causing the gas supply to the main circuit-breakers to be cut olf, whereupon the main circuit-breaker moving contact rods C1 are at once closed under the action of their springs C2 leaving th'e isolating switches open. The main contacts are locked in the closed position by their latches N2. The closing of the main circuit is eiected, when required, by admitting compressed gas to the under surface of the piston M'I of the pneumatic operating motor MB which accordingly operates to close the three isolating switches, the latch N at once becoming operative to prevent opening of the isolating switches until after the main circuit-breakers have opened.

VIt will be appreciated that the narrangements above described have been given by wayof eX- ample only and that the circuit-breaker construction may be modified in various ways Within -the scope of the invention and may be employed in switchgear other than the vhorizontal `draw-out switchgear described. Furthermore, lalthough it will usually be preferable to providechannels-for the gas ow behind and around both arcing tips, it may sometimes suffice to provide `such 'channels around one arcing tip only.

What we claim as our invention and desire to secure by Letters Patent is:

1r. An A. C. electric circuit-breaker, comprising Vin combination a casing, relatively movable contacts with-in thecasing, means for separating the contacts, a gas-out flow member in the 'wallof the casing having a nozzle throat, a

Y source of gas under pressure, means whereby on opening of the'circuit-breaker gas is admitted from the source to the casing at high pressure and escapes Ain the Vform of a powerful blast through the nozzle throat, spaced arcing tips separate from thegas-outow member and associated with the contacts and'between which the arc vformed on separating the contacts extends, such arcing tips being located close to the Ynozzle throat on the high pressure side thereof in such positions that the-arc-gap between them extends across the entrance to -the nozzle throat transversely to the direction of illow of the gasblast through therthr'oa't, and passages leading from theinterior ofthe casing around at least one of the arcing tips Vtothe nozzle throat and separat- Ying such-arcing-tip from the surface of the gasow member, the Aarrangement being such that thegas-'blastrwi-ll flow not only through the arcgap Ybetween the arcing tips but also through the Vsaid passages land thence out from the casing lthrough the vnozzle throat `thereby cooling and deionising the arc'lpath.

`2. AnYA.' C. electric circuit-breaker, comprising in combination `a casing., two fixed contacts mounted with-in 4the icasing, a Amovable bridging contact for connecting .the two fixed contacts, means v for actuating l.the 'bridging contact, a gasoutowmember of insulating'material in .the wall of the casingha'ving `a nozzle throat, -a source of Ygas under pressure, means whereby on opening of the circuit-breaker gas .is ladmitted from the Vsource to thecasing at high l.pressure and escapes in the form of `a powerful blast through the nozzle throat, arcing tips on the fixed contacts `affording an arc-gap'to which the arc formed on the opening movement of the bridging contact is transferred, such 'arcing tips :being located close passages and thence out from-the casing through the nozzle throat thereby-cooling and deionising the arc path, l

3. An A. C. electriccircuit-breaker, comprising in combination a casing, a xed Contact in the casing,-a cooperating movable contact in the casing, a gas-outflow member of insulating material in the wall of the casing having a nozzle throat, a

source of -gas under pressure, means whereby on opening of the circuit-breaker gas is admitted from `the source tothe casing at high pressure and escapes in the form of a powerful blast through the nozzle throat, means for moving the movable contact away from the xed contact through a predetermined Vshort distance in a direction transverse to the direction of flow of the gas-blast through the nozzle throat, arcing tips on the fixed and moving contacts affording an arc gap across which the arc extends when the circuit-breaker is open, such arcing tips being located close to the nozzle throat on the high pressure side thereof, and passages leadingfrom the interior of the casing around the Xed Varcing tip to the nozzle throat and separating the fixed arcing tip from the surface of the gas-flow member, the arrangement being such' that the gas blast will flow not only through the arc-gap between the arcing tips but also through the said passages and thence out from the casing through the nozzle throat thereby cooling and deionising the arc path.

4. An A. C. electric circuit-breaker, comprising in combination a casing, relatively movable contacts within the casing, means for separating the contacts, a gas-outflow member in the wall of the casing having a nozzle throat, a source of gas under pressure, means whereby an opening of the circuit-breaker gas is admitted from the source to the Vcasing at high pressure and escapes in the form of a powerful blast through the nozzle throat, and arcing tips associated with the contacts and between which the arc formed on separating the contacts extends, such arcing tips being located close to the nozzle Vthroat and on the high pressure side thereof in such' positions that the arc-gap between them .extends across the entrance to the nozzle throat transversely to the direction of ow of the gas-blast through the throat, the nozzle throat having a cross-section elongated in a direction substantiallyrparallel to the arcegap between the arcing tips with a narrow central portion adjacent to such arc-gap and at least one of its ends broader than the arcing tip adjacent to such end 5. The combination with the features set forth in claim 4, of passages around at least one of the arcing tips and leading from the interior vof the casing past such arcing tip to the broadened end of the nozzle throat, the arrangement being such that the gas lblast flows not only through the arcgap between the arcing tips and through the narrow central portion of the nozzle throat but also through such passages.

6. An electric circuit-breaker as claimed in claim 2 in which the nozzle throat has a crosssection elongated in a direction substantially parallel to the arc-gap between the arcing tips with a narrow central portion adjacent to such arc-gap and with relatively broad ends adjacent respectively to the arcing tips.

'7. An A. C. electric circuit-breaker, comprising in combination a casing having a discharge vent in its wall, main contacts disposed ywithin the casing adjacent to the discharge vent, means for causing a blast of deionising gas to flow out from the casing through the vent in a direction through and transverse to the arc-gap between the main contacts when open, an isolating switch in series with the main contacts, and means for opening the isolating switch automatically at a time interval after the opening of the main contacts sufficient 'for arc extinction, the conductors'leading to the main Acontacts and to the isolating switch forming a U-shaped circuit, one limb of which contains the main contacts while the oth'er limb contains the isolating switch and is disposed on the side of the main contacts remote from the discharge Vent, whereby the electrodynamic interaction of the currents owing in the two limbs tends to force the arc into th'e discharge vent.

8. For use in an alternating current electric circuit-breaker of the gas-blast type, a, discharge nozzle for the blast having a, constricted throat near one end and diverging therefrom to a relatively large discharge opening at the other end, the throat of the nozzle having an elongated cross-section with a, narrow central portion and relatively broad ends at th'e sides of the throat.

ARCHIBALD ALLAN. DONALD FOSTER AMER.

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