US1860918A - Electric switch gear - Google Patents

Description

y 1932- A. ALLAN ET AL ELECTRIC SWITCH GEAR Filed July 20,

1951 3 Sheets-Sheet l M via/rams I 2 5 v I M m a y 1932- A. ALLAN ET AL ELECTRIC SWITCH GEAR Filed July 20.. 1951 v k l itl 90nd!!! a 4 W y 31, 1932- A. ALLAN 'ET AL 8 ELECTRTC SWITCH GEAR Filed July 20,. 1951 s Sheets-Sheet s mwwz Patented May 31, 1932 ARCHIBALD ALLAN, OF'TYNEMOUTH, AND JOHN CHRESTIE, F SUNDERLAND, ENGLAND,

ASSIG-NORS TO A.

REYROLLE COIEI ANY LIMITED, OF T-IEBBUBN-ON-TYNE,

ENGLAND, A REGISPEB-EDICOMPANY OF GREAT BRITAIN ELECTRIC SYVITCH' GEAR Application filedd'uly 20,1931, Serial No. 552 010, and in This invention'relates to electric switchgear of the inetaleclad type, and has for its primary object to provide a satisfactory control for the connection from a bus-bar to one of the main contacts ofa circuit-breaker or to a termiualof other apparatus.

In such arrangement-it is common practice to. provide anisolating switch between the husbar. and the circuitebreaker, and a more detailedzobiect of the invention is so to arran ge the-connection from the busbar to the circuit-breaker or other apparatus as to providezfor isolation. at at' least two points when the isolating switch is open.

To this endthe connection preferably includes a withdrawable insulated conductor mechanically interconnected with the isolating switch; A further object is so to arrange the interconnection between the withdrawable conductor and the isolating switch as to reduce risk of flash-over from the busbar to the earthed' metal: casing of the isolating switch chamber.

lVit-hmetahclad circuit-breakers or other apparatus dealing with high voltages, provision has often to be made for the entrance and sealing of a cable, and in many. cases, for example when the circuit-breaker or apparatus is oil-immersed, aseparate chamber has to be provided for the cable end. Another object of the invention'is to provide a satisfactory cable sealing arrangement for such apparatus; avoiding the use of separate ca ile sealing chamberbut yet ensuring that the oil in the circuit-breaker or other appara tus shall not have access to the cable end.

Further objects of the invention will be apparentfrom the appended claims and from the following description of the accompanying drawings, which illustrate a preferred arrangement according to the invention as applied to switchgear for connecting a feeder cable to a busbar through an oil-immersed circuit-breaker. In these drawings,

Figure 1 is a side elevation partly insection of the ireterred arrangement,

Figure 2 is a sectional side elevation on an enlarged scale of part of the arrangement, certain details being slightly modified,

Figure 3 is an end elevation of the busbar :2. August 5, 1930.

chamber and the associated mechanism, and

Figure at is a sectional side elevation on an enlarged scale of a modified form of part of the arrangement.

In Figure 1 a main circuit-breaker having a tank Qi is a tached by the cover A of the tank to a supporting frame B so that the bottom of the tank is a short distance above the floor. One fixed contact C of the circuitbreaker is mounted on the underside of a cup D of conducting material which is attached to the lower end of a hollow insulator E secured at its upper end by a flanged sleeve F round an opening A in the tank cover A The cup D is fixed to the end of the insulator E by a ring G so that the insulator supports the fined contact C and the cup forms an end cap for the insulator, suitable oil-tight packing indicated at G being provided which prevents oil leakage between the inside of the insulator and the main body of the tank. T he inside of the cup D is provided with an upwardly projecting pin or plug D which is adapted to engage a conductor within the insulator as will be more fully described hereafter.

The other fixed contact C of the circuitbreaker is mounted on the end cap D of a hollow insulator E similar to the insulator E, the upper end of which is secured by a flanged sleeve F round an opening A in the cover A The contacts C and C are adapted to be connected, when the circuit-breaker is closed, by a movable bridging piece H carried on an operating rod H connected to any suitable form of operating mechanism.

The busbar J terminates in an oil-filled busbar chamber K mounted on a suitable framework (not shown) above the circuitbreaker cover A so that apertures K K in the top and bottom of the chamber are in line with the pening A in the tank cover A A tubular casing L of insulating material such as porcelain or impregnated papereXten ds through the busbar chamber K and is secured at its ends round the apertures K K in the chamber by clamping rings L and L". The lower end of the tubular casing L is connected to the opening 1 2 in the cover A leading to the hollow insulator E, with which the casing is in line, by means of a flexible sleeve M of corrugated metal having a flange at one end which is bolted to the bottom of the chamber K round the aperture K and a flange at the other end which is bolted to the cover A round the opening A The interiors of the tubular casing and the hollow insulator are thus effectively isolated from the main circuitbreaker tank and also from the busbar chamber thus providing a space independent of the chamber and of the tank which can be filled with oil-or may contain air or any other suitable insulating medium.

The casing L is provided with an internal contact N preferably arranged approximately midway between its ends, connected by a stud N to an external contact N suitable oiltight packing being provided round the stud N to prevent oil leakage between the chamber and the inside of the casing. The external contact N has pivoted to it the blade 0 of an isolating switch by means of which this contact and thus the internal contact N can be connected either to the busbar J or to an earthing contact 0 mounted on the wall of the chamber K. The blade 0 of the isolating switch is operated through a link 0 of suitable insulating material by a crank O mounted on an operating shaft 0 arranged to pass through the chamber K near an opening K in the top thereof, this opening being provided with an oil-tight cover K.

The internal contact N in the casing L is adapted to be connected to the fixed contact C of the circuit-breaker by a conductor P provided with an insulator P which may be of the condenser bushing or any other suitable type. The insulated conductor P is arranged in the casing so that it can be moved in the direction of its length by means of a pinion R mounted within the sleeve M and cooperating with a rack R on the insulator P The conductor P is provided at its lower end with spring-linger contacts P which, with the conductor in the lower position in which it is shown, engage the pin D on the inside of the cap I). The upper end of the conductor P is provided with spring contacts P which in the position shown engage the internal contact N. The conductor P thus forms a connection between the fixed contact C of the circuit-breaker and the isolating switch blade 0.

The casing L is provided with a metal cap or cover L which is electrically connected to the wall of the busbar chamber K or to any other suitable earthed point. The inside of the cap is so shaped that when the insulated conductor P is raised to its upper position the spring contacts P engage the inside of the cap thus earthing the conductor. The cap L is conveniently provided with a window L through which this earthed position of the conductor is visible and through which the level of oil in the tubular casing, if that casing is oil-filled, can be seen.

Simultaneous movement of the switch blade 0 to isolate the busbar J and of the insulated conductor P to disconnect this conductor from the fixed contact O of circuitbreaker and raise it until it is earthed by the engagement of the spring contacts at its upper end with the inside of the cap on the tubular casing is effected by arranging the operating mechanism so that the operating shaft 0 of the switch blade 0 also actuates the pinion R In the preferred form of this operating mechanism as shown in Figures 2 and 3, the pinion R is keyed to a shaft R which passes through an oil-tight gland M in the flange at the upper end of the sleeve M and is supported in a bearing K indicated diagrammatically in Figure 8, carried on the outside of the chamber K. A second pinion R also keyed to the shaft R engages a toothed quadrant R pivoted on a fixed pin K mounted on the outside of chamber K. A link R is pivoted at one end to the quadrant R and at the other end to a crank R on the operating shaft 0 of the isolating switch so that movement of this shaft causes rotation of the quadrant R and thus, through the pinion R the shaft R the pinion R and the rack R, longitudinal movement of the insulated conductor P.

The operating mechanism for moving the switch blade and the conductor is such that rotation of the shaft 0 through approximately a quarter of a revolution to move the switch blade 0 to the postion shown in dotted lines, in which it engages the earthing contact O raises the conductor P from the position shown to a position in which the contacts at its upper end engage the inside of the earthed metal cap of the casing.

\Vhen the insulated conductor P is surrounded by an insulator of the condenser bushing type, as is indicated diagrammatically by the insulator P in Figure 2, it is desirable to avoid the simultaneous movements of the switch blade and the conductor being such that when the blade is partly opened a comparatively short flash-over path is provided from the busbar J across the partly open isolating switch contacts, the internal contact of the casing to one or more of the outer conducting layers of the bushing insulator and thence to the earthed metal bottom of the chamber K or the cover A of the circuit-breaker.

This is prevented in the preferred arrangement shown in Figures 2 and 3 by so positioning the cranks O and R on the shaft 0 that during the first part of the isolating movement of this shaft the switch blade 0 is moved comparatively rapidly and the con ductor P is moved slowly whilst during the final movement of the shaft 0 the switch blade moves slowly and the conductor rapidly.. The switch blade can thus be opened sufiiciently to prevent a flash-over before the conducting layers on the condenser bushing enter the danger zone.

A counterweight mounted on an endless belt or chain driven from the shaft R is preferably provided to balance the weight of the insulated conductor P.

The other fixed contact C of the circuit breaker is also provided with an insulated conductor P similar to the conductor P, which is capable of moving longitudinally within thehollow insulator E and a tubular casing L extending through an oil-filled chamber S mounted above the cover A of the circuit-breaker. The lower end of the casing L is connected to the cover A by a flexible sleeve M similar to the sleeve M.

The upper end of the conductor P is pro vided with spring contacts P adapted to engage an internal contact N in the casing if or with the inside of a cap L on this casing in accordance with the postion of the con ductor The contact N is connected to an external contact N carrying an isolating switch blade 0 operated through a link 0 by a crank O mounted on a. shaft 0 The conductor P is moved by means of a pinion (not shown) housed within the sleeve M and engaging a rack R on the insulator P surrounding the conductor P". If desired ope"- ating mechanism, similar to that desc 'b d above for the switch blade O and conductor P may be pro ided for operating switch blade 0 and conductor P from the shaft O In the position in which the apparatus is shown in Figure l the busbar J is connected through the switch blade 0, contacts N and N and the insulated conductor P to the fixed contact C of the circuit-breaker, whilst the blade 0 of the isolating switch in the chamber S engages an earthing contact S and the insulated conductor P is raised so that its up per contact P is earthed y engagement i th the inside of the cap L and its lower contact P only projects a short distance into the circuit-breaker tank A A tubular casing L similar to the ca sing L is provided in the chamber S for sealing the end of the cable T which is to be connected to the fixed contact C of the circuit breakcr. The casing L is secured at its ends round vertically aligned apertures S and S in the chamber S and the cable T is passed up through the aperture S The lead sheath of hecable is sweated into a gland S of the usual type attached to the bottom of the chamber S round the opening S and the upper end T of the conductor of the cable is connected to an internal contact U in the tubular casing L The internal contact U is connected to an external contact U by means of a stud U this external contact carrying an isolating switch contact U which is adapted to be engaged by the blade 0 of the isolating switch to connect the cable to the fixed contact C Thus the cable can be directly connected through the blade 0 of the switch and the insulated conductor P to the fixed contact C of the circuit-breaker. The top of the casing L is closed by a cap or cover S, which projects above the chamber S and, in the case of an oil-filled cable, provides an expansion chamber for the cable oil. An inspection window S is provided in the cap S through which the level of oil in the casing L can be viewed.

Since the insulated conductors P and P can be raised so that their lower ends are approximately level with the tank cover, this construction permits the removal of the circuit-breaker and its tank without any considerable lowering of the tank as soon as the flexible sleeves M and M are detached from the cover A The main switch tank can thus be arranged so that it is only a short distance above the ground level. If desired however the lengths of the insulated conductors and tubular casings within which they move can be so adjusted that the conductors can be moved to bring their lower ends above the level of the cover in which case the tank can be mounted on wheels or a trolley and can then be wheeled away horizontally as soon as the conductors are raised and the flexible sleeves detached. If the circuit-breaker is mounted on a framework which permits lowering of the circuit-breaker unit it is only necessary to raise the conductor P to isolate the busbar and to open the isolating switch on the cable side of the conductor, without raising the conductor P before lowering the circuit-breaker.

It will be appreciated that when the circuitbreaker and its tank is to be removed it is only necessary to run out the oil from the tubular casings L and L, providing these casings are filled with oil, before detaching the sleeves M and M and that therefore re moval of the circuit-breaker for inspection or repairs does not necessitate removal of the oil from the comparatively large busbar chamber and other metal-clad gear directly connected thereto. Although the tubular casings, flexible sleeves and hollow insulators may he oil-filled this is not necessarily the case and, for instance the tubular casings and flexible sleeves may contain air and only the portions thereof which are within the circuitbreaker tank, i. e. the hollow insulators E, E may contain oil. in such cases the oil may be arranged to flow in from the main body of the circuit-breaker tank through an opening in the bottom of each hollow insulator.

In order to control the electrical stress within the tubular casings these casings may be provided with condenser insulators or may be formed as condenser insulators, the layers of foil or conducting material being incorporated therein in a well known way. A preferred form of tubular casing composed of two insulating tubes L and L having condenser layers L and L is shown in Figure 2, the abutting ends of these tubes being connected by oil-tight joints to an annular ring N having flanges N which form the internal contact of the casing. The ring N carries a lug N on which the isolating switch blade is pivoted.

Although the spring contacts at the upper end of the insulated conductors which are shown in Figure 1 are suitable for low values of current contacts of this type tend to reduce their pressure when heavy currents are flowing. Accordingly the preferred form of contacts as shown in Figure 2 make use of a current loop which is so shaped that the elec tromagnetic forces induced by the current flowing tends to increase the contact pressure.

In this preferred form of contact, blocks V are carried on the ends of U-shaped flexible copper connecting straps V fixed at their other ends to a ring V on the end of the conductor P. Each block is normally retained in position by a steel spring V fixed at one end to the ring V and.provided at the other end with a hole through which a stud V on the back of the block freely passes. The block has thus limited movement which enables it readily to engage the internal contact in the tubular casing or the inner surface of the cap at the top of the casing. As the current flows from the conductor P to the internal contact mainly through the connecting strap V it flows in the direction of the arrow V thus setting up an electromagnetic force which will tend to straighten the strap and thus to force the block V against the internal contact. The springs V are arranged to be sufficiently strong to ensure good contact pressurefor low values of current.

Figure 4 shows a modified cable sealing arrangement in which the reference letters used in Figure 1 are employed for similar parts. In this modification accommodation for a current transformer X surrounding the cable T is provided by an extension S of the chamber S. To permit the transformer X to be inserted and removed from the top of the chamber S without disturbing the tubular casing or the oil therein, the openings S S are made large enough to allow the transformer to pass through them and are provided with cover plates X X The cable gland S is attached to the bottom of the extension S and in order to isolate the cable from the main part of this extension, an annular disc X carrying an upwardly projecting tube X through which the cable passes, is clamped between the extension S and the cable gland S The upper end of the tube X is secured to the lower end of the tubular casing by an oil-tight joint.

The tubular casing in this figure is shown as divided into two parts L L connected by oil-tight joints to a conducting ring U, the inside of which constitutes the internal contact connected to the bared end T of the cable and the outside the external contact carrying the isolating switch contact (not shown). The tubular casing may be formed as a con denser insulator similar to the tubular casing L L of Figure 2, if desired.

To control the electric stress where the earthed lead sheath of the cable terminates within the tubular casing L, a condenser insulator Y is provided, which extends from the end of the sheath to the point where the insulation is bared to expose the cable conductor T Such condenser insulator is preferably of the kind having two groups of conducting layers in series, as shown.

It will be appreciated that the above description is by way of example only and that many structural modifications may be made within the scope of the invention. For example the insulated conductors may be moved by any convenient mechanism such as linkage or screw gear other than the rack and pinion mechanism specifically described, such mechanism being coupled to the control handle or the like for the isolating switch in any suitable manner so that the switch and conductor are moved simultaneously.

that we claim as our invention and desire to secure by Letters Patent is 1. In metal-clad electric switchgear, the combination of a busbar, a chamber for the busbar, an electric apparatus forming part of the switchgear, a tank containing such apparatus, a tubular casing passing through the busbar chamber, an insulated conductor movably mounted within the tubular casing and normally projecting into the apparatus tank to make connection with the apparatus, an isolating switch in the busbar chamber controlling a connection from the busbar to the insulated conductor, and means for eifecting simultaneous movement of the insulated conductor and the isolating switch whereby the apparatus can be isolated from the busbar at at least two points.

2. In metal-clad oil-immersed electric switchgear, the combination of a busbar, an oil-tank, a circuit-breaker having its main contactsimmersed in oil in the tank, a chamber for the busbar, a tubular casing of insulating material passing through the busbar chamber, an insulated conductor so mounted within the tubular casing that it can be moved to project into the circuit-breaker tank and make connection with a main circuit-breaker contact or can be withdrawn from the tank, an isolating switch in the busbar chamber controlling a connection from the busbar to the insulated conductor, and means for simultaneously opening the isolating switch and withdrawing the insulated conductor.

3. In metal-clad oil-immersed electric switchgear, the combination of a busbar, an

electric apparatus forming part ofthe switchgear; an oil-tank containing such apparatus, an 'oilfilled chamber for the busbar, a tubular casing passing'throu'gh the busbar chamber and formed of insulating material interleaved with conducting layers so as to constitute a condenser insulator, an insulated contactor so mounted within the tubular casing that it-canbe moved to'project into the apparatus tank to make connection with'the apparatus or can be withdrawn therefrom, an isolating switch in the busbar chamber controlling a connection from the busbar to the insulated conductor, and-means for simultaneously Opening the isolating switch and Withdrawing the insulated conductor.

4Q- In metal-clad electric switchgear, the combination of a busbar, a circuitbreaker, a tank containing the main circuit-breaker contacts, a chamber for the busbar, atubular easing passing-through the busbar chamber, an'insul'ated conductor so mounted within thetub-ular casing that it can be moved to project into the circuit-breaker tank to make connection with one circuit-breaker contact or can be-withdrawn therefrom, an isolating switch inthe busbarchamber controlling the connection betweenthe busbar and the insulatedconductor, and operating mechanism for simultaneously opening the isolating switch and-withdrawing"the insulated concluctor,-such operatingmechanism being so arranged'that the isolatingswitch moves rapidly during itsinitial opening movement and slowly during its finalopening movement whilst the insulated conductor moves slowly during its initial withdrawing movement and rapidly during its final withdrawing movemen't.

5. In metal-clad electric switchgear, the combination of abusbar, a'chamber for the busbar, an electric" apparatus forming part ofthe'switchgear, a tank containingsuch apparatus, a tubular casing of insulating materialpa'ssingthrough the busbar chamber, a con'ductor normallyprojecting into the apparatus tank to make connection with the apparatus, a condenser insulating bushing around such conductor somoun'ted within the tubularcasingjt'hat' the conductor with its bushing can be withdrawn from the 'aparatus tank, an isol-atingswitch in'the busa-r chamber controlling a connection from the-busbar'to the withdrawable conductor, and operating mechanism for simultaneously opening the isolating switch and withdrawing the insulated conductor, such operating mechanism: being so arranged that the isolating 'switch moves rap-idly during-its initial opening movement and slowly during its final opening movement whilst the insulated conductor moves slowly during its initial withdrawing movement and rapidly during its If final withdrawing 1 movement.

i 6. In 7 metal+clad electric switchgear, :the

combination of a busbar, a chamber for the busbar, an electric apparatus forming part of the switchgear, a tank containing such apparatus, a tubular casing of insulating material passing through the busbar chamber, a conductor normally projecting into the apparatus tank to make connection with the apparatus, a condenser insulating bushing around such conductor so mounted within the tubular casing that the conductor with its bushing can be withdrawn from the apparatus tank, a rack formed on the outside of the condenser bushing, a pinion engaging with the rack, a counterweight for balancing the weight of the insulated conductor and its bushing, an isolating switch in the busbar chamber controlling a connection from the busbar to the insulated conductor, and an operating mechanism for simultaneously opening the isolating switch and withdrawing the insulated conductor comprising an operating shaft, a toothed sector engaging with the pinion, and two arms on the operating shaft operatively connected respectively to the isolatingswitch and to the toothed sector, the arrangement being such that dnrin the opening movement of the isolating switch the switch :moves at first rapidly and afterwards slowly and the wit'hdrawable' conductor moves at first slowly and afterwards rapidly.

7. In metal-clad electric switchgear, the combination of a busbar, a chamber for the busbar, :an electric apparatus forming part of the switchgear, a tank containing such apparatus, a tubular casing of insulating material passing through the busbar chamber, a contact fixed in the tubular casing, an insulated conductor so mounted within the tubular casing that it can be moved toproject into the apparatus tank and make connectionwiththe apparatus or can be withdrawn from the tank, spring contacts on the insulated conductor cooperating with the contact fixed in the tubular casing, an isolating switch in the busbar chamber controlling a-connection from the busbar to the contact in the tubular casing, and means-for simultaneously opening the isolating switch and withdrawing the insulated conductor, the spring contacts and their connections to the insulated conductor being so shaped that the electric current passing therethrough induces a force tending to pressthespring contacts intoengagement with the fixed'contact in the tubular casing.

8. In metal-clad oilimmersed electric switchgear, the combination of a busbar, an oil-tank, a circuit-breaker immersed in oil in the tank, a chamber for the busbar, a tubular casing passing through the busbar chamber and formed of insulating material interleaved with conducting layers so asto constitute a condenser insulator, a conductor normally projecting into the circuit-breaker tank to make connection with the circuitbreaker, a condenser insulating bushing around such conductor so mounted within the tubular casing that the conductor with its bushing can be withdrawn from the circuit-breaker tank, a contact fixed in the tubular casing, spring contacts on the insulated conductor normally engaging with the contact in the tubular casing, an isolating switch in the busbar chamber controlling a connec tion from the busbar to the contact in the tubular casing, and means for simultaneously opening the isolating switch and withdrawing the insulated conductor, the spring contacts and their connections to the insulated conductor being so shaped that the electric current passing therethrough induces a force tending to press the contacts into engagement with the fixed contact in the tubular casing.

9. In metalclad oil-immersed electric switchgear, the combination of a busbar, an oil-tank, a circuit-breaker having its main contacts immersed in oil in the tank, an external circuit to be connected to the bus bar through the circuit-breaker, a chamber for the busbar, a second chamber for the external circuit, two tubular casings respectively passing through the two chambers, an insulated conductor movably mounted within each tubular casing and normally projecting into the circuit-breaker tank such conductors respectively making connection with the two main circuit-breaker contacts, an isolating switch in the busbar chamber controlling a connection from the busbar to the associated insulated conductor, an isolating switch in the second chamber controlling a connection from the external circuit to the associated insulated conductor, and means for withdrawing each insulated conductor from the circuit-breaker tank simultaneously with the opening of the associated isolating switch.

10. The combination with the features set forth in claim 4, of anexternal circuit to be connected to the busbar through the circuitbreaker, a second chamber for the external circuit, atubular casing passing through the second chamber, an insulated conductor so mounted within such tubular. casing that it can be movedto project into the circuitbreaker tank to make connection with the second main circuit-breaker contact or can be withdrawn therefrom, and an isolating switch in the second chamber controlling the connection between the external circuit and the insulated conductor.

11. The combination with the features set forth in claim 1, of an earthed contact in the tubular casing with which the insulated conductor engages when withdrawn from the apparatus tank.

12. The combination with the features set forth in claim 2, of an earthed contact in the tubular casing with which the insulated conductor engages when withdrawn from the circuit-breaker tank, and a window in the tubular casing through which the insulated conductor can be viewed when in its withdrawn and earthed position.

13. The combination with the features set forth in claim 7, of an earthed contact in the tubular casing with which the insulated conductor engages when withdrawn from the ap paratus tank.

14. The combination with the features set forth in claim 9, of an earthed contact in each tubular casing with which the insulated conductor engages when withdrawn from the circuit-breaker tank, and a window in each tubular casing through which the insulated conductor can be viewed when in its withdrawn and earthed position.

15. In metal-clad electric switchgear, the combination fo an electric apparatus forming part of the switchgear, a tank containing such apparatus, an electric cable to be connected to the apparatus, a chamber associated with the apparatus, an isolating switch in the chamber, an oil-filled insulating tubular casing in the chamber into which the end of the cable is sealed, a contact on the tubular casing connected to the cable, and means for connecting such contact through the isolating switch to the apparatus.

16. In metal-clad electric switchgear, the combination of an electric apparatus forming part of the switchgear, a tank containing such apparatus, an electric cable to be connected to the apparatus, a chamber associated with the apparatus, an isolatin switch in the chamber, a tubular casing passing through the chamber, an insulated conductor so mounted within the tubular casing that it normally projects into the apparatus tank and makes connection between the isolating switch and the apparatus but can be withdrawn from the tank to break such connection, an oil-filled insulating casing in the chamber into which the end of the cable is sealed,,and a contact or such insulating casing through which the cable is normally connected to the isolating switch.

17. In metal-clad electric switchgear, the combination of a busbar, an oil-tank, a circuit-breaker having its main contacts immersed in oil in the tank, an electric cable to be connected to the busbar through the circuit-breaker, a chamber for the busbar, a second chamber associated with the cable, two tubular casings respectively passing through the two chambers, an insulated conductor withdrawably mounted in each tubular casing and normally projecting into the circuitbreaker tank such conductors respectively making connection with the two main circuit-breaker contacts, an isolating switch in the busbar chamber controlling a connection from the busbar to the associated insulated conductor, means for simultaneously opening such isolating switch and withdrawing the associated insulated conductor, an oilfilled insulating casing in the second chamher into which the end of the cable is sealed. a contact on such insulating casing connected to the cable, and an isolating switch in the second chamber controlling a connection between such contact and the associated withdrawable insulated conductor.

18. The combination with the features set forth in claim 15, of an extension of the chamber around the tubular casing, and a current transformer so mounted within such extension as to encircle the cable and to be removable through the chamber.

19. For use in metal clad electric switchgear, a cable sealing arrangement for connecting an electric cable to an electric apparatus, comprising a chamber associated with the apparatus, and an oil filled tubular casing in such chamber into which the end of the cable is sealed, said chamber being provided with an extension around the tubular cas ing, and a current transformer so mounted Within such extension as to encircle the cable and to be removable through the chamber.

In testimony whereof we have signed our names to this specification.

ARGHIBALD ALLAN. JOHN CHRISTIE.

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