Parametric voltage limiter

Abstract

A parametric voltage limiter comprising at least one semiconductor switching element (3), at least one control device (4) for controlling the semiconductor switching element (3), a protective element (5), and a first connecting conductor (1) and a second connecting conductor (2), wherein at least one semiconductor switching element (3) is connected between the first connecting conductor (1) and the second connecting conductor (2), wherein the output of at least one control device (4) is connected to the input of the at least one semiconductor switching element (3), and the protective element (5) is connected in parallel to the at least one semiconductor switching element (3) between the first connecting conductor (1) and the second connecting conductor (2), characterized in that the parametric voltage limiter comprises at least one electrically operated switch (6) and at least one presence sensor (8) for objects,wherein the control device (4) is connected via at least one electrically operated switch (6), wherein at least one presence sensor (8) for objects is communicatively connected to the at least one electrically operated switch (6).

Description

Technical area

[0001] This technical solution concerns a protective device designed to reduce the voltage between two points with different potentials, particularly in railway traffic at points where grounded and insulated rails meet. The protective device establishes a temporary electrical connection between these points for the time the permissible voltage value is exceeded and the rolling stock is present, thus eliminating the possibility of an arc and preventing damage to the rail and wheel surfaces. State of the art

[0002] Voltage limiters are known in the art and reduce the voltage in certain parts of the circuit or at certain points where dangerous contact voltage can occur. Voltage limiters therefore have a wide range of applications, particularly in rail transport such as railways, trams and metros. When rails of different traction current systems come into contact or when an insulated part of the rail and an earthed part of the rail come into contact with the rail vehicle, sparking can occur. When a rail vehicle travels towards the point of contact between the insulated part of the rail and the earthed part of the rail, an electric arc is generated between the wheels and the rails if the first axle of the wagon group comes into contact with a rail whose potential is different from that of the rail on which the rail vehicle has been previously located.This phenomenon is even more pronounced when the last axle of the rail vehicle leaves the rail at a different electrical potential. The current can reach hundreds of amperes and thus has enough energy to create an electric arc and thus cause melting and welding of the material on the surface of the rail vehicle's wheels, which in turn causes the wheels to strike the rails. This leads to damage to the rail surface and the transmission of vibrations to the rail vehicle. This is an undesirable condition that must be eliminated by rotating the wheels. Sparking also occurs when multiple system rail vehicles change from one traction system to another, for example, when changing between a DC traction power system and an AC traction power system.

[0003] An example of a voltage limiter design is known from document CZ307422 B6. The described solution is a voltage limiter design based on semiconductor switching elements controlled by control circuits and a protection element against impulse overvoltages. The limiter design features a symmetrical distribution of components between the contact plates, which ensures uniform and efficient cooling of the components. The disadvantage of this solution is that when used to connect insulated and grounded busbars, high compensating currents can flow through the limiter, leading to permanent overload and subsequent failure.

[0004] Another limiter solution is known from document EP1855365 A1. The described solution is a voltage limiter based on a parallel counter-connection of two thyristors controlled by a trigger circuit. The circuit is additionally supplemented by a varistor, which serves as protection against impulse overvoltages. The document further describes the structural arrangement of the individual components. The disadvantages of this solution are its large space requirement, the complexity of the design, and also the fact that this limiter does not eliminate the problems of the generation of large compensating currents when connecting insulated and non-insulated rails or when connecting two traction power systems.

[0005] Another limiter solution is known from document EP0806071 B1, which primarily describes the limiter's electrical circuit, which also uses a circuit with multiple thyristors. The circuit is additionally supplemented by a short-circuit relay that short-circuits the connected components when necessary. The disadvantages of this solution are the same as those of the previous solutions, which do not eliminate the problems with large compensating currents, and in this case, there are also problems with the possible burning of the short-circuit relay contacts.

[0006] It was therefore desirable to find a solution that prevents sparking at the contact between an insulated and an earthed rail or at the contact between two traction current systems and at the same time ensures a reduction of leakage and compensating currents. Essence of the technical solution

[0007] The deficiencies of the prior art solutions are partially overcome by a parametric voltage limiter comprising a first connecting conductor and a second connecting conductor for connection to the traction system, between which at least one semiconductor switching element and at least one control device are connected, the output of which is connected to a control electrode of the semiconductor switching element, as well as at least one electrically operated switch connected between the control device and one of the connecting conductors of the control device or between the control device and the semiconductor switching element. The parametric voltage limiter further comprises at least one protective element, which preferably comprises at least one metal oxide varistor (MOV) and / or a gas-filled surge arrester (GDT) and / or a controlled spark gap.The protective element is connected in parallel to at least one semiconductor switching element between the first connecting conductor and the second connecting conductor. The parametric voltage limiter further comprises at least one object presence sensor communicatively connected to the at least one electrically operated switch.

[0008] The parametric voltage limiter is suitable for connection to two different points via connecting conductors. These two different points are characterized by the fact that they can each have a different electrical potential, meaning that an electrical voltage can exist between the points. A parametric voltage limiter reduces this electrical voltage. The voltage level between the connecting conductors is evaluated by the control device connected between the connecting conductors. The connecting conductors therefore also supply power to the control device. The active element for reducing the voltage between the first connecting conductor and the second connecting conductor is a semiconductor switching element connected between the first connecting conductor and the second connecting conductor. The semiconductor switching element has an input that controls its switching.This input of the semiconductor switching element is connected to the output of the control device. The control device switches the semiconductor switching element on or off based on the detected voltage between the connecting conductors. High pulse overvoltages can also occur on the connecting conductors, which can be caused, for example, by a lightning strike or another fault. A parametric voltage limiter therefore comprises at least one protective element connected in parallel to the control device. The protective element increases its internal conductivity at high voltage and is then passed through by the pulse current. This protects other parts of the circuit, in particular the control device, from the effects of overvoltages.

[0009] The control device is connected to the connecting conductors via an electrically operated switch, or the output of the control device is connected to a semiconductor switching element via an electrically operated switch. An electrically operated switch thus blocks or enables the operation of the control device. When the electrically operated switch is open, the function of the control device is blocked, and the parametric voltage limiter only reacts to a possible overvoltage with the help of a protective element. When the electrically operated switch is switched, the control device is active, and the parametric voltage limiter reacts to a voltage that exceeds the set limit by switching the semiconductor switching element. An object presence sensor is connected to the electrically operated switch and controls the electrically operated switch.In other words, when an object presence sensor detects the presence of an object—in a practical application, this is typically a rail vehicle—this sensor activates an electrically operated switch, which in turn activates a control device that switches on a semiconductor switching element through which a compensating current can flow, thereby limiting the voltage between the connecting conductors. The trip voltage level at the parametric limiter is preferably set to a value between 15 V and 25 V, which corresponds to a typical range of arc flash voltage values.A compensating current between the first and second connecting conductors only flows through the parametric voltage limiter if the object presence sensor detects an object and, at the same time, the voltage between the first and second connecting conductors is greater than the specified trigger voltage level. If both conditions are not met simultaneously—i.e., if the voltage between the rails is higher than the trigger voltage and the presence of an object is detected—the parametric voltage limiter will not react, or it is desirable for both rails to remain insulated. This effectively limits the potential occurrence of stray currents.

[0010] A parametric voltage limiter can comprise a control device for each semiconductor switching element. This means that each semiconductor switching element has its own control device. The advantage of separate control devices lies in the possibility of placing them symmetrically within the structure of the parametric voltage limiter, thus simplifying connection to the semiconductor switching element and also ensuring their uniform cooling. These control devices are connected via an electrically operated switch between the connecting conductors. Each control device can be connected via its own electrically operated switch, or preferably several control devices can be connected in parallel and connected to the connecting conductors preferably via a common electrically operated switch.

[0011] The parametric voltage limiter can comprise at least one control device, which preferably has at least two outputs. These outputs are connected to at least two semiconductor switching elements. One control device can therefore control two or more semiconductor elements. Multiple control devices with at least two outputs can be connected in the circuit, and each control device can control a group of multiple semiconductor switching elements. It is also possible to combine a control device with one output for controlling a single semiconductor switching element and a control device with multiple outputs for controlling multiple semiconductor switching elements. Preferably, the space required to accommodate a control device in the parametric voltage limiter is smaller.

[0012] The semiconductor switching element in a parametric voltage limiter can preferably be a thyristor, since thyristors are manufactured with sufficient parameters such as switching speed, maximum current, and power handling capacity. The voltage across the connecting leads can have different polarities, so it is preferable to choose a parallel counter-connection of at least two thyristors. This allows the thyristors to be arranged symmetrically in the parametric voltage limiter structure, 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. A thyristor always responds to the voltage between the connecting leads, which is forward-biased with respect to the voltage polarity.Each thyristor may be controlled by its own control device, or the parametric limiter may comprise a single control device having at least two outputs and controlling the corresponding thyristors according to the polarity of the voltage on the connecting conductors.

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

[0014] Preferably, the object presence sensor may be an optical sensor that responds to a change in the luminous flux caused by the presence of the detected object at the monitored location.

[0015] A camera with an object detection system can be advantageously used as an object presence sensor. Cameras with an object detection system can be configured to detect only a specific class of objects as needed, reducing the possibility of false detections that can occur, for example, due to changing lighting conditions. When an object is detected, the camera evaluates this condition and, based on this condition, activates the electrically operated switch and thus the control device.

[0016] The object presence sensor is preferably a light barrier. The light barrier comprises a light source and a light detector. A light source can emit light in the visible spectrum of radiation, but it can also emit light in the infrared range of radiation. Opposite the light source is an optical detector or several adjacent detectors arranged in a detector strip. The light from the light source hits these detectors, and the space between the light sources and the detectors is the space in which the sensor monitors the presence of the object. The present object partially or completely blocks the light falling on the optical detectors, and thanks to the decrease in the detected light, the light barrier evaluates the presence of the object in the monitored area.The light barrier detects objects in the monitoring area with sufficient accuracy even in changing lighting conditions and at the same time contains only simple evaluation logic.

[0017] The object presence sensor can be a pressure sensor. The pressure sensor can be mounted on the rail near the insulated contact of the grounded and insulated rail. A pressure sensor, based on the principle of a piezoelectric or resistance strain gauge, for example, responds to the pressure caused by the presence of a material object.

[0018] The parametric voltage limiter can be adapted by the first connecting conductor for connection to the earthed busbar and by the second connecting conductor for connection to the insulated busbar near the insulated contact of the two busbars. The first connecting conductor and the second connecting conductor can be terminated, for example, with electrically conductive cable lugs. These cable lugs are attached to the busbars, e.g. by a screw connection, to minimize contact resistance. The first connecting conductor and the second connecting conductor can also be terminated with terminals that are attached to the busbars. Alternatively, the first connecting conductor and the second connecting conductor can be provided with connection elements other than eyelets or terminals, if such connection elements enable a conductive connection of the connecting conductors to the busbar.The object presence sensor is designed to detect a rail vehicle. Some traction systems, such as the subway system, use rails insulated from the ground for operation. In some places, such as train washing systems, these rails are grounded. Another example is the contact between the DC and AC traction systems of trains. The DC traction system has insulated rails, while the AC traction system has grounded rails. Between the insulated rail and the grounded rail there is an insulated part, i.e. an insulated contact, to prevent permanent leakage currents. There may be a voltage difference between the insulated rail and the grounded rail. At the time when an insulated contact is passed over by a rail vehicle, the wheels and chassis of the vehicle temporarily connect the insulated rail to the grounded rail.The voltage difference causes electrical arcs to occur, which can damage the wheels of the rail vehicle or the top surface of the rail. The presence of a vehicle near the point of insulated contact between the grounded rail and the insulated rail is detected by the object presence sensor. This sensor activates the switching part of the parametric voltage limiter, which is connected to the grounded rail by the first connecting conductor and to the insulated rail by the second connecting conductor.If the voltage difference between the grounded rail and the insulated rail is greater than the set switching voltage, the semiconductor switching element is switched to a low-impedance state, establishing electrical connection between the insulated rail and the grounded rail. A compensating current flows through the switching semiconductor element, equalizing the electrical potential between the rails and preventing arcing. Once the rail vehicle has some wheels on the grounded rail and some on the insulated rail, the compensating current between the rails begins to flow through the rail vehicle structure, since the vehicle has a lower impedance than the impedance of the parametric voltage limiter. This restores the high-impedance state of the switching semiconductor element.The moment the last wheel passes from the rail to the insulated contact between the rails, the voltage between the rails suddenly rises to its original value. If it exceeds the arc voltage, an arc is created between the wheel and the rail. The parametric voltage limiter reacts to the voltage of this initial arc, and since the object presence sensor still detects the rail vehicle, the control device switches on the semiconductor switching element, which connects the insulated rail and the grounded rail and re-equalizes the electrical potential between the two rails, thus interrupting the resulting arc.

[0019] The object presence sensor can preferably be connected wirelessly to an electrically operated switch. As already mentioned above, the object presence sensor is communicatively connected to at least one electrically operated switch, with a wireless connection being one of the possible communication connection forms. Various wireless technologies such as radio signals, Wi-Fi, ZigBee, Bluetooth, and others can be used for wireless communication. Alternatively, the communication connection can also be established via electrical conductors.

[0020] An electromagnetic relay with electromagnetically actuated contacts can be used as an electrically actuated switch. In a preferred embodiment, the electromagnetic relay is double-pole, which further simplifies the design of the parametric voltage limiter.

[0021] In another preferred embodiment, the electrically operated switch is a semiconductor relay, known in technical practice as a solid-state relay (SSR). Solid-state relays (SSRs) can, in some cases, simplify the design and increase the reliability of the device.

[0022] In some embodiments, the electrically actuated switch may comprise a combination of conventional semiconductor and passive components, meaning it may be fabricated in many different ways and should not be considered limited to the embodiments disclosed herein.

[0023] When used herein, the term “and / or” includes all combinations of one or more of the related listed items.

[0024] A parametric voltage limiter can thus limit the occurrence of sparking and the formation of electrical arcs at the contact points of insulated and earthed rails. Explanation of drawings

[0025] The essence of the invention is further explained by means of embodiments which are described with the aid of the accompanying drawings, which show: Fig. Figure 1a shows a schematic representation of the electrical circuit of the switching part of the parametric voltage limiter, where the electrically operated switch is connected between the control device and the connecting conductor. Fig. Figure 1b shows a schematic diagram of the electrical circuit of the switching part of the parametric voltage limiter, where the electrically operated switch is connected between the output of the control device and the electrode of the semiconductor switching element. Fig. Figure 2 shows a schematic diagram of the circuit of the parametric voltage limiter for suppressing sparking at the transition of the rail vehicle between the insulated rail and the earthed rail. Examples of the technical solution

[0026] The technical solution is explained in more detail using exemplary embodiments with reference to the corresponding drawings.

[0027] The one in the Fig. 1a and Fig. The parametric voltage limiter shown in Figure 2 comprises, in its exemplary main embodiment, two semiconductor switching elements 3, two control devices 4, a protection element 5, a first connecting conductor 1, and a second connecting conductor 2. In this exemplary main embodiment, the semiconductor switching elements 3 are thyristors connected in parallel in opposite directions between the first connecting conductor 1 and the second connecting conductor 2. This means that the thyristors are connected in parallel but are oppositely oriented with respect to current flow. Each control device 4 is connected in parallel to the thyristor between the first connecting conductor 1 and the second connecting conductor 2 via an electrically operated switch 6. The output of each control device 4 is connected directly to the input of a thyristor.The protective element 5 is a metal oxide varistor (MOV) and is connected in parallel to the control devices 4. The protective element 5 protects the control device 4 from the potential effects of the pulse current. The basic structural arrangement of the thyristors, the control device 4, and the protective element in this main embodiment is identical to the embodiment in document CZ307422 B6, with the exception that the conductors for connecting the control devices 4 to the second connecting conductor 2 are routed outside the housing of the parametric voltage limiter and interrupted by electrically operated switches 6, which are also located outside the housing of the parametric voltage limiter. The circuit shown is the switching part 7 of the parametric limiter.

[0028] The parametric voltage limiter in this exemplary main embodiment further comprises an object presence sensor 8. The object presence sensor 8 is, for example, a light barrier comprising a light source and a light detector, and the barrier is connected via a conductor to the electrically operated switches 6. The light detector of the light barrier is arranged opposite the light source. At the moment the light beam is interrupted, the light detector of the light barrier detects this drop and activates the electrically operated switch 6.

[0029] The parametric voltage limiter in this exemplary main embodiment is adapted for connection between a grounded rail 9 and an insulated rail 10, wherein the first connecting conductor 1 and the second connecting conductor 2 are terminated with a cable lug. The grounded rail 9 and the insulated rail 10 have an insulating, non-conductive part, i.e., an insulated contact 12, at the contact point. The first connecting conductor 1 of the parametric voltage limiter is connected to the grounded rail 9 by a screw connection, and the second connecting conductor 2 of the parametric voltage limiter is connected to the insulated rail 10 by a screw connection. The light barrier is arranged at a location on the insulated contact 12 of the grounded rail 9 and the insulated rail 10, wherein the field of view of the light barrier is perpendicular to the direction of the rails.The light barrier detects the presence of the rail vehicle 11 at the location of the insulated contact 12 of the grounded rail 9 and the insulated rail 10. The rail vehicle 11 interrupts the light beam of the light barrier at the location of the insulated contact 12 of the grounded rail 9 and the insulated rail 10, which is detected by the light barrier's light detector, thereby activating the electrically operated switches 6, which switch on the control device 4. The control device is set to a trigger voltage level of 20 V.In the event that the voltage between the grounded rail 9 and the insulated rail 10 is greater than the trigger voltage, the control device 4 switches the thyristor, which is oriented in the forward direction, according to the polarity between the grounded rail 9 and the insulated rail 10. Thus, a compensating current begins to flow through the open thyristor, which limits the electrical voltage between the grounded rail 9 and the insulated rail 10. As soon as the wheels of the rail vehicle 11 are simultaneously 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 a lower impedance than the impedance of the open thyristor, thereby closing the thyristor.The moment the last wheels of the rail vehicle 11 approach the insulated contact 12 between the grounded rail 9 and the insulated rail 10, a brief electric arc is created between the wheels of the rail vehicle 11 and the rail from which they are dismounting. As soon as the voltage of the resulting brief electric arc exceeds the trigger voltage of 20 V, the control device 4 switches the corresponding thyristor according to the polarity of the voltage, forming a parallel current path to the brief electric arc with a much lower impedance than the impedance of this arc. Thus, a compensating current begins to flow through it between the grounded rail 9 and the insulated rail 10. Subsequently, the voltage between the wheel of the rail vehicle 11 and the rail is reduced to a few volts, and the resulting electric arc is interrupted.The energy of this arc is therefore low, which prevents damage to the surface of the wheels or rails. Alternative version:

[0030] The following describes alternative implementations of the individual features of the technical solution, which can be combined with each other where possible. The remaining features of these alternative implementations are identical to those of the exemplary main implementation.

[0031] In another exemplary embodiment, the Fig. The parametric voltage limiter shown in Figure 1b connects the output of the control device 4 to the control electrode of the semiconductor switching element 3 via an electrically operated switch 6. The object presence sensor 8 thus switches the electrically operated switch 6, which blocks or activates the output of the control device 4.

[0032] In a further exemplary embodiment, the parametric voltage limiter comprises a semiconductor switching element 3, which is a triac.

[0033] In another exemplary embodiment, the parametric voltage limiter comprises a control device 4 having two outputs. Each output of the control device 4 is connected directly to a semiconductor switching element 3.

[0034] In another exemplary embodiment, the parametric voltage limiter includes a camera as an object presence sensor 8, which contains a program for detecting the object in the image. The camera is aimed at the location of the insulated contact 12 of the grounded rail 9 and the insulated rail 10. The detection program in the camera is set to detect the presence of the rail vehicle 11.

[0035] In another exemplary embodiment, the parametric voltage limiter comprises a passive infrared sensor as the object presence sensor 8, whose field of view is directed toward the location of the insulated contact 12 of the grounded rail 9 and the insulated rail 10. The sensor registers the change in infrared radiation in the field of view due to the presence of the rail vehicle 11.

[0036] In another exemplary embodiment, the parametric voltage limiter includes a pressure sensor as an object presence sensor 8. This pressure sensor is a strain gauge sensor located at the end of the rails at the location of the insulated contact 12 of the grounded rail 9 and the insulated rail 10.

[0037] In a further exemplary embodiment, the presence sensor 8 for objects is connected to the electrically operated switch 6 via a radio signal. Industrial applicability

[0038] The parametric voltage limiter described above can be used in transportation systems with traction lines, such as railways, subways, or overhead contact lines, to prevent sparking at the contact between the insulated and the earthed rail or at the contact between two traction power systems, e.g., DC and AC traction power systems. List of reference symbols 1 First connecting conductor 2 Second connecting conductor 3 semiconductor switching element 4 Control device 5 protective element 6 Electrically operated switch 7 Switching part of a parametric voltage limiter 8 Presence sensor for objects 9 Earthed rail 10 Insulated rail 11 Rail vehicle 12 Isolated contact QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 1855365 A1

[0004] EP 0806071 B1

[0005]

Claims

[1] Parametric voltage limiter comprising at least one semiconductor switching element (3), at least one control device (4) for controlling the semiconductor switching element (3), a protective element (5) and a first connecting conductor (1) and a second connecting conductor (2), wherein at least one semiconductor switching element (3) is connected between the first connecting conductor (1) and the second connecting conductor (2), wherein the output of at least one control device (4) is connected to the input of the at least one semiconductor switching element (3) and the protective element (5) is connected in parallel to the at least one semiconductor switching element (3) between the first connecting conductor (1) and the second connecting conductor (2), characterized byin that the parametric voltage limiter comprises at least one electrically operated switch (6) and at least one object presence sensor (8), wherein the control device (4) is connected via at least one electrically operated switch (6), wherein at least one object presence sensor (8) is communicatively connected to the at least one electrically operated switch (6). [2] Parametric voltage limiter according to claim 1, characterized by that it comprises a control device (4) for each semiconductor switching element (3). [3] Parametric voltage limiter according to claim 1, characterized by that it comprises at least one control device (4) having at least two outputs, said outputs being connected to at least two semiconductor switching elements (3). [4] Parametric voltage limiter according to one of the preceding claims, characterized bythat the semiconductor switching element (3) is a thyristor, wherein the parametric voltage limiter comprises a parallel counter-connection of at least two thyristors. [5] Parametric voltage limiter according to one of the preceding claims, characterized by that the protective element comprises at least one varistor. [6] Parametric voltage limiter according to one of the preceding claims, characterized by that the presence sensor (8) for objects is an optical sensor. [7] Parametric voltage limiter according to claim 6, characterized by that the optical sensor is a light barrier. [8] Parametric voltage limiter according to one of claims 1 to 5 characterized by that the presence sensor (8) for objects is a pressure sensor. [9] Parametric voltage limiter according to one of the preceding claims, characterized byin that the first connecting conductor (1) is adapted for connection to the earthed rail (9) and the second connecting conductor (2) is adapted for connection to the insulated rail (10) at the point of insulating contact between the earthed rail (9) and the insulated rail (10), wherein the presence sensor (8) for objects is adapted for detection of the rail vehicle (11). [10] Parametric voltage limiter according to one of the preceding claims, characterized by that the presence sensor (8) for objects is wirelessly connected to the electrically operated switch (6).

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