US2009335A - Metal-clad electric switch gear - Google Patents

Description

July 23, 1935. A. ALLAN 2,009,335

I I METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1935 13 Sheets-Sheet 1 5 ww iwa July 23, 1935. A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR- Filed March 17, 1933 13 Sheets-Sheet 5 lild I A. ALLAN July 23, 1935.

METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 15 SheetsSheet 4 A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 13 Sheets-Sheet 5 July 23, 1935. A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR 1s Sheets-Sheet 6 Filed March 17, 1935 July 23, 1935. A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1935 13 Sheets-Sheet '7 i W m A. ALLAN Juiy 23, 1935.

METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 15 Sheets-Sheet 8 Juiy 23, 1935. A, ALLAN 2,@09,335

METAL CLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 13 Sheets-Sheet 9 //VVEA/T07? Z. Em 5 MM.

y 3,1935 A. ALLAN v METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 13 Sheets-Sheet 1O July 23 1935. A. ALLAN 2&093555 METAL GLAD ELECTRIC SWITCH GEAR Filed March 17, 1933 13 Sheets-Sheet ll a %4/ 01mm 70?? July 23, 1935 A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR l5 Sheets-Sheet 12 Filed Maroh l'F, 1953 W 6 MM WW E L m mm 5 m mm 2 July 23, 1935. A. ALLAN METAL CLAD ELECTRIC SWITCH GEAR 7 Filed March 1'7, 1933 15 Sheets-Sheet l3 VII/Ill INVE'N T03 Patented July 23, 1935 UNITED STATES PATENT OFFICE METAL-GLAD ELECTRIC SWITCH GEAR Application March 17, 1933, Serial No. 661,405 In. Great Britain March 24, 1932 9 Claims.

This invention relates to metal-clad electric switchgear and has for its primary object to provide an improved arrangement of the metalclad apparatus (such for example as circuitbreakers, reactors and transformers) forming part of or associated with aswitchgear layout for an electric power station or substation to enable such apparatus to be more readily handled and overhauled and to simplify and reduce the dimensions of the switchgear.

Metal-clad switchgear according to the present invention comprises a tank or chamber containing a circuit-breaker or other electrical apparatus, a chamber containing a busbar or like conductor, an insulated conductor-so mounted that it can projectv into the apparatus tank and into the busbar chamber to connect the busbar or like conductor to a terminal of the apparatus and can be moved longitudinally to break such connection, the arrangement being such that the insulated conductor can be withdrawn bodily from the busbar chamber towards or into the apparatus tank to facilitate removal of such tank together with the insulated conductor from the switchgear. Preferably the insulated conductor,

- when in its operative position, directly connects two contacts permanently connected respectively to the busbar or like conductor and to the apparatus terminal so that it constitutes the sole isolating member between the busbar or like conductor and the terminal.

When withdrawn from the busbar chamber, the insulated conductor may lie wholly within a hollow insulator in the apparatus tank, or partly within a hollow insulator in the tank and partly within a metal trunk carried by the tank and normally connecting the tank to the busbar chamber. The connection between the metal trunk and the busbar chamber is conveniently in the form of a flexible bellows which is attached to the trunk and can be clamped to the wall of the busbar chamber or to a fitting thereon. The insulated conductor is preferably immersed in an insulating liquid and to obtain a liquid-tight joint between the bellows and the busbar chamber, a flange on the bellows may be bolted to the chamber Wall or may be mechanically forced into close engagement therewith by means of an arm which is pivoted to the chamber wall and is pressed against the flange by a toggle mechanism. The movements of the insulated conductor may be effected hydraulically or by other means.

A considerable reduction in the size of the busbar chamber, and consequently also in the cost of the whole installation, can be effected by so arranging the switchgear as to ensure that there Will always be a body of insulating liquid between the busbar or like conductor and the metal'walls of the chamber, even during movement of the insulated conductor and after it has been withdrawn from the busbar chamber. For this purpose a sealing device may be provided, in a manner which in itself forms the subject of a separate concurrent patent application, for sealing the orifice in the wall of the busbar chamber in a liquid-tight manner when the insulated conductor has been withdrawn from the chamber. This also eliminates the necessity for draining the insulating liquid out of the busbar chamber when removing the tank containing the circuit-breaker or other apparatus from the switchgear.

The arrangement of the insulated conductor itself may vary, but in one convenient form, more especially intended for use in high voltage installations, the movable conductor is surrounded by insulation of the condenser type movable with the conductor and comprising conducting layers interleaved with insulating layers within an outer metallic sheath, the conductor itself preferably being in the form of one or more flexible leads within a rigid tube supporting the condenser insulation. In cases where the fixed circuit-breaker contact or the apparatus terminal, with which the insulated conductor cooperates, can be alive from another circuit during movement of the insulated conductor, as for example in duplicate busbar installations, it is desirable to arrange the conducting layers in the insulation around the conductor in such a manner as to avoid risk of flash-over from the fixed circuitbreaker contact to earth through such layers. For this purpose the insulation may include overlapping short conducting layers arranged in two groups respectively extending from the ends of the conductor at gradually increasing radii to the ends of the outer metallic sheath, one of the intermediate layers in one of the groups being connected to a contact on the outside of the insulation. Alternatively the overlapping short conducting layers may be arranged in three groups, of which one extends from one end of the conductor to one end of the sheath, and one extends from the other end of the conductor to a contact on the outside of the insulation, whilst the third extends from a point of the conductor near such contact to the other end of the sheath. Instead of employing condenser insulation, it may in some cases be more advantageous to employ a liquid-filled type of insulating bushing around the conductor. In such an arrangement the movable conductor is immersed in insulating liquid in a surrounding tube so mounted as to be movable with the conductor, spaced barriers of solid insulating material being mounted concentrically in the liquid between the conductor and the outer tube.

The invention may be carried into practice in a variety of ways, but some convenient practical arrangements according thereto, as applied to oil-immersed circuit-breakers forming part for example of a high voltage switchgear layout, are illustrated in the accompanying drawings, in which t Figure 1 is an elevation (with the circuitbreaker tank in section) of an arrangement in which the circuit-breaker controls a simple connection from a busbar to a feeder or other circuit,

Figure 2 is an enlarged sectional View of part of Figure 1 showing the arrangement of the withdrawable conductor,

Figures 3 and 4 are vertical and horizontal sections'through the sealing device,

Figures 5 and 6 are detached views on a larger scale of parts of Figure 2,

V Figure '7 illustrates a modification of the arrangement of Figures 1-6 for the case of a duplicate busbar installation,

Figures 8-9 are views similar to that of Figure '7 showing alternative constructions of withdrawable conductor,

Figure 10 illustrates an alternative duplicate busbar arrangement, V

Figure 11 is a side elevation of a low voltage three-phase switchgear arrangement,

Figure 12 is a front elevation (with the supporting framework removed) of the arrangement of Figure 11, parts being shown in section,

Figures 13 and 14 are respectively a side elevation-and a front elevation of an alternative low voltage arrangement,

Figure 15 is a sectional View of part of the arrangement of Figures 13 and 14,

Figure 16 is a View similar to that of Figure 15 showing a modified arrangement,

Figures 17 and 18 are sectional views respectively illustrating two alternative forms of sealing device,

Figure 19 illustrates a further alternative form of sealing device, I

Figure 20 is a section on the line 20-20 of part of the arrangement of Figure 19,

Figure 21 illustrates a modified arrangement in which the sealing device is dispensed with,

Figure 22 illustrates an alternative driving arrangement for the withdrawableconductor, and

Figures 23 and 24 respectively illustrate two further alternative duplicate busbar arrangements.

In the arrangement shown in Figures 1-6, which is applicable to a simple installation in which the circuit-breaker controls a connection from a busbar to a feeder or other circuit, the circuit -breaker oil tank 50 rests on the ground and two oil-filled chambers 60 and 1B are mounted above the tank.

on supporting pillars or a suitable framework (not shown). The chamber 60 constitutes the busbar chamber and contains a contact 6| to which the sections of the busbar 62 are directly connected.

The chamber is is associated with the feeder circuit and contains a contact Tl carried by a supporting insulator l2; Extending down from this contact I [to the bottom wall of the chamber 10 is a hollow insulator 73 which surrounds in an oil-tight manner an orifice in the chamber wall, and a sealing end 74 on the feeder-cable 15 is inserted through this orifice so as to make connection with a terminal within the top of the insulator 13 connected through the insulator to the main feeder contact 1' l. The cable sealing end 74 carries a flange 15 which can be secured to the chamber wall around the orifice with suitable insulation to isolate the cable sheath from the chamber wall. A small compartment is thus enclosed between the sealing end 14 and the hollow insulator 13 and this compartment may be filled with oil from the chamber HG through a valve on the insulator 73. Means are provided to allow the oil to be drained off from this compartment after closing the valve, when it is desired to remove the sealing end, and it will be appreciated that this arrangement permits removal of the sealing end without the necessity for draining the oil out from the chamber 10 itself.

The circuit-breaker comprises two fixed main contacts 5|, 52 and a movable bridging contact member 53, the arrangement preferably being such as to, give six breaks in series. The bridging contact member 53 is operated by suitable mechanism, indicated at 55, carried by the cover plate 55 of the oil tank 50 containing the circult-breaker;

Extending upwardly at a smallangle to the vertical from each of the fixed main'contacts 5|, 52 of the circuit-breaker is a hollow condenser insulator 88,, comprising short overlapping conducting layers 8l interleaved with insulating layers and surroundedin its upper portion by a metal sleeve 82, which projects through an orifice in the cover plate 5510f the tank and is provided with a flange 83 bolted to the cover plate. The lower end of each hollow insulator 8B is closed in an oil-tight manner by a metal cap 84 connected to the main fixed circuit- breaker contact 51 or 52, and a metal tube 85 extends up from this cap 84 within the lower portion of the in sulator. At the upper end of each insulator the surrounding metal sleeve 32 carries a flange 86, to which is bolted a metal casing 99 including a cylindrical metal trunk 91 surrounded by an, annular chamber 92 in which current transformers can be located. Around the upper end of the metal trunk 9! is a flexible metal bellows 33, which is attached to the top of the casing 9 and can be. clamped to the bottom of a valve chest mounted below the appropriate oil-filled chamber 69 or 1, a metal shield 94 being provided around the bellows 93 to protect it from damage. The busbar contact 6! or the feeder contact H as the case may be, is in line with the axes of the metal trunk 9| and the hollow insulator 85, and communication between the chamber 6B or 1 and the tubular compartment formed by, the trunk and the insulator can be cut 01f by means of a valve in the valve chest in a manner to be described later.

Mounted to slide longitudinally in this tubular compartment is an insulated conductor IUD, which serves when in its operative position to connect the busbar contact 6! or the feeder contact ll to theinner metal tube 85 in the insulator and thence to the main circuit-breaker.

contact 5| or 52. This insulated conductor comprises a rigid central tube ill I surrounded by insulation I02, which in the case of the higher voltage installations is in the form of condenser insulation as shown, the insulation being enclosed for part of its length by an outer metallic sheath I03,

which engages with the metal trunk 9 I. The central tube I0! serves to contain flexible connections I04 between contacts at the upper and lower ends of the insulated conductor. The lower contacts (see Figure 6) are in the form of outwardly spring-pressed plungers I35 engaging with the metal tube and carried in a metal block I06 to which the lower ends of the flexible leads I04 are connected. The upper contacts consist of a bundle of butt contacts I0'I independently springpressed in a longitudinal direction so as together to constitute a self-aligning butt contact for engagement with the busbar contact GI or the feeder contact II.

l."he insulated conductor can be withdrawn downwards from its operating position into an isolating position, in which it lies within the tubular compartment formed by the metal trunk GI and the insulator 80. In Figure l the conductor associated with the feeder is indicated in its raised operating position, whilst that assocated with the busbar is shown withdrawn into its isolating position, and Figure 2 similarly shows the conductor in the isolating position.

The movements of the withdrawable conductor are effected hydraulically by varying the oil pressure above and below the conductor, the metal sheath I03 on the conductor being provided with piston rings I08 so that the sheath acts as a piston movable in a cylinder constituted by the metal trunk 9L For this purpose an oil pumpv H0 driven by an electric motor III is mounted on the casing and is connected by suitable ducts I 32, I I3 to the upper and lower ends of the tubular compartment in which the withdrawable conductor moves. The upper duct [I2 opens intothe transformer chamber 92 and is thus connected through the interior of the metal bellows 93 to the open upper end of the metal trunk 9!. The lower duct H3 opens into the lower part of the casing 00 beneath the transformer chamber and is thus connected through openings in the flange 86 to the interior of the insulator 00, parts of the metal sheath I03 being cut away as indicated at I09 to permit the oil to flow into the lower end of the insulator 80. Thus to raise the conductor the pump I I0 is started up to withdraw oil from the upper end of the trunk SI and to drive it into the interior of the insulator 83. To lower the conductor the pump is driven in the reverse direction, the Weight of the conductor assisting the movement. Alternatively a by-pass valve may be provided, which is opened to connect the two oil ducts together, the weight of the conductor being relied upon to effect the downward movement. If desired, instead of forming the sheath I03 as a piston moving in the cylinder formed by the metal trunk Hi, the upper and lower parts of the tubular compartment may be separated from one another by a cup leather or sealing ring fixed in' the metal trunk and embracing the insulated conductor, so that the movements of the conductor are effected after the manner of a hydraulic ram.

Whilst theoil pressure may be utilized to hold the insulated conductor in its raised operating position, it will usually be preferable to provide a mechanical latch for this purpose. A convenient construction of latch, which will hold the conductor either in its operating position or in its'isolating position, is shown in Figures 2 and 5. This latch consists of a ring I20 surrounding the insulated conductor and pivoted about a vertical pin I2I at the lower end of the casing 90 at one side, the ring having two internal flanges I 22 and I 23 at different levels on opposite sides of the conductor. These flanges cooperate with grooves I24 and I25 in appropriate positions in the metal sheath I03 of the conductor, and to ensure correct positioning of the lower groove I25 a collar is provided at the upper end of the metal trunk 9| with which the upper end of the metal sheath I03 engages when the conductor is in its raised position. The metal block I06 containing the lower contacts I05 similarly engages with a shoulder 86 at the lower end of the metal tube 85 within the insulator 80 for pcsitioning the upper groove I24 correctly when the conductor is in the isolating position. The latch ring I20 is moved to one side or the other about its pivot I 2| by a pair of spring crank arms I30 on a horizontal shaft I 3! suitably mounted outside the metal sleeve 82. The shaft I3I is rotated by an operating arm I32 movable between fixed stops I 33, I34 under the control of an operating rod I35 (see Figures 1 and 2). Thus with the conductor held in its raised position (as indicated on the right-hand side of Fig. 1) by the engagement of the lower latch flange I23 in the lower groove I25, movement of the operating arm I32 to its other limiting position against the stop I34 will cause the spring arms I30 to release the flange I23 from the groove I25 and will hold the upper latch flange I22 spring-pressed against the surface of the metal sheath I 03, so that when the conductor reaches its isolating position (as indicated on the left-hand side of Figure 1) the upper latch flange I22 will spring into engagement in the upper groove I24, the converse latch operation taking place when the conductor is raised. The latch operating mechanism is also utilized to operate through levers I36 a number of auxiliary switches I31 housed in a box I38 0n the casing 90 for indicating or interlocking purposes. The shaft of the auxiliary switches may also operate an indicator visible through a window M9 on the box 538 to indicate whether the conductor is in its operating position or in its isolating position. The latch-operating rods I35 are actuated by suitable control mechanism which also operates contacts controlling the energization of the electric motors III for driving the pumps, the energizing circuits for the pump motors being taken through certain of the auxiliary switches I 31 controlled by the latch, the arrangement being such that a pump motor cannot be energized until the corresponding latch has been released.

As has been mentioned, a valve is provided for sealing the orifice at the bottom of the busbar chamber 60 or the feeder chamber I0 when the insulated conductor has been withdrawn. A preferred construction for this valve is indicated in Figures 1 and 2 and is shown in detail in Figures 3 and 4. In this arrangement the valve is mounted in a valve chest I40 and is in the form of a sluice valve II, which is caused to slide over the orifice by rotation of a screwthreaded shaft I42 by means of a handwheel I43. The valve shaft I42 carries a notched disc I44, with which an arm I45 carried by a spindle M0 cooperates. This spindle E46 is connected to part of the control mechanism for actuating the associated latch-operating rod I35, the arrangement being such that when the control mechanism is operated to cause the insulated conductor to be raised, the spindle I46 is rotated to cause the arm I45 to engage in a notch on the disc I44 and thus to prevent the handwheel I43 from being the upper chamber.

rotatedito closethe valve. Since the arm -I 45 may not alwaysbe opposite a notchin the disc I 44, the spindle I46 is made of suificie'nt flexibilityto permit it to twist when operated, sothat aftera slight rotation of the handwheel. the arm I45 will spring into the first notch on-the disc and will thuslock the handwheelagainst furthermtation. In order to prevent 'energization of the pump motor I I I to raise 'the insulatedconductor when the sluice valveis closed; the energizing circuit tothe pumpmotor is controlled-byan-auxiliary switch operated by the sluice Valve. For this purpose the-valve shaft J42 carries aworm I4! for operating a rotary auxiliary switch I48- housed in a casing I49 carried by the valve-chest.

At one side of the valve chest I40, a by-passvalve is provided'in the form of a rotary tapered plug I55 having-two holes II; I52- bored in itE One of these holes I5I cooperates with two passages (one of which is indicated at I53) in the valve" chest communicating respectively with the spaces above and below-the valve itself. The second hole I52 controls-a connection fromthe space below the valve tothe atmosphere. In

1 the normal position of the plug I5ll both holes are closed, but by rotating the plug into-one position itispossible to completea by-pass con' nection through the hole I5I from one sideof the valve to the otherand at thesame time a further connection from the space below the valve to the atmosphere. This allows-themteriorof the bellows 93 to be filled 'with oil from the upper chamber, when the bellows isagain connected thereto after having been disconnected 3 for removal of the circuit-breaker; without permitting entry of air into the upper chamber. The plug I50 can also be rotated into a further position in which the by-pass connectionis closed; but the connection of the space below-the valve to the atmosphere through the hole I52 is open. This position is utilized to permit air to, enter the interior of the bellows 93; when oil is being drained therefrom by a suitable draincock (not shown) prior to disconn ection of the bellows from In thebody of the sluice valve MI itself two small non-return valves I55, I 56 are provided which act in opposite directions. The valve I55 is arranged to open when the pres sure in the upper chamber exceeds-that within the bellows by a predetermined amount to permit oil to flow into the bellows when contraction of the oil below the valve takes place as the result of temperature variations, and the valve l56 likewise allows oil to flow out from the bellows into the upper chamber in the event of excessive pressure being set up within the bellows owing to expansion of the oil thereindue to temperature; changes. a v

The above arrangement may bemodified in various ways. Thus for instance the hollow insulator 80 in-the circuit-breaker tank may be taken right past-the circuit breaker fixed contact and may be of such a length as to permit the whole of the withdrawable conductor to liewith- 1. in the tank itself in the isolating position, thus enabling the'overall height of the switchgear to" be still further reduced. Again by leaving the lower end of the hollow insulator in the tank open, the raising of the insulated conductor couldbe effected hydraulically by raising the pressure in the gas space in the tank itself, so thatoil from the tank is forced'up within the hollow insulator to drive the conductor in front of' it.

The foregoing arrangement has been described 2 and illustrated as applied to-a circuit-breaker controlling a simple connection from a'busbarto afeeder circuit-but it is equally-applicable to the case of a duplicate busbar layout-wherein each busbar is connected to the feeder or othercircuit through a separate circuit-breaker, and generally to all cases where it is impossible for the fixed circuit-breaker contact with which the insulated conductor cooperates to be alive from another circuit during movement of the insulated conductor from one position to the other. Thus in the arrangement actually illustrated in Figures 1-6 the metal sheath I63 of the conductor connects the circuit-breaker contact through thetube 85 to the earthed metal trunk 9|, and even if the metal sheath were shortened to avoid such a direct earth connection, the inclusionof metallayers in the insulation around the conductor would in many instances reduce the dielectric value of the insulation between the circuit breaker contact and the earthed metal trunk to too low a value. In cases therefore where the circuit-breaker contact may be alive from'another circuit and where'it is desirable to employ condenser insulator around the conductor, it is preferable tovmodify the construction of the insulated conductor to avoid'risk-of flash-over from themain circuit-breaker contact to earth.

Figure '7 illustrates such a'modified form of insulated conductor in its application to a duplicate busbar installation, wherein a single circuitbreaker providedwith busbar selecting means controls theconnectionsfrom both busbars to the feeder or other circuit. In this arrangement three oil-filled chambers are mounted above the circuit-breaker oil tank, two of these. chambers respectively containing contacts connected to the two busbars, whilst'the third containsa contact connected to the feeder or other circuit. The three contacts in the upper chambers'are conne'ctedto the circuit breaker fixed contacts" by withdrawable insulated'conductors, the conductors associated with the two busbar contacts both cooperating with one of the main circuit-breaker contacts, whilst the other main circuit-breaker contact cooperates with the conductorassociated with-the feeder contact.-

Figure 7.shows.thetwobusbar chambers I'll! and I75 respectively containing contacts I'H'and I 'IGconnected to the two .busbars I I2..and I11; and the connections therefrom to one of the fixed main circuit breakercontacts. IBI contained within the circuit-breaker tank I 80. The other circuitbreakercontact andthe connection therefromto the contact in the feeder chamber are-notshown in the drawings butare preferably identical with the correspondingparts of the arrangement of Figures 1-6, and a description of the. connections. to thebusbars will be sufiicient to enable the. whole.

arrangement tobe understood.

Mounted one on either side of the circuitbreakercontact v I 8! are two hollow insulators 190,:

by a metalicap I Sit-{carrying a short internal tube. I; and to :grade the .stress'es set-up the insulaetion is in theform of: condenser insulation with suitably arranged overlapping short metal layers I 96 interleaved with; the insulating layers. The

flange i I 92 at the upper end of the metal sleeve 75 I9! carries a metal tube I9! extending from within the top of the insulator I90 upwardly and having at its upper end a flange I98, to which is bolted a casing 2% containing a cylindrical metal trunk 20! surrounded. by a current transformer chamber 202, the metal trunk constituting a continuation of the metal tube I91. The casing 200 and the parts carried thereby (including the motordriven pump and the latch device) are substantially identical with the corresponding parts of the arrangement of Figures 1-6. A valve chest 205 containing a sluice valve is mounted beneath the busbar chamber as in the previous arrangement and is similarly connected to the top of the casing 2B0 by a flexible metal bellows 206.

Mounted to slide longitudinally in the tubular compartment constituted by the metal trunk 20!, the metal tube I9! and the hollow insulator I90, is an insulated conductor, which serves when in its operative position to connect the busbar contact I7! or !'!5 to the ring contact I93 and thus to the main circuit-breaker contact ISI. This insulated conductor comprises a rigid central tube 2H1 containing flexible leads connecting upper butt contacts 2!! and lower spring contacts 2I2 in a manner similar to that described with reference to Figures 1-6. The central tube 2 I is surrounded by layers of paper insulation 2I3 interleaved with overlapping short metal layers 2", and the upper part of the condenser insulation is enclosed within a metal sheath 2 I 5. Spring contacts 2 I6 are provided on one of the intermediate metal layers approximately midway between the lower end of the conductor and the lower end of the sheath 2! 5. The metal sheath 2I5 carries piston rings 2!! sliding in the cylindrical metal trunk 20! and is provided with upper and lower grooves 2 I8, 2 I 9 coacting with the latch device in the casing 200 in a manner similar to that described for the arrangement of Figs. 1-6.

Since the metal sheath 2I5 slides within the metal trunk 29! it always remains in contact with earthed metal. When the insulated conductor is in its operative position with its upper butt contacts 2! engaging with the busbar contact and its lower spring contacts 2I2 engaging with the ring contact I93 connected to the circuit-breaker contact, the contacts 2 I6 on the intermediate metal layer, are earthed through the metal tube Nil (as indicated on the right-hand side of the drawings), whilst when the insulated conductor is in its isolating position (as shown on the left-hand side) the intermediate contact 2I6 engages with the ring contact I93 and the central conductors are earthed through the short tube v1% on the bottom cap I94 on the hollow insulator um. Thus in the isolating position the intermediate contact 2H5 may be alive, owing to the connection of the circuit-breaker contact I8! to the other busbar, but is located between two earthed points from which it is separated by condenser insulation.

Thus with the circuit-breaker in operation connecting the feeder to, say, the busbar I!!, the insulated conductors associated with the feeder and with this busbar will both be in their raised operative positions, whilst the insulated conductor associated with the busbar I12 is in its isolating position. If now it is desired to change over to the busbar I12, the main circuit-breaker contacts are opened, and the insulated conductor for the busbar I1! is lowered by operation of its pump and latch device, the insulated conductor for the busbar I'I2 then being raised into its operative position and the main circuit-breaker contacts closed. The change-over can alternatively be effected without opening the main circuit-breaker contacts by first raising the insulated conductor for the busbar I12, so that the two busbars are connected together and to the feeder, and then lowering the conductor for the busbar Ill. To remove the circuit-breaker for inspection or overhaul, the procedure is similar to that for the arrangement of Figures 1 6, namely to open the circuit-breaker contacts and lower all the insulated conductors, after which the sluice valves are closed and the flexible bellows detached (after draining the surplus oil out of them). The circuit-breaker operating mechanism, if it is not arranged to be movable with the circuit-breaker, is then uncoupled, so that the circuit-breaker with the insulated conductors inside it can be removed laterally without the necessity of lowering it.

Instead of employing two separate tubes I9! and 2:3! in line with one another, the cylindrical metal trunk 26! may itself be extended downwardly, to beyond the cover plate I82 of the tank, the metal sleeve i9! and the hollow insulator I90 then extending right up to the flange I98 with the metal trunk 20! within the insulator. This modification is shown in Figure 8, which also shows a modified arrangement of the insulated conductor. In other respects the arrangement of Figure 8 is similar to that of Figure 7 and the same reference letters are employed. The insulated conductor employed in the arrangement of Figure 8 has a central tube 2!!) with the internal leads connecting the upper and lower contacts 2! I, 2! 2 and also a metal sheath 2I5 with its piston rings 2!! and grooves 2I8, MS, as in the arrangement of Figure 7, but it' difiers from that arrangement in the form of the condenser insulation. In the arrangement of Figure 7 the overlapping short metal layers 2I4 in the lower part of the insulation extend from close to the central tube 2 ill at the lower end of the conductor at steadily increasing radii right up to the lower end of the metal sheath 2 i5, the spring contacts 2 I6 being connected to'a layer at an intermediate radius. In the arrangement of Figure 8, however, overlapping short metal layers 22!! extend from close to the central tube 2! D at the lower end of the conductor to a layer 22! at the full radius of the metal sheath 2I5 but at a position in the length of the conductor corresponding to that of the spring contacts 2 it in the arrangement of Figure 7. This layer 22! is connected through the insulation to spring contacts 222. A further series of overlapping short metal layers 223 extends from close to the central tube 2 I0 directly within the layer 22! up to the lower end of the metal sheath 2 !5. At the upper end of the conductor, both in this arrangement and in the arrangement of Figure 7, a similar series of overlapping short layers is provided between the sheath 2I5 and the upper end of the conductor, and the layers at the upper end are separated from the layers at corresponding radii in the lower part of the conductor by a considerable axial distance which is such as to ensure adequate insulation between the circuit-breaker contact and the earthed metal trunk at all stages in the movement of the insulated conductor.

In the arrangements shown in Figures l-8 the insulation around the withdrawable conductor has in each case been described as of the graded condenser type. Whilst this is generally preferable in the case of apparatus used in high voltage installations on account of the reduction in dimensions which it allows, it may in some instances be more advantageous to employ an oil-filled type of insulating bushing around the conductor. Such an arrangement is shown'in Figure 9 for a duplicate busbar installation. With the exception of the insulated conductor itself, this arrangement is identical with that shown in Figure 7 and the same reference letters are employed.

"The with-drawable insulated conductor shown in Figure 9 comprises a rigid central tube 23!], which may itself constitutethe conductor or may enclose flexible leads in the manner above described, an upper buttcontact 231 and lower spring contacts 232 being provided. A number of concentric insulating tubes 233 of graded lengths surround the central tube 2363 within an outer insulating sleeve 23 3, the intervening spaces being filled with oil, so that the conductor is surrounded by a series of more or less uniformly thick layers of oil alternating with solid insulating layers. The outer sleeve 234% carries a metal sheath 235 provided with piston rings 236 and upper and lower latch grooves 231, 238 as in the previous arrangements. On lower voltage installations it is unnecessary to employ either condenser insulation or an oil-filled bushing arrangement, and simple insulation may be satisfactorily employed.

Figure 10 illustrates an alternative duplicate busbar arrangement, in which the necessity for employing a special arrangement of the condenser insulation around the withdrawable conductor is avoided. In this arrangement a single withdrawable conductor'is utilized for controlling the connections from one circuit-breaker contact to the two busbar contacts, whilst the other circuit-breaker contact is connected to the feeder contact by a withdrawable conductor, which is arranged. (together with the parts within which it moves) exactly in the manner shown in Figures 1-6. Figure 10 illustrates only the parts of the arrangementassociated with the busbar side of the circuit-breaker. i

In the arrangement of Figure 10, the two bus bar chambers 25c, 25! are mounted close together above the circuit-breaker tank, and each is provided beneath an orifice in its bottom wall with a valve chest 255 containing a sluice valve arranged in the manner previously described. The fixed circuit-breaker contact associated with the two busbars is supported beneath a hollow insulator 2 50 of oval cross-section carried by the cover plate 265 of the circuit-breaker oil tank, and is connected through the bottom of the insulator to a curved contact member 26 l. Extending up from the cover plate 265 towards the two busbar chambers is a metal casing 2'10 of generally oval cross-section, to the upper end of which is attached a flexible metal bellows 21! which can be clamped to a suitable oval fitting 256 carried beneath the two valve chests 255. This casing carries'a hollow horizontal shaft 212 about which is pivoted an inner metal casing 28% carrying at its upper end a cylindrical metal tube 28! and at its lower end a metal sheath 282 for a condenser insulator 283. This insulator is closed at its lower end by a metal cap 284 having a pro jection 285 engaging with the curved contact member 28! and a metal tube 286 extends up from the cap 28 l for a suitable distance within the insulator 233. The curvature of the contact member 25% is such that the projection 285 remains in engagement therewith when the casing 28!] rocks about its pivot, and the metal tube 286 is thus permanently connected to the fixed circuitbreakercontact. The metaltubes 28! and 286 are in.-linewith .one another and the metal casing 280 can be swung about theshaft 212 by suitable means (not shown) between two positions in which the axis of the tubular structure ESL-286 is in line respectively with thebusbar contacts in the two busbar chambers 25!) and255. -An insulatedconductor 2% generally'similar in construction to'those employed in the arrangement of Figures 1-6, has its metal sheath 2!)! provided with piston rings 292 sliding within the metal tube 28!, so that its lower spring contacts 293 always engage with the metal tube 286-whilst its upper butt contacts 234 can engage with either busbar contact. The metal sheath 2% has upper and lower grooves 295, 296 cooperating'with a latch device 297 operated by a latch-operating rod 238 outside the casing 270 through a universal coupling 299. The conductor is raised and lowered hydraulically within the surrounding tubular structure by means of a motor-driven pump 2??) carried by the casing 270, one side of the pump communicating directly with the interior of the casing 219 through a duct 214, whilst the other side communicates with the interiorof the pivoted inner casing 288 through a pipe215 coupled to the hollow shaft 212. Thus to change over from one busbar to-another the circuitbreaker'contacts are first. opened and the insulated conductor is withdrawn into the tubular structure 23l, 286, after which the inner casing 2% is rocked about its pivot to the other position and the conductor is raised again intoengagement with the other busbar, the circuit-breaker contacts then being re-closed. The circuitbreaker can be removedfor inspection or repair, when the insulated conductor has been withdrawn by detaching the flexible bellows 21! from the busbar chambers.

Figuresll and 12 illustrate the application of the invention to a relatively low voltage threephase-switch-gear installation. In this arrangement three single-phase circuit-breakers 380 are mounted one behind the other on a wheeled truck 3!". Each circuit breaker has two fixed main contacts SEZcooperating .with a movable main contact 363 and four sets ofarcingcontacts 304 areprovided with one set on each side of each fixed -main contact. wards from each circuit-breaker fixed main contact 302 is a tubular structure containing a withdrawable conductor, the six tubular structures being-in line with one another. Each tubular structure comprises a hollow insulator 3H) surrounded in its upper part by a metal sheath 3| l and closed at its lower end by. a metal cap 312 WhiChiS connected to the fixed circuit-breaker contact 362 and carries a metal tube 3E3. extending up within the insulator 3H3. The metal sheath Silis flanged'for attachment to an upwardprojection 306 on the cover plate 305 of the circuit-breaker tank and carries an upper casing 315 within which is mounted a cylindrical metal trunk 3E5. Attached to the top of the casing 3M is a flexible metal-bellows 3H5, which can be clamped to the underside of a valve chest 32!] containing a sluice valve arranged in the manner above described; The six valve chests 320 are respectively secured beneath six upper oilfilled chambers carried on a suitablesupporting framework 32!, three of these upper chambers constituting busbar chambers 322, whilst the other three are feeder chambers 323. Each of the busbar chambers 322 has in it a contact 324, having a downwardly extending cylindrical fiange325 connected to'the busbar sections .326

Extending vertically upand a similar contact is provided in each feeder chamber.

Mounted to slide within each metal trunk 3!5 is an insulated conductor surrounded by a metal sheath 330 provided with piston rings 33! and upper and lower latch grooves 332, 333 cooperating with a latch device 334 operated by an arm 335 outside the casing 3!4, the movements of the conductor being effected hydraulically by a pump 336 driven by an electric motor 331. The conductor is provided with upper and lower contacts 338, 339 cooperating respectively with the flange 325 on the busbar or feeder contact and with the metal tube 3!3. In order to carry the heavy current without introducing excessive end thrust on the movable conductor, these contacts 338, 339 are each in the form. of a group of four brushes sliding edgeways in the cylindrical contact members with which they cooperate.

The contact in each feeder chamber 323 is connected through a metal trunk 340 into an intermediate chamber 34! containing a current transformer 342 and a cable earthing switch 343. From the intermediate chambers 34! leads pass down through lower chambers 344 to the feeder cables, and in each lower chamber 344 (as shown on the left-hand side of Figure 11) a tapping 345 is taken off for connection to a single-phase potential transformer. Each potential transformer is contained in a wheeled oil tank 350 from which projects upwardly a tubular structure 35! terminating in a flexible metal bellows 352 which can be clamped to a valve chest 353 mounted beneath the chamber 344 and containing a sluice valve, the tubular structure 35! serving to accommodate a withdrawable insulated conductor 354 cooperating at its lower end with a contact connected to the potential transformer winding and at its upper end with a contact 355 to which the tapping 345 leads. The whole potential transformer arrangement is analogous to the circuit-breaker arrangement, so that when the insulated conductor 354 has been lowered and the sluice valve closed, the bellows 352 can be detached from the valve chest 353 to permit the potential transformer tank 350 to be wheeled away for inspection or overhaul.

Figures 13-16 illustrate another application of the invention to three-phase switchgear for use on the lower voltages. In this arrangement the three phases of the circuit-breaker are all contained in a single oil-tank 360 mounted on wheels on the ground beneath a framework 36! carrying an upper chamber 362 for the external circuit connections. Six tubular structures 363 arranged in two rows extend upwardly from the circuit-breaker tank, each structure serving to,

contain a withdrawable insulated conductor arranged generally in the manner above described and terminating at its upper end in a flexible metal bellows 364. In this arrangement the three tubular structures on each side of the circuitbreaker are so close together as to make it inconvenient to employ a separate sluice valve at the top of each structure, and the three sluice valves are accordingly arranged in a single valve chest 365 for operation by a single hand-wheel 366. Figure 15 indicates somewhat diagrammatically one arrangement of the valve chest 365, wherein the three sluice valves 361 are mounted integrally with one another and are driven by a screwthreaded shaft 368 carrying the handwheel 366 to cooperate with a wedging action with the orifices 369 in the upper wall of the valve chest I communicating with the upper chamber 362. It

is sometimes desirable, however, to allow some slight relative movement between the three sluice valves in order to ensure correct seating over the orifices in the upper wall, and Figure 16 shows a modified construction for effecting this. In this modification the screwthreaded shaft 358 connected to the handwheel 3B6 cooperates with a nut 31!] engaging with the first sluice valve 31!, which is connected to the second sluice valve 312 through a compression spring 314 and a pull rod 315, the valve 312 being in turn connected to the third sluice valve 313 by another compression spring 316 and pull rod 311. Thus on closing the valves, the third valve 313 seats itself first and tight engagement is ensured by the spring 316 as the second valve 312 seats itself, the spring 314 forcing the second valve into engagement whilst the first valve 31! is positively driven against its seating.

In the arrangement illustrated in Figures 13-16 the circuit-breaker is utilized for controlling the connection from a feeder circuit 383 to a threephase power transformer contained within an oil tank 38! mounted on wheels on the ground at one side of the circuit-breaker. The connections from the contacts in the upper chamber 362 to the power transformer windings are controlled by three insulated conductors 332 mounted in tubular structures 383 connected by flexible bellows 384 to a single valve chest 385 containing sluice valves arranged in the manner described with reference to Figure 15 or 16, the general arrangement of the insulated conductors 382 being similar to that above described for conductors cooperating with circuit-breakers with the exception that the conductors are arranged horizontally and are withdrawable into the tubular structures 383 and the transformer tank 33! to permit removal of the tank for inspection or overhaul after detaching the flexible bellows 384 from the valve chest 385.

In the foregoing arrangements the device for sealing the orifice in the busbar or other chamber after withdrawal of the insulated conductor has in each case been in the form of a sliding sluice valve. The sealing device may however be arranged in other ways, and Figures 17 and 18 show two alternative arrangements in each of which the sealing device is in the form of a plug which can be swung away from the orifice within the busbar chamber itself by suitable mechanism, whilst Figures 19 and 20 show a further alternative arrangement in which the sealing device is in the form of a plug which is detachably carried by the withdrawable conductor and remains in and seals the orifice when the conductor is withdrawn.

Figure 1'? also serves to show a convenient form of readily releasable joint between the flexible bellows and the busbar or other chamber (or the sluice valve chest) in place of bolts or like clamping devices. In this arrangement a flange 39! on the flexible bellows 39!! is mechanically forced into close contact with a sealing ring 40? on the wall of the busbar chamber 49! around the orifice 402 therein so as to seal the joint in an oil-tight manner. This is effected by means of an arm 392 which is pivoted to a lug 393 on the chamber wall and is pressed against the flange 39! by a toggle mechanism constituted by the levers 394, 395. Thus, when the toggle is broken by rotating the spindle 393 carrying the lever 395, the flange 39! will be moved clear of the chamber wall by the elasticity of the bellows 390 or by means of a separate spring,

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