Three-position, medium-voltage, compact switch-disconnector with vacuum interruption and disconnection in air up to 17 kv or in a sealed pressurised enclosure with isolation in dry air up to 36 kv, and method of operation

Abstract

A medium-voltage, compact, three-position (closed, open, earthed) switch-disconnector with current interruption in a vacuum-sealed chamber, and insulated between the phases and disconnected in air up to 17 kV or, in a sealed pressure-tight enclosure, insulated between the phases and disconnected in dry air up to 36 kV, said switch-disconnector comprising a three-pole assembly, wherein each pole comprises: a support element (11, 13) of insulating material carrying: - a first male plug-in current-carrying and disconnecting contact in air (23) associated with a fixed upper right-angled contact (21); - a telescopic, movable, current-carrying and disconnecting contact in air (39, 41, 43) arranged on a hollow cylindrical support (37) of insulating material rotatable with respect to the support element (11, 13); and - a second fixed male lower plug-in contact (27) associated with a fixed right-angled earthing contact (25), wherein said support element (11, 13) is T-shaped with curved arms and with a widened hollow base (29) in which said hollow cylindrical support (37) made of insulating material and carrying said movable telescopic contact (39, 41, 43) is rotatably arranged, and wherein said movable current-carrying and disconnecting contact in air (39, 41, 43) is rotatable between a first closed position engaged with said first, male, plug-in current-carrying and disconnecting contact in air (23), a second disconnected position, and a third position connected to earth via said second fixed earth contact (27); said switch further comprising a vacuum extinguishing chamber (57) fixed near one end of the support element (11, 13) near the fixed upper right-angled contact (21), said vacuum-sealed chamber (57) containing two axially aligned contact rods (59, 61), one of which (59) is fixed and connected to said fixed upper right-angled contact (21), and the other (61) is movable for vacuum interruption by means of an electrical connection linkage operatively connected to a free end of said movable current-carrying and disconnecting contact in air (39, 41, 43).

Description

[0001] The present invention relates to a medium-voltage compact switch-disconnector with three positions, i.e. closed, open and earthed, with current interruption in a vacuum-sealed chamber, and insulated between the phases and disconnected in air up to 17 kV, or, in a sealed pressure-tight enclosure, insulated between the phases and disconnected in dry air up to 36 kV, said switch-disconnector up to 36 kV being isolated in dry air inside a sealed pressure-tight enclosure.

[0002] For particular location and operational requirements various types of load-breaking switch-disconnectors isolated in SF 6 (sulphur hexafluoride) for medium voltages up to 36 kV are known.

[0003] The gas SF 6 , owing to its electric arc extinguishing and isolating properties, is used very much in high-voltage and medium-voltage equipment and is considered to be difficult to replace, but its potential greenhouse effect is high because its global heating potential is equal to 23,900 times that of carbon dioxide (CO 2 ) and the time it remains in the atmosphere is 3,200 years and it is the most powerful greenhouse gas known.

[0004] SF 6 is not toxic and it is a stable gas from a chemical and thermal point of view, but during operation of the switches owing to the supply of energy, in particular in the presence of moisture, it may lose its dielectric resistance, decompose and become toxic and corrosive and damaging for the equipment and for human beings. The gas, if it spreads into the environment, owing to its heavy weight, is deposited on the ground, but in confined spaces, if it is breathed in, even if not decomposed and therefore not toxic, again because of its weight, is deposited on the bottom of the lungs and displaces the oxygen and causes respiratory problems for the maintenance personnel working in the environment.

[0005] One object of the present invention is to provide a medium-voltage switch-disconnector and / or isolator with three positions which, combining the use of air or dry air and vacuum for disconnecting and extinguishing of the arc, satisfies the particular location and operational requirements of equipment isolated in SF 6 , but protects the environment and, owing to its extreme constructional simplicity, also represents a valid alternative from a technical and cost point of view, to equipment in SF 6 .

[0006] A further aim is to provide a switch-disconnector which is constructionally simple, easy to use and safe and does not involve the presence of gas. Last but not least, a further aim is to provide a switch-disconnector, the components of which do not require special positioning within the containment frame, but which may be entirely mounted far therefrom before insertion. Moreover, such a switch-disconnector is made so that the mechanical and electrical operation is not influenced by the enclosure which, however, in the case of use in conditions higher than 17 kV is pressure-sealed so as to preserve the presence of dry air which ensures the established electrical insulation and extinguishing of the arc.

[0007] These objects are achieved according to the present invention by a medium-voltage switch-disconnector and / or isolator with three positions, provided in accordance with the independent claim 1 and the following dependent subclaims.

[0008] According to the invention, the medium-voltage compact switch-disconnector disconnected in air or in dry air with vacuum interruption having three positions, i.e. closed, isolated and earthed, comprises a series of three poles, wherein each pole is provided with a double fixed contact and a double movable contact. Said double fixed contact consists of a fixed current-carrying and disconnecting contact in air, joined via an electrical connection to a fixed contact situated in a vacuum-sealed chamber where the interruption occurs. Said double movable contact consists of a movable current-carrying and disconnecting contact in air, arranged on an arm pivotably mounted and rotatable between a closed position engaged with a fixed current-carrying and disconnecting contact in air, a second isolated position, and a third position connected to earth via a fixed earth contact, said movable current-carrying and disconnecting contact in air being joined, by means of a simple electrical connection linkage, to a movable breaker contact situated in the vacuum-sealed chamber, said vacuum-sealed chamber being integrally mounted on the fixed insulating part which supports the rotatable, insulating, pivotably mounted arm which carries the movable contact device.

[0009] Operation anti-clockwise in the direction of the arrow in Figure 2 detaches in air the movable current-carrying and disconnecting contact in air from the fixed current-carrying and disconnecting contact in air and immediately an electrical connection linkage, connected to the movable current-carrying and disconnecting contact in air, causes the breaking of the load, guiding the separation of the movable and fixed contacts located inside the vacuum-sealed chamber, said movable current-carrying and disconnecting contact in air continuing the operation and becoming detached from the electrical connection linkage and from the movable vacuum contact so as to reach the open / isolated in air position, while, by means of a spring and the electrical connection linkage, the movable breaker contact closes again onto the fixed breaker contact inside the vacuum-sealed chamber, and the two contacts are already closed and ready for the next closing movement of the switch-disconnector.

[0010] The movable current-carrying and disconnecting contact in air then by means of a further operating movement reaches the third earthed position.

[0011] The double movable and fixed contacts of the series of three poles are arranged so that the air contacts are located on insulating support elements, these insulating elements being fastened together by support ties, while the vacuum contacts are located inside sealed vacuum chambers integrally fastened to said insulating supports and are electrically connected to the air contacts, the movable air contact being connected to the movable vacuum contact so as to be able to release after the opening in air, the vacuum interruption and before reaching the horizontal open / isolated position, and the fixed current-carrying and disconnecting contact in air being connected to the fixed vacuum contact in a constrained manner.

[0012] Each insulating support element of the three poles has a T-shaped form containing an insulating arm in the form of a rotationally movable fork which, on the one hand, carries a cylinder which moves in circular fashion and encloses the movable air contact, which moves inside said cylinder in a telescopic manner, and, on the other hand, has a seat for an actuating shaft, which passes inside said fork-shaped insulating arm and inside said T-shaped support element. Said T-shaped insulating support element carries, in the top part at its curved ends of the T shape, two contacts, one of which is an current-carrying and disconnecting contact in air and the other one an earth contact, and in the central part in a position equidistant from the two contacts, a seat for an actuating shaft which also links the fork-shaped insulating arm. Said fork-shaped insulating arm moves integrally with the actuating shaft, rotating and causing the rotation of the insulating cylinder which carries the movable current-carrying and disconnecting contact in air and moving during rotation telescopically the movable contact inside the insulating cylinder.. At least one metal draining element is arranged on each of the insulating support elements, between the portion carrying the fixed contact and the remaining portion of the support elements. Each movable air contact is connected to a movable contact inside the vacuum-sealed chamber by means of an electrical connection linkage which causes first the movement of the movable vacuum contact guided by the movable air contact and instantaneously the separation of the two before the movable air contact reaches the open / isolated position and before the movable vacuum contact closes again onto the fixed vacuum contact by means of a spring and the electrical connection linkage which are actuated by the movable air contact during the same opening operation. Each fixed air contact is connected to a fixed contact inside the vacuum-sealed chamber by means of an integral electric connection. The vacuum-sealed chamber is integrally connected to the insulating support which carries the movable arm with the telescopic cylinder.

[0013] When the present invention is located in the earthing position, the movable current-carrying and disconnecting contact in air is closed onto the fixed earthing contact. By means of simple guided operation of the actuating shaft in the clockwise direction, separation from the fixed earthing contact occurs and the entire movable arm assumes a horizontal position with the isolating switch in an open / isolated position. With the continued operation of the same shaft in the clockwise direction, the tulip-shaped, telescopic, movable current-carrying and disconnecting contact in air closes onto the fixed current-carrying and disconnecting contact in air so as to allow normal flowing of the current, while immediately an integral metallic recessed contact extension engages with two circular-shaped bosses or reliefs of the electrical connection linkage and restores the electrical connection between the tulip-shaped, telescopic, movable contact and the movable contact inside the vacuum-sealed chamber, said movable vacuum contact being connected beforehand to the fixed contact of the chamber.

[0014] The structural and functional characteristics of the present invention and its advantages compared to the prior art will emerge even more clearly and will become evident from a reading of the following description, with reference to the attached schematic drawings, which show an example of embodiment of the said invention. In the drawings: Figure 1 shows a perspective view of a medium-voltage switch-disconnector or isolator with three poles and three positions with isolation in air up to 17 kV and, when in a sealed pressurised enclosure, in dry air up to 36 kV and immediate vacuum interruption; Figure 2 is a partially cross-sectioned detail, on a larger scale, of one pole of the isolator of Figure 1 shown in the closed position; Figure 3 is a cross-sectioned view similar to that of Figure 2 which shows the isolator according to the invention in the open position; Figure 4 is a cross-section of the detail in the open position of Figure 3 along the line IV-IV of Figure 3; Figure 5 is a cross-sectioned view, similar to that of Figure 2, which shows the isolator according to the invention in the earthing position; Figure 6 is a cross-section of the detail, similar to that of Figure 2, of the pole while it is isolating in air or dry air; Figure 7 is a cross-section of the detail similar to that of Figure 2 of the pole while it is breaking in a vacuum; Figure 8 is a cross-section of the detail similar to that of Figure 2 of the pole while it is closing; Figures 9, 10, 11 and 12 are schematic representations of an isolator according to the invention, respectively closed, while it is breaking, open and earthed; Figure 13 shows a perspective view of a detail of the fixing of the vacuum extinguishing chamber arranged at one end of a support element.

[0015] In the following description, for illustration of the figures, identical reference numbers are used to indicate constructional elements with the same function. Moreover, for clearer illustration, some reference numbers may not have been repeated in all the figures.

[0016] Indications such as "vertical" and "horizontal", "upper" and "lower" (if not otherwise indicated) must be read with reference to the assembled (or operational) conditions and with reference to the normal terminology in use in everyday language, where "vertical" indicates a direction substantially parallel to that of the gravitational force vector "g" and horizontal a direction perpendicular thereto.

[0017] The expression "current-carrying and disconnecting contact in air" is used herein to define a main contact suitable for performing two distinct functions: (i) conducting the nominal current of the apparatus when in the closed position; and (ii) performing the electrical disconnecting function by creating a specified isolating gap in an insulating medium consisting of air when in the open position.

[0018] This single component is therefore configured to ensure both the required current-carrying capacity in the closed state and the required dielectric strength in the open state. Throughout this specification, where related but abbreviated expressions such as "current-carrying contact" are used, they refer to the respective function of this single, dual-function component.

[0019] The figures show a three-position, medium-voltage, switch-disconnector or isolator with air isolation and vacuum interruption according to the present invention, comprising a set of insulating support elements arranged alongside each other and locked together in position by means of brackets (15) (see Fig. 1) on supports (not shown), for example so as to form the set of three poles on which the air isolation devices and the vacuum breaking devices are connected together.

[0020] Each support element has a box-like form consisting of two parts (11) and (13) (e.g. see Figs. 1, 2, 4 and 13) in a mirror image arrangement and identical in the form of a T with curved arms and a widened base (29). The two parts (11) and (13) are connected together by male and female interlocking fastening points (19) (Fig. 2) with an internal hole (17) (Fig. 2) for locking with connection elements.

[0021] When a support element (11) is connected to the mirror-image identical support element (13), an upper right-angled fixed contact (21) (Figs. 2, 3 and 13) which carries an associated male plug-in contact (23) (e.g. Figs. 2, 8 and 13) is fixed onto a curved arm. Said contacts (21) and (23) together form the fixed current-carrying and disconnecting contact in air. Differently, the other curved arm receives, fixed thereon, a lower contact (25) which carries an associated male plug-in contact (27) (Figs. 2-8) and which together form the fixed earth contact. Furthermore, in a hollow part of the widened base (29) (Figs. 2-8) it is envisaged fixing a contact (31) (Figs. 2-8) for connection to the medium-voltage circuit together with two L-shaped elements which form a U-piece (33) (Figs. 2-8) joined together at the bottom by the connection contact (31) (Figs. 2-8).

[0022] The upper fixed current-carrying and disconnecting contact in air (21) is connected in a known manner to a respective distribution bar (not shown) and to a fixed breaker contact (59) (Figs. 2-8) which is located in a vacuum-sealed extinguishing chamber (57) (Figs. 2, 8 and 13).

[0023] This thus results in the formation of a double fixed contact consisting of a fixed current-carrying and disconnecting contact in air (21), (23), integrally connected via an electrical connection to a fixed contact (59) situated in a vacuum-sealed chamber (59) where the interruption and extinguishing take place. More precisely, the chamber (57) interrupts the arc in a vacuum-sealed environment and allows the insulating capacity of the air in a free environment or of the dry air in the sealed pressurised enclosure to be maintained.

[0024] The vacuum-sealed chamber (57) is secured to the insulating support (11), (13) by means of an insulating support-piece (63) (Figs. 1, 8 and 13) fixed onto a curved arm of the T by screws (65). Moreover, the lower fixed earth contact (25), (27), which is located on the other curved arm, is connected by means of a bushing (not shown) to an earthing bar (also not shown and known).

[0025] The connection contact (31) is connected in the lower part to the medium-voltage circuit by means of a distribution bar not shown) and in the upper part is connected to the two L-shaped elements which form a U (33) and are provided with pin-like extensions (35) (Fig. 4) which connect the connection contact (31) to a movable current-carrying and disconnecting contact in air system.

[0026] This movable current-carrying and disconnecting contact in air system consists mainly, but not exclusively, of a hollow insulating cylinder (37) (Figs. 2, 4 and 8), a metal part (39) integral with the cylinder, a sliding metallic inner tube (41) and a tulip-shaped contact (43) integral with the sliding metallic inner tube (41).

[0027] The pin-like extensions (35) which enter into the hollow cylindrical support (37) are connected to the cylindrical metal part (39) and connect it to the connection contact (31).

[0028] The metallic inner tube (41) slides inside this insulating cylinder (37) with which the metal part (39) is integral and is connected to the connection contact (31) by means of the fixed metal part (39) and the pins (35).

[0029] The metal tube (41) is guided slidably inside the fixed metal part (39) and, in the vicinity of its free end, has rigidly joined inside it a tulip-shaped contact element (43) (Figs. 2, 4 and 8) which acts as a movable female contact.

[0030] Said movable female contact (43) is connected to the fixed current-carrying and disconnecting contact in air (23) when the isolator is closed, is free when the isolator is open and is connected to the earth contact (27) when the isolator is earthed. Said telescopic movement of the movable current-carrying and disconnecting contact in air is guided by an actuating shaft.

[0031] An annular insulating element (45) (Figs. 2, 4 and 8) is fixed onto the free end of the cylindrical part (41) where the tulip-shaped contact (43) is located and is pivotably mounted at 47 (Fig. 4) inside a first end of two insulating half-arms (49) (51) (Figs. 2, 4 and 8) which form an end fork. In this way the insulating cylinder (37) moves by means of rotation, while the other end of the two half-arms (49) (51) is provided with a through-hole (53) (Figs. 2, 4 and 8) and is pivotably mounted in the support element (11) (13) inside a corresponding hole by means of a central shaft (55) (Figs. 2, 4 and 8) which is also the actuating shaft of the isolator.

[0032] According to the invention the vacuum extinguishing chamber (57) contains two contact rods, a first rod (59) of which forms a fixed contact and a second rod (61) of which forms a movable contact, said rods (59) (61) being axially aligned (Figures 2 to 8).

[0033] The first rod (59) is integrally connected on the outside to the fixed contact (21) and extends inside the vacuum chamber, while the second rod (61) may be made to slide inside the chamber (57) (Fig. 8) by the circular movement of the movable air contact device (49, 51, 45, 37).

[0034] Figures 1 and 13 show more clearly the positioning of the extinguishing chamber (57) of the single pole in the isolator according to the present invention. A first upper end of the chamber is arranged against the upper, right-angled, fixed contact (21) and connects to it the fixed contact rod (59) inside the vacuum chamber in an integral manner. The other lower end of the chamber (57) extends downwards inside an insulating support (63) (Figs. 8, 13) fastened by means of screws (65) to the support element (11), (13).

[0035] With reference to the figures, it can be seen how what may be described as being a simple electrical connection linkage, connected to the movable current-carrying and disconnecting contact in air (43, 41), allows breaking of the electric contact by acting on the movable breaker contact (61) situated inside the vacuum-sealed chamber (57).

[0036] In particular, it is pointed out that a first spindle (67) is arranged inside said insulating support (63) (Figs. 2, 8 and 13) and is fixed transversely so as to be transverse to the vacuum chamber. It should be noted that a U-shaped bar (69) is hinged on said spindle (67) (Figs. 2, 8 and 13), moving rotatably in the direction of the vacuum-sealed chamber (57), and has a slot (71). A further spindle (73) is arranged in said slot (71), being also transversely fixed to the vacuum chamber and sliding inside the slot (71). The spindle (73) is integrally connected to the end of the movable contact rod (61) which slides inside the vacuum-sealed chamber (57).

[0037] A spring (81) is wound onto the first spindle (67) (Figure 13) and reacts against the U-shaped bar (69) and keeps it normally in contact with the lower part of the chamber or ampoule (57) as well as keeping the two contact rods (59) and (61) in contact.

[0038] The U-shaped bar (69), integrally joined via the spindle (73) to the movable contact rod (61) inside the vacuum chamber (57), extends, at the opposite end to that on which the insulating support (63) is pivotably mounted, in the form of a finger (79) (Fig. 8). The finger (79) has inside the U two reliefs in the metal plate, i.e. bosses with a circular shape (77) (Fig. 8). These bosses (77) may engage inside a recessed metal contact extension (75) which projects from the annular support element (45) and is connected to the movable current-carrying and disconnecting contact in air (41), (43).

[0039] The above description illustrates how the said electrical connection linkage is formed, being connected to the movable current-carrying and disconnecting contact in air (43, 41), and therefore also how a double movable contact (43), (61) is provided.

[0040] Said double movable contact consists of a movable current-carrying and disconnecting contact in air (43, 41), arranged on an arm (37) pivotably mounted and rotatable (at 35) between a closed position of engagement with a fixed current-carrying and disconnecting contact in air (23, 21), a second isolated position (Fig. 3) and a third position connected to earth (Fig. 5) by means of a fixed earth contact (25), (27). It is pointed out that said movable current-carrying and disconnecting contact in air (43, 41) is joined, by means of a simple electrical connection linkage, to a movable breaker contact (61) situated inside the vacuum-sealed chamber (57), where said vacuum-sealed chamber (57) is integrally mounted on the fixed insulating part (63) (11, 13) which supports the rotatable, pivotably mounted, insulating arm which carries the movable contact device.

[0041] In order to activate the three positions of the switch-disconnector according to the present invention, a quick-action mechanism or a lever (not shown since they are known per se) is used and is actuated using the hollow central shaft (55), thus obtaining the displacement between the various positions, i.e. closed, isolated and open, and earthed, as is required.

[0042] Figure 2 shows the position of the components of the isolator according to the invention when there is a current flow and everything is functioning normally with the switch-disconnector closed. When the switch-disconnector is closed, the movable current-carrying and disconnecting contact in air (41), (43) is closed onto the fixed current-carrying and disconnecting contact in air (21), (23), the recessed metal contact extension (75) is engaged with the bosses (77) (Fig. 8) provided on the finger (79) of the shaped bar (69) and is connected via the spindle (73) to the movable vacuum breaker contact (61) which is closed on the fixed breaker contact (59) and connects to the movable vacuum breaker contact (61) the movable current-carrying and disconnecting contact in air (41), (43) to which it is integrally connected.

[0043] When it is required to interrupt the current flow and open the switch-disconnector closed in the position shown in Figure 2, it is necessary to proceed as described below. The operation of one pole is described, but the other two poles move in the same way and at the same time.

[0044] Hence, for this purpose, the two half-arms (49) (51) are actuated anti-clockwise in the direction of the arrow F shown in Figure 2 so as to attempt to disengage the closed contacts.

[0045] During the rotation in the direction of the arrow F, with the separation of the movable current-carrying and disconnecting contact in air (41), (43) from the fixed current-carrying and disconnecting contact in air (21), (23) isolation occurs, while the current flow remains between the two axially aligned contact rods (59), (61), the U-shaped bar (69), (79), the recessed metal contact extension (75) and the contact element (41) (43), as shown in Figure 6.

[0046] The continuation of the rotational movement results in the situation shown in Figure 7, namely the said rotation, via the U-shaped bar (69) with its slot (71), and the movement of the spindle (73) forces, inside the vacuum-sealed chamber (57), the contact rod (61) to be disengaged from the contact rod (59), interrupting the flow, while subsequently with the disengagement of the recessed metal contact extension (75) from the bosses (77), the air isolation device (75), (37), (39), (41), (43) separates completely from the breaking device (69), (79), (59), (61) and assumes a horizontal isolated / open position (Fig. 3) and, at the same time, the spring (81) (Fig. 13) causes, via the rotation about the spindle (67) of the shaped bar (69), the spindle (73) and the movable contact rod (61), integral therewith, to close again onto the fixed contact rod (59), inside the vacuum chamber (57), thus arranging the breaking device (59) (61) in the correct position for the subsequent closing operation of the switch-disconnector which at present is in the isolated / open position with the air isolation device (75), (37), (39), (41), (43) in the horizontal position as can be seen in Figure 3. It has thus been seen how extinguishing of the electric arc in air and a vacuum is performed without the use of gas or other measures of the prior art and the open isolator position is reached.

[0047] Figure 5, finally, shows how earthing of the isolator is achieved by rotating the two half-arms (49), (51) anti-clockwise in the direction of the arrow F from the open isolator position shown in Figure 3.

[0048] For the purposes of better comprehension, operation of the switch-disconnector according to the present invention is summarised again in different words.

[0049] Operation anti-clockwise in the direction of the arrow F shown in Figure 2 detaches in air the movable current-carrying and disconnecting contact in air (43, 41) from the fixed current-carrying and disconnecting contact in air (23) and, immediately, an electrical connection linkage (67, 69, 71, 79, 77), connected to the movable air contact (43, 41) via the recessed metal contact extension (75), causes breaking of the load, guiding the separation of the movable contact (61) and the fixed contact (59) located inside the vacuum-sealed chamber (57). Then, as shown in Figure 7, said movable air contact (43, 41) continues the operating movement, detaching itself from the electrical connection linkage and from the movable vacuum contact, in order to reach the open / isolated in air position shown in Figure 3. Then, by means of a spring (81) and the electrical connection linkage, the movable breaker contact (61) closes again onto the fixed breaker contact (59) inside the vacuum-sealed chamber (57), and the two contacts are already closed and ready for the next closing of the switch-disconnector.

[0050] The movable air contact (41, 43) then by means of a further operating movement reaches the third earthed position shown in Figure 5.

[0051] It should be emphasized again that the double movable and fixed contacts of the series of three poles are arranged so that the air contacts are located on insulating support elements and that these insulating elements are fastened together by support ties, while the vacuum contacts are inside the vacuum-sealed chamber and firmly secured to said insulating support-pieces.

[0052] It should also be emphasized that each insulating support element (11, 13) of the three poles in the form of a T contains a fork-shaped insulating arm (49, 51) movable by means of rotation. This fork-shaped insulating arm (49, 51), on the one hand, is connected to the cylinder (37) which moves in circular fashion and which encloses the movable air contact (43, 41) and moves in said cylinder (37) telescopically, and, on the other hand, has the seat or hole (53) for an actuating shaft (not shown) which passes inside said fork-shaped insulating arm and inside said T-shaped support element. When the present invention is located in the earthing position, the movable current-carrying and disconnecting contact in air is closed onto the fixed earthing contact. By means of simple guided operation of the actuating shaft in the clockwise direction, separation from the fixed earthing contact occurs and the entire movable arm assumes a horizontal position with the switch-disconnector in an open / isolated position. With the continued operation of the same shaft in the clockwise direction, the tulip-shaped telescopic movable contact closes onto the fixed current-carrying and disconnecting contact in air for normal flow of the current, while immediately, by means of an integral metallic recessed contact extension, engagement occurs with two circular-shaped bosses or reliefs of the electrical connection linkage, and the electrical connection between the tulip-shaped telescopic movable contact and the movable contact inside the vacuum sealed chamber is restored, said movable vacuum contact being connected beforehand to the fixed contact of the chamber.

[0053] Figures 9, 10, 11 and 12 show schematically, for the sake of completeness, an isolator according to the invention, respectively closed, while it is breaking, open and earthed.

[0054] The object mentioned in the preamble of the description is thus achieved. The scope of protection of the present invention is defined by the attached claims.

Claims

1. A medium-voltage compact, three-position (closed, open, earthed) switch-disconnector with current interruption in a vacuum-sealed chamber, and insulated between the phases and disconnected in air up to 17 kV or, in a sealed pressure-tight enclosure, insulated between the phases and disconnected in dry air up to 36 kV, said switch-disconnector comprising a three-pole assembly, wherein each pole comprises: - a support element (11, 13) of insulating material carrying: - a first, male, plug-in, current-carrying and disconnecting contact in air (23) associated with a fixed upper right-angled contact (21), - a telescopic, movable, current-carrying and disconnecting contact in air (39, 41, 43) arranged on a hollow cylindrical support (37) of insulating material and rotatable with respect to the support element (11, 13); and - a second. fixed, male, lower plug-in contact (27) associated with a fixed right-angled earthing contact (25), wherein said support element (11, 13) is T-shaped with curved arms and with a widened hollow base (29) in which said hollow cylindrical support (37) made of insulating material and carrying said movable telescopic air isolation and flow contact (39, 41, 43) is rotatably arranged, and wherein said movable current-carrying and disconnecting contact in air (39, 41, 43) is rotatable between a first position engaged with said first, male, plug-in current-carrying and disconnecting contact in air (23), a second disconnected position, and a third position connected to earth via said second fixed earth contact (27), and - a vacuum extinguishing chamber (57) which, by interrupting the arc in the vacuum-sealed environment, maintains the insulating capacity of the free ambient air or dry air in the sealed pressurised enclosure, which is fixed at one end of the support element (11, 13) near the fixed upper right-angled contact (21), said vacuum-sealed chamber (57) containing two axially aligned contact rods (59, 61), one contact rod (59) of which is fixed and connected to said fixed upper right-angled contact (21), and the other contact rod (61) is movable for vacuum interruption so as to slide within the extinguishing chamber (57) by means of an electrical connection linkage operatively connected to a free end of said movable current-carrying and disconnecting contact in air (39, 41, 43).

2. Switch-disconnector according to claim 1, characterised in that said telescopic movable contact (39, 41, 43) arranged on said hollow cylindrical support (37) made of insulating material comprises a first, fixed, expandable, elastic, outer cylindrical portion (39), which is electrically connected to a connection contact (31) for connection to a medium voltage circuit, and within which there is slidably mounted a second, inner, cylindrical portion (41) carrying near its free end, rigidly joined to its inside, a tulip-shaped contact element (43) acting as a female contact.

3. Switch-disconnector according to one or more of the preceding claims, characterised in that said free end of said second cylindrical portion (41) is supported inside an annular support element (45) which is made of insulating material and pivotably mounted (at 47) inside a first end of two half-arms (49, 51) made of insulating material and forming an end fork, a second opposite end of the two half-arms (49, 51) being pivotably mounted on said support element (11, 13) and a hollow central shaft (55) being provided for actuation of the isolator.

4. Switch-disconnector according to one or more of the preceding claims, characterised in that a first upper end of said chamber (57) is integrally mounted on said fixed upper right-angled contact (21), while another lower end of said chamber (57) extends downwardly within a U-shaped insulating support-piece (63) fastened by screws (65) to said support element (11, 13).

5. Switch-disconnector according to one or more of the preceding claims, characterised in that an annular support member (45) made of insulating material is arranged at a free end of said movable telescopic current-carrying and disconnecting contact in air (39, 41, 43) and, extending from said annular support member (45), there is a metal recessed contact extension (75) which engages with two bosses (77) internally arranged on a hollow finger (79) extending from a U-shaped bar (69) pivotably mounted (at 67) on a U-shaped insulating support-piece (63) fastened by screws (65) to the support element (11, 13).

6. Switch-disconnector according to claim 5, characterised in that said U-shaped bar (69) has a slot (71) inside which a spindle (73) connected to one end of said contact rod (61), sliding inside the chamber (57), is arranged.

7. Switch-disconnector according to claim 6, characterised in that said U-shaped bar (69) is pivotably mounted on a U-shaped insulating support-piece (63) by means of a spindle (67) on which there is wound a spring (81) which reacts against said U-shaped bar (69) and keeps it normally in contact with a lower part of the chamber (57) as well as keeping said two contact rods (59, 61) in contact.

8. Switch-disconnector according to claim 2, characterised in that said connection contact (31) is attached to said support element (11, 13) together with a U-shaped member (33) closed at the bottom and provided with pin-like extensions (35) which engage rotatably with said first, fixed, expandable, elastic outer cylindrical portion (39) of said telescopic arm.

9. Method for operating a switch-disconnector according to one or more of the preceding claims 1 to 8, wherein, when said switch-disconnector is in the closed position, the movable current-carrying and disconnecting contact in air (41), (43) is closed on the fixed current-carrying and disconnecting contact in air (21), (23), the recessed metal contact extension (75) of the movable current-carrying and disconnecting contact in air (41), (43) is engaged with the bosses (77) and by means of the electrical connection linkage (69), (73), (75) the movable current-carrying and disconnecting contact in air (41), (43) is connected to the movable vacuum breaker contact (61) closed on the fixed vacuum breaker contact (59), which in turn is connected to the fixed current-carrying and disconnecting contact in air (21), (23), so that the current passes through both the current-carrying and disconnecting contact in air and the vacuum breaker contacts; and when it is required to break the current flow, with a single opening operation, there is in a first moment the disconnection of the movable current-carrying and disconnecting contact in air (41), (43) from the fixed current-carrying and disconnecting contact in air (21), (23), while maintaining the current flow between the two contact rods (59), (61) in a vacuum, the electrical connection linkage (69), (73), (75) in the air and the movable current-carrying and disconnecting contact in air (41), (43); in a second moment, when the movable current-carrying and disconnecting contact in air is sufficiently far from the fixed current-carrying and disconnecting contact in air, there is interruption in the vacuum-sealed chamber (57) with the movement away of the breaker contact rod (61) from the breaker contact rod (59); and in a third moment with the disengagement of the recessed metal contact extension (75) from the bosses (77), the movable current-carrying and disconnecting contact in air (75), (37), (39), (41), (43) separates completely from the movable vacuum breaker contact (59), and moves into the horizontal isolated / open position, and simultaneously the movable vacuum breaker contact rod (61) closes back onto the fixed vacuum breaker contact rod (59), inside the vacuum chamber (57), setting up the vacuum breaker contacts (59), (61) for the next closing operation.

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