Rail potential limiting device for suppressing leakage of stray current and power supply system

Abstract

The application belongs to the technical field of electrified rail transit, and relates to a rail potential limiting device for suppressing stray current leakage and a power supply system. The device comprises a protection switch unit and a power electronic conversion unit. When it is detected that the rail potential at a traction substation of a rail transit direct-current traction power supply system exceeds a safety threshold, the protection switch unit clamps the rail potential at the traction substation to zero, and the power electronic conversion unit builds a zero potential point on the rail, thereby reducing stray current leakage to the ground. When it is detected that the rail potential at the traction substation is within the safety threshold, the protection switch unit does not act, and the power electronic conversion unit actively adjusts the rail potential at the traction substation, significantly suppresses the rail potential and stray current of the rail transit direct-current traction power supply system, and thus greatly reduces the frequency of action of the rail potential limiting device due to excessive rail potential.

Description

Technical Field

[0001] This application belongs to the field of electrified rail transit technology, and relates to rail potential and stray current protection technology in urban rail transit. Specifically, it relates to a rail potential limiting device for suppressing stray current leakage in rail transit and a DC traction power supply system for rail transit. Background Technology

[0002] Rail transit, with its outstanding advantages of large capacity, high speed, safety, reliability, energy saving, and environmental protection, has become an important part of modern urban public transportation. The DC traction power supply system, as the backbone of power transmission in urban rail transit, undertakes the critical task of providing power to trains. However, DC traction power supply systems generally use rails (also called tracks or running rails) as the return path for train current to return to the negative terminal of the traction substation. Since the rails and the ground are not completely insulated, some current leaks from the rails to the ground; this leakage current is called stray current. Simultaneously, the leakage current creates a potential difference between the rails and the ground; this potential difference is called the rail potential (also called track potential). Stray currents accelerate the electrochemical corrosion of buried metal pipes and structural steel reinforcement, induce DC bias in neutral-point grounding transformers along the line, and even trigger the DC frame protection devices in the traction substation, leading to large-scale power outages. Furthermore, excessively high rail potentials seriously threaten passenger safety and the normal operation of station equipment. Therefore, rail potential and stray current problems have become significant hidden dangers hindering the safe operation of rail transit.

[0003] Currently, the commonly used protection solution in rail transit systems is to install rail potential limiting devices in traction substations or stations. These devices monitor the rail potential at the installation location in real time. When the detected potential exceeds a set threshold, they clamp the rail potential to zero by directly short-circuiting the negative terminal of the traction substation or the rail to the grounding grid, thereby eliminating dangerous voltage in a localized area and achieving safety protection. However, while these rail potential limiting devices effectively control local potential in practical applications, they also bring several significant negative impacts. First, because the device directly short-circuits the rail to the grounding grid when activated, the train current that should flow back along the rail will leak in large quantities to the ground through this low-resistance branch. This leaked stray current will far exceed the stray current leaked during normal system operation, seriously threatening the normal and stable operation of rail transit, underground pipelines, and urban power grids along the line. Secondly, abnormal fluctuations in rail potential are often sudden and frequent, especially during morning and evening rush hours or periods of high-volume operation. Repeated exceedances of rail potential will cause frequent activation of rail potential limiting devices, posing a severe challenge to the high-power contactors inside the devices and significantly increasing the daily maintenance costs and risk of failure. Finally, the protection logic of this device also has systemic flaws. When a rail potential exceeds the limit at a certain location, causing the device to activate, although the rail potential at that location is suppressed, it causes an abnormal rise in the rail potential of adjacent sections or nearby stations. This causes nearby rail potential limiting devices to activate successively due to the increased voltage, affecting the overall operational stability and safety of the system.

[0004] In summary, while traditional rail potential limiting devices meet the basic requirements for rail transit safety protection to a certain extent, there is still considerable room for improvement in terms of stray current suppression, equipment durability, and global collaborative protection. Further research on the topology and control of rail potential limiting devices is urgently needed. Summary of the Invention

[0005] This application addresses the aforementioned problems in existing technologies, such as increased stray current leakage, frequent operation during peak hours, and abnormal rise in rail potential. It provides a rail potential limiting device and a DC traction power supply system for rail transit to suppress stray current leakage, which can effectively suppress abnormal rise in rail potential and stray current leakage in rail transit.

[0006] In a first aspect, this application provides a rail potential limiting device for suppressing stray current leakage in rail transit, including a protective switch unit and a power electronic conversion unit;

[0007] When the rail potential at the traction substation of the DC traction power supply system of the rail transit is detected to exceed the safety threshold, the protection switch unit directly short-circuits the negative terminal of the traction substation to the grounding grid of the DC traction power supply system of the rail transit, clamping the rail potential at the traction substation to zero. The power electronic conversion unit actively adjusts the output voltage to make the rail potential at the traction substation and the switch device connected to the DC traction power supply system of the rail transit equal, that is, to build a zero potential point on the rail to suppress rail potential and stray current.

[0008] When the rail potential at the traction substation is detected to be within a safe threshold, the protection switch unit does not operate, and the power electronic conversion unit actively adjusts the rail potential at the traction substation to limit the rail potential at the traction substation within a set threshold, thereby suppressing rail potential and stray current.

[0009] In some embodiments, the protection switch unit detects the rail potential at the traction substation and the status of internal components of the power electronic conversion unit in real time.

[0010] When an open-circuit or short-circuit fault is detected in the internal components of the power electronic converter unit, the protection switch unit directly short-circuits the negative terminal of the traction substation to the return line of the DC traction power supply system of the rail transit, so as to ensure that the fault of the power electronic converter unit will not affect the rail potential safety protection of the rail potential limiting device.

[0011] In some embodiments, the power electronic conversion unit draws power from the AC power grid or the contact network, and through its internal power electronic energy conversion and the duty cycle control of its switching transistors, it outputs multipolarity and actively adjusts the distribution pattern of rail potential within the power supply section, so that the rail potential at the location of the traction substation is limited within a safe threshold.

[0012] In a second aspect, this application provides a DC traction power supply system for rail transit, including a traction substation, a contact network, rails, a train, a rail potential limiting device, a switching device, a return line, and a grounding grid.

[0013] The positive terminal of the traction substation is connected to the contact network, the negative terminal is connected to the rail, and the AC terminal is connected to the AC power grid. The return line is arranged along the rail. The switching device is installed between adjacent traction substations. The first connection terminal of the switching device is connected to the rail, and the second connection terminal of the switching device is connected to the return line. The rail potential limiting device is installed in each traction substation. The first connection terminal of the rail potential limiting device is connected to the negative terminal of the traction substation, the second connection terminal of the rail potential limiting device is connected to the grounding grid, the third connection terminal of the rail potential limiting device is connected to the AC power grid, and the fourth connection terminal of the rail potential limiting device is connected to the return line.

[0014] The rail potential limiting device includes a protection switch unit and a power electronic conversion unit. When the rail potential at the traction substation is detected to exceed a safety threshold, the protection switch unit directly short-circuits the negative terminal of the traction substation to the grounding grid, clamping the rail potential at the traction substation to zero. The power electronic conversion unit actively adjusts the output voltage to make the rail potential at the traction substation equal to that at the conducting switch device, thus creating a zero-potential point on the rail to reduce stray current leakage to ground. When the rail potential at the traction substation is detected to be within the safety threshold, the protection switch unit does not operate, and the power electronic conversion unit actively adjusts the rail potential at the traction substation to limit it within a set threshold, thereby suppressing rail potential and stray current.

[0015] In some embodiments, when the system is in normal operating condition:

[0016] The switching device monitors the running position of the train, and the switching device closest to the left and right ends of the train is turned on, while the other switching devices are turned off.

[0017] When the protection switch unit does not operate, the first contactor and thyristor located between the first and second connection terminals of the rail potential limiting device in the protection switch unit are disconnected, and the second contactor located between the first and fourth connection terminals of the rail potential limiting device is disconnected.

[0018] The power electronic conversion unit outputs a negative voltage during train traction, a positive voltage during train braking, and zero voltage during train coasting.

[0019] In some embodiments, when the rail potential at the traction substation is detected to exceed a safety threshold:

[0020] The switching device monitors the running position of the train, and the switching device closest to the left and right ends of the train is turned on, while the other switching devices are turned off.

[0021] The protection switch unit operates to implement a two-stage protection strategy for rail potential exceeding the limit: when the rail potential at the traction substation reaches the first protection threshold, the first contactor in the protection switch circuit, located between the first and second connection terminals of the rail potential limiting device, closes, directly short-circuiting the negative terminal of the traction substation to the grounding grid, and automatically disconnects after a set time; when the rail potential at the traction substation reaches the second protection threshold, the thyristor in the protection switch circuit, located between the first and second connection terminals of the rail potential limiting device, conducts, and then the first contactor closes and is permanently locked.

[0022] The power electronic conversion unit outputs a negative voltage during train traction, a positive voltage during train braking, and zero voltage during train coasting.

[0023] In some embodiments, when a component fault is detected inside the power electronic conversion unit:

[0024] All the switching devices are turned on, and the rail and the return line are equivalent to being connected in parallel.

[0025] When the output capacitor voltage of the power electronic conversion unit is detected to be lower than the cut-off threshold, the first contactor between the first and fourth connection terminals of the rail potential limiting device in the protection switch unit is closed, directly short-circuiting the negative terminal of the traction substation with the return line.

[0026] When all the switching devices inside the power electronic conversion unit are turned off, the input side stops transferring energy to the output side, the output capacitor will discharge rapidly under the traction power supply circuit, and the voltage amplitude of the output capacitor will quickly drop below the cut-off threshold. Then the first contactor closes, and the faulty power electronic conversion unit is equivalent to being cut off from the DC traction power supply system of the rail transit.

[0027] In some embodiments, when the system is in normal operation, the rail potential limiting device and the switching device work together to limit the rail potential at the traction substation to within a safe threshold.

[0028] When the system detects that the rail potential exceeds the standard, the protection switch unit clamps the rail potential to zero. At the same time, the power electronic conversion unit continues to work in coordination with the switch device to build a zero potential point on the rail.

[0029] When the system detects a fault in the power electronic conversion unit, the return line is equivalent to the rail in parallel, and the rail potential limiting device is equivalent to a traditional rail potential limiting device through fault protection action. At this time, the longitudinal resistance of the system return path is reduced, and the system still retains the rail potential safety protection capability after the fault.

[0030] Compared with the prior art, the advantages and positive effects of this application are as follows:

[0031] (1) The rail potential limiting device provided in this application is applied to the DC traction power supply system of rail transit. It includes a protection switch unit and a power electronic conversion unit. When the rail potential at the traction substation is detected to exceed the safety threshold, the protection switch unit will clamp the rail potential at the traction substation to zero. The power electronic conversion unit will construct a zero potential point on the rail to reduce stray current leakage to ground. When the rail potential at the traction substation is detected to be within the safety threshold, the protection switch unit will not operate. The power electronic conversion unit will actively adjust the rail potential at the traction substation to within the set threshold. Ideally, the rail potential at the traction substation will be controlled to zero, so that the rail potential and stray current in the DC traction power supply system of rail transit are significantly suppressed.

[0032] (2) The DC traction power supply system for rail transit provided in this application, based on the existing DC traction power supply system for rail transit, replaces the traditional rail potential limiting device with a rail potential limiting device, and adds a switching device and a return line. The rail potential limiting device includes a protection switching unit and a power electronic conversion unit. When the rail potential at the traction substation is detected to exceed the safety threshold, the protection switching unit operates to clamp the rail potential at the traction substation to zero, and the power electronic conversion unit constructs a zero potential point on the rail to reduce stray current leakage to ground. When the rail potential at the traction substation is detected to be within the safety threshold, the protection switching unit does not operate, and the power electronic conversion unit actively adjusts the rail potential at the traction substation to within the set threshold. Ideally, the rail potential at the traction substation is controlled to zero, so that the rail potential and stray current in the DC traction power supply system for rail transit are significantly suppressed.

[0033] (3) The DC traction power supply system for rail transit provided in this application, when the system is in normal operation, the protection switch unit in the rail potential limiting device does not operate, the power electronic conversion unit draws power from the AC power grid or the contact network and realizes multi-polarity output control, that is, outputting negative voltage when the train is in traction mode, outputting positive voltage when braking mode, and outputting zero voltage when coasting mode, thereby actively adjusting the rail potential distribution in the power supply section and suppressing stray current leakage.

[0034] (4) In the DC traction power supply system for rail transit provided in this application, when the system detects that the rail potential exceeds the standard, the protection switch unit in the rail potential limiting device operates and clamps the rail potential at the traction substation to zero according to the two-stage protection strategy. The power electronic conversion unit constructs a zero potential point at the connection between the conducting switch device and the rail, reducing the rail potential distribution in the entire power supply section, thereby reducing the system's stray current leakage to ground after the rail potential limiting device operates.

[0035] (5) In the DC traction power supply system for rail transit provided in this application, when the system detects a fault in the power electronic conversion unit, the power electronic conversion unit in the rail potential limiting device is cut off in time to protect the normal operation of the switch unit and ensure the rail potential safety protection capability; at the same time, all the switch devices are turned on to connect the return line in parallel with the rail, thereby reducing the longitudinal resistance of the system return path and thus suppressing the rail potential distribution and stray current leakage in the system to a certain extent.

[0036] (6) The DC traction power supply system for rail transit provided in this application ensures that the power electronic conversion unit and the switching device in the rail potential limiting device always work together when the system is working normally or when the rail potential exceeds the standard, thereby improving the rail potential distribution in the entire power supply section and suppressing the system's stray current leakage to ground from the source.

[0037] (7) The DC traction power supply system for rail transit provided in this application, when the system is working normally, the power electronic conversion unit regulates the rail potential and reduces the frequency of rail potential exceeding the standard. When the rail potential of the system exceeds the standard, the two-stage protection strategy of the protection switch unit can respond in a timely manner and avoid frequent blocking. The power electronic conversion unit also avoids abnormal rise of rail potential in adjacent sections by constructing a zero potential point on the rail.

[0038] (8) The DC traction power supply system for rail transit provided in this application automatically disconnects the power electronic conversion unit and connects the return line in parallel with the rail when the power electronic conversion unit fails; at the same time, the protection switch unit can still operate independently, so that the new traditional rail potential limiting device is equivalent to the traditional rail potential limiting device, ensuring the rail potential safety protection capability and improving the overall reliability of the system. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the rail potential limiting device described in this application;

[0040] Figure 2 This is a schematic diagram of a traditional rail potential limiting device.

[0041] Figure 3 This is a schematic diagram of a DC traction power supply system for rail transit based on a traditional rail potential limiting device.

[0042] Figure 4 This is a schematic diagram of the DC traction power supply system for rail transit in this application;

[0043] Figure 5 This is a schematic diagram of the switching device structure described in this application;

[0044] Figure 6 This is a schematic diagram of the current flow direction of the switching device described in this application when the train is running in traction mode;

[0045] Figure 7 This is a schematic diagram of the current flow direction of the switching device described in this application when the train is in braking condition;

[0046] Figure 8 This is a schematic diagram of the current path of the DC traction power supply system for rail transit under normal operating conditions.

[0047] Figure 9 This is a schematic diagram of the current path two of the DC traction power supply system for rail transit under normal operating conditions.

[0048] Figure 10 This is a schematic diagram of the current path of the DC traction power supply system for rail transit under normal operating conditions.

[0049] Figure 11 This is a schematic diagram of the current path in a DC traction power supply system for rail transit based on a traditional rail potential limiting device during normal system operation.

[0050] Figure 12 This is a schematic diagram comparing the rail potential distribution within the power supply range of a DC traction power supply system for rail transit based on a traditional rail potential limiting device and the DC traction power supply system for rail transit of this application during normal system operation.

[0051] Figure 13 This is a schematic diagram of the current path in the DC traction power supply system for rail transit in this application when the rail potential exceeds the standard;

[0052] Figure 14 This is a schematic diagram of the current path in a traditional rail transit DC traction power supply system when the rail potential exceeds the standard.

[0053] Figure 15 This is a schematic diagram comparing the rail potential distribution within the power supply range of a DC traction power supply system for rail transit based on a traditional rail potential limiting device and the DC traction power supply system for rail transit of this application when the rail potential exceeds the standard.

[0054] Figure 16 This is a schematic diagram of the current path in the DC traction power supply system for rail transit described in this application when the power electronic conversion unit fails and the rail potential does not exceed the standard.

[0055] Figure 17 This is a schematic diagram comparing the rail potential distribution within the power supply range of a DC traction power supply system for rail transit based on a traditional rail potential limiting device and the DC traction power supply system for rail transit of this application when the power electronic conversion unit fails but the rail potential does not exceed the standard.

[0056] Figure 18This is a schematic diagram of the current path in the DC traction power supply system for rail transit described in this application when the power electronic conversion unit fails and the rail potential exceeds the standard;

[0057] Figure 19 This is a schematic diagram comparing the rail potential distribution within the power supply range of a DC traction power supply system for rail transit based on a traditional rail potential limiting device and the DC traction power supply system for rail transit of this application when the power electronic conversion unit fails and the rail potential exceeds the standard.

[0058] Figure 20 This is a schematic diagram of the type of power electronic switch inside the rail potential limiting device of this application. Detailed Implementation

[0059] The present application will now be described in detail with reference to the accompanying drawings through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0060] The first aspect of this application provides a rail potential limiting device for suppressing stray current, which is applied to a DC traction power supply system for rail transit. This device can effectively overcome the inherent defect of traditional rail potential limiting devices that exacerbate stray current leakage in the DC traction power supply system for rail transit due to grounding during operation, and reduce the frequency of rail potential exceeding the standard by adjusting the rail potential distribution in the power supply section.

[0061] Figure 1 The diagram shown is a structural schematic of the rail potential limiting device according to an embodiment of this application. See also... Figure 1 The rail potential limiting device 100 includes a protection switch unit 110 and a power electronic conversion unit 120. When applied to a DC traction power supply system for rail transit, the first connection terminal 101 of the rail potential limiting device 100 is used to connect to the negative terminal of the traction substation, the second connection terminal 102 of the rail potential limiting device 100 is used to connect to the grounding grid, the third connection terminal 103 of the rail potential limiting device 100 is used to connect to the AC power grid, and the fourth connection terminal 104 of the rail potential limiting device 100 is used to connect to the return line.

[0062] The protection switch unit 110 consists of a first control module 111, a first contactor KM1, a thyristor VS, a second contactor KM2, and a second control module 112. The first control module 111, the first contactor KM1, and the thyristor VS are connected in parallel to form a first parallel circuit, which is connected between the first connection terminal 101 and the second connection terminal 102 of the rail potential limiting device 100. The second control module 112 and the second contactor KM2 are connected in parallel to form a second parallel circuit, which is connected between the fourth connection terminal 104 of the rail potential limiting device 100 and the power electronic conversion unit 120. The power electronic conversion unit 120 is connected to the third connection terminal 103 of the rail potential limiting device 100. The first control module 111 is used to detect the rail potential at the traction substation of the rail transit DC traction power supply system, and the second control module is used to detect the status of the internal components of the power electronic conversion unit 120.

[0063] The power electronic conversion unit 120 includes a power electronic energy conversion module and a switching circuit connected in series. The power electronic energy conversion module is connected to the third connection terminal 103 of the rail potential limiting device 100, and the switching circuit is connected to the second parallel circuit of the protection switching circuit 110. The power electronic conversion unit 120 achieves multi-polarity output through energy conversion by the power electronic energy conversion module and duty cycle control of the switching transistor in the switching circuit, actively adjusting the distribution pattern of rail potential within the power supply section to ensure that the rail potential at the traction substation is within a safe threshold.

[0064] Specifically, during train traction, the power electronic converter outputs a negative voltage to offset all or part of the voltage drop of the traction current flowing through the return line. During train braking, the power electronic converter outputs a positive voltage to offset all or part of the voltage drop of the braking current flowing through the return line 700. During train coasting, the power electronic converter outputs zero voltage, at which point the rail transit DC traction power supply system has no current and no voltage drop in the return line.

[0065] In this embodiment of the novel rail potential limiting device, when the first control module 111 detects that the rail potential at the traction substation of the DC traction power supply system of the rail transit exceeds a safety threshold, the protection switch unit 110 directly short-circuits the negative terminal of the traction substation to the grounding grid of the DC traction power supply system of the rail transit, clamping the rail potential at the traction substation to zero. The power electronic conversion unit 120 actively adjusts the output voltage to make the rail potential at the traction substation equal to that at the switching device connected to the DC traction power supply system of the rail transit, i.e., establishing a zero potential point on the rail to reduce stray current leakage to ground. When the first control module 111 detects that the rail potential at the traction substation is within the safety threshold, the protection switch unit 110 does not operate, and the power electronic conversion unit 120 adjusts the rail potential at the traction substation to limit the rail potential at the traction substation within a set threshold, thereby suppressing rail potential and stray current. It should be noted that the threshold is usually much smaller than the safety threshold and can be set according to the actual situation. Ideally, the threshold should be set to zero, that is, the rail potential at the traction substation should be zero.

[0066] Specifically, the novel rail potential limiting device described in this application embodiment employs a two-stage protection strategy during operation. The protection switch unit 110 monitors the rail potential at the traction substation and the status of internal components in the power electronic conversion unit 120 in real time.

[0067] When the first control module 111 detects that the rail potential at the traction substation exceeds a certain safety threshold, the first control module 111 controls the first contactor KM1 in the protection switch unit 110 to close, directly short-circuiting the negative terminal of the traction substation to the grounding grid of the railway DC traction power supply system, thus clamping the rail potential at the traction substation to zero. The first contactor KM1 automatically disconnects after a set time. When the first control module 111 detects that the rail potential at the traction substation reaches a second safety threshold, the first control module 111 controls the thyristor VS in the protection switch unit 110 to immediately conduct, and then controls the first contactor KM1 to close and permanently lock out.

[0068] When the second control module 112 detects an open circuit or short circuit fault in the internal components of the power electronic conversion unit 120, the second control module 112 controls the second contactor KM2 of the protection switch unit 110 to close, directly short-circuiting the negative terminal of the traction substation with the return line of the rail transit DC traction power supply system. The faulty power electronic conversion unit is equivalent to being disconnected from the rail transit DC traction power supply system, ensuring that the fault of the power electronic conversion unit will not affect the rail potential safety protection of the rail potential limiting device.

[0069] Figure 2This is a schematic diagram of a traditional rail potential limiting device. (See also...) Figure 2 The conventional rail potential limiting device 900 includes a contactor KM, a thyristor VS, and a control module 911, which are connected in parallel to form a parallel circuit. Unlike the novel rail potential limiting device 100 described in this application, the conventional rail potential limiting device 900 adopts a three-stage protection strategy. The control module 911 monitors the rail potential at the traction substation. When the control module 911 detects that the rail potential at the traction substation reaches a certain protection threshold, it controls the contactor KM between the first connection terminal 901 and the second connection terminal 902 of the conventional rail potential limiting device 900 to close, directly short-circuiting the negative terminal of the traction substation to the grounding grid. The contactor KM automatically disconnects after a set time. When the control module 911 detects that the rail potential at the traction substation reaches the second-stage protection threshold, the control module 911 controls the thyristor VS between the first connection terminal 901 and the second connection terminal 902 of the conventional rail potential limiting device 900 to immediately conduct, controlling the contactor KM to close and lock without delay, requiring manual reset. When the control module 911 detects that the rail potential at the traction substation reaches the third-stage protection threshold, it controls the thyristor VS to conduct without delay. After receiving the closing signal sent by the control module 911, the contactor KM closes and permanently locks, requiring manual reset.

[0070] Figure 3 This is a structural diagram of a DC traction power supply system for rail transit based on a traditional rail potential limiting device (hereinafter referred to as: traditional rail system DC traction power supply system). Figure 3 As shown, the conventional rail transit DC traction power supply system includes a traction substation 200, a catenary 300, rails 400, a train 500, a conventional rail potential limiting device 900, and a grounding grid 800. The positive terminal 201 of the traction substation 200 is connected to the catenary 300, the negative terminal 202 is connected to the rails 400 for the train 500 to travel on, and the AC terminal 203 is connected to the medium-voltage AC power grid. The first connection terminal 901 of the conventional rail potential limiting device 900 is connected to the negative terminal 202 of the traction substation 200, and the second connection terminal 902 is connected to the grounding grid 800.

[0071] The second aspect of this application provides a DC traction power supply system for rail transit. Based on the existing DC traction power supply system for rail transit, a rail potential limiting device is used to replace the traditional rail potential limiting device, and a new switching device and return line are added, which can effectively suppress abnormal rise of rail potential and stray current leakage in rail transit.

[0072] Figure 4The diagram shown is a structural schematic of the DC traction power supply system for rail transit according to an embodiment of this application. This system employs the novel rail potential limiting device 100 described in the above embodiment of this application, which can limit the rail potential of the DC traction system for rail transit and suppress stray current leakage.

[0073] See Figure 4 The DC traction power supply system for rail transit includes a rail potential limiting device 100, a traction substation 200, a contact network 300, rails 400, a train 500, a switching device 600, a return line 700, and a grounding grid 800.

[0074] The positive terminal 201 of the traction substation 200 is connected to the contact network 300, the negative terminal 202 is connected to the rail 400, and the AC terminal 203 is connected to the AC power grid. The return line 700 is arranged along the rail 400. The switch device 600 is installed between adjacent traction substations 200. The first connection terminal 601 of the switch device 600 is connected to the rail 400, and the second connection terminal 602 of the switch device 600 is connected to the return line 700. The rail potential limiting device 100 is installed in each traction substation 200. The first connection terminal 101 of the rail potential limiting device 100 is connected to the negative terminal of the traction substation 200. The second connection terminal 102 of the rail potential limiting device 100 is connected to the grounding grid 800. The third connection terminal 103 of the rail potential limiting device 100 is connected to the AC power grid, and the fourth connection terminal 104 of the rail potential limiting device 100 is connected to the return line 700.

[0075] Specifically, the structure of the rail potential limiting device 100 is the same as that of the rail potential limiting device described in the first aspect embodiment of this application, and will not be repeated here.

[0076] Figure 5 The diagram shown is a structural schematic of the switching device described in this application. See also... Figure 5 The switching device 600 mainly consists of bidirectional controllable switching transistors K1 and K2 connected in reverse series. Switch K1 is connected to the first connection terminal 601 of the switching device 600, and switch K2 is connected to the second connection terminal 602. The switching device 600 controls the current flow between the connection terminals through the bidirectional controllable switch. When the train 500 is running in traction mode, the current flows from the positive terminal 601 to the negative terminal 602 of the switching device 600 (see...). Figure 6 When the train 500 is in braking condition, current flows from the negative terminal 602 of the switching device 600 to the positive terminal 601 (see...). Figure 7 ).

[0077] like Figures 8 to 10The diagram shows three current paths of the DC traction power supply system for rail transit under normal operating conditions. The power electronic conversion unit 120 in the rail potential limiting device 100 outputs a negative voltage during train traction, thereby offsetting all or part of the voltage drop of the traction current flowing through the return line 700; it outputs a positive voltage during train braking, thereby offsetting all or part of the voltage drop of the braking current flowing through the return line 700; and it outputs zero voltage during train coasting, at which point the new DC traction power supply system has no current and the return line 700 has no voltage drop.

[0078] To simplify the analysis, the following assumptions are made: the length of rail 400 in the power supply section is L, the traction substation 200 is the zero point, the train 500 is located in the middle of the track, the track is divided into five sections by four evenly distributed switch devices 600, and the resistance on rail 400 and return line 700 is evenly distributed and equal.

[0079] Figure 8 This is a schematic diagram of the current path of the DC traction power supply system for rail transit in the normal operating state of the system. At this time, the voltage output by the rail potential limiting device 100 is less than the voltage drop of the traction current flowing through the return line 700, and the current flows back in the positive direction on the rail 400. Figure 9 This is a schematic diagram of the current path two of the DC traction power supply system for rail transit in the normal operating state of the system. At this time, the voltage output by the rail potential limiting device 100 is equal to the voltage drop of the traction current flowing through the return line 700, and there is no current return on the rail 400. Figure 10 This is a schematic diagram of the current path of the DC traction power supply system for rail transit in the normal operating state of the system. At this time, the voltage output by the rail potential limiting device 100 is greater than the voltage drop of the traction current flowing through the return line 700, and the current flows back in the reverse direction on the rail 400.

[0080] Figure 11 This is a schematic diagram of the current path in a traditional DC traction power supply system for rail transit during normal operation. At this time, the rail potential is within a safe range, the traditional rail potential limiting device 900 does not activate, and the rail potential rises from the traction substation 200 to the location of the train 500. The rail potential at the traction substation 200 is relatively low, and there is a positive return current on rail 400.

[0081] Figure 12This diagram illustrates a comparison of rail potential distribution within the power supply range of a traditional rail transit DC traction power supply system and the rail transit DC traction power supply system of this application, under normal operating conditions. It is assumed that the rail potential in the traditional rail transit DC traction power supply system is -Umax at traction substation 200 and Umax at train position 500. The relative magnitude of stray current is represented by the shaded area enclosed by the rail potential curve and the horizontal axis, and the stray current is denoted as Imax. At this time, the power electronic conversion unit 120 of the rail potential limiting device 100 actively adjusts the output voltage to limit the rail potential at the traction substation 200. The figure shows the limiting effect of the rail potential limiting device 100 on the rail potential at the traction substation 200 under the above three current paths. Under the three current paths, the rail potential at the traction substation 200 is -0.52Umax, -0.04Umax, and 0, respectively, and the rail potential at the train 500 is 0.68Umax, 0.36Umax, and 0.33Umax, respectively. The stray currents are 0.54Imax, 0.13Imax, and 0.11Imax, respectively. Obviously, under the optimal output voltage regulation of the power electronic conversion unit 120 of the rail potential limiting device 100, the rail potential at the traction substation 200 in the DC traction power supply system of rail transit in this application is 0, the rail potential at the train 500 is 0.33Umax, and the stray current is 0.11Imax. At this time, the rail potential at the traction substation 200, the rail potential at the train 500, and the stray current in the DC traction power supply system of rail transit in this application are reduced to 0%, 33%, and 11% of those in the traditional DC traction power supply system of rail transit, respectively.

[0082] Figure 13 This is a schematic diagram of the current path in the DC traction power supply system for rail transit in this application when the rail potential exceeds the limit. When the protective switch unit 110 of the rail potential limiting device 100 operates, it short-circuits the rail 400 with the grounding grid 800. The rail potential at the traction substation 200 is zero. The power electronic conversion unit 120 of the rail potential limiting device 100 actively adjusts the output voltage to ensure that the rail potential at the traction substation 200 is equal to that at the conducting switch device 600, i.e., a zero-potential point is constructed on the rail 400 (shown in the red box in the diagram), thereby limiting the rail potential on the rail 400. At this time, there is no current return on the rail 400.

[0083] Figure 14 This diagram illustrates the current path in a traditional DC traction power supply system for rail transit when the rail potential exceeds the limit. The traditional rail potential limiting device 900 short-circuits rail 400 to the grounding grid 800. The rail potential at traction substation 200 is zero, and the overall rail potential is raised, maintaining the same trend. At this time, the rail potential at traction substation 200 is low, and there is a positive return current on rail 400.

[0084] Figure 15 This diagram illustrates a comparison of rail potential distribution within the power supply section of a traditional DC traction power supply system for rail transit and the DC traction power supply system for rail transit in this application, when the rail potential exceeds the limit. In this case, the traditional rail potential limiting device 900 activates, short-circuiting rail 400 to the grounding grid 800. The rail potential at traction substation 200 is zero, and the rail potential rises from traction substation 200 towards the train, where the rail potential is 2Umax and the stray current is 4Imax. The protective switch unit 110 of the rail potential limiting device 100 activates, short-circuiting rail 400 to the grounding grid 800. The rail potential at traction substation 200 is zero, and the power electronic conversion unit 120 of the rail potential limiting device 100 activates, adjusting the conducting switch device 600 to match the rail potential at traction substation 200, thus limiting the rise in rail potential. The rail potential at the train is 0.4Umax and the stray current is 0.16Imax. Obviously, under the premise of ensuring that the rail potential clamp at the traction substation 200 is zero, the rail potential and stray current at the train in the DC traction power supply system of rail transit in this application are reduced to 20% and 4% of those in the traditional DC traction power supply system of rail transit, respectively.

[0085] Figure 16 This is a schematic diagram of the current path in the DC traction power supply system for rail transit under the present application, when the power electronic converter unit 120 fails and the rail potential does not exceed the standard. When the second control module 112 of the protection switch unit 110 detects an abnormality in the power electronic converter unit 120, the contactor directly short-circuits the negative terminal 202 of the traction substation 200 with the return line 700. The faulty power electronic converter unit 120 is equivalent to being disconnected from the DC traction power supply system for rail transit, ensuring that the failure of the power electronic converter unit 120 will not affect the rail potential safety protection of the device. All switching devices 600 are turned on, which is equivalent to the rail 400 being connected in parallel with the return line 700. The total resistance on the current return path decreases, the rail potential amplitude decreases, and at this time, there is a positive return current on the rail 400.

[0086] Figure 17This diagram illustrates a comparison of rail potential distribution within the power supply range of a conventional DC traction power supply system for rail transit and the DC traction power supply system of this application, assuming a fault in the power electronic converter unit 120 and no exceedance of rail potential limits. In the conventional DC traction power supply system for rail transit, the conventional rail potential limiting device 900 is inactive, the rail potential at traction substation 200 is -Umax, the rail potential at the train is Umax, and the stray current is Imax. In the DC traction power supply system of this application, the power electronic converter unit 120 of the rail potential limiting device 100 is disconnected, the protection switch unit 110 operates normally, and all switch devices 600 are conducting. Rail 400 and return line 700 are equivalently connected in parallel, the train current return resistance is halved, the rail potential at traction substation 200 is -0.5Umax, the rail potential at the train is 0.5Umax, and the stray current is 0.5Imax. Obviously, when the power electronic conversion unit 120 fails and the rail potential does not exceed the standard, the rail potential at 200 traction substations, the rail potential at 500 trains, and the stray current in the DC traction power supply system for rail transit in this application are all reduced to 50% of those in the traditional DC traction power supply system for rail transit.

[0087] Figure 18 This is a schematic diagram of the current path in the DC traction power supply system for rail transit in this application when the power electronic converter unit 120 fails and the rail potential exceeds the limit. In the rail potential limiting device 100, when the first contactor KM1 of the protection switch unit 110 is closed, the rail 400 is short-circuited to the grounding grid 800, and the rail potential at the traction substation 200 is zero. When the second control module 112 of the protection switch unit 110 detects an abnormality in the power electronic converter unit 120, it directly short-circuits the negative terminal 202 of the traction substation 200 to the return line 700 through the second contactor KM2. The faulty power electronic converter unit 120 is equivalent to being disconnected from the DC traction power supply system for rail transit, ensuring that the failure of the power electronic converter unit 120 will not affect the rail potential safety protection of the device. All switching devices 600 are turned on, which is equivalent to the rail 400 and the return line 700 being connected in parallel. The total resistance on the current return path decreases, and the rail potential amplitude decreases. At this time, there is a positive return current on the rail 400.

[0088] Figure 19This diagram illustrates a comparison of rail potential distribution within the power supply range of a traditional DC traction power supply system for rail transit and the DC traction power supply system of this application, when the power electronic converter unit malfunctions and the rail potential exceeds the limit. In the traditional DC traction power supply system for rail transit, the conventional rail potential limiting device 900 activates, short-circuiting rail 400 to the grounding grid 800. The rail potential at traction substation 200 is zero, and the rail potential at train 500 is 2Umax, with a stray current of 4Imax. In the DC traction power supply system of this application, the power electronic converter unit 120 of the rail potential limiting device 100 is disconnected, the protection switch unit 110 operates normally, all switches 600 are on, rail 400 and return line 700 are effectively connected in parallel, the train current return resistance is halved, and simultaneously, rail 400 is short-circuited to the grounding grid 800. The rail potential at traction substation 200 is zero, the rail potential at train 500 is Umax, and the stray current is 2Imax. Obviously, when the power electronic conversion unit 120 fails and the rail potential exceeds the standard, the rail potential at 200 locations in the traction substation is clamped to zero, and the rail potential and stray current at 500 locations in the train of the DC traction power supply system for rail transit in this application are reduced to 50% of those in the traditional DC traction power supply system for rail transit.

[0089] Figure 20 This is a schematic diagram of the type of power electronic switch in the rail potential limiting device 100 described in this application. In the new rail limiting device 100 and the switching device 600, the power electronic switch can be a turn-off switching device such as IGBT, SiC-MOSFET or IGCT or a combination of these switching devices. The anti-parallel diode or freewheeling diode is a fast recovery diode that matches the power electronic switch.

[0090] This application presents a DC traction power supply system for rail transit based on a rail potential limiting device. Through the coordinated operation of the rail potential limiting device and the switching device, the system effectively suppresses rail potential and stray current, providing key technical support for the safety protection of rail potential and stray current in urban rail transit.

[0091] The above embodiments are used to explain this application, not to limit it. Any modifications and changes made to this application within the spirit and scope of the claims shall fall within the protection scope of this application.

Claims

1. A rail potential limiting device for suppressing stray current leakage, applied to a DC traction power supply system for rail transit, characterized in that, The rail potential limiting device includes a protective switch unit and a power electronic conversion unit; The protection switch unit consists of a first control module, a first contactor, a thyristor, a second contactor, and a second control module. The first control module, the first contactor, and the thyristor are connected in parallel to form a first parallel circuit, which is connected between the first and second connection terminals of the rail potential limiting device. The second control module and the second contactor are connected in parallel to form a second parallel circuit, which is connected between the fourth connection terminal of the rail potential limiting device and the power electronic conversion unit. The power electronic conversion unit is connected to the third connection terminal of the rail potential limiting device. The first control module is used to detect the rail potential at the traction substation of the rail transit DC traction power supply system, and the second control module is used to detect the status of the internal components of the power electronic conversion unit. When the rail potential at the traction substation of the DC traction power supply system of the rail transit is detected to exceed the safety threshold, the protection switch unit directly short-circuits the negative terminal of the traction substation to the grounding grid of the DC traction power supply system of the rail transit, clamping the rail potential at the traction substation to zero. The power electronic conversion unit actively adjusts the output voltage to make the rail potential at the traction substation and the switch device connected to the DC traction power supply system of the rail transit equal, that is, to build a zero potential point on the rail to reduce stray current leakage to ground. When the rail potential at the traction substation is detected to be within a safe threshold, the protection switch unit does not operate, and the power electronic conversion unit actively adjusts the rail potential at the traction substation to limit the rail potential at the traction substation within a set threshold, thereby suppressing rail potential and stray current.

2. The rail potential limiting device for suppressing stray current leakage as described in claim 1, characterized in that, The protection switch unit detects the rail potential at the traction substation and the status of internal components of the power electronic conversion unit in real time. When an open-circuit or short-circuit fault is detected in the internal components of the power electronic converter unit, the protection switch unit directly short-circuits the negative terminal of the traction substation to the return line of the DC traction power supply system of the rail transit, so as to ensure that the fault of the power electronic converter unit will not affect the rail potential safety protection of the rail potential limiting device.

3. The rail potential limiting device for suppressing stray current leakage as described in claim 1, characterized in that, The power electronic conversion unit draws power from the AC grid or contact network of the DC traction power supply system of the rail transit. Through its internal power electronic energy conversion and the duty cycle control of its switching transistors, it outputs multipolarity and actively adjusts the distribution pattern of rail potential in the power supply section, so that the rail potential at the location of the traction substation is limited within a safe threshold.

4. A DC traction power supply system for rail transit based on a rail potential limiting device, characterized in that, This includes traction substations, overhead contact lines, rails, trains, rail potential limiting devices, switching devices, return lines, and grounding grids; The positive terminal of the traction substation is connected to the contact network, the negative terminal is connected to the rail, and the AC terminal is connected to the AC power grid. The return line is arranged along the rail. The switching device is installed between adjacent traction substations. The first connection terminal of the switching device is connected to the rail, and the second connection terminal is connected to the return line. The rail potential limiting device is installed in each traction substation. The first connection terminal of the rail potential limiting device is connected to the negative terminal of the traction substation, the second connection terminal is connected to the grounding grid, the third connection terminal is connected to the AC power grid, and the fourth connection terminal is connected to the return line. The rail potential limiting device includes a protection switch unit and a power electronic conversion unit. The protection switch unit consists of a first control module, a first contactor, a thyristor, a second contactor, and a second control module. The first control module, the first contactor, and the thyristor are connected in parallel to form a first parallel circuit, which is connected between the first and second connection terminals of the rail potential limiting device. The second control module and the second contactor are connected in parallel to form a second parallel circuit, which is connected between the fourth connection terminal of the rail potential limiting device and the power electronic conversion unit. The power electronic conversion unit is connected to the third connection terminal of the rail potential limiting device. The first control module is used to detect the rail potential at the traction substation of the rail transit DC traction power supply system, and the second control module is used to detect the status of the internal components of the power electronic conversion unit. When the rail potential at the traction substation is detected to exceed the safety threshold, the protection switch unit directly short-circuits the negative terminal of the traction substation to the grounding grid, clamping the rail potential at the traction substation to zero. The power electronic conversion unit actively adjusts the output voltage to make the rail potential at the traction substation equal to that at the conducting switch device, that is, to create a zero potential point on the rail to reduce stray current leakage to ground. When the rail potential at the traction substation is detected to be within a safe threshold, the protection switch unit does not operate, and the power electronic conversion unit actively adjusts the rail potential at the traction substation to limit the rail potential at the traction substation within a set threshold, thereby suppressing rail potential and stray current.

5. The DC traction power supply system for rail transit based on a rail potential limiting device as described in claim 4, characterized in that, The protection switch unit detects the rail potential at the traction substation and the status of internal components of the power electronic conversion unit in real time. When the rail potential at the traction substation is detected to exceed the safety threshold, the protection switch unit directly short-circuits the negative terminal of the traction substation to the grounding grid, thereby clamping the rail potential at the traction substation to zero. When an open-circuit or short-circuit fault is detected in the internal components of the power electronic conversion unit, the protection switch unit directly short-circuits the negative terminal of the traction substation to the return line to ensure that the fault of the power electronic conversion unit will not affect the rail potential safety protection of the rail potential limiting device.

6. The DC traction power supply system for rail transit based on a rail potential limiting device as described in claim 4, characterized in that, The power electronic conversion unit draws power from the AC power grid or the contact network, and through its internal power electronic energy conversion and the duty cycle control of its switching transistors, it outputs multi-level characteristics to actively adjust the distribution pattern of rail potential within the power supply section, so that the rail potential at the location of the traction substation is limited to within a safe threshold.

7. The DC traction power supply system for rail transit based on a rail potential limiting device as described in claim 4, characterized in that, When the system is in normal operating condition: The switching device monitors the running position of the train, and the switching device closest to the left and right ends of the train is turned on, while the other switching devices are turned off. When the protection switch unit does not operate, the first contactor and thyristor located between the first and second connection terminals of the rail potential limiting device in the protection switch unit are disconnected, and the second contactor located between the first and fourth connection terminals of the rail potential limiting device is disconnected. The power electronic conversion unit outputs a negative voltage during train traction, a positive voltage during train braking, and zero voltage during train coasting.

8. The DC traction power supply system for rail transit based on a rail potential limiting device as described in claim 4, characterized in that, When the rail potential at the traction substation is detected to exceed the safety threshold: The switching device monitors the running position of the train, and the switching device closest to the left and right ends of the train is turned on, while the other switching devices are turned off. The protection switch unit operates to implement a two-stage protection strategy for rail potential exceeding the limit: when the rail potential at the traction substation reaches the first protection threshold, the first contactor in the protection switch circuit, located between the first and second connection terminals of the rail potential limiting device, closes, directly short-circuiting the negative terminal of the traction substation to the grounding grid, and automatically disconnects after a set time; when the rail potential at the traction substation reaches the second protection threshold, the thyristor in the protection switch circuit, located between the first and second connection terminals of the rail potential limiting device, conducts, and then the first contactor closes and is permanently locked. The power electronic conversion unit outputs a negative voltage during train traction, a positive voltage during train braking, and zero voltage during train coasting.

9. The DC traction power supply system for rail transit based on a rail potential limiting device as described in claim 4, characterized in that, When a fault is detected in an internal component of the power electronic converter unit: All the switching devices are turned on, and the rail and the return line are equivalent to being connected in parallel. When the output capacitor voltage of the power electronic conversion unit is detected to be lower than the cut-off threshold, the first contactor between the first and fourth connection terminals of the rail potential limiting device in the protection switch unit is closed, directly short-circuiting the negative terminal of the traction substation with the return line. When all the switching devices inside the power electronic conversion unit are turned off, the input side stops transferring energy to the output side, the output capacitor will discharge rapidly under the traction power supply circuit, and the voltage amplitude of the output capacitor will quickly drop below the cut-off threshold. Then the first contactor closes, and the faulty power electronic conversion unit is equivalent to being cut off from the DC traction power supply system of the rail transit.

10. The DC traction power supply system for rail transit based on a rail potential limiting device as described in claim 4, characterized in that, When the system is in normal operation, the rail potential limiting device and the switching device work together to limit the rail potential at the traction substation to within a safe threshold. When the system detects that the rail potential exceeds the standard, the protection switch unit clamps the rail potential to zero. At the same time, the power electronic conversion unit continues to work in coordination with the switch device to build a zero potential point on the rail. When the system detects a fault in the power electronic conversion unit, the return line is equivalent to the rail in parallel, and the rail potential limiting device is equivalent to a traditional rail potential limiting device through fault protection action. At this time, the longitudinal resistance of the system return path is reduced, and the system still retains the rail potential safety protection capability after the fault.

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