Electrical switching device

Abstract

The invention relates to an electrical switching device comprising a switching path (2) and a flow device having a control valve (13, 13a, 13b, 13c). By means of the flow device, a fluid can flow on the switching path (2). The control valve (13, 13a, 13b, 13c) additionally has a valve body (14a, 14b, 14c). The valve body (14a, 14b, 14c) is pressed into a sealing position by the flow pressure of the flowing fluid.

Description

[0001] The invention relates to an electrical switching device comprising a switching path and a flow device with a control valve for flowing the switching path, wherein the control valve has a movable valve body, wherein the valve body is pressed into a sealing position by the flow pressure of a flowing fluid during a switching-off process and the valve body is movable in the manner of a clearance fit between a first stop and a second stop.

[0002] An electrical switching device is known, for example, from the international publication WO 2019 / 024978 A1. There, a flow device is assigned to a switching path of the switching device. The operation of the flow device is controlled by a control valve. For this purpose, the control valve has a movable valve body, which can be moved either assisted or inhibited by a spring. With a control valve designed in this way, the response behavior can be considered relatively erratic. Accordingly, pulses can occur that affect the electrical switching device as a whole. Therefore, the operation of the control valve must be taken into account when designing the switching device. Furthermore, the known design has the disadvantage that fatigue symptoms occur with an increasing number of actuations of the control valve.Due to fatigue phenomena, the response behavior of the control valve can change, which in turn can lead to changing conditions, for example, in the switching path of the electrical switching device. US patent US 8,232,497 B2 discloses an interrupter chamber in which a flow of dielectric gas between two volumes is controlled by a valve device. International publication WO 93 / 20573 and European patent application EP 3 419 039 A1 each disclose interrupter chambers in which the transfer of gas is controlled by a valve device.

[0003] The object of the invention is therefore to provide an electrical switching device which has a stable switching behavior even after a large number of switching operations.

[0004] According to the invention, the object is achieved in an electrical switching device of the type mentioned at the outset in that the valve body has a through opening which can be blocked by one of the stops.

[0005] An electrical switching device is used to break or create an electrically conductive current path in a phase conductor. For this purpose, the electrical switching device has a switching path which preferably extends between switching contact pieces which can be moved relative to one another. Discharge phenomena can occur in the switching path both when the switching device is switched on, i.e. when the switching contact pieces come closer together and are galvanically contacted, and when the switching device is switched off, i.e. when the switching contact pieces are galvanically separated and moved away from one another,. These discharge phenomena are referred to, for example, as pre-arcs during a switching-on process. During a switching-off process, these discharge phenomena are referred to, for example, as switching-off arcs. Such discharge phenomena are associated with increased thermal loads which occur in the switching path.Due to thermal stress, the switching contact pieces or other components of the electrical switching device are exposed to increased wear. The switching path can be exposed to a fluid flow by means of a flow device. The flow device can, for example, inject a fluid into the switching path or direct a fluid out of the switching path, so that cooling is caused in the switching path. The flow device can, for example, have a piston-cylinder arrangement, wherein a relative movement of the piston and cylinder can cause an overpressure or underpressure to generate a corresponding flow. The operation of the flow device should be synchronized with a relative movement of the switching contact pieces of the switching device. Depending on the condition of the switching path, ieDepending on the relative position of the switching contact pieces, current can be applied to the switching path. Switching contact pieces that can be moved relative to one another, as well as elements of the flow device (cylinder / piston) that can be moved relative to one another, can be actuated in a synchronized manner. This can, for example, trigger a synchronous relative movement in the flow device depending on the progression of a relative movement of the switching contact pieces.

[0006] Depending on the switching processes to be controlled, it may be advantageous to apply a current to the switching gap during both a making and a breaking operation. If necessary, for example, blowing the switching gap can be provided during a breaking operation, and suctioning a fluid from the switching gap may be preferred during a making operation. However, it may also be provided that the flow device is effective only during a making operation or only during a breaking operation.

[0007] Depending on requirements, a control valve can be provided which, for example, only allows the flow device to operate when it is switched on or off. By means of the control valve, for example, a relief opening in the flow device can be opened or closed as required, thus preventing or causing the build-up of overpressure or underpressure in the flow device. A flowing fluid can pass through the relief opening, which is opened or blocked under the control of the control valve. The flowing fluid generates a flow pressure. This flow pressure can be used to press the valve body into a sealing position, i.e. to block the relief opening. The valve body is mounted so as to oscillate freely in the manner of a clearance fit. The valve body is arranged so as to be movable (oscillating) between a first stop and a second stop.Free movement can occur without external forces acting on the valve body.

[0008] The relief opening can have a channel. The valve body can be movably mounted within the channel or at an opening of the relief opening. A stop can prevent the valve body from escaping from the channel. Thus, the valve body can be arranged in a shielded manner within the channel. Dielectric shielding is advantageous in this case, so that the dielectric properties of the switching device are maintained when using a movable control valve.

[0009] When the relief opening is blocked, the flow device can take effect. This allows overpressure or underpressure to be generated in the flow device, resulting in corresponding flow to the switching device. The valve body is advantageously moved into its sealing position by the flow pressure. Using the flow pressure to actuate the valve body has the advantage that it can be actuated with almost no wear. In addition, as the flow pressure increases, the force acting on the valve body and thus its sealing seat in the control valve or its release is increased. The valve body can be moved with play, for example, slidable or foldable, so that the valve body can be actuated smoothly even at low flow pressures. This means that the control valve can be actuated at an early stage.For example, it is possible to initially partially block the relief opening. The control valve can have a soft characteristic, i.e. depending on the rate of change of the flow pressure, the valve body can cause a comparatively slow blocking of the relief opening and thus a (slow) change in the pressure inside the flow device with a comparatively low rate of change. This results in a gentle response of the control valve, which avoids sudden pressure changes. The electrical switching device is therefore only subjected to a small amount of additional forces when the valve body is engaged or disengaged. A gentle decrease in the blocking effect of the valve body can also occur when the direction of flow is reversed and thus the flow pressure on the valve body is reversed.Furthermore, by using the flow pressure, additional actuating means such as springs for actuating the valve body can be dispensed with. This can result in a freely movable valve body within set limits (stops). Accordingly, almost fatigue-free actuation of the valve body can be assumed. The control valve is located, for example, in a channel which can be formed, for example, by a relief opening on a cylinder or a piston of the flow device. A differential pressure between the interior and exterior of the flow device can cause a flow pressure of a fluid that flows around or through the flow device. The flowing fluid should preferably be electrically insulating. This electrically insulating fluid can also serve to electrically insulate the switching path and also to supply flow to the switching path.Examples of suitable electrically insulating fluids include fluorine-based fluids such as sulfur hexafluoride, fluoronitriles, fluoroketones, or fluoroolefins. However, nitrogen-based fluids such as mixtures with oxygen (e.g., purified air) can also be used. These fluids are preferably in gaseous form, but they can also be in liquid form.

[0010] It is intended that the valve body is movable in the manner of a clearance fit between a first stop and a second stop.

[0011] The valve body can, for example, be guided so that it can move in the manner of a clearance fit. For example, the valve body can be designed like a piston, which can freely move and oscillate in a channel. The valve body's freedom of movement is limited by a first and a second stop. This means that the valve body remains between a closed position and an open position and, depending on the flow pressure acting between the first stop and the second stop and vice versa, can be pressed from the first to the second stop or from the second to the first stop. The design of the clearance fit can vary depending on the expected flow pressure. At a first stop, it can be provided that the valve body is pressed into a sealing position at the first stop, whereas in a position at the second stop the valve body makes the control valve permeable.Depending on the design of the stops with corresponding recesses, projecting edges or shoulders, a gap in the valve body can be opened or closed. For example, it can also be provided that a channel in which the valve body is movable has a changing cross-section, whereby a sealing seat is created when the valve body rests against the first stop, and continuity of the control valve is ensured when it rests against the second stop. The first stop can, for example, have a receptacle for the valve body that is complementary in shape. When the valve body rests against the first stop, the control valve is blocked. Recesses, e.g. teeth or incisions, can be provided on a second stop, which allows a fluid flow to pass between the second stop and the valve body.The valve body itself can have a through-opening (overflow channel) which is blocked when positioned at the first stop and permeable when positioned at the second stop.

[0012] The valve body can be shaped, for example, like a disc or cylinder, but other shapes can also be provided for the valve body. For example, the valve body can also be shaped like a sphere or a cone. By correspondingly designing the stops or a (section of a) channel extending between the stops, a sealing seat or a passage can be formed at the first or second stop.

[0013] It is intended that the valve body has a through opening which can be blocked by one of the stops.

[0014] A through-opening (overflow channel) in the valve body enables the use of simplified structures for the stops. Depending on the shape of the stops, a through-opening in the valve body can be blocked when the valve is in contact with the first stop (e.g., sealing position), whereas the through-opening of the valve body is open when the valve body is in contact with the second stop. This results in a low-wear design in order to achieve a consistent response behavior after numerous switching cycles of the control valve at similar flow pressures. When using a valve body with a cylindrical or rotational shape, the through-opening can preferably extend essentially parallel to the cylinder axis or rotational axis.

[0015] An elastic valve body allows the sealing seat or sealing position of the valve body to be easily implemented. Depending on the flow pressure, an elastic valve body can be pressed into a sealing position. Even after numerous switching cycles of the valve body, it can be pressed into a sealing position again. The valve body can be deformed to engage or detach from a stop. An elastic valve body can be formed, for example, using an elastomer disc or an elastomer plate. However, it is also possible to use a spherical or conical elastic valve body.

[0016] A local, selective fixation of the valve body makes it possible to specifically induce or permit deformation, particularly when using an elastic valve body. This allows the control behavior of a smoothly moving valve body, which is movable between a first and a second stop depending on the flow pressure, to be influenced. A local fixation also makes it possible to restrict the degree of freedom of the valve body and thus simplify the control of the reproducibility of its movement within a flowing medium or caused by a flow pressure. The valve body can, for example, be fixed centrally or in an edge area, which promotes preferential deformation, for example. Especially when using an elastically deformable valve body, the locking and unlocking behavior of the valve body can be improved.An elastic valve body can be arranged in front of a relief opening and, to seal the relief opening, can be positioned against a wall bordering the relief opening. To release the relief opening, the elastic valve body can deform and lift itself from the wall.

[0017] If a stop is used to position the valve body, it can move away from the stop in a targeted manner, but only to the extent that a specific local fixation allows. The valve body can, for example, fold over or over by being exposed to flow pressure like a barrier and being pressed against the first or second stop depending on the flow pressure. If a stop is used to fix the valve body locally, it can be easily positioned between the first and second stops, allowing fatigue-free operation of the valve body.

[0018] A stop can provide a convex stop surface for the valve body. The convex design of the stop surface prevents pressure marks or notches when the valve body hits a stop. This increases the durability of the valve body, and the sealing functions of the valve body are maintained because notches or pressure marks that form undesirable bypasses or other deformations are prevented. The convex stop surface can, for example, represent a section of a spherical cap. However, it can also be provided that the convex stop surface is designed like a section of a cylinder jacket surface. In particular, when the valve body is positioned centrally on a stop surface, a spherical cap-like convex stop surface can be used, which can allow all-round movement of the valve body around the point-based fixation of the valve body.The mobility of the valve body with such a pronounced convex stop surface is limited evenly and on all sides. When gripping a valve body from the side, an approximately cylindrical surface-shaped stop surface design is recommended, which can force a flap-like movement of the valve body. When using an elastically deformable valve body, the deformation can be supported by the convex shape of the stop surface. Sharp-edged deformation of the valve body can be counteracted.

[0019] Furthermore, it can advantageously be provided that the control valve is positioned stationary relative to the switching path.

[0020] The switching distance can be limited by switching contact pieces that can move relative to one another. Regardless of the relative position of the switching contact pieces to one another, the control valve can remain stationary when at rest. When using a stationary switching contact piece that limits the switching distance, the control valve can remain stationary relative to this stationary switching contact piece. This reduces the mass to be moved in an electrical switching device with switching contact pieces that can move relative to one another. At the same time, the control valve is protected from mechanical vibrations caused by movements and the like. This ensures reliable function of the control valve. Even at low flow pressures, the valve body of the control valve is actuated because overlapping movements are avoided and any accelerations that occur are kept away from the valve and valve body.

[0021] A further advantageous embodiment can provide that the electrical switching device is an earthing switch, in particular a rapid earthing switch.

[0022] An earthing switch has a switching path which serves to apply earth potential to a phase conductor. For this purpose, a switching contact piece usually has a permanent earth potential, whereby earth potential can be transferred to a phase conductor by bringing the switching contact pieces closer together and making galvanic contact between them. Earthing switches are generally safety devices which are intended to reliably earth a phase conductor. In this respect, the closing process of an earthing switch is to be classified as the more significant switching action. In particular when using high-speed earthing switches, i.e. earthing switches which are intended, for example, to contribute to a safety shutdown in the event of a fault, i.e. to forced earthing, the fastest possible movement of switching contact pieces which can move relative to one another must be induced.In order to achieve this reliably, the flow device should be designed in such a way that forces that delay the switch-on process are avoided. This avoids an additional braking effect from the flow device. During a switch-on process, the control valve should therefore be open and the orifice should be clear. Conversely, during a switch-off process on an earthing switch, it is advantageous for the flow device to take effect. In this respect, in the case of earthing switches or other electrical switching devices, the control valve should be pressed into the sealing position during the switch-off process, whereas during a switch-on process the sealing position of the control valve should be removed. For example, a free orifice can be used during a switch-on process to fill the flow device with fluid, in particular unused, i.e.It is recommended to fill the valve with a cooled and, if possible, charge-carrier-free fluid so that the flow device is ready for switching off. For other switching devices, a reversed effect of the control valve may be advantageous, depending on the requirements.

[0023] In the following, an embodiment of the invention is shown schematically in a drawing and described in more detail below.

[0024] The Figure 1 is a side view of an electrical switching device in the switched-off state, Figure 2 is a top view of the Figure 1 known electrical switching device in the switched-off state, Figure 3 shows a plan view of the electrical switching device as shown in the Figures 1 and 2 known in the switched-on state, Figure 4 is a perspective view of the Figures 1 to 3known electrical switching device in the switched-off state and Figure 5 shows a piston plate with a control valve in a first embodiment variant according to the invention, in a perspective view. Figures 6, 7 and 8 show sections through the piston plate known from Figures 1 to 5 with a control valve in a first embodiment variant, Figures 9, 10 and 11 show a modification of the Figures 6, 7 and 8in section of the control valve in the first embodiment. Figure 12 shows a piston plate with a control valve in a second embodiment, which is not part of the invention, in a perspective view, Figures 13, 14 and 15 each show a section through the piston plate together with the control valve in the second embodiment, Figure 16 shows a piston plate with a control valve in a third embodiment, which is also not part of the invention, in a perspective view and Figures 17 to 19 each show a section through the Figure 16 known control valve in the third design variant.

[0025] In the Figures 12 to 19 The valve bodies shown do not have a through opening that could be blocked by a stop.

[0026] Based on the Figures 1 to 4The structure of an electrical switching device and the operation of a control valve are described. Figures 5 to 19 Details of control valves in three design variants are shown.

[0027] The Figure 1 shows a sectional side view of an electrical switching device. The electrical switching device has an encapsulating housing 1. The encapsulating housing 1 surrounds active parts (live parts) of the electrical switching device, thus providing mechanical protection. Furthermore, the encapsulating housing 1 can hermetically enclose active parts of the electrical switching device, so that the interior of the encapsulating housing can be filled with an electrically insulating fluid. The encapsulating housing 1 prevents the electrically insulating fluid from evaporating.

[0028] The electrical switching device has a switching path 2. The switching path 2 extends between a first movable switching contact piece 3 and a second stationary switching contact piece 4. The second switching contact piece 4 is supported on the encapsulating housing 1 in an electrically insulated manner. The encapsulating housing 1 has walls made of an electrically conductive material which carry ground potential. The second switching contact piece 4 also has ground potential, with a ground wire of the second switching contact piece 4 being led outward through the encapsulating housing 1 in an electrically insulated manner. This makes it possible to isolate the second switching contact piece 4 from ground potential if necessary. This is advantageous, for example, for inspection and testing purposes. The first switching contact piece 3 is mounted on a cylinder 5. The cylinder 5 is part of a flow device and defines a compression volume 6.The first switching contact piece 3 is designed as a hollow cylinder and has a blow-out channel 7 inside it. The blow-out channel 7 opens at the free end of the first switching contact piece 3 in the switching gap 2. The other end of the blow-out channel 7 opens inside the compression volume 6, so that the compression volume 6 can communicate with the environment, particularly in the area of ​​the switching gap 2, via the blow-out channel 7. The cylinder 5 is movably mounted and made of electrically insulating material. Via a connecting lug 8, which is arranged between the first switching contact piece 3 and an end face of the cylinder 5, an electrically insulated connecting line is led out through the wall of the encapsulating housing 1 and can be connected there to a phase conductor to be earthed. In order to ensure displaceable guidance of the cylinder 5, a piston plate 9 is fixedly positioned on a stem 10.The stem 10 is in turn fixedly supported on the encapsulating housing 1. The piston plate 9 forms a fixed wall on the compression volume 6, so that a relative movement of the piston plate 9 to the cylinder 5 causes a change in the compression volume 6. During a switching-on process, i.e. when the first switching contact piece 3 approaches the second switching contact piece 4, the compression volume 6 increases. Conversely, when the switching contact piece 3 moves away from the second switching contact piece 4 (switching-off process), the compression volume 6 decreases. In the event of a switching-off process, a compression of electrically insulating fluid is thus caused within the compression volume. This is expelled into the switching gap 2 via the blow-out channel 7 and flows, cooling and solidifying the switching gap 2 there and flowing around any burning arc.A relief opening opening into the compression volume 6 can be switched by a control valve 13. The relief opening is advantageously arranged in the stationary piston plate 9. At least one control valve 13 (see position). Figure 2 ) is arranged in the piston plate 9.

[0029] To effect a displacement of the first switching contact piece 3 together with the cylinder 5, a rotatably mounted lever arm 11 is provided. The lever arm 11 is guided with its free end in a groove on the cylinder 5, so that a pivoting movement can be converted into a linear movement of the cylinder 5 via a pin of the lever arm 11 engaging in the groove (see. Figures 2 , 3 , 4 ). In order to support the braking of the cylinder 5 in the on and off positions, stop buffers 12 are arranged on the stem 10 carrying the piston plate 9. In the top view of the Figure 2 It can be seen that the switching device is Figure 1 This means that several first switching contact pieces 3 and several second switching contact pieces 4 are arranged parallel to one another and are actuated together. Thus, a switching device as shown in the Figures 1 and 2 shown, can be used for switching a multi-phase electrical power transmission system. The piston plate 9 is a substantially rectangular piston plate in which two similarly constructed control valves 13 are arranged. The control valves 13 serve to control the filling or emptying of the compression volume 6 with a fluid that is intended to flow through the switching path 2.

[0030] Starting from the off state as in Figures 1 and 2shown, a switching-on process will now be described. In order to bring the first switching contact pieces 3 closer to the second switching contact pieces 4, a rotation of the lever arm 11 is triggered. This moves the cylinder 5 in the direction of the second switching contact pieces 4. The compression volume 6 increases in the process. The control valves 13 are aligned in such a way that a valve body 14a, 14b, 14c now opens, so that an inflow of fluid into the compression volume 6 preferably takes place via the control valves 13. In addition, fluid can also flow in via the blow channels 7 of the first switching contact pieces 3. In the switched-on state ( Figure 3 ), the first and second switching contact pieces 3, 4 are electrically connected to one another. The compression volume 6 is filled with the largest possible amount of electrically insulating fluid. During a switching-off process ( Figure 3 after Figure 2), i.e., the first switching contact pieces 3 are separated from the second switching contact pieces 4 and moved away by them, a reduction of the compression volume 6 occurs. To carry out a switching operation, the lever 11 is moved with a changed direction of rotation. The stop buffers 12 each form stops for the moving cylinder 5 in order to brake it in its end positions. The valve bodies 14a, 14b, 14c block the control valves 13, so that fluid located within the compression volume 6 must flow out via the blow channels 7 of the first switching contact pieces 3 in the direction of the second switching contact pieces 4. As a result, the switching path 2 is flooded with uncontaminated, preferably cool, electrically insulating fluid, so that contaminated fluid is forced out of this area and any arc that may be present is flushed with the electrically insulating fluid. Figure 4In the off state, the position of the control valves 13 is symbolically shown. Figures 5 , 12 and 16 show variants of possible control valves 13. In the corresponding Figures 6 to 11 , 13 to 15 , as well as 17 to 19 show the functioning of the control valves 13, or their valve bodies 14a, 14b, 14c.

[0031] Regardless of the design of the control valves 13, 13a, 13b, 13c in terms of shape, number, etc., their function is selected to be identical for the switching device shown in the figures (earthing switch / quick earthing switch). During a switch-on process, the control valves 13, 13a, 13b, 13c are switched in such a way that a valve body 14a, 14b, 14c is moved out of its sealing position, allowing a fluid flow from the environment into the interior of the compression volume 6. During a switch-off process, the valve body 14a, 14b, 14c is pressed into its sealing position, allowing fluid to flow out of the compression volume 6, which decreases during a switch-off process, via the blow channels 7 of the first switching contact pieces 3.

[0032] The Figure 5 shows a piston plate 9 with stem 10 as shown in the Figures 1 to 4known. In the piston plate 9, a first embodiment of a control valve 13a is arranged twice, with a similar design being selected in each case. By doubling the control valves 13a, the flow capacity is increased. The control valve 13a in the first embodiment has a substantially cylindrical valve body 14a with a circular cross-section. The valve body 14a of the control valve 13a in the first embodiment is arranged between a first stop 15 and a second stop 16 (see Figures 6 to 11) is freely movable in the direction of a displacement axis of the cylinder 5. The valve body 14a is displaceably mounted in the manner of a clearance fit between the first and the second stop 15, 16. In the edge region of the valve body 14a of the control valve 13a in the first embodiment, a plurality of curved elongated holes are arranged distributed around the circumference, each forming a through opening 17. The cross section of the first stop 15 is selected such that it completely covers the through openings 17 and, when the valve body 14a of the control valve 13a rests against the first stop 15, these are blocked or dammed (cf. Figure 6 ). In contrast, the second stop 16 is dimensioned in such a way that it is positioned on the side viewed by the viewer of the Figure 5facing away, a support or a contact of the valve body 14a of the control valve 13a of the first embodiment in the edge area, so that when the valve body 14a contacts the second stop 16, the through openings 17 are not blocked (cf. Figure 8 ). The Figure 6 shows the position of the valve body 14a during a switch-off process, i.e., the valve body 14a is pressed into its sealing position at the first stop 15. A contact force is caused by the flow pressure of the flowing fluid, which is compressed inside the compression volume 6. With increasing pressure inside the compression volume 6, the contact force on the seat of the valve body 14a in its sealing position also increases. During a switch-on process, the direction of the flow pressure is reversed ( Fig. 7). This means that the compression volume 6 increases, whereby the flow pressure of the flowing fluid moves the valve body 14a away from the first stop 15 and presses it towards the second stop 16 ( Fig. 8 ). Now the recesses 17 are released and fluid can flow through the recesses 17 of the valve body 14a into the interior of the compression volume 6. In the embodiment according to the Figures 6 to 8 In each case, it is provided that the first or second stop 15, 16 is placed in front of a continuous channel of a relief opening in the piston plate 9, so that between the first or second stop 15, 16, the essentially cylindrical valve body 14a is guided by the inner surface of the channel in the piston plate 9 in the manner of a clearance fit.

[0033] In the Figures 9 to 11An alternative design of a first stop 15 is shown. The first stop 15 is formed by a shoulder in the channel of the piston plate 9. Only the second stop 16 is represented by a discretely mounted plate, which can be removed to insert the valve body 14a into its clearance seat. However, the function and mode of operation are different from the design variant shown in the Figures 6, 7 and 8 shown, identical.

[0034] The Figure 12shows, starting from the piston plate 9, a second embodiment of a control valve 13b, which is not part of the invention. Again, two similar control valves 13b are provided on the piston plate 9. Now, the use of an elastically deformable valve body 14b is provided. The elastically deformable valve body 14b again has a cylindrical shape with a circular cross-section. However, the valve body 14b of the second embodiment of a control valve 13b is positioned flat on the side of the piston plate 9 that faces the compression volume 6. For this purpose, a central screw connection is provided, wherein in the overlap area of ​​the valve body 14b of the second embodiment 13b, a relief opening with several channels is arranged in the piston plate 9, which is covered by the valve body 14b. Based on the Figures 13 to 15The operation of the control valve 13b in the second embodiment will now be described. During a switch-off process and the resulting reduction in the compression volume 6, the flow pressure presses a valve body 14b of the second embodiment of the control valve 13b against the wall (first stop 15) of the piston plate 9 and blocks the channels in the piston plate 9. Thus, during a switch-off process, the fluid in the compression volume 6 is pressed through the blow channels 7 of the first switching contact pieces 3 in the direction of the switching path 2. During a switch-on process, the direction of the flowing fluid is reversed. Now, due to the elastic deformability of the valve body 14b of the second embodiment, the flow pressure presses it out of the sealing seat and lifts it off the piston plate 9 at its free circumference.Held centrally by the second stop 16, elastically deformed, fluid flows into the interior of the compression volume 6 via the channels in the piston plate 9. The valve body 14b of the control valve 13b in the second embodiment variant is fixed at a point by the second stop 16.

[0035] The Figure 16shows a piston plate 9 with a control valve 13c in a third embodiment, which also does not form part of the invention. In the third embodiment, it is provided that an elastically deformable valve body 14c is clamped on one side (at the edge), so that a flap-like opening of the valve body 14c of the control valve 13c is possible in the third embodiment. A second stop 16, which has a convexly curved stop surface, serves to attach the valve body 14c at specific points. This makes it possible for the valve body 14c of the third control valve 13c to lift off from the first stop 15, which is formed by the surface of the piston plate 9, and to press against the second stop 16. Due to the convex curvature of the second stop 16, excessive deformation or mechanical stress, e.g. notching of the valve body 14c of the control valve 13c in the third embodiment, is prevented. In the Figures 17, 18, 19is essentially equivalent to the Figures 13, 14 and 15 The function of the control valve 13c in the third embodiment is shown. During a switch-off process, the compression volume 6 is reduced, whereupon a flow pressure presses the valve body 14c of the control valve 13c of the third embodiment against the first stop 15, whereby the valve body 14c completely covers and seals a relief opening in the piston plate 9 ( Figure 17 ). The valve body 14c is pressed into its sealing position. During a switching-on process, the compression volume 6 increases. Driven by the flow pressure, the valve body 14c of the control valve 13c in the third embodiment is moved away from the first stop 15 and pressed against the second stop 16. Fluids can now flow into the interior of the compression volume 6 via the relief opening in the piston plate 9.

Claims

1. Electrical switching device comprising a switching path (2) and a flow device with a control valve (13, 13a) for applying flow to the switching path (2), the control valve (13, 13a) comprising a movable valve body, the valve body (14a) being pressed into a sealing position by way of the flow pressure of a flowing fluid in the case of a switch-off operation and the valve body (14a) being movable in the manner of a clearance fit between a first stop (15) and a second stop (16), characterized in that the valve body (14a) comprises a through opening (17) which can be blocked by way of one of the stops (15, 16).

2. Electrical switching device according to Claim 1, characterized in that the control valve (13, 13a) is positioned in a stationary manner relative to the switching path (2).

3. Electrical switching device according to either of Claims 1 and 2, characterized in that the electrical switching device is an earthing switch, in particular a fast-acting earthing switch.

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