US2009334A - Metal-clad electric switch gear - Google Patents

Description

July 23, 1935. A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Original Filed March 17, 1933 14 Sheets-Sheet l V WMW july 23, 1935. A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Original Filed March 1'7, 1933 14 Sheets-Sheet 2 NS C m x R m B .L E D A L C L A T M flsily 9 i935 Original Filed March 17, 1935 14,5heets-Sheet Q A i U July 23, 1935. A. ALLAN METAL GLAD ELECTRIC SWITCH'GEAR Original Filed March 17, 1933 14 Sheets-Sheet 4 5111111 23, 935, A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Original Filed March 1'7, 1933 14 Sheets-Sheet 5 lNVf/VTOF Fwy? aw MW July 23, 1935. A. ALLAN METAL CLAD ELECTRIC SWITCH GEAR Oriinal Filed March 17, 1933 14 Sheets-Sheet 6 A. ALLAN U .Ziy 523, 1935 METAL CLAD ELECTRIC SWITCH GEAR Original Filed March 1'7, 1933 14 Sheets-Sheet '7 Juiy 23, 1935 A. ALLAN METAL GLAD ELECTRIC SWITCH GEAR Original Filed March 17, 1953 14 Sheets-Sheet 8 INVEA/Ta A A. ALLAN METAL CLAD ELECTRIC SWITCH GEAR Original Filed March 17, 1933 14 Sheets-Sheet 9 July 23, 1935. ALLAN 2,009,334

METAL CLAD ELECTRIC SWITCH GEAR Original Filed March 17, 1933 14 Sheets-Sheet l0 July 23, 1935. A. ALLAN METAL CLAD ELECTRIC SWITCH GEAR Original Filed March 17, 1935 14 Sheets-Sheet l1 IIIIIIIIIIIIII/Ifllffl Illllllllllllllllfl July 23, 1935.

A. ALLAN 2,099,334

METAL GLAD ELECTRIC SWITCH GEAR Origihal Filed March 17, 1933 14 Sheets-Sheet l2 M F/azz.

July 23, 1935. A. ALLAN 2,009,334

METAL GLAD ELECTRIC SWITCH GEAR Original Filed March 17, 1933 14 Sheets-Sheet 13 insulating liquid, in which Patented July 23, 1935 UNITED STATES PATENT OFFICE 2,009,334 METAL-GLAD ELEo'rnio swrron GEAR Application March 17, 1933, Seerial No.

Renewed May 14, 1935. In Great Britain March 23 caims. (o1. 175 2os) This invention relates to metal clad electric switch-gear 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 a switchgear layout for an electric power station or substation to enable such apparatus to be more readily handled and overhauled.

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 project into the apparatus tank and 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, and fluid-pressure operated means foreffecting the longitudinal movements of the insulated conductor. Conveniently part of the insulated conductor moves within a tubular sleeve and constitutes a piston therein, means being provided for controlling the fluid'pressures on the two sides of the piston. The tubular sleeve within which the piston moves may conveniently be constituted wholly or in part by metal trunk connecting the busbar or like chamber and'the apparatus tank. Alternatively a cup leather 'or other sealing ring may be provided around the insulated conductor to constitute a fluid-tight partition between the spaces on either side of it, means being provided for controlling the fluid pressures on the two sides of the sealing ring so that the insulated conductor will be moved after the manner of a hydraulic ram. The insulated conductor is preferably immersed in oil or other case the insulating liquid may itself be utilized as the fluid-pressure medium, a pump being provided to transfer such liquid from one side of the piston or sealing ring to the other and thereby to effect movement of the insulated conductor.

Whilst the fluid pressure may be utilized to hold the insulated conductor in its operative position or in its isolating position, it will usually befpr ferable to employ a mechanically operated latch for this purpose. This latch may comprise a pivoted ring embracing the conductor and cooperating with a recess in a metal sheath surrounding the insulated conductor. In one convenient arrange ment the latching ring has two inwardly directed flanges on opposite sides of the conductor and can be rocked in either direction about its pivot by spring means so as to move one flange towards bar chamber, and consequently also in the cost of the whole installation, be effected by so arranging "the switch-gear to ensure that there will always be a body of insulating liquid between the busbar or other conductor and the metal walls of the chamber, even during movement of the insulated conductor and when the conductor has been withdrawn. 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 been withdrawn from the chamber. This also enables the tank containing the circuit-breaker or other apparatus to be removed from the switchgear for overhaul or repair without the necessity for draining the insulating liquid out of the busbar chamber. The insulated conductor is preferably so mounted that it can be withdrawn towards or into the apparatus tank so as to be removable therewith. 'Thus the insulated conductor when withdrawn may lie wholly within the apparatus tank or alternatively partly within the apparatus tank and partly within a metal trunk carried by the tank and normally connecting the tank to the busbar chamber. The insulated conductor in its operative position preferably directly connects two contacts permanently connected respectively to the busbar or like conductor and to a terminal of the apparatus, so that it constitutes the sole isolating member between the busbar or like conductorand the apparatus terminal.

In a duplicate busb-ar installation, the apparatus terminal be selectively connected to the two busbars by means of two similar movable insulated conductors respectively associated with two busbar chambers disposed side by side, or a single movable insulated conductor may be mounted to slide within a pivoted tubular structure which can be rocked from one position wherein the conductor can be moved to cooperate with one busbar into another position wherein theconductorcanbe moved to cooperate with the other busbar. Alternatively thetwobusbarchambers maybe mounted in line with the apparatus tank and may be connected together and to the tank by a tubular structure within which can move one or more insulated conductors for selectively connecting a terminal of the apparatus to the two busbars. Thus there may be two concentric insulated conductors independently movable within the tubular structure and in this case a single pump may control the movements of the two conductors, suitable latches being provided to determine which conductor will move when the pump is operated. Again a single insulated conductor withdrawable towards or into the apparatus tank for isolating purposes may cooperate with one or more movable contact-carrying insulators in the busbar chambers to effect selective connection of the busbars to the apparatus terminal, the movements'of such insulator or in sulators preferably being effected by fluid-pressure operated means.

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 Figure '1 is an elevation (with the circuit- -breaker 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. 7

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,

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

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,

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 lowvoltage arrangement, a

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

Figure 16 is a view similar to that ofFigure 15 showing a modified arrangement,

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

Figure 19 illustrates a further alternative form of sealing device,

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

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

Figure 22 shows an arrangement in which the insulated conductor is withdrawable into the busbar chamber for isolating purposes, I

Figure 23 illustrates a further alternative duplicate busbar arrangement, and

Figures 24 and 25 respectively illustrate modifications of the arrangement of Figure 23.

In the arrangement shown in Figures 1-6,

which is applicable to a simple installation in which the circuit-breaker controls a connection portion of the insulator.

from a busbar to a feeder or other circuit, the circuit-breaker oil tank 56 rests on the ground and two oil-filled chambers 68 and ID are mounted above the tank on supporting pillars or a suitable framework (not shown). The chamber 69 constitutes the busbar chamber and contains a contact 6i to'which the sections of the busbar 62 are directly connected.

The chamber iii is associated with the feeder circuit and contains a contact "ii carried by a supporting insulator 12. this contact 7! to the bottom wall of the cham ber '56 is a hollow insulator it which surrounds in an oil-tight-manner an orifice in the chamber wall, and a sealing end 74 ori the feeder-cable i5 is inserted through this orifice so as to make connection with a terminal within the top of the insulator E3 connected through the insulator to the main feeder contact ii. The cable sealing end T4 carries a flange 16 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 M and the hollow insulator l3 and this compartment may be filled with oil from the chamber 10 Extending down from i ing contact member 53 is operated by suitable mechanism, indicated at 55, carried by the cover plate of the oil tank 5% containing the circult-breaker.

Extending upwardly at a small'angle to the vertical from each of the fixed main contacts El, 52 of the circuit-breaker is a hollow condenser insulator .39, comprising short overlapping conducting layers 8! interleaved with in-' sulatinglayers and surrounded in its upper portion by a metal sleeve 82,; which projects through an orifice in the 'cover plate 55 of the tank and is provided with a flange 83 bolted'to the cover plate. The lower end of each hollow insulator 89 is closed in an oil-tight manner by a metal cap B l connected to -*the main fixed circuitbreaker contact. 55 or 52, and a metal tube extendsfup from this cap as within thelower At the upper end of each insulator the surrounding metal sleeve 82 carries a flange 86, to which is bolted a metal casing 98 including a cylindrical metal trunk '9i surrounded by an annular chamber 92 in which current transformers can be located. Around the upper end of the metal trunkt i is r a flexible metal bellows 93, which is attached to the top of the casing 98 and can be clamped to the, bottom of a valve chest mounted below 'the appropriate oil-filled chamber 6% or '58, a

metal shield 94 being provided around the bellows 93 to protect it fromdamage. The busbar contact 6! or the feeder contact 1 i, as the case may be, is in line with the aXesof the metal trunk ti and the hollow insulator 853, and communication between the chamber 50 or it and the tubular compartment formed by the trunk and the insulator can be out off by means of a valve in the valve chest in later. V I

Mounted to slide longitudinally in't'his tubular compartment is an insulated conductor I09, which serves when in connect the busbar contact BI or the feeder contact 7! to the inner metal tube 85 in the insulator 88 and thence to the main circuitbreaker contact 5I or 52. This insulated conductor comprises a rigid-central tube iiEI surrounded by insulation i112, 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 vI03, which engages with the metal trunk 8|. The central tube I! serves to contain flexible connections" :04 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 I95 engaging with the metal tube 85 and carried in a metal block ms to which the lower ends of the flexible leads I34 are connected. The upper contacts consist of a bundle of butt contacts l0! independently spring-pressed in a longitudinal direction so as together to constitute a self-aligning butt contact for engagement with'the busbar contact i or the feeder contact II.

The 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 82 and the insulator 80. In Figure 1 the con ductor associated with the feeder is indicated in its raised operating position, whilst that associated 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 eilected hydraulically by varying the oil pressure above and below the conductor, the metal sheath I83 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 9|. For this purpose an oil pump I I0 driven byan electric motor III is mounted on the casing 99 and is connected by suitable ducts H2, H3 to the upper and lower ends of the tubular compartment in which the withdrawable conductor moves. The upper duct H2 opens into the transformer chamber 92 and is thus connected through the interior of the metal bellows 93 to the open upper end of the metal trunk SI, The lower duct H3 opens into the lower part of the casing SIlbeneath the transformer chamber and is thus connected through openings in the flange 86 to the interior of the insulator 80, 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'8fi. Thus to raise the conductor the pump H0 is started up to withdraw oil from the upper end of the trunk BI and to drive it into the interior of the insulator 80. 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 thetwo 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 mov ing in the cylinder formed by the metal trunk SI the upper and lower parts of the tubular compartment may be separated from one another a mariner to be described its operative position to bar chamber 53 or t by a cupleather 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 the oil 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 I23 surrounding the insulated conductor and pivoted about a vertical pin I2I at the lower end of the casing 93 at one side, the ring having two internal flanges I22 and I23 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 lowerv contacts I05 similarly engages with a shoulder 85 at the lower end of the metal tube 85 within the insulator 80 for positioning the upper groove I24 correctly when the conductor is in the isolating position. The latch ring I28 is moved to one side or the other about its pivot I2I by a pair of spring crank arms I39 on a horizontal shaft I3I suitably mounted outside the metal sleeve 82. The shaft !SI is r0- tated by an operating arm I32 movable between fixed stops I33, I34 under the control of an operating rod 235 (see Figures 1 and 2). Thus with the conductor held in its raised position (as indicated on the right-hand side of Fig. l) 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 5 ring arms I32 to release the flange I23 from the groove I25 and will hold the upper latch flange I 22 spring-pressed against the surface ofthe metal sheath E33, that when the conductor reaches its isolating position (as indicated on the lefthand side of Figure l) 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 also utilized to operate through levers we a number of auxiliary switches I3! housed in a box I38 on the casing 99 for indicating or interlocking purposes. The shaft of the auxiliary switches may also operate an indicator visible through a window I39 on the box I33 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 II I for riving the pumps, the energizing circuits for the pump motors being taken through certain of the auxiliary switches I32 controlled by the latch, the arrangement being such that a pump motor cannot be energized until the corresponding latch hasbeen released.

As has been mentioned, a valve is provided for sealing the orifice at the bottom of the buse feeder chamber l9 when the insulated conductor has been withdrawn. A preferred construction for this valve is indicated in Figures 1 and 2 and shown in detail in Figures 3 and 4. In this arrangement the valve is mounted in a valve chest I UTand is in theform of a sluice valve Ml, which is caused to slide over the orifice by rotation ofa screwthreaded shaft l izpby means of a handwheel M3. The valve shaft it? carries a notched disc Hi l, with which an arm ME carried by a spindle M5 cooperates. This spindle M6 is connectedto part of the control mechanism for actuating the associated latch-operating rod i351, the arrangement being such that when the control mechanism is operated to cause'the insulated conductor to be raised, the spindle M6 is rotated to cause the arm M5 to engage in a notch on the disc i 54 and thus to prevent the handwheel M3 from being rotated to close the valve. Since the arm I45 may not always be opposite a notch in the disc M4, the spindle is made of sulficient flexibility to permit it to twist when operated, so that after a slight rotation of the handwheel, the arm Hi5 will spring into the first notch on the disc and will, thus lock the handwheel against further rotation. In order to, prevent energization of the pump motor l I l to raise the insulated conductor when the sluice valve is. closed, the energizing circuit to the pump motor is controlled by an auxiliary switchoperated by the sluice valve. For this purpose ries a worm iil for operating a rotary auxiliary switch hi8 housed in a casing M9 carried by the valve chest.

At one side of the valve chest E li), aby-pass valve is provided in the form of a rotary tapered plug E56 having two holes EM, @522 bored in it. One of these holes liil cooperates with two passages (one of which is indicated at i533) in the valvechest communicating respectively with the spaces above and below the valve. itself. The second hole I52 controlsa connection from the space belov. the valve to the atmosphere. In the normal position of the plug E58 both holes are closed, but by rotating the plug into one position it is possible to complete a by-pass connection through the hole lhl from one side of the valve to the other and at the same time a further connection from the space below the valve to the atmosphere. This allows the interior of the bellows $3 to be filled with oil from they upper chamber, when the bellows is again connected thereto after having been disconnected for removal of the'circuit-breaker, without permitting entry of air into the upper chamber. The plug Hill can also be rotated into a further position in which the by-pass connection is closed, but the connection of the space below the valve to the atmosphere through the hole id? is open. This position isutilized to permit air to enter the interior of the bellows 93, when oil is being drained therefrom by a suitable draincocl: not shown) prior to disconnection of the bellows from the upper chamber. In the body of the sluice valve Ml itself two small non-return valves J55, 556 are provided which act in opposite di- 'rections.

The valve i555 is arranged to open when the pressure 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 i525 likewise allows oil to flow out from the bellows into the upper chamber in the event of excessive pressure being setup within the bellows owing to expansion of the oil therein due, to temperature changes.

The above arrangement may be modified in various ways. Thus for instance the hollow inthe valve shaft Hi2 car sulator 8B in the circuit-breaker'tank may be taken right past the circuit-breaker fixed con tact and'may be of such a length as to permit the whole of the withdrawable conductor to lie within 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 could be effected hydraulically by raising the pressure in the gas space in the tank itself, so that oilfrom the tank is forced up within the hollow insulator to drive the conductor in front of it.

The foregoing arrangement has been described and illustrated as applied to a circuit-breaker controlling a simple connection from a busbar to a feeder circuit, but it is equally applicable to the case of a duplicate busbar. layout wherein each busbar is connected to the feeder or other circuit 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 Hit of the conductor connects the circuit-breaker contact through the tube to the earthed metal trunk 9i, and even if the metal sheath were shortened to avoid such a direct earth connection, the inclusion of metal layers in the insulation around the conductor would in many instances reduce the dielectric value of the insulation between the circuitbreaker contact and the earthed metal trunk to too low a value. vIn cases therefore where the circuit-breaker contact may be alive from another circuit and where it is desirable .to employ condenser insulation around the conductor, it is preferable to modify the construction of the insulated conductor to avoid risk of flash-overfrom the main 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 provided with busbar selecting means controls the connections from 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 contains a contact connected to the feeder or other circuit. The three contacts in the upper chambers are connected to 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 conductor associated with the feeder contact. i

Figure 7 shows the two busbar chambers I'll] and H5 respectively containing contacts Ill and H6 connected to the two busbars l'lE'and Ill;

to enable the whole arrangement to be understood.

Mounted one on either side of the circuitbreaker contact I8I are two hollowinsulators I98, each surrounded at its upper portion by a metal sleeve I QI carrying a flange I92 bolted to the cover plate I82 of the tank. Each insulator extends down past the circuit-breaker contact i8I and a connection from this contact "passes through the wall of the'insulator to an internal ring contact I53. The insulator is closed at its lower end a inetal'cap E94, carrying a short internal tube I95; and to grade the stresses set up the insulation is in the form oi condenser insulation with suitably arranged overlapping short metal layers I96 interleaved with the'insulating layers. The flange 92 at the upper end of the metal sleeve I9I carries a metal tube E91 extending from within the top of the insulator I99 upwardly and having atitsupper end a flange I98, to which is bolted a casing 286 containing a cylindrical metal trunk 20I surrounded by a' current transformer chamber 202, the metal trunk constituting a continuation of themetal tube I91. The casing 250 and the parts carried thereby (including the motor-driven pump and the latch device) are substantially identical with the corresponding parts of the'arrangement of Figures Le. A valve chest 205 containing a sluice valve is mounted beneath the busbar chamber as in the previous arrangement and is similarly 'con nest-ed to the top of thecas'ing 253 by a flexible metal bellows 206.

Mounted to slide longitudinally in the tubular compartment constituted by the metal trunk?!) l, the m tal tube I97 and the hollow insulator i flfl, is an insulated conductor, which serves when in its operative position to connect the busbar contact Ill or I76 to thering contact I93 and thus to the main circuit-breaker contact i8I. This insulated conductor comprises a rigid central tube 2h? containing flexible leads connecting upperbutt contacts H I andlower spring contacts in a manner similar to that described with reference to Figures 1-6. The central tube 2!!! is surrounded by layers of paper insulation 213 interleaved with overlappingshort'rnetal layers 22M, and the upper par't'of the condenser insulation is enclosed Within a metal sheath 2I 5. Spring contacts 2. 6 are provided on one of the intermediate metal layers approximately.rnid way between the lower end'o'f the conductora'nd the lower end of the sheath 2I5f' The metal sheath 2.! carries piston rings 2'Il' sliding in the cylindrical metal trunk 29] and is provided with upper lower grooves 2i 8, 2I9 coacting with the device in the casing 290 in a manner similar tothat' described for' the arrangement of Since the metal sheath 2l5 slides within the metal trunkilil! it always remains in contact with cai'thed metal. "When the insulated conductor in its operative position with its upper butt contacts 2H engaging with the busbar contact and its lower spring contacts 2I2 engaging'with the ring contact 'I93 connected to thecir'cuitbreaker contact, the contacts 215 on the intermediate metal layer are earthed through the metal tube it)? (as indicated on the-righthan'd side of the drawing), whilst whenthe insulated conductor is in its isolating position (as shown on the left-hand side) the intermediate contact HIE engagesrwiththe ring ci'ontacti 93 the centralconductorsare ea thed' through the short tube I95 on thefbo'ttorncap IM' on the hollow insulator I90, Thus in the isolating position the intermediate contact ZiIimay be alive, owing to the connection of the circuit-breaker contact I8I to the other bu'sbar, but is located between two eartliedpoints from which it is separated by condenserinsulatiom with the circuit-breaker in operation connecting the feeder to, say, the busbar -I 11, the insu'lated conductors associated with the feeder and withthis busbar will 'both' be iii-their raised operative positions, whilst the insulated conductor'associated"with the busbar H2 is in its isolating position; If new it is desired to change over to "the busbar N2, the main circuit-breaker contacts arec-pened, and the insulated conductor for the busbar I'll is lowered by operation of its pump and latch device, the insulated conductor for the busbar 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 !!2, so that the two busbars are connected together and to the feeder, and'then lowering the conductor for the busbar Il'I. 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 circuitoreaker, is then uncoupled, so that the circuitbreaker with the insulated conductors inside it can be removed laterally without the necessity of lowering it.

Instead of employing two separate tubes I91 and 2B in line with one another, the cylindrical metal trunkfZilI may itself be'extended downwardly to beyond the cover plate I82 of the tank, the metal sleeve-I 9i and the hollow insulator I 90 then extending right up to the flange '98 with the metal trunk 20I within the insulator. This modification-is shown inFigure 8, which also shows a modified arrangement of the insulated conductor; In other respects the arrangement of Figure 8 is-shnilar to that of Figure '7 and the same reference letters are employed. The insulated conductor employed in the arrangement of Figure 8 has a centraltube '2I fl with the internal leads connecting the uppenand lower contacts "2 I i, 2I2and also a metal sheath 2I5 with its piston rings 2|"! and" grooves H8, 249, as in the arrangement of Figure 7, but it differs from that arrangement in the form of the condenser insulation. In the arrangement of Figure 7 the overlapping short metal layers 2M in the lower part of the insulation extend from close'to the central tube 2IIJ' at the lower end'of the'conductor at steadily increasing radii'right up to the lower end of the metal'sheath 2I5, the spring contacts 2H3 being connected to a layer at an intermediate radius, In the arrangement of Figure -8, however, overlapping short metal layers 220 extend from close to the central tube 2 l O at thelower end of the conductor to a layer 22 I at the full radius or the metal sheath 2I5 but at a position in-the length of the conductor corresponding to that of the spring contacts ZIG in the arrangement of Figure 7. This layer 22I is connected through theinsuiation' to s ring contacts 222. A further series ofoverlapping short m'etal'layers 223 extends from close'to the central tube'2l0 directly 6 within thelayer 225 up to the lower end of the metal sheath 2i5. 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 2-55 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 rnetal trunk at all stages in the movementof the insulated conductor.

In the arrangements shown in Figures 1-8 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 oilfilled type or" insulating bushing around the conarrangements.

ductor. 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 withdrawable insulated conductor shown in Figure?) comprises "a rigid central tube 23d, which may itself constitute the conductor or may enclose flexible leads in the manner above described, an upper butt contact 2% and lower spring contacts being provided. A number of concentric insulatingtubesfitfi of graded lengths surround the central tube 2353 within an outer insulating sleeve"23 i, the intervening spaces being filled with oil, so that the conductor surrounded by a series of more or less uniformly thick layers of oil alternating with solid insulating layers.

The outer sleeve 236 carries a metal sheath 235 Fan provided with piston rings are and upper and lower latch grooves 23?, 238 as in the previous On lower voltage installationsit 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 contactto 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 1-8. Figure 16 illustrates only the parts of the arrangement associated with the busbar side of the circuit-breaker.

In the arrangement of Figure 10, the' two busbar chambers 25l are mounted ciose together above the circuit-breaker tank, and each is provided beneath an orifice in its bottom wall with a valve chest 1255 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. 23E} of oval cross-section carried by the cover plate of the circuit-breaker oil tank, and is connected through the bottom of the insulator to a curved contact member 26E. Extending up from the coverplate 2235 towards the two busbar chambers is'a metal casing 2% of generally oval cross-section, to' the upper end of which is at V tached a flexible metal bellows 2?! which can be clamped to a suitable oval fitting 25% carried beneath thetwo valve cheststiie. This-casing carries a hollow horizontal shaft Hi2 about which is pivoted an inner metal casing 288 carrying at its upper end a cylindrical metal tube Edi and at its lower end a metal sheatn 232. for a condenser insulator 233. This insulator is closed at its lower end by a metal cap 285% having a projection 2B5 engaging with the curved contact member 26! and a metal tube 235 extends up from the cap 28 for a suitable distance withinthe insulator 283. The curvature of the contact member 262 is such that the projection 285 remains in engagement therewith when the casing 23% rocks about its pivot, and the metal tube 283 is thus permanently connected to the fixed circuit-breaker contact. The metal tubes 28% and 2% are another and the metal casing 285? can be swung about the shaft 2712 by suitable means (not shown) between two positions in which the axis of the tubular structure 2% i, 285 is in line respectively with the busbar contacts in the two busbar chambers 22 19 and 2%. An insulated conductor 2% generally similar in construction to those employed'in the arrangement of Figures 1-6, has its metal sheath 2st provided with piston rings 2: 32 sliding within the metal tube i, so that its lower spring contacts 293 always engage with the metal tube 285 whilst its upper butt contacts 296 can engage with either busbar contact. Th metal sheath 2% has upper and lo- wergrooves 295, 298 cooperating with a latch device Zdl operated by a latch-operating rodEQS outside the'casing 2W through a universal coupling 295, The conductor is raised and lowered hydraulically within the surrounding tubular structure by means of a motor-driven pump 2% carried by the casing Z'lii one side of the pump communicating directly with the interior of'the casing 2w through a duct 21d, whilst the other side communicates with the interior of'the pivoted inner casing 2% through a pipe 2'55 coupled to the hollow shaft 2'52. Thus tochange over from one busbar to another the circuit-breaker contacts are first opened and the insulated conductor is withdrawn into the tubular structure 28%, 28%, 7 after which the inner casing 285 is rocked about its pivot to the other position and the conductor is raised again into engagement with the other busbar, the circuitbreaker contacts then being 'reclosed. The cir= cuit-breaker can be removed for inspection or repair, when the insulated conductor has been withdrawn by detaching the flexible bellows 2'55 from the busbar chambers.

Figures 11 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 see are mounted one behind the other on a wheeled truck 3M. Each circuit breaker has two fixed main contacts 3%32 cooperating with a movable main contact 383 and four sets of arcing con,- tacts 306 are provided with one set on each side of each fixed main contact. Extending vertically upwards from each circuit-breaker fixed main contact 382 is a tubular structure containing a withdrawable conductor, the six tubular struc-' in line with one

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