Parametric voltage limiter

Abstract

The invention relates to a parametric voltage limiter comprising at least one semiconductor switching element (3), at least one control device (4), a protection element (5), and a first connecting wire (1) and a second connecting wire (2). The parametric voltage limiter further comprises at least one electrically actuated switch (6) and at least one object presence detector (8). The control device (4) is connected between the first connecting wire (1) and the second connecting wire (2) via at least one electrically actuated switch (6). The at least one object presence detector (8) is communicatively connected to at least one electrically actuated switch (6). Figure 1a

Description

Title of the invention: Parametric voltage limiter technical field

[0001] The present technical solution relates to a protective device whose function is to reduce the voltage between two points having a different voltage potential, particularly in rail transport, at the points where grounded and insulated rails meet. The protective device ensures a temporary electrical connection of these points during the period when the permissible voltage value is exceeded and a rail vehicle is present, thus eliminating the possibility of arcing and preventing damage to the rail surface and wheels. Prior art

[0002] Voltage limiters that reduce voltage in certain parts of a circuit or at certain points where a dangerous touch voltage may occur are known from the current state of the art. Voltage limiters therefore have a wide range of applications, particularly in rail transport such as trains, trams, and subways. In the event of contact between rails of different railway electrification systems, or in the event of contact between an insulated section of the rail and an earthed section of the rail with a railway vehicle, sparks may occur. If the railway vehicle is moving towards the point of contact between the insulated and earthed sections of the rail, at the moment the first axle of the train makes contact with the rail, which has a different potential than the rail on which the railway vehicle was previously traveling, an electric arc forms between the wheels and the rails.This phenomenon is even more intense when the last axle of the rail vehicle leaves the rail with a different electrical potential. The current can reach hundreds of amperes, providing sufficient energy to create an electric arc. This causes the material on the surface of the rail vehicle's wheels to melt and weld together, resulting in the wheels impacting the rails. This damages the rail surface and transmits vibrations to the rail vehicle. This undesirable situation must be eliminated by repairing the wheels through machining. Sparks also occur when multi-system rail vehicles switch from one railway electrification system to another, for example, when switching from a direct current (DC) to an alternating current (AC) system.

[0003] An example of a voltage limiter design is known from document CZ307422 B6. The described solution presents the design of a voltage limiter based on semiconductor switching elements controlled by control circuits and on an element for protection against impulse overvoltages. The limiter is designed with a symmetrical arrangement of different parts between the contact plates, which ensures uniform and efficient cooling of the components. The disadvantage of this solution is that, when used to connect an insulated track and a grounded track, it can be subjected to high equalizing currents, leading to its permanent overload and, subsequently, its failure.

[0004] Another limiter solution is known from document EP1855365 AL. The described solution presents a voltage limiter based on an antiparallel arrangement of two thyristors controlled by a trigger circuit. The circuit is further supplemented by a varistor which serves as protection against impulse overvoltages. The document also describes the structural arrangement of the various parts. The disadvantages of this solution are its large size, the complexity of the design, and the fact that this limiter does not eliminate the problems associated with the occurrence of high equalizing currents when connecting an insulated rail and a non-insulated rail or when connecting two electrification systems.

[0005] Another limiter solution is known from document EP0806071 B1, which describes, in particular, the electrical connection of the limiter, which also uses a multi-thyristor connection. The circuit is further completed by a short-circuit relay which, if necessary, short-circuits the connected parts. The disadvantages of this solution are identical to those of the previous solutions, since it does not eliminate the problems associated with high equalizing currents and, moreover, here it adds problems related to the possible burning of the short-circuit relay contacts.

[0006] It was therefore desirable to provide a solution to prevent sparks when an insulated rail contacts an earthed rail or when two electrification systems contact each other, while ensuring a reduction in leakage currents and equalization. Description of the technical solution

[0007] The drawbacks of known prior art solutions are partially eliminated by a parametric voltage limiter comprising a first connecting wire and a second connecting wire for connection to the railway electrification system, between which are connected at least one solid-state switching element and at least one control device, the output of which is connected to the control electrode of the solid-state switching element, and at least one electrically controlled switch which is connected between the control device and one of the connecting wires of the control device, or which is connected between the The control device and the solid-state switching element. The parametric voltage limiter further includes at least one protection element, preferably comprising at least one metal oxide varistor (MOV) and / or a gas discharge tube (GDT) and / or a controlled spark gap. The protection element is connected in parallel to at least one solid-state switching element between the first and second connecting wires. The parametric voltage limiter further includes at least one object presence detector communicating with at least one electrically controlled switch.

[0008] The parametric voltage limiter is adapted to be connected to two different points via connecting wires. These two different points are characterized in that they may each have a different electrical potential, and an electrical voltage may therefore exist between them. The parametric voltage limiter reduces this electrical voltage. The voltage between the connecting wires is evaluated by the control device, which is connected between the wires. Thus, the connecting wires simultaneously supply power to the control device. The active element for reducing the voltage between the first and second connecting wires is a semiconductor switching element connected between the first and second connecting wires. This semiconductor switching element has an input through which its switching is controlled.This input of the solid-state switching element is connected to the output of the control device. Thus, the control device opens or closes the solid-state switching element depending on the voltage detected between the connecting wires. High impulse overvoltages can also occur on the connecting wires, for example, as a result of a lightning strike or other fault. Therefore, the parametric voltage limiter includes at least one protective element connected in parallel with the control device. At high voltage, the protective element increases its internal conductivity and is then traversed by the impulse current. In this way, other parts of the circuit, including the control device, are protected from the effects of overvoltages.

[0009] The control device is connected to the connecting wires via the electrically operated switch, or the output of the control device is connected via the electrically operated switch to the solid-state switching element. The electrically operated switch thus blocks or activates the operation of the control device. If the electrically operated switch is open, the operation of the control device is blocked, and the parametric voltage limiter reacts only to possible overvoltages using the protective element. If the electrically operated switch is closed, the control device is active, and the parametric voltage limiter reacts to Voltages exceeding the defined limit are prevented by closing the solid-state switching element. An object presence detector is communicatively connected to the electrically operated switch, thereby controlling the switch. In other words, if the object presence detector senses an object—typically a railway vehicle in a practical application—it closes the electrically operated switch. This switch then activates the control device, which closes the solid-state switching element. An equalizing current can then flow through this element, reducing the voltage between the connecting wires. The trip voltage level of the parametric voltage limiter is preferably set to a value between 15 and 25 V, representing a typical range of DC arc voltage values.The parametric voltage limiter is therefore not affected by the equalizing current between the first and second connecting wires unless the object presence detector detects an object and, at the same time, the voltage between the first and second connecting wires exceeds the tripping voltage level. If both conditions are not met simultaneously—that is, the voltage between the rails exceeds the tripping voltage and an object is detected—the parametric voltage limiter does not react. Therefore, it is desirable for the two rails to remain isolated. This effectively limits the potential occurrence of stray currents.

[0010] The parametric voltage limiter may include a control device for each solid-state switching element. This means that each solid-state switching element has its own control device. The advantage of separate control devices is the possibility of placing them symmetrically in the design of the parametric voltage limiter, thus simplifying the connection to the solid-state switching element and also ensuring uniform cooling. These control devices are connected between the connecting wires via the electrically controlled switch. Each control device may be connected via its own electrically controlled switch, or, preferably, several control devices may be connected in parallel and, preferably, connected to the connecting wires via a common electrically controlled switch.

[0011] The parametric voltage limiter may include at least one control device having, preferably, at least two outputs. These outputs are connected to at least two semiconductor switching elements. A control device can thus control two or more semiconductor elements. Several control devices having at least two outputs can be connected to the circuit, each control device thus being able to control a group of It is also possible to combine a single-output control device to control one solid-state switching element and a multi-output control device to control several solid-state switching elements. Advantageously, this reduces the space required to integrate a control device into the parametric voltage limiter.

[0012] The semiconductor switching element of a parametric voltage limiter can preferably be a thyristor, since thyristors are manufactured with sufficient parameters, such as switching speed, maximum current, and load capacity. As the voltage across the connecting wires can have different polarities, it is advantageous to choose an antiparallel arrangement of at least two thyristors. The thyristors can thus be placed symmetrically in the design of the parametric voltage limiter, which ensures more efficient cooling. The anode of the first thyristor is connected to the cathode of the second thyristor, and the cathode of the first thyristor is connected to the anode of the second thyristor. Therefore, the thyristor connected in the forward direction with respect to the voltage polarity always reacts to the voltage across the connecting wires.Each thyristor can be controlled by its own control device, or the parametric limiter can include a control device having at least two outputs and controlling the corresponding thyristors according to the polarity of the voltage on the connecting wires.

[0013] The protection element of the parametric voltage limiter may preferably comprise at least one varistor, for example a metal oxide varistor (MOV), and / or a gas discharge tube (GDT), and / or a controlled spark gap. These elements may be combined and connected in series-parallel to improve the protection parameters against impulse currents.

[0014] The object presence detector is preferably an optical sensor that reacts to a variation in the luminous flux caused by the presence of an object detected in the monitored area.

[0015] A camera equipped with an object recognition system can preferably be used as an object presence detector. Cameras with object recognition systems can be configured, as needed, to detect only a specific class of objects, and they also reduce the risk of false detections due, for example, to varying lighting conditions. When an object is present, the camera evaluates this state and, based on this state, activates the electrically controlled switch, thereby activating the control device.

[0016] The object presence detector is preferably a light barrier. The light barrier comprises a light source and a light detector. The light source may emit light in the visible spectrum, but it may also emit Light is also detected in the infrared range. Opposite the light source is an optical detector, or several detectors arranged side-by-side in a detector strip. Light from the light source reaches these detectors, and the space between the light sources and the detectors is the area in which the sensor monitors for the presence of an object. The object partially or completely blocks the light reaching the optical detectors, and due to the reduction in detected light, the light barrier detects the presence of an object in the monitored area. The light barrier detects objects within the monitored area with sufficient accuracy, even under varying lighting conditions, while requiring only simple evaluation logic.

[0017] The object presence detector can be a pressure sensor. The pressure sensor can be installed on the track, near the insulated contact of a grounded rail and an insulated rail. The pressure sensor, for example according to the principle of a piezoelectric or resistance tensiometer, reacts to the pressure due to the presence of a physical object.

[0018] The parametric voltage limiter can be adapted for connection via the first connecting wire to the grounded rail and the second connecting wire to the insulated rail near the insulated contact point of the two rails. The first and second connecting wires can be terminated with conductive ring terminals, for example. These ring terminals are fixed to the rails, for example, by means of a screw connection in order to minimize transient resistance. The first and second connecting wires can also be terminated with rail-connected terminals. Alternatively, the first and second connecting wires can be provided with connection elements other than ring terminals or terminals, where such connection elements allow a conductive connection of the connecting wires to the rail. The object presence detector is adapted for detecting a railway vehicle.Some electrification systems, such as subways, use rails insulated from the ground. In certain locations, such as train wash stations, these rails are grounded. Another example is the contact between the direct current (DC) and alternating current (AC) electrification systems of trains. The DC electrification system uses insulated rails, while the AC electrification system uses grounded rails. Between the insulated rail and the grounded rail is an insulated section, or isolated contact, to prevent continuous leakage currents. There may be a voltage difference between the insulated and grounded rails. When a train passes over this isolated contact, the wheels and chassis of the train temporarily connect the insulated and grounded rails.The voltage difference causes electrical arcs that can damage the wheels of the railway vehicle or the . upper part of the rail. The presence of a vehicle near the isolated contact between the grounded and insulated rails is detected by the object presence detector. This detector activates the switching section of the parametric voltage limiter, which is connected by the first wire to the grounded rail and by the second wire to the insulated rail. If the voltage difference between the grounded and insulated rails exceeds the defined switching voltage value, the solid-state switching element switches to a low-impedance state, thus establishing the electrical connection between the insulated and grounded rails. The solid-state switching element is then supplied with equalizing current, thereby equalizing the electrical potential between the rails and preventing arcing.Once some wheels of the rail vehicle are resting on the grounded rail and others on the insulated rail, the equalizing current between the rails begins to flow through the rail vehicle structure because the vehicle's impedance is lower than that of the parametric voltage limiter. The high-impedance state of the solid-state switching element is thus restored. As the last wheel moves from the track to the insulated contact between the tracks, the voltage between the rails rises sharply to its initial value, and if it exceeds the arc voltage, an electric arc will form between the wheel and the rail.The parametric voltage limiter reacts again to the voltage of this initial arc and, as the object presence detector continues to detect the railway vehicle, the control device closes the solid-state switching element that connects the insulated rail and the grounded rail and the electrical potential between the two rails is rebalanced, thus interrupting the nascent electric arc.

[0019] The object presence detector can preferably be wirelessly connected to the electrically operated switch. As described above, the object presence detector is connected, via a communication interface, to at least one electrically operated switch, with wireless connection being one possible embodiment of the communication link. Various wireless technologies such as radio signal, Wi-Fi, Zig-Bee, Bluetooth, and others can be used for wireless communication. Alternatively, the communication link can be established using electrical wires.

[0020] The electrically controlled switch can be an electromagnetic relay having electromagnetically controlled contacts. In a preferred embodiment, the electromagnetic relay is bipolar, which further simplifies the design of the parametric voltage limiter.

[0021] In another preferred embodiment, the electrically controlled switch is a solid-state relay, known in technical practice as a solid-state relay (SSR). The solid-state relay (SSR) can, in certain cases, simplify the design and increase the reliability of the device.

[0022] In some embodiments, the electrically controlled switch may comprise a combination of conventional semiconductor and passive components, which allows it to be manufactured in many different ways and it should not be interpreted as being limited to the embodiments described in this document.

[0023] In this document, the term "and / or" includes any combination of one or more of said associated elements.

[0024] Thus, a parametric voltage limiter can limit the occurrence of sparks and electric arcs at the contact points of an insulated rail and a grounded rail. Drawing description

[0025] The essence of the technical solution is explained in more detail with the help of examples of its implementation, described with the aid of the accompanying drawings, on which:

[0026] Fig. 1a is a schematic representation of the electrical connection of the switching part of the parametric voltage limiter, where the electrically controlled switch is connected between the control device and the connecting wire.

[0027] The [Fig. 1b] is a schematic representation of the electrical connection of the switching part of the parametric voltage limiter, where the electrically controlled switch is connected between the output of the control device and the control electrode of the semiconductor switching element.

[0028] Figure 2 is a schematic representation of the limiter connection parametric voltage for spark suppression when a railway vehicle passes between an insulated rail and an earthed rail.

[0029] Examples of implementation of the technical solution

[0030] The technical solution will be explained in more detail by the implementation examples, with reference to the corresponding drawings.

[0031] The parametric voltage limiter, illustrated in [Fig. 1a] and 2, comprises, in its principal embodiment, two semiconductor switching elements 3, two control devices 4, a protection element 5, a first connecting wire 1, and a second connecting wire 2. In this principal embodiment, the semiconductor switching elements 3 are thyristors connected in antiparallel between the first connecting wire 1 and the second connecting wire 2. This means that the thyristors are connected in parallel, but with opposite orientations in terms of the direction of electric current flow. Each control device 4 is connected in parallel to the thyristor between the first connecting wire 1 and the second connecting wire 2 via an electrically controlled switch 6. The output of each control device 4 is connected to the input of a single thyristor.The protection element 5 is an oxide varistor. metallic (MOV) and is connected in parallel to the control devices 4. The protective element 5 protects the control device 4 against the possible effects of the impulse current. The basic structure of the thyristors, the control device 4, and the protective element is identical in this main embodiment to that of the embodiment in document CZ307422 B6, the difference being that the connecting wires from the control devices 4 to the second connecting wire 2 exit the housing of the parametric voltage limiter and are interrupted by electrically operated switches 6, also located outside the housing of the parametric voltage limiter. This connection constitutes the switching section 7 of the parametric voltage limiter.

[0032] The parametric voltage limiter of this main embodiment further includes an object presence detector 8. This object presence detector 8 is, for example, a light barrier comprising a light source and a light detector, and the barrier is connected by a wire to the electrically operated switches 6. The light detector of the light barrier is located opposite the light source. When the light beam is interrupted, the light detector of the light barrier detects this interruption and activates the electrically operated switch 6.

[0033] In this principal embodiment, the parametric voltage limiter is adapted for the connection between the grounded rail 9 and the insulated rail 10, the first connecting wire 1 and the second connecting wire 2 being terminated by a cable lug. The grounded rail 9 and the insulated rail 10 have a non-conductive insulating section at the point of contact, hence an insulated contact 12. The first connecting wire 1 of the parametric voltage limiter is connected to the grounded rail 9 by a screw connection and the second connecting wire 2 of the parametric voltage limiter is connected to the insulated rail 10 by a screw connection. The light barrier is positioned at the insulated contact point 12 of the grounded rail 9 and the insulated rail 10, the field of vision of the light barrier being perpendicular to the direction of the rails.The light barrier detects the presence of a rail vehicle 11 at the insulated contact point 12 of the grounded rail 9 and the insulated rail 10. The rail vehicle 11, at the insulated contact point 12 of the grounded rail 9 and the insulated rail 10, interrupts the light beam of the light barrier, which is detected by the light barrier's light detector. This activates the electrically controlled switches 6, which close the control device 4. The control device is set to a trip voltage level of 20 V. If the voltage between the grounded rail 9 and the insulated rail 10 is higher than the trip voltage, the control device 4 closes the forward-biased thyristor, according to the polarity between the grounded rail 9 and the insulated rail 10, consequently equalizing the current. Current begins to flow through the open thyristor, which limits the electrical voltage between the grounded rail 9 and the insulated rail 10. Once the wheels of the rail vehicle 11 are simultaneously positioned on the grounded rail 9 and the insulated rail 10, the rail vehicle 11 connects the grounded rail 9 to the insulated rail 10. This connection has an impedance lower than the impedance of the open thyristor, causing the thyristor to close. As the last wheels of the rail vehicle 11 enter the insulated contact 12 between the grounded rail 9 and the insulated rail 10, a short electrical arc forms between the wheel of the rail vehicle 11 and the rail it is leaving.As soon as the voltage of the incipient short electric arc exceeds the 20 V trigger voltage, the control device 4 closes, according to the voltage polarity, the corresponding thyristor, which creates a parallel current path to the short electric arc. This path has a much lower impedance than the arc itself, and therefore the equalizing current between the grounded rail 9 and the insulated rail 10 begins to flow through it. Subsequently, the voltage between the wheel of the rail vehicle 11 and the rail is reduced to a level of several units of volts, and the forming electric arc is interrupted. The energy of this arc is thus low, preventing damage to the surface of the wheels or rails. Alternative embodiment

[0034] Alternative embodiments of various features of the technical solution, which can be combined where possible, are described below. The other features of these alternative embodiments are identical to those of the main embodiment.

[0035] In another embodiment, the parametric voltage limiter, illustrated in [Fig.lb], is connected at the output of the control device 4 via an electrically controlled switch 6 to the control electrode of the semiconductor switching element 3. The object presence detector 8 thus closes the electrically controlled switch 6, which blocks or activates the output of the control device 4.

[0036] In another embodiment, the parametric voltage limiter includes a semiconductor switching element 3 which is a triac.

[0037] In another embodiment, the parametric voltage limiter includes a control device 4 having two outputs. Each output of the control device 4 is connected to a single solid-state switching element 3.

[0038] In another embodiment, the parametric voltage limiter includes, like the object presence detector 8, a camera containing an object detection program in an image. The camera is directed towards the insulated contact point 12 of the grounded rail 9 and the insulated rail 10. The camera's detection program is adapted to detect the presence of a railway vehicle 11.

[0039] In another embodiment, the parametric voltage limiter includes, like the object presence detector 8, a passive infrared sensor whose field of vision is directed towards the isolated contact point 12 of the grounded rail 9 and the isolated rail 10. The sensor records a variation of the infrared radiation in the field of vision due to the presence of a railway vehicle 11.

[0040] In another embodiment, the parametric limiter includes, like the object presence detector 8, a pressure sensor. This pressure sensor is a strain gauge sensor, located at the end of the rails, at the insulated contact point 12 of the grounded rail 9 and the insulated rail 10.

[0041] In another embodiment, the object presence detector 8 is connected to the electrically controlled switch 6 by a radio signal. Industrial applicability

[0042] The parametric voltage limiter described above can be used in transport using traction lines, such as trains, subways or trolleybuses, where it serves to prevent the formation of sparks at the contact of an insulated rail and an earthed rail or at the contact of two electrification systems, for example, DC and AC traction systems. List of reference signs

[0043] 1 - First connecting wire 2 - Second connecting wire 3 - Semiconductor switching element 4 - Control device 5 - Protective element 6 - Electrically operated switch 7 - Switching section of the parametric voltage limiter 8 - Object presence detector 9 - Rail grounded 10 - Insulated rail 11 - Railway vehicle 12 - Isolated contact

Claims

Demands

1. A parametric voltage limiter comprising at least one solid-state switching element (3), at least one control device (4) for controlling the solid-state switching element (3), a protection element (5), and a first connecting wire (1) and a second connecting wire (2), at least one solid-state switching element (3) being connected between the first connecting wire (1) and the second connecting wire (2), the output of at least one control device (4) being connected to the input of at least one solid-state switching element (3), and the protection element (5) being connected in parallel to at least one solid-state switching element (3) between the first connecting wire (1) and the second connecting wire (2), characterized in that the parametric voltage limiter comprises at least one electrically controlled switch (6) and at least one object presence detector (8),the control device (4) being connected via at least one electrically operated switch (6), at least one object presence detector (8) being connected, in a communicative manner, to at least one electrically operated switch (6).

2. The parametric voltage limiter according to claim 1, characterized in that it comprises for each semiconductor switching element (3) a control device (4).

3. The parametric voltage limiter according to claim 1, characterized in that it comprises at least one control device (4) having at least two outputs, these outputs being connected to at least two semiconductor switching elements (3).

4. Parametric voltage limiter according to any one of the preceding claims, characterized in that the semiconductor switching element (3) is a thyristor, the parametric voltage limiter comprising an antiparallel arrangement of at least two thyristors.

5. Parametric voltage limiter according to any one of the preceding claims, characterized in that the protection element comprises at least one varistor.

6. Parametric voltage limiter according to any one of the preceding claims, characterized in that the object presence detector (8) is an optical sensor.

7. Parametric voltage limiter according to claim 6, characterized in that the optical sensor is a light barrier.

8. Parametric voltage limiter according to any one of claims 1 to 5, characterized in that the object presence detector (8) is a pressure sensor.

9. Parametric voltage limiter according to any one of the preceding claims, characterized in that the first connecting wire (1) is adapted to be connected to the grounded rail (9) and the second connecting wire (2) is adapted to be connected to the insulated rail (10) at the insulating contact point between the grounded rail (9) and the insulated rail (10), the object presence detector (8) being adapted to detect the railway vehicle (11).

10. Parametric voltage limiter according to any one of the preceding claims, characterized in that the object presence detector (8) is wirelessly connected to the electrically controlled switch (6).

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