Negative Ground Limit Protection Device for Rail Transit Power Supply System

Abstract

The present invention discloses a negative ground limit protection device for a rail transit power supply system, belonging to the technical field of rail power supply. The present invention includes: a negative ground voltage limiting module, including a first contactor and a thyristor module connected in parallel. When the potential difference between the negative return rail and the ground exceeds a specified voltage value, the thyristor module and the first contactor are turned on; a negative ground voltage and current detection module, used to detect the current and / or voltage between the negative return rail and the ground and upload them to the intelligent control module; an intelligent control module, used to receive the voltage detected by the negative ground voltage and current detection module, and control the thyristor cut-off control module to immediately turn off the thyristor module after the first contactor is closed; a thyristor cut-off control module, used to immediately turn off the thyristor module after the thyristor module is forward-conducted. The present invention can reduce the stray current increased due to continuous conduction of the thyristor and extend the service life of the thyristor; discharge small frame leakage current to the negative pole to avoid stray current flowing into the ground.

Description

Technical Field

[0001] The present invention belongs to the technical field of rail power supply, and in particular relates to a negative ground limiting protection device for a rail transit power supply system. Background Art

[0002] The contactor is an important component of the rail potential limiting device to realize the personnel and equipment protection function. It is installed between the negative return rail (hereinafter referred to as the rail) and the ground. Its function is to quickly short-circuit the rail and the ground when the voltage between the rail and the ground exceeds or equals the set value, ensuring the "zero" potential of the rail.

[0003] Traditional rail potential limiting devices consist of thyristors, DC contactors, voltage measuring elements, and a PLC logic control module. The voltage and current measuring elements detect the voltage between the rail and the ground and transmit the result to a controller for display. The DC contactor and thyristor work together to implement the limiting function. When the detected voltage exceeds a specified threshold, the DC contactor and thyristor module short-circuit the rail to the ground, reducing the rail potential and protecting personnel. DC contactors are cheaper than thyristors and are easier to implement logical control. Therefore, when the rail-to-ground voltage is low (for example, when the rail-to-ground voltage reaches the first or second specified thresholds), the protection action is carried out by the DC contactor and the PLC controller in coordination to reduce the rail-to-ground voltage, avoid unnecessary short circuits, and ensure the normal operation of the subway. However, when the rail-to-ground voltage is greater than about 600V, the DC contactor cannot achieve fast short circuit due to mechanical structure limitations. The thyristor connected in parallel with the DC contactor needs to use its own characteristics to quickly short circuit to offset the mechanical delay of the DC contactor. At the same time, the DC contactor is activated to realize the negative ground short circuit pressure relief function. At this time, the thyristor is immediately bypassed, and the voltage difference on the thyristor gradually disappears until it approaches "zero", at which time the thyristor is turned off.

[0004] When using the traditional control method to limit the rail potential, the DC contactor is closed, turned on and locked, and the thyristor is bypassed until the negative ground potential returns to "zero", at which time the thyristor is turned off and the DC contactor can be reset; otherwise, the thyristor will continue to conduct, which will increase stray current. This method has the following problems:

[0005] 1. In order to ensure that the pressure is released to zero and to avoid repeated impacts on the thyristors caused by overvoltage, the DC contactor can only be designed to be locked (i.e. locked) after closing. At this time, the reset button must be manually pressed to reset the contactor, thus losing the remote control function.

[0006] 2. If the thyristor cannot be turned off immediately during the bypass process, the conduction time will be increased, seriously damaging the life of the thyristor. As the thyristor continues to be used, the DC contactor will be turned on to return the negative ground voltage to zero, but the thyristor will continue to conduct, increasing the stray current.

[0007] On the other hand, due to geographical installation conditions, it is impossible to install the rails for traction return current in a fully insulated manner, and there is a certain loop resistance along the line direction. As the train load current increases, a part of the traction current will leak into the ground. In addition, the short circuit of the positive pole of the DC equipment in the traction substation to the equipment shell and the catenary to the overhead ground wire will also cause stray current to leak into the ground; the stray current will corrode the steel bars of the civil engineering structure, rails and other underground metal pipelines, directly threatening the safety of the DC power supply system and equipment.

[0008] In order to prevent the power supply equipment from being damaged and the stray current corrosion caused by the frame leakage current, a DC frame protection device is provided in the DC switchgear. The DC frame protection device mainly consists of a current measurement element and a voltage measurement element. One end of the current measurement element is connected to the equipment shell, and the other end is grounded, which is used to detect the fault current flowing between the shell and the ground. One end of the voltage measurement element is connected to the negative pole of the equipment, and the other end is connected to the equipment shell, which is used to measure the voltage between the equipment shell and the negative pole of the DC equipment. When the positive pole of any DC equipment is short-circuited to the shell, the grounding current flows into the ground grid through the current measurement element, and then returns to the rail through the transition resistance between the rail and the ground. When the grounding current reaches the specified threshold, the current element of the frame protection device performs a protection action; at the same time, the voltage measurement element detects the voltage value between the negative pole of the equipment and the equipment shell. When this voltage is greater than the specified threshold, the voltage element operates within the specified time to trip the corresponding AC and DC side circuit breakers to cut off the fault.

[0009] The frame protection device protects the equipment from damage when the positive pole is short-circuited to the frame. However, since it cannot ensure that the frame leakage current flows into the ground, it causes electrochemical corrosion of underground metal objects due to the frame leakage current. In the initial stage of the operation of the rail transit, the insulation performance of the rail to the ground is relatively good. When a frame leakage fault occurs in the DC equipment of the traction substation, the current flowing through the current measurement element is very small, and the current element of the frame protection device does not operate. The continuous frame leakage current flows into the ground, causing immeasurable electrochemical corrosion. When a frame leakage fault occurs in a certain traction substation, the potential of the rail to the ground in the rectifier line will increase, causing false protection actions of the frames of other traction substations that have not had frame leakage faults, expanding the scope of the accident power outage. Summary of the Invention

[0010] The purpose of the present invention is to provide a negative ground limit protection device for a rail transit power supply system, which can reduce the stray current increased due to the continuous conduction of thyristors; enable a smaller frame leakage current to be drained to the negative pole, and avoid the stray current from flowing into the ground.

[0011] Specifically, the present invention provides a negative ground limit protection device for a rail transit power supply system, including:

[0012] The negative ground voltage limiting module includes a first contactor and a thyristor module connected in parallel, with one end connected to the negative return rail and the other end connected to the ground. When the potential difference between the negative return rail and the ground exceeds the specified voltage value, it quickly shorts the negative return rail to the ground.

[0013] The negative ground voltage and current detection module is used to detect the current and / or voltage between the negative return rail and the ground and upload it to the intelligent control module.

[0014] The intelligent control module is used to receive the voltage value detected by the negative ground voltage and current detection module and control the closing of the first contactor; after the first contactor is closed, it controls the thyristor cutoff control module to immediately turn off the thyristor module.

[0015] The thyristor cutoff control module is used to immediately turn off the thyristor module after the thyristor module conducts forward.

[0016] Furthermore, the first contactor includes at least one set of auxiliary contacts, which are used to judge the opening and closing of the first contactor and transmit the corresponding first contactor closing signal to the intelligent control module.

[0017] Furthermore, the negative ground voltage and current detection module includes a voltage measurement element and a current measurement element. The voltage measurement element is connected in parallel across the negative return rail and the ground, and real-time detects the voltage across the negative return rail and the ground to achieve grading of the voltage detection value; the current measurement element is connected in series with the thyristor module, and judges whether the negative ground voltage is higher than the specified value by measuring the current flowing through the thyristor module.

[0018] Furthermore, the negative ground voltage and current detection module further includes a rectification module, the rectification module is a double rectifier diode, the voltage measurement element is a plurality of voltage relays connected in parallel, and the current measurement element is a current relay connected in series with the thyristor module; the potential difference between the negative return rail and the ground is applied to the voltage relay after passing through the rectification module.

[0019] Furthermore, the thyristor module includes a set of thyristors connected in anti-parallel and the corresponding thyristor overvoltage triggering module. The thyristor module is connected in series with the current relay between the negative return rail and the ground, and is connected in parallel with the first contactor. When the current relay detects that the negative ground voltage is greater than the specified value, the thyristor overvoltage triggering module causes the thyristor module to be quickly short-circuited.

[0020] Furthermore, the thyristor cutoff control module includes a thyristor cutoff circuit and a capacitor energy storage circuit connected in parallel;

[0021] The thyristor cutoff circuit and the capacitor energy storage circuit share a power supply, a first capacitor, a voltage stabilizing tube, a grounding resistor, a first diode and a first resistor;

[0022] The thyristor cut-off circuit includes a capacitor discharge trigger loop and a capacitor discharge circuit. Among them, the capacitor discharge trigger loop is formed by connecting a first optocoupler, a third resistor, a first capacitor, and a third thyristor in series; the capacitor discharge circuit is formed by connecting the first capacitor, the third thyristor, the first thyristor in the thyristor module, and a second diode in series.

[0023] The capacitor energy storage circuit includes a capacitor charging trigger loop and a capacitor charging circuit. Among them, the capacitor charging trigger loop is formed by a second optocoupler, a third resistor, a first capacitor, a second resistor, and a fourth thyristor; the capacitor charging circuit is formed by connecting a first diode, a first resistor, a first capacitor, a second resistor, and a fourth thyristor in series between the positive and negative poles of the power supply.

[0024] After the thyristor module conducts forward, a reverse voltage is applied to the thyristor by using the capacitor discharge circuit, so as to quickly turn off the thyristor module.

[0025] Furthermore, the first optocoupler and the second optocoupler respectively include a light-emitting diode and a photosensitive triode; the zener diode is connected in series with the first resistor and the first diode between the positive and negative poles of the power supply to stabilize the voltage of the photosensitive diode.

[0026] Furthermore, the negative ground limit protection device of the rail transit power supply system further includes:

[0027] A frame leakage current discharge module, which is connected between the negative return rail and the ground and is connected in parallel with the negative ground voltage limiting module, and is used to drain the frame leakage current when the frame leakage current is greater than a specified value.

[0028] Furthermore, the frame leakage current discharge module includes:

[0029] A protection fuse, a second contactor, a silicon diode, a first adjustable resistor, a fixed current limiting resistor, and a cut-off switch connected in series between the negative return rail and the ground;

[0030] A protection circuit, the protection circuit includes an RC oscillation circuit formed by connecting a second capacitor and a fourth resistor in series and then in parallel with a second adjustable resistor, one end of the second adjustable resistor is connected to the fixed current limiting resistor and the cut-off switch, and the other end is connected to the protection fuse and the second contactor;

[0031] A frame monitoring system for detecting the frame leakage current flowing through the frame; and

[0032] A small controller, when the frame leakage current is greater than a specified value, the small controller controls the second contactor to close, determines the discharge amount, and adjusts the first adjustable resistor according to the discharge amount to make the frame leakage current quickly flow to the negative return rail.

[0033] Furthermore, when the negative ground voltage current detection module detects that the frame leakage current is lower than the specified value, it sends a stop drainage command to the intelligent control module, and the frame leakage current drainage module stops draining.

[0034] The beneficial effects of the present invention are as follows:

[0035] During the negative ground voltage limiting process of the present invention, when a negative ground high voltage appears, the thyristor conducts quickly to release pressure prior to the first contactor. After the first contactor closes, the thyristor turn-off circuit intervenes and applies reverse pressure to quickly turn off the thyristor, reducing the stray current increased due to continuous conduction of the thyristor and also avoiding the situation of inability to turn off immediately and serious damage to the thyristor life caused by long-term conduction;

[0036] The present invention enables the thyristor to be immediately cut off, and when the negative ground voltage is at a safe voltage, the first contactor can be reset, increasing the operating efficiency of the limit device; when the thyristor is cut off, remote operation or automatic reset of the first contactor can be easily achieved;

[0037] The present invention drains a relatively small frame leakage current (or leakage current caused by short circuit of the catenary to the overhead ground wire) to the negative pole, avoiding the electrochemical corrosion of underground metal caused by stray current flowing into the ground. Continuous drainage can also prevent misoperation of the frame protection of traction substations where no frame leakage fault has occurred, and even the voltage element in the frame protection device can be cancelled;

[0038] The present invention avoids damage to the device caused by large current through the voltage limiting and drainage protection device;

[0039] The present invention realizes intelligent current limiting monitoring of the DC contactor, ensuring that the DC contactor breaks in the case of almost no load current, greatly prolonging the electrical life of the product. Description of the Drawings

[0040] Figure 1 It is a schematic diagram of the system composition of an embodiment of the present invention.

[0041] Figure 2 It is a circuit schematic diagram of an embodiment of the present invention.

[0042] Reference numerals in the figure: 1 - negative ground voltage limiting module, 2 - negative ground voltage current detection module, 3 - intelligent control module, 4 - thyristor cut-off control module, 5 - frame leakage current drainage module. Detailed Embodiments

[0043] The present invention will be further described in detail below in conjunction with the embodiments and with reference to the drawings.

[0044] Embodiment:

[0045] An embodiment of the present invention is a negative ground limit protection device for a rail transit power supply system. As Figure 1 shown, the negative ground limit protection device for a rail transit power supply system includes five major modules: a negative ground voltage limiting module 1, a negative ground voltage and current detection module 2, an intelligent control module 3, a thyristor cut-off control module 4, and a frame leakage current discharge module 5.

[0046] The negative ground voltage limiting module 1 is composed of a DC contactor and a thyristor module connected in parallel. One end is connected to the rail (i.e., the negative return rail, hereinafter referred to as the negative pole), and the other end is connected to the grounding busbar. When the potential difference between the negative pole and the ground exceeds the set voltage, the thyristor and the DC contactor are turned on, quickly short-circuiting the negative pole and the ground, thereby ensuring the safety of passengers and operating personnel. Under normal conditions, the coil of the DC contactor is energized, the DC contactor is disconnected, and at the same time, the thyristor is in the cut-off state. The controller controls the cut-off of the DC contactor according to the voltage value collected by the voltage detection element to achieve voltage grading; for example, it is divided into low voltage (hereinafter referred to as U<), first-stage voltage (hereinafter referred to as U>), and second-stage voltage (hereinafter referred to as U>>). When the negative ground voltage is greater than 600V (the detected value can vary up and down by 50V from 600V), the thyristor is quickly short-circuited, and the DC contactor closes after a mechanical delay to ensure the "zero" potential of the track. After the negative ground limit protection device of the rail transit power supply system in this embodiment ensures that the DC contactor is closed and the pressure relief function is achieved, the controller will send a cut-off signal to the thyristor cut-off control module 4 to quickly turn off the thyristor using the thyristor cut-off control module 4. The thyristor module is configured with a thyristor overvoltage trigger module. When the negative ground voltage is less than the dangerous voltage and a certain time delay occurs, the AC and DC side circuit breakers trip.

[0047] The negative ground voltage and current detection module 2 is composed of a voltage measurement element, a current measurement element, and a rectification module, which detects the current and voltage between the negative pole and the ground and uploads them to the controller for display. The voltage measurement element is connected in parallel between the negative pole and the ground to detect the voltage at both ends of the negative pole and the ground in real time, mainly realizing the detection of low voltage (U<), first-stage voltage (U>), and second-stage voltage (U>>); the current measurement element is connected in series in the thyristor module circuit to detect the current flowing through the thyristor module to achieve the detection of the third-stage voltage (U>>>).

[0048] The intelligent control module 3 adopts a new generation of microcomputer measurement and control protection technology, which has functions of integrated control, protection logic, fault data recording, event recording, and communication. The biggest advantage compared with the traditional control module is that it can not only collect analog quantity modules at high speed, collect and detect data in real time, but also record and save fault data in time when a protection fault occurs, that is, it has an event tracing function.

[0049] Its functions are:

[0050] 1) Control the closing of the DC contactor by the voltage value collected by the negative ground voltage current detection module 2, so as to play the role of negative ground voltage limiting;

[0051] 2) When the thyristor is already closed, after the DC contactor is closed, control the thyristor cutoff control module 4 to achieve immediate turn-off of the thyristor, reduce stray current, avoid repeated impact on the thyristor and reduce its service life; it can also realize free charge and discharge of the capacitor through the capacitor voltage monitoring device;

[0052] 3) Communicate with the frame monitoring system to display the frame leakage current status in real time; it can also record the faults caused by the frame leakage current, which is convenient for troubleshooting and beneficial for maintenance;

[0053] 4) Connect to the SCADA system through the RS485 interface, and realize interactive data transmission of each functional block through the CAN bus technology, and can realize remote control according to customer requirements;

[0054] 5) It can realize the interlock with the negative cabinet of this station and the adjacent OVPD, and can also interlock with the train door to ensure safety.

[0055] The thyristor cutoff control module 4 is a control circuit composed of an optocoupler, a capacitor, a small thyristor, a voltage regulator diode, a diode, a resistor, a capacitor voltage monitoring device, etc. After the thyristor is forward-conducted, the capacitor in the circuit is discharged to apply a reverse voltage to the thyristor, so as to achieve the purpose of quickly turning off the thyristor module. The working mode of the thyristor cutoff control module 4 is as follows:

[0056] 1) After the controller receives the signal that the DC contactor is closed and the pressure is released normally, send a thyristor cutoff signal;

[0057] 2) At this time, current flows through the light-emitting diode of the optocoupler, then the photosensitive triode of the optocoupler conducts, and at this time the gate of the small thyristor is triggered, so that the capacitor discharge circuit forms a path, achieving the purpose of applying a reverse voltage to the thyristor;

[0058] 3) When the capacitor voltage monitoring device detects that the capacitor voltage is low and the thyristor is cutoff at this time, the controller sends a energy storage signal. At this time, current flows through the light-emitting diode of the optocoupler, then the photosensitive triode conducts, so that the gate of the small thyristor is triggered, forming a capacitor charging circuit. When the capacitor energy storage is completed, the charging completion signal is sent to the controller through the capacitor voltage monitoring device and displayed. The voltage value at both ends of the capacitor can be observed during charging. When the voltage value reaches the battery voltage, it indicates that the charging is completed.

[0059] The main circuit diode and the series resistor in the circuit are used to provide a stable and appropriate DC power supply for the photosensitive triode. The resistor in series with the capacitor plays a role in voltage limiting and protection during the capacitor charging process. The zener diode is used to provide a stable voltage for the photosensitive triode. This circuit can control the switching current by controlling the phase shift angle of the small thyristor.

[0060] The frame leakage current discharge module 5 includes a small controller (interacting with the frame monitoring system), a protection fuse, a small contactor, a silicon diode, a first adjustable resistor, a fixed current limiting resistor, a cut-off switch and a protection part. It mainly uses the forward conduction and reverse cut-off characteristics of the silicon diode to achieve the polar drainage of stray current. The frame leakage current discharge module 5 is protected by an RC oscillation circuit, which is composed of a capacitor, a resistor and a second adjustable resistor. The working mode of the frame leakage current discharge module 5 is as follows:

[0061] 1) The small controller is connected to the frame monitoring system through a communication cable to achieve information interaction with the frame monitoring system;

[0062] 2) The frame monitoring system detects the current flowing through the frame and transmits the current information to the small controller. When the small controller determines that the leakage current exceeds the set threshold, it controls the DC contactor to close. At this time, the drainage line is turned on, so that the frame leakage current quickly flows to the negative pole through the drainage device, avoiding the electrochemical corrosion of stray current. During the drainage process, the small controller adjusts the IGBT conduction angle state in real time according to the magnitude of the drainage volume, thereby adjusting the resistance value of the first adjustable resistor, and thus controlling the discharge volume of stray current. It is easy to think that other methods can also be used to adjust the resistance value of the first adjustable resistor, so as to control the discharge volume of stray current.

[0063] 3) When it is detected that the frame current is in a safe state, the frame monitoring system sends a stop drainage command to the controller.

[0064] Through the frame leakage current discharge module 5, it is possible to prevent the inestimable electrochemical corrosion caused by small frame leakage currents; it can also be used as a backup protection method and become a further protection measure for frame leakage protection; at the same time, since the leakage current is discharged in time, there will be no phenomenon of the misoperation and refusal of the frame protection voltage element to cause the expansion of the accident range; at the same time, the use of the RC oscillation protection circuit protects the thyristor, liberates some protection devices such as reactors, overcurrent relays and fast fuses, and saves the manufacturing cost.

[0065] The circuit schematic diagram of the negative ground limit protection device of the rail transit power supply system is as Figure 2 shown.

[0066] The negative ground voltage limiting module 1 is connected between the negative electrode return rail of the device and the ground. The negative ground voltage limiting module 1 includes a DC contactor K2 connected in series between the negative electrode and the ground. K2 includes multiple sets of auxiliary contacts including K2-1. K2-1 is used to judge the opening and closing of K2 and transmit relevant signals to the intelligent control module 3. The negative ground voltage limiting module 1 also includes a thyristor module V1. The thyristor module V1 includes thyristors V2 and V3 connected in antiparallel and their respective thyristor overvoltage trigger modules. The thyristor module V1 is connected in series with a current relay between the negative electrode and the ground and is connected in parallel with K2.

[0067] The potential difference between the negative electrode of the device and the ground is applied to the parallel-connected voltage relays K3, K4, and K5 after passing through the double rectifier diode module V12. V12, K3, K4, K5, plus the current measuring element K6 connected in series with V1, constitute the negative ground voltage and current detection module 2. The voltage and current collected by this module will be uploaded to the intelligent control module 3.

[0068] The thyristor turn-off control module 4 is composed of a thyristor turn-off circuit and a capacitor energy storage circuit connected in parallel. The thyristor turn-off circuit and the capacitor energy storage circuit share the power supply 3, the capacitor C1, the zener diode V7, the grounding resistor R4, the diode V5, and the resistor R1.

[0069] In the thyristor turn-off circuit, the optocoupler V10 (including a light-emitting diode and a photosensitive triode), the resistor R3, the capacitor C1, and the thyristor V8 are connected in series to form a capacitor discharge trigger circuit; C1 is connected in series with V8, V2, and the diode V6 to form a capacitor discharge circuit.

[0070] In the capacitor energy storage circuit, the optocoupler V11 (including a light-emitting diode and a photosensitive triode), R3, C1, the resistor R2, and the thyristor V9 form a capacitor charging trigger circuit; the diode V5, R1, C1, R2, and V9 are connected in series between the positive and negative poles of the power supply 3 to form a capacitor charging circuit.

[0071] The zener diode V7 is connected in series with R1 and V5 between the positive and negative poles of the power supply 3, which has the function of stabilizing the voltage of the photosensitive diode.

[0072] The frame leakage current discharging module 5 is connected between the negative return rail and the ground, and is in parallel with the negative ground voltage limiting module 1. The protection fuse F1, small contactor K7, silicon diode V4, adjustable resistor R5, fixed current limiting resistor R6, and cut-off switch K8 in the frame leakage current discharging module 5 are connected in series between the negative return rail and the ground to form a leakage current discharging circuit. The protection circuit mainly includes an RC oscillation circuit composed of a capacitor C2, a resistor R7, and an adjustable resistor R8, which is connected in parallel with the leakage current discharging circuit to protect the leakage current discharging circuit. The small controller (which exchanges information with the frame monitoring system) is connected to the small contactor K7 and the IGBT device and is used to control the discharging of stray current. The IGBT device is connected in parallel with the adjustable resistor R5, and the resistance value of the resistor R5 is adjusted according to different conduction angle states of the IGBT. The frame monitoring system transmits the frame leakage current amount information to the small controller in the frame leakage current discharging module 5. Specifically, when the current amount is greater than the specified threshold, the small controller controls the small contactor K7 to close, and the leakage current discharging circuit is turned on to discharge the frame leakage current. The small controller controls the conduction angle state of the IGBT according to the magnitude of the frame leakage current amount, thereby adjusting the resistance value of the adjustable resistor R5, and thus controlling the leakage current discharging amount.

[0073] The intelligent control module 3 is powered by the power supply 2 and exchanges information with other modules in the negative ground limit protection device of the rail transit power supply system. These information include but are not limited to voltage and current detection signals, contactor opening and closing signals, capacitor voltage signals, thyristor cut-off signals, capacitor energy storage signals, train door closing signals, interlock signals between the negative cabinet of this station and the adjacent OVPD, and SCADA communication signals.

[0074] As Figure 2 shown, the specific methods for implementing the three functions of negative ground limit, thyristor cut-off, and frame leakage current discharging in the negative ground limit protection device of the rail transit power supply system are as follows:

[0075] 1. Negative ground limit function

[0076] The inside of the contactor includes two parts: a coil and a switch. In the initial state, the controller controls the coil Q2 of the contactor to be energized, and the normally closed contact of the switch K2 of the contactor opens, that is, the contactor is disconnected. At this time, the thyristor is also in the cut-off state. When the voltage relays K3, K4, and K5 of the negative ground voltage current detection module 2 detect that the negative ground voltage reaches the corresponding protection action thresholds of a certain voltage (denoted as U> in the figure), a second-stage voltage (denoted as U>> in the figure), and a low voltage (denoted as U< in the figure) (for example, the threshold of the first-stage voltage is 90V, the threshold of the second-stage voltage is 150V, and the low voltage is less than 90V), the controller controls the coil Q2 of the contactor to lose power, and the switch K2 of the contactor quickly closes to form a negative ground path. When the negative ground voltage reaches the safety voltage, the switch K2 of the contactor is reset (it can be reset manually or remotely controlled); when the negative ground voltage reaches the protection action threshold of the first-stage voltage, after a certain delay, the switch K2 of the contactor is reset, and after another certain delay, the switch K2 of the contactor opens. If K2 repeatedly opens and closes 3 times, then K2 is locked; when the negative ground voltage reaches the protection action threshold of the second-stage voltage, K2 immediately opens.

[0077] When K6 detects that the negative ground voltage is greater than 600V (the detected value can vary up and down by 50V from 600V), the thyristor overvoltage trigger module comes into play, the thyristor module V1 is quickly short-circuited, and the switch K2 of the contactor closes after a mechanical delay to ensure the "zero" potential of the track. When the negative ground voltage is less than the dangerous voltage and a certain time has elapsed, the AC / DC side circuit breaker trips.

[0078] 2. Thyristor cut-off function

[0079] 1) After the controller receives the signal that the AC / DC side circuit breaker is closed (auxiliary contact K2-1 is closed) and the signal of normal pressure relief, it sends a thyristor cut-off signal to the thyristor cut-off control module 4.

[0080] 2) At this time, current flows through the light-emitting diode of the optocoupler V10, then the photosensitive triode of the optocoupler conducts, and at this time the gate of the small thyristor V8 is triggered, so that the capacitor discharge circuit forms a path, achieving the purpose of applying a reverse voltage to the thyristor V2.

[0081] 3) The capacitor voltage monitoring device in the thyristor cut-off control module 4 detects that the voltage of the capacitor C1 is low and the thyristor V2 is cut off at this time, then the controller sends a energy storage signal. At this time, current flows through the light-emitting diode of the optocoupler V11, then the photosensitive triode conducts, so that the gate of the small thyristor V9 is triggered, forming a capacitor charging circuit. When the capacitor energy storage is completed, the capacitor voltage monitoring device sends a full signal to the controller and displays it. The voltage value at both ends of the capacitor can be observed during charging. When the voltage value reaches the capacitor voltage, it indicates that the charging is completed.

[0082] The main diode V5 and the series resistor R1 in the circuit are used for the stability and unidirectionality of power supply. The resistor R2 in series with the capacitor plays a role in voltage limiting protection during the capacitor charging process. The zener diode V7 is used to provide a stable voltage for the photosensitive triode. This circuit can control the switching current by controlling the phase shift angle of the small thyristors V8 and V9.

[0083] 3. Frame leakage current discharge function

[0084] 1) Communication between the controller and the frame monitoring system is carried out through cables to achieve information interaction.

[0085] 2) The frame monitoring system detects the current flowing through the frame. When drainage is required, the frame monitoring system determines the drainage volume and transmits the value of the drainage volume to the small controller in the frame leakage current discharge module 5. The small controller controls the small contactor K7 to close and adjusts the adjustable resistor R5 according to the drainage volume, so that the frame leakage current quickly flows to the negative pole through the drainage circuit, avoiding the electrochemical corrosion of the leakage current.

[0086] 3) When the frame monitoring system detects that the frame current is in a safe state, it issues a stop drainage command to the controller.

[0087] The silicon diode V4 in the frame leakage current discharge module 5 ensures the unidirectional conductivity of the ground negative. The fuse F1 plays a role in protecting the drainage line. The switch K8 can quickly remove the drainage device.

[0088] Although the present invention has been disclosed above with preferred embodiments, the embodiments are not intended to limit the present invention. Any equivalent changes or modifications made without departing from the spirit and scope of the present invention also belong to the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the content defined by the claims of this application.

Claims

1. A negative ground limit protection device for a rail transit power supply system, characterized in that, Comprising: A negative ground voltage limiting module, including a first contactor and a thyristor module connected in parallel, with one end connected to the negative return rail and the other end connected to the ground. When the potential difference between the negative return rail and the ground exceeds a specified voltage value, it quickly shorts the negative return rail to the ground; A negative ground voltage and current detection module, used to detect the current and / or voltage between the negative return rail and the ground and upload it to the intelligent control module; An intelligent control module, used to receive the voltage value detected by the negative ground voltage and current detection module and control the closing of the first contactor; after the first contactor closes, it controls the thyristor cut-off control module to immediately turn off the thyristor module; A thyristor cut-off control module, used to immediately turn off the thyristor module after the thyristor module conducts forward; the thyristor cut-off control module includes a thyristor cut-off circuit and a capacitor energy storage circuit connected in parallel; A frame leakage current discharge module, the frame leakage current discharge module is connected between the negative return rail and the ground, and is connected in parallel with the negative ground voltage limiting module, used to drain the frame leakage current when the frame leakage current is greater than a specified value; The thyristor cut-off circuit and the capacitor energy storage circuit share a power supply, a first capacitor, a zener diode, a grounding resistor, a first diode and a first resistor; The thyristor cut-off circuit includes a capacitor discharge trigger loop and a capacitor discharge circuit; among them, the capacitor discharge trigger loop is composed of a first optocoupler, a third resistor, a first capacitor and a third thyristor connected in series; the capacitor discharge circuit is composed of a first capacitor, a third thyristor, a first thyristor in the thyristor module and a second diode connected in series; The capacitor energy storage circuit includes a capacitor charging trigger loop and a capacitor charging circuit; among them, the capacitor charging trigger loop is composed of a second optocoupler, a third resistor, a first capacitor, a second resistor and a fourth thyristor; the capacitor charging circuit is composed of a first diode, a first resistor, a first capacitor, a second resistor and a fourth thyristor connected in series between the positive and negative poles of the power supply; After the thyristor module conducts forward, a reverse voltage is applied to the thyristor by using the capacitor discharge circuit, so as to quickly turn off the thyristor module; The frame leakage current discharge module includes: A protection fuse, a second contactor, a silicon diode, a first adjustable resistor, a fixed current limiting resistor, and a cut-off switch connected in series between the negative return rail and the ground; A protection circuit, the protection circuit includes an RC oscillation circuit composed of a second capacitor and a fourth resistor connected in series and then in parallel with a second adjustable resistor, one end of the second adjustable resistor is connected to the fixed current limiting resistor and the cut-off switch, and the other end is connected to the protection fuse and the second contactor; A frame monitoring system, used to detect the frame leakage current flowing through the frame; and A small controller, when the frame leakage current is greater than a specified value, the small controller controls the second contactor to close, determines the discharge amount, and adjusts the first adjustable resistor according to the discharge amount, so that the frame leakage current quickly flows to the negative return rail.

2. The negative ground limit protection device for the rail transit power supply system according to claim 1, wherein The first contactor includes at least one group of auxiliary contacts, used to judge the turn-off and closing of the first contactor and transmit the corresponding first contactor closing signal to the intelligent control module.

3. The negative ground limit protection device for the rail transit power supply system according to claim 1, characterized in that, The negative ground voltage current detection module includes a voltage measurement element and a current measurement element. The voltage measurement element is connected in parallel across both ends of the negative return rail and the ground, and real-time detects the voltage across the negative return rail and the ground, achieving grading of the voltage detection value. The current measurement element is connected in series with the thyristor module, and determines whether the negative ground voltage is higher than a specified value by measuring the current flowing through the thyristor module.

4. The negative ground limit protection device for the rail transit power supply system according to claim 3, characterized in that, The negative ground voltage current detection module further includes a rectification module, the rectification module is a double rectifier diode, the voltage measurement element is a plurality of voltage relays connected in parallel, and the current measurement element is a current relay connected in series with the thyristor module; the potential difference between the negative return rail and the ground is applied to the voltage relay after passing through the rectification module.

5. The negative ground limit protection device for the rail transit power supply system according to claim 4, characterized in that, The thyristor module includes a set of thyristors connected in anti-parallel and a corresponding thyristor overvoltage triggering module. The thyristor module is connected in series with the current relay between the negative return rail and the ground, and is connected in parallel with the first contactor. When the current relay detects that the negative ground voltage is greater than the specified value, the thyristor overvoltage triggering module causes the thyristor module to be quickly short-circuited.

6. The negative ground limit protection device for a rail transit power supply system according to claim 1, characterized in that, The first opto-coupler and the second opto-coupler respectively include a light-emitting diode and a photosensitive triode; the zener diode is connected in series with the first resistor and the first diode between the positive and negative poles of the power supply, and is used to stabilize the voltage of the photosensitive diode.

7. The negative ground limit protection device for a rail transit power supply system according to claim 6, characterized in that, When the negative ground voltage current detection module detects that the frame leakage current is lower than the specified value, it sends a stop drainage command to the intelligent control module, and the frame leakage current drainage module stops draining.

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