US2214518A - Liquid-insulated electric circuit breaker - Google Patents

Description

Sept. 10, 1940. A. ALLAN LIQUID-INSULATED ELECTRIC cmcun BREAKER 4 Sheets-Sheet 1 Filed Nov. 5. 1938 In ventor Attorney Sept. 10, 1940. A. ALLAN I LIQUID-INSULATED ELECTRIC CIRCUIT BREAKER 4 Sheets-Sheet 2 Filed Nov. 5, 1938 I nventor l Ila- H T Q. tull 5 I lwl F F Attorney Sept. 10, 1940. ALLAN LIQUID-INSULATED ELECTRIC CIRCUIT-BREAKER Filed Nov. 5, 1958 4 Sheets-Sheet 3 Sept. 10, 1940.

A. ALLAN LIQUID-INSULATED ELECTRIC CIRCUIT BREAKER Filed Nov. 5, 1938 4 Sheets-Sheet 4 by m m 844M M A ttorn e y Patented Sept. 10, 1940 UNITED STATES PATENT OFFICE LIQUID INSULATED ELECTRIC CIRCUIT BREAKER Application November 5, 1938, Serial No. 239,169 In Great Britain November 15, 1937 4 Claims.

This invention relates to a liquid-insulated alternating current electric circuit breaker of the kind having a fixed contact surrounded by an arc-control device and a cooperating longi- 5 tudinally movable contact rod. The arc-control device is preferablyof the kind described in one or other of British Patent Specifications Nos. l35,250,

435,398, 452,146 and 460,219 standing in the names of one of the present applicants and othlO ers, comprising a laterally vented insulating enclosure, within which the relatively high pressure generated by the arc during the arcing period causes a blast of deionising fluid to be ejected through the arc path and through the vents 15 during the Zero current pause, whereby the arc is extinguished during the first cycle or the first few cycles of the alternating current wave. In such circuit breakers the pressure developed within the arc-control device may vary within wide limits in accordance with the severity of the fault and it will be appreciated that with usual construction of the arc-control device and the cooperating contacts such pressure variations have a marked effect on the speed of movement of the contact rod, thus tending to cause some degree of irregularity in the operation of the circut breaker.

An object of the invention is to provide a. liquid-insulated electric circuit breaker employing no a longitudinally movable hollow contact rod which cooperates with a fixed contact surrounded by an arc-control device so that when the said contact rod is moved in a direction to open the circuit breaker insulating liquid is displaced S from a chamber through the hollow rod and injected into the arc-control device.

A further object of the invention is to provide the said injection by means of a plunger carried by the hollow rod and movable in a D liquid-filled cylinder communicating through the hollow rod with the interior of the arc-control device. Another object of the invention is to eiiect the said injection by means of a displacement member projecting into the hollow .5 contact rod so that when the hollow rod moves a direction to open the circuit breaker the displacement member causes liquid to be injected from the interior of the hollow rod into the interior of the arc-control device.

50 Although applicable to other types of switchear, the invention is especially suitable for an lydraulically operated circuit beraker, whose cntacts are immersed in a relatively small volme of oil or other insulating liquid, for use 55 eit er in metal-clad or in open-type switchgear for the higher ranges of voltage. Three practical arrangements, each embodying the invention are, however, shown by way of example in the accompanying drawings, in which Figure 1 shows, in vertical section, a circuitbreaker unit for metal-clad switchgear.

Figures 2 and 3 are diagrammatic representations of an hydraulic operating mechanism which may be employed,

Figure 4 shows, partly in section, one form of open-type switchgear incorporating the invention,

Figure 5 is an enlarged longitudinal section of the hydraulic cylinders and plungers for operating the contact rod in Figure 4, and

Figure 6 illustrates, in vertical section, another form of open-type gear but with mechanical operation.

In the construction shown in Figure 1, the circuit breaker which is adapted to be inserted in and withdrawn as a unit from a metal casing, comprises a tank A of insulating material containing fixed contacts A carried by a metal end fitting A and consisting of a group of segmental contacts pressed inwardly by springs. The end fitting A ,which is suspended from the top plate of the gear by an insulator A serves also to support an arc-control device B, having lateral vents B and which is preferably of the kind described in one or other of the patent specifications above mentioned. The fixed contacts A are electrically connected to a metal part A which in. turn is connected to a conductor A passing through the wall of the tank A and arranged to cooperate with a downwardly extending busbar isolating contact.

The lower end of the circuit-breaker tank A is closed by a housing C furnished with spring loaded segmental contacts C which bear against a hollow movable contact rod D extending from the circuit-breaker tank A through a gland G into a short cylinder D The hollow rod D is provided with a plunger D which makes a sliding fit in the cylinder D the rod being extended through a gland D in an outer cylinder D The rod D is open at its lower end and cooperates with a conical plug D which, for centering purposes, is a loose fit in an end plug D The end plug D is provided with contacts D for cooperation with a feeder isolating contact.

The circuit-breaker tank A contains insulating liquid, for example oil, so that the arccontrol device B is immersed therein. The annular space E within the cylinder D above the plunger D is in open communication with a With the parts in the positions shown the plunger D is in its lowermost position so that the movable contact rod D lies clear of the arccontrol device B. If new it is desired to close the circuit breaker oil under pressure is supplied to the cavity E1 so that the plunger D rises in the cylinder D and the rod D enters the arc-control device B and establishes contact with the fixed contacts A The rod D is now held in the closed position by a spring-loaded latch D engaging a groove D in the plunger D To open the circuit breaker oil is supplied under pressure to the cavity E the oil pressure releasing the latch D so that the plunger D moves down in the cylinder D From the commencement of this downward stroke of the movable contact rod D oil is displaced from the enclosure D (between the gland D and end plug D through the hollow rod D into the arc-control device B. This injection of oil into the arc-control device B assists, in extinguishing the are drawn out since the amount of oil in the neighbourhood of the arc is thus increased. This effect may be enhanced by so dimensioning the two ends of the rod D as to cause flow through the the rod into the arc-control device B in excess of the amount necessary to fill the space vacated by the upper end of the rod within the circuit-breaker tank. The excess must, however, not be too great since it would then produce a tendency to reclosure of the contacts, but satisfactory results have been obtained with the amount of liquid injected into the arc-control device nearly double that vacated by the upper end of the rod D. The varying pressure developed will not materially affect the speed of movement of the rod D since the pressures on the opposite ends of the rod will more or less balance each other.

When the rod D approaches the fully open position the cylindro-conical plug D enters the open end of the rod so as to restrict the flow of oil into the rod thus givin a dashpot effect to bring the rod to rest without shock. Similarly, at the end of the upstroke of the rod D, a head E thereon enters an annular recess E in the gland D to provide for the absorption of shock. If desired a small vent controlled by a ball valve may be provided in the gland D soas to allow the escape of gas which may happen to collect in the enclosure D the valve automatically closing, the vent when the oil in the compartment is placed under pressure.

It will be seen that oil in the circuit-breaker tank A, which may become contaminated by the efiects of arcing when the circuit breaker operates, is segregated by the gland C from. the oil for operating the movable contact rod.

Figures 2 and 3 illustrate one form of hydraulic device for operating the movable contact rod D. As shown in Figure 2 the circuit breaker is closed, the plunger D though fully. raised in practice being shown lower down in the cylinder D for the sake of clarity. An hydraulic actuating piston F operated through a rod F is arranged in a cylinder F which communicates at opposite sides of the piston F through insulating pipes F F with the cavities E E shown in Figure 1. In order to open the circuit breaker the rod F and piston F are moved to the left as viewed in Figure 2 so that oil is drawn into the cylinder F on one side of the piston F through the pipe F and oil is delivered under pressure from the cylinder F on the opposite side of the piston F, to the pipe F The plunger D and therefore the movable contact rod D, is thus moved downward so that, as above described, oil is displaced from the enclosure D through the hollow rod D into the arc-control device B. The parts are now in the positions shown in Figure 3, though it will be appreciated that in practice the hydraulic piston F will, at each end of its stroke, cover the port through which the corresponding pipe F or F communicates with the cylinder F Tho-ugh only a single circuit breaker is shown in each of Figures 1, 2 and 3, a plurality of circuit breakers each as above described may be employed together for polyphase working, the actuating pistonsF for the several circuit breakers being preferably mounted on a common rod F so that the circuit breakers can be operated in synchronism. The cylinder F or each such cylinder is conveniently immersed in the actuating oil within a reservoir F It is desirable to ensure that every operation of the piston F will commence with the correct length of liquid column, notwithstanding expansion and contraction due to temperature changes or any leakage that may occur. With the arrangement shown in Figure 1 wherein the latch D holds the rod D in its closed position, a certain degree of leakage may be provided for between the interior of the cylinder F and the reservoir F This corresponds, in efiect, to the provision of a small vent between each pipe F F and the reservoir F the piston F having a diameter such that the volume of liquid dclivered at each stroke is slightly in excess of that required to produce the full movement of the rod D. Thus, though there will be leakage of oil from the cylinder F into the reservoir F for ensuring that each operating stroke of the actuating piston F commences with the same length of liquid column in the pipe F or F. For example, according to one simple arrangement the actuating piston acts at each end of its stroke to open a port and thereby establish communication between the corresponding liquid column and the reservoir, this relief port being closed at the beginning of the inward stroke of the piston. Thus (except during actual operation) one of the two liquid columns controlling the contact rod will be open to the reservoir, whilst the other is sealed and any temperature changes will cause a slight movement of the contact rod insufi'icient to affect its engagement with the fixed contact.

It will be understood that though as above dcscribed a single double-acting hydraulic actuating piston is employed for controlling the two liquid columns of each circuit breaker, separate single-acting hydraulic pistons may control the liquid columns respectively, such actuating pistons being, however, preferably operated in unison.

Figures 4 and 5 illustrate one form of opentype switchgear embodying the invention. In this construction an earthed metal casing G upon which the circuit breaker is supported (for example on a pillar or like structure) carries an insulating tube G closed at its outer end by a housing G for fixed contacts H and the said housing carrying an arc-control device I-I whose lateral vents H are upwardly directed. The tube G thus constitutes a circuit-breaker tank within which the arc-control device H is immersed in insulating liquid, e. g. oil. The movable contact of the circuit breaker is constituted by ahollow rod K furnished at one end with a plunger K which can slide within a cylinder K carried by the casing G so as to be concentric with and spaced from the cylinder K and from an outer tubular extension K A hollow displacement member K furnished with a piston K projects into the hollow rod K which extends through a gland K within the casing G. Two conduits L L in the casing G communicate with an hydraulic actuating device, for example as above described, the conduit L leading to a cavity L in open communication with the cylinder K on one side of the plunger K whilst the conduit L leads to a cavity L and thence through the annular space between the cylinder K and outer tube K to the opposite end of the cylinder K With the parts in the positions shown, the movable contact rod K is in its fully retracted position and the circuit breaker is open. If now the circuit breaker is to be closed, actuating oil is drawn through the conduit L and delivered under pressure through the conduit L A spring controlled latch M is thus released from a collar M on the plunger K which is moved to the right as viewed in the drawing. The rod K enters the arc-control device and establishes the circuit through the fixed contacts H A latch M now engages a recess M in the plunger K and retains the rod K in the closed position. As the rod K approaches the end of its closing stroke an annular rim within the plunger K engages the piston K so that the displacement member K is moved to the right as viewed in the drawing and a fiange M strikes against a floating collar M which in turn acts through a spring M on a second floating collar M The spring M thus acts to bring the rod K to rest in the closed position with a minimum of shock. The piston K now leaves uncovered a leakage port L in the cylinder K so that the liquid columns in the conduits L L communicates through this leakage port. Thus, except during actual operation of the contact rod K the piston K is bypassed and, even if, as is preferred, each actuating piston controlling the liquid columns in the conduits L L is such as to deliver a quantity of oil in excess of that necessary to produce the full stroke of the rod K, each operation of the hydraulic piston will commence with the correct length o liquid column.

In order to open the circuit breaker, oil is supplied under pressure through. the conduit L to the cavity L this pressure releasing the latch M and moving the plunger K to the left as viewed in the drawing. The piston K thus displaces oil from the interior of the rod K causes this oil to be injected under pressure into the arc-control device H. The displacement member is capable of limited longitudinal movement so that when the piston K approaches the fully open position shown in the drawing it engages a flange or enlargement on the displacement member K so as to move this to the left as viewed in the drawing. A flange M strikes against the collar M so that the spring M absorbs the shock. With the circuit breaker open, as in Figures 4 and 5, the piston K uncovers small vents L in the cylinder K for the purpose described with reference to the vents L Since the external diameter of the end of the hollow rod which enters the arc-control device is substantially equal to the internal diameter of the part of the hollow contact rod in which the displacement piston moves, the volume of oil injected from the hollow rod is approximately equal to the volume vacated by the end of the hollow rod within the turbulator. If desired, however, the internal diameter of the part of the hollow rod in which the displacement member moves may exceed the external diameter of the part of the hollow rod lying within the turbulator so that, during the opening movement of the hollow rod and while this still projects into the turbulator, the volume of oil injected into the turbulator will exceed the volume vacated therein by the end of the hollow contact rod.

A further arrangement of the invention, as applied to vertical open-type gear, is illustrated in Figure 6 in which the arc-control device N and fixed contacts N are suspended from a top plate 0 closing the upper end of the insulating circuit-breaker tank 0 arranged within a shedded insulating bushing 0 the lower end of the tank 0 being closed by a housing 0 so that the arc control device is immersed in insulating liquid within the circuit-breaker tank.

The movable contact member of the circuit breaker is constituted by a hollow rod P which extends from the circuit-breaker tank 0 through a liquid-tight gland 0 into a liquid enclosure P An intermediate metal housing Q carries an insulating cylinder 0 constituting an extension of the tank 0 the extension 0 as also a surrounding insulating bushing 0 being carried by a member 0 supported on a frame 0 The hollow rod P is furnished with a plunger P which slides within the enclosure P the rod P being extended beyond the plunger P and through the interior of the extension 0 into a tube P carried by the frame 0 the extension 0 and the tube P being filled with oil. The lower end of the rod P is secured to a guide P which is connected as indicated at P to external means for operating the moving contact rod. For polyphase working each guide P is furnished with a rack P engaged by a pinion P, the pinions being keyed to a common shaft P so as to cause simultaneous operation of the several circuit breakers.

With the parts in the position shown, the plunger P is in its lowermost position and the circuit breaker is open. In order to close the circuit breaker the guide P is forced upwards in the tube P so that the plunger moves upwards in the enclosure P and apertures P through the wall of the rod P and communicating with the bore thereof, are raised into the enclosure P The rod P now projects into the arc-control device N and engages the fixed contacts N so that the circuit breaker is closed. When the rod P approaches the end of its upstroke the plunger P covers vents P in the enclosure P thus providing a dashpot action to absorb shock at the end of the closing movement of the contact rod P.

To open the circuit breaker the guide P is pulled downwards in the tube P so that as the rod P moves away from the contacts N and arccontrol device N, the plunger P displaces oil from the enclosure P through'the apertures P and thence through the hollow rod P into the arc-control device N. The apertures P are so arranged below the plunger P that communication between the apertures and the enclosure P is cut off shortly before the plunger P reaches the end of its stroke, thus providing a dashpot action to absorb shock at the end of q the opening movement of the contact rod P.

. for the moving contact.

With polyphase working, the contact rods of the several circuit breakers are operated in synchronism by the coupling P P", P the operating force being preferably applied at P to one phase only.

It will be appreciated that the above arrangements have been described by way of example only and that the invention can be applied to other constructions of open-type switchgear and also to metal-clad switchgear. In some instances (especially in metal-clad switchgear) the hydraulic operating compartment and the inner compartment are located in a tubular vessel forming an extension of the circuit-breaker tank and constituting therewith a complete circuit-breaker unit, which may cooperate with isolating switches or may itself be movable within an outer casing for isolating purposes. This tubular extension vessel may be made of insula'ting material or of metal and the circuitbreaker tank may likewise be of insulating material or of metal. In some instances the tubular vessel may be mounted in an insulating bushing and may itself constitute the lead-in conductor In this case the movingcontact rod will pass right through the closed liquid-filled chamber, holes being provided in the rod to maintain communication between such chamber and the interior of the rod. In order to effect the displacement of the liquid from the chamber through the rod into the arccontrol device during the opening movement the cross-sectional area of the rod where it: enters the chamber may be greater than that where it leaves the chamber by an amount equal to or somewhat greater than the area of the end of the rod in the arc-control device.

In each of the constructions above described the eiiective area of the face of the plunger carried by the hollow contact rod may be equal to or somewhat greater than the area of the end of the rod within the arc-control device. When hydraulic operation is employed the two pipes or conduits containing the liquid columns may approach the hydraulic operating enclosure or cylinder at the end remote from the circuit breaker, or one pipe may lead to one end of the cylinder and the second to the other end, this latter arrangement allowing the construction of the cylinder to be simplified since the inner cylinder may be omitted, the plunger sliding along the wall of the enclosure thereof.

'What I claim as my invention and desire to secure by Letters Patent is:

1. In a liquid-insulated electric circuit breaker, in combination, a circuit-breaker tank formed at least in part of insulating material, a fixed contact within the tank, an arc-control device having lateral vents and surrounding the fixed contact, a liquid-tight gland in one end wall of the tank, a hollow rod-like contact longitudinally movable through said gland and cooperating with the fixed contact, a closed liquid-filled displacement cylinder forming an extension of the tank and into which extends the open outer end portion of the rod-like contact'remote from the fixed contact, a

plunger part on the said outer end portion of the rod-like contact, the cross-sectional area of the plunger portion being at least equal to the crosssectional area of that part of the moving contact which enters the arc-control device, an hydraulic operating cylinder concentric with the displace ment cylinder within the said tank extension, an hydraulic operating piston carried by the rod-like contact and lying Within the hydraulic operating cylinder, an hydraulic actuating cylinder, a double-acting piston within the actuating cylinder, and two conduits leading respectively from the actuating cylinder on opposite sides of the actuating piston to the hydraulic cylinder on opposite sides of the operating piston carried by the rod-like contact for efiecting the opening and closing movements of the latter, movement of the rod-like contact to open the circuit breaker causing the plunger part to displace through the hollow rod-like contact into the arc-control device a volume of liquid at least equal to the volume vacated within the arc-control device by the moving contact.

2. In a liquid-insulated electric circuit breaker, in combination, a circuit-breaker tank formed at least in part of insulating material, a fixed contact within the tank, an arc-control device having lateral vents and surrounding the fixed contact, a liquid-tight gland in one end Wall of the tank, a hollow rod-like contact longitudinally movable through said gand and cooperating with the fixed contact, a displacement cylinder forming an ex tension of the circuit-breaker tank, a displacement plunger carried by the extension and lying within the hollow rod-like contact, the cross-sectional area of the displacement plunger being at least equal to the cross-sectional area of that part of the rod-like contact which enters the arc-control device, an hydraulic operating cylinder concentric with and surrounding the rod-like contact and displacement plunger within said tank extension, an hydraulic operating piston carried by the rod-like contact and lying within the hydraulic operating cylinder, and two conduits through which liquid can be supplied under pressure to the hydraulic cylinder on opposite sides respectively of the operating piston, the said conduits being maintained in communication with each other through seepage ports when the rod-like contact is at the end of its stroke, movement of the rodlike contact to open the circuit breaker causing the displacement member to displace from the rod-like contact into the arc-control device a volume of liquid at least equal to the volume vacated within the arc-control device by the moving contact.

3. In a liquid-insulated electric circuit breaker, in combination, a circuit-breaker tank formed at least in part of insulating material, a fixed contact within the tank, an arc-control device having lateral vents and surrounding the fixed contact, a liquid-tight gland in one end wall of the tank, a liquid-filled displacement cylinder forming an extension of said tank, a hollow rod-like contact longitudinally movable through the gland and cooperating with the moving contact, mechanism for effecting longitudinal movement of the rodlike contact which extends through the displacement cylinder to said mechanism, a displacement plunger on that part of the rod-like contact lying within the displacement cylinder, the cross-sectional area of the displacement plunger being at least equal to the cross-sectional area of that part of the rod-like contact which enters the arc-control device, the hollow rod-like contact having at least one lateral aperture on that side of the displacement plunger remote from the fixed contact, movement of the rod-like contact to open the circuit breaker causing the displacement plunger to displace, through the lateral aperture and hollow rod-like contact into the arc-control device, a volume of liquid at least equal to the volume vacated within the arc-control device by the moving contact.

4. In a liquid-insulated electric circuit breaker, in combination, a circuit-breaker tank, a fixed contact within the tank, an arc-control device surrounding the fixed contact, a liquid-tight gland in one end wall of the tank, a liquid-filled 15 displacement cylinder constituting an extension of and lying Wholly outside said tank, a hollow rod-like contact cooperating with the fixed contact and extending through said gland into the displacement cylinder, the rod-like contact being longitudinally movable through said gland, a displacement plunger on that part of the rod-like contact lying Within the displacement cylinder, and mechanism for efiecting longitudinal movement of the rod-like contact, such longitudinal movement in a direction to open the circuit breaker causing the displacement plunger on the rod-like contact to displace liquid from the displacement cylinder through the hollow rod-like contact into the arc-control device.

ARCHIBALD ALLAN.

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