Analysis and Location Method of the Influence of Subway DC Traction Power Supply System on Grid Substations

Abstract

The present invention discloses an analysis and positioning method for the influence of a subway DC traction power supply system on a power grid substation, specifically: using an on-vehicle waveform generator to emit a superimposed signal of a sine wave and a DC wave with a certain frequency and amplitude, forming a stray current by injecting it into the earth through the working ground; obtaining the inflowing stray current through a current transformer at the grounding end of the traction substation, filtering out the noise signal through an EMI filter, performing a fast Fourier transform through a microcomputer module and extracting the amplitude and frequency information of the sine waveform, matching the frequency information with the frequencies of each line stored in the matching module to obtain a matching value, obtaining the attenuation coefficient through the calculation module from the amplitude information, and thus obtaining the approximate distance between the leakage location and the substation from the DC leakage fitting function of the corresponding subway line, and finally positioning and displaying the leakage location through the display module. The present invention can effectively analyze and position the stray current generated by the subway rail, improving the safety and reliability of the operation of the subway line.

Description

Technical Field

[0001] The present invention belongs to the field of electrified rail transit, and in particular relates to a method for analyzing and locating the impact of a subway DC traction power supply system on a power grid substation. Background Art

[0002] At present, my country's subways mainly use 750v / 1500v / 3000v DC traction power supply systems. During long-term operation and use, the insulating gaskets between the rails and the sleepers are prone to aging, resulting in incomplete insulation between the rails and the ground. In the current subway architecture, the rails are the only way for the subway line to return traction, which will cause part of the traction return to leak to the ground near the rails. In addition, the underground layout of the city is complicated, and long-term DC leakage will cause electrochemical corrosion of cables and metal pipes buried deep underground. In addition, the traction substation in the power grid will also be affected by the leaked DC component, which will produce DC bias magnetism and cause damage to the transformer, resulting in a reduced service life. Not only that, "traction substation-contact network-train-rail-ground network" constitutes a complete DC loop. During the operation of the subway, since the running direction of the subway remains unchanged, a magnetic field with a constant direction and strength that changes with the current will be generated. The electromagnetic induction phenomenon generated will cause induced current in the surrounding AC power grid.

[0003] At present, due to the complex structure of urban underground railways and network management in real life, the surrounding metal network pipes or substations are affected by the leaked DC current, and the exact location of the leak cannot be accurately determined, and most of the targeted protection and repair cannot be carried out. Summary of the invention

[0004] In view of the current DC leakage caused by subway grounding problems, in order to reduce the shortened service life of AC substations and electrochemical corrosion of urban underground pipes caused by DC leakage, and to facilitate subway maintenance to carry out more targeted emergency repairs, the present invention provides a method for analyzing and locating the impact of subway DC traction power supply systems on power grid substations.

[0005] The present invention provides a method for analyzing and locating the impact of a subway DC traction power supply system on a power grid substation, comprising the following steps:

[0006] Step 1: Install a sine wave generator and a DC wave generator on the train to form a frequency of f i , a sine wave y with amplitude A Ai and a DC wave y with amplitude D Di At the same time, after being superimposed, the traction current leaks to the ground through the working ground together with the working current through the leakage point where the rail and the ground are connected, thus forming stray current.

[0007] To prevent the sine wave and DC wave generated by the on-vehicle sine wave generator and DC wave generator from affecting the VVVF inverter box of the train, a diode is installed behind the VVVF inverter box to prevent the sine wave and DC wave from flowing in.

[0008] Step 2: The stray current propagates through the ground to the neutral grounding wire of the substation transformer. The current sensor obtains the stray current from the ground and other interference signal waves from the neutral grounding wire of the transformer, and after being processed by the EMI filter, the interference signal waves are filtered out.

[0009] Step 3: After being filtered by the EMI filter, the stray current enters the microcomputer Fourier transform matching platform for processing. First, it is decomposed by the fast Fourier transform module through Fourier transform, and a series of sine waves with a frequency of f i and an amplitude of A i are obtained through the waveform amplitude acquisition module and the specific frequency data frequency of the waveform obtained by preprocessing.

[0010] Step 4: After obtaining a series of sine waves with a frequency of f i and an amplitude of A i , the waveform data is sent to the matching module for processing. The matching module stores the frequencies of the specific signals injected by the trains on each subway line. The microcomputer system matches the frequency of the specific signal in the stray current obtained from the grounding end of the transformer with the stored signal frequencies to screen out the subway line data with matching values, thereby obtaining the source of the main stray current.

[0011] Step 5: After obtaining the source information of the main stray current, the operation module will divide the obtained sine wave amplitude A i by the reference amplitude A to obtain the coefficient λ i characterizing the waveform attenuation degree.

[0012] Step 6: Through the DC leakage fitting function f(λ) k of the subway line, the approximate straight-line distance d i between the DC leakage location and the substation is obtained.

[0013] Step 7: The distance information d i and the frequency information f i are output to the display module, and the stray current leakage line section is accurately located based on these two data.

[0014] A subway DC bias identification system of the present invention consists of a sine wave generator and a DC wave generator to form a signal wave generation module. The signal leaks to the ground through the working grounding axis, conducts through the ground to the neutral grounding point of the power transformer, and then flows into the neutral grounding wire. A current transformer is set on the neutral grounding wire to draw current from the neutral line. After the current is drawn, interference is filtered by an EMI filter, and then transmitted to the microcomputer system through a current sensor. The fast Fourier transform module decomposes the current signal. The frequency and amplitude data of a series of waveforms obtained after decomposition are sent to the matching module for calculation and pairing. After the pairing is completed, the data is sent to the operation module for calculating the attenuation coefficient of the amplitude. The obtained attenuation coefficient is brought into the fitting function to obtain the approximate straight-line distance data of the DC leakage point from the substation, so as to accurately identify and locate the subway line with DC leakage and the distance.

[0015] The technical principle of the present invention:

[0016] The present invention consists of four parts: on-vehicle waveform injection along the subway line, microcomputer Fourier transform matching, waveform coefficient processing, and DC bias line positioning. The on-vehicle waveform injection part along the subway line mainly includes a DC waveform generation device, a sine wave generation device, an on-vehicle waveform superposition instrument, and an EIM filter, which are mainly used to inject DC waves and sine waves on each subway operation line, as well as superpose waveforms and filter interference waves. By adding an electrical signal with a specific frequency in each line through the traction return current, the bias current generated by the train operation on each line is recorded and marked. The microcomputer Fourier transform matching part includes a fast Fourier transform module, a data pre-storage module, a waveform decomposition module, and a data analysis module, which are mainly used to perform Fourier decomposition on the captured electrical signal, calculate and analyze the content of harmonics, and match with the pre-stored data, so as to judge and analyze the influence of each subway line on the substation. The waveform coefficient processing platform includes a periodic signal waveform recognition and transmission device and a parameter measurement device with an ARM Cortex-M4 processor as the main controller, which are mainly used to realize the discrimination of the signal waveform type and the measurement of related parameters such as frequency and peak-to-peak value based on the processor through corresponding algorithms, so that the microcomputer system can identify and measure related parameters such as the frequency, peak value, and duty cycle of the signal waveform. The DC bias line positioning platform mainly consists of a distance operation module, a section determination module, and a display module, which are mainly used to calculate the distance between the leakage point and the substation by using the coefficient representing the waveform attenuation degree obtained by the operation module, judge the specific section of the leakage point, and judge which subway line has a DC bias phenomenon through the specific frequency of the obtained electrical signal. Then, the relevant coefficients detected on each line are reflected through the display module, so as to carry out targeted maintenance work on the corresponding section to achieve the purpose of accurately suppressing DC bias.

[0017] The beneficial technical effects of the present invention are:

[0018] 1. The present invention comprehensively considers the generation path and process of subway DC bias, accurately locates and identifies the source of stray current that affects the power transformer of the substation due to DC bias. Past research has mostly focused on the impact and interference of DC bias on power transformers, while ignoring the location of stray current that invades the transformer winding from the neutral grounding wire of the transformer. The present invention comprehensively considers the generation and conduction mechanisms of stray current, decomposes the composition of the stray current invading the power transformer, accurately locates which subway lines the stray current comes from, and provides an important basis for the protection of stray current in the substation.

[0019] 2. For the subway DC bias identification technology of the present invention, a sine wave with a specific frequency is injected into the working grounding wheelset of the subway vehicle on each subway line. This sine wave is conducted to the neutral grounding point of the substation power transformer together with the stray current. By identifying the current at the neutral grounding point of the power transformer, the source of the stray current can be located.

[0020] 3. For the wheelset current injection technology of the present invention, a diode is connected in series before the injection point. The injected current is composed of a sine wave with a specific frequency and a DC wave whose amplitude is slightly larger than the amplitude of the sine wave, making it a direct current with a positive direction all the time. The purpose is to prevent the injected identification current from conducting reversely along the working grounding to the subway traction power supply circuit and avoid interfering with and affecting the equipment of the subway vehicle.

[0021] 4. For the DC bias identification method of the present invention, relying on Fourier transform, current is taken at the neutral grounding wire of the power transformer. After filtering out the interference signals by a filter, it is decomposed. According to Fourier transform theory, a series of sine signals with different frequencies and amplitudes and a DC component can be obtained. The present invention matches the frequencies of the obtained sine components, compares with the sine waves with specific frequencies injected into each subway line, and can accurately identify which subway lines the stray current in the neutral grounding wire of the power transformer comes from, which is of great significance for the protection of stray current in the substation.

[0022] 5. For the DC bias identification technology of the present invention, the amplitudes of the sine waves after Fourier decomposition and pairing are also taken, divided by the amplitude at the time of injection, and after fitting function operation, the distance from the DC leakage location of this subway line to the substation can be roughly obtained, further improving the identification accuracy of DC bias. Description of the Drawings

[0023] Figure 1 It is a schematic diagram of the formation mechanism of stray current.

[0024] Figure 2 It is a diagram of the positional relationship between the subway line and the substation.

[0025] Figure 3Flowchart of the analysis and location method for the impact of the subway DC traction power supply system on the grid substation.

[0026] Figure 4 Schematic diagram of the structure of the subway DC bias identification system.

[0027] Figure 4 Explanation of the reference numerals in the figure: 1 - display module, 2 - operation module, 3 - matching module, 4 - fast Fourier transform module, 5 - current sensor, 6 - EMI filter, 7 - neutral grounding wire of the transformer, 8 - power transformer, 9 - pantograph, 10 - catenary, 11 - traction motor, 12 - sine wave generator, 13 - DC wave generator, 14 - diode, 15 - filter reactor, 16 - rail, 17 - working grounding resistance, 18 - working grounding shaft.

[0028] Figure 5 Schematic diagram of the hardware module.

[0029] Figure 6 Schematic diagram of injecting a specific waveform frequency into the subway line. Specific implementation manner

[0030] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0031] The formation mechanism of the leakage current of the subway is as Figure 1 shown. The subway mainly uses 1500V DC power supply. The DC power on the catenary is transmitted to the subway vehicle through the pantograph and is supplied to the AC motor after being inverted by the inverter to drive the subway vehicle forward. The working current is discharged to the rail through the working grounding shaft and then returns to the DC traction substation through the rail. Since the rail is not completely insulated from the ground and the insulation gasket between the rail and the sleeper may be damaged due to aging, a part of the current will leak to the ground from the damaged insulation. Although most of the leakage current will be absorbed by the main drainage network and flow back to the DC traction substation through the drainage cabinet, there will still be some DC leakage to the ground, resulting in DC leakage. In addition, since the subway is powered by DC, a complete DC loop is formed by "traction substation - catenary - train - rail - ground grid". During the operation of the subway, due to the constant running direction of the subway, a magnetic field with a constant direction and an intensity changing with the current magnitude will be generated. The electromagnetic induction phenomenon will cause induced current in the surrounding AC power grid, thus affecting the normal operation of the power grid.

[0032] The positional relationship between the subway line and the AC substation is as Figure 2As shown in the figure, compared with high-speed railways, subway lines are more intricate and have a higher density. Between subway operation lines, there are often AC substations, and there is a grounding wire at the neutral point of the power transformer in the substation. Therefore, the DC leakage generated by each subway line often conducts to the neutral grounding wire of the power transformer through the ground, and then flows into the transformer winding through the neutral grounding wire, resulting in DC bias magnetization, seriously affecting the normal operation of the transformer and shortening the service life of the transformer.

[0033] An analysis and positioning method for the impact of a subway DC traction power supply system on a grid substation is as Figure 3 shown, and specifically includes the following steps:

[0034] Step 1: Install a sine wave generator and a DC wave generator on the train to form a sine wave y with a frequency of f i and an amplitude of A Ai as well as a DC wave y with an amplitude of D Di ; at the same time, the traction current leaks to the ground through the leakage point at the connection between the rail and the ground together with the working current after superposition, thus forming stray current.

[0035] To prevent the sine wave and DC wave generated by the on-vehicle sine wave generator and DC wave generator from affecting the VVVF inverter box of the train, a diode is installed behind the VVVF inverter box to prevent the sine wave and DC wave from flowing in.

[0036] Step 2: The stray current propagates through the ground to the neutral grounding wire of the substation transformer. The current sensor obtains the stray current from the ground and other interference signal waves from the neutral grounding wire of the transformer, and after being processed by the EMI filter, the interference signal waves are filtered out.

[0037] Step 3: After being filtered by the EMI filter, the stray current enters the microcomputer Fourier transform matching platform for processing. First, it is decomposed by the fast Fourier transform module through Fourier transform, and a series of sine waves with a frequency of f i and an amplitude of A i are obtained through the waveform amplitude acquisition module and the specific frequency data frequency of the waveform obtained by preprocessing.

[0038] Step 4: After obtaining a series of sine waves with a frequency of f i and an amplitude of A i , the waveform data is sent to the matching module for processing. The matching module stores the frequencies of the specific signals injected by the trains on each subway line. The microcomputer system matches the frequency of the specific signal in the stray current obtained from the transformer grounding end with the stored signal frequencies to screen out the subway line data with matching values, so as to obtain the source of the main stray current.

[0039] Step 5: After obtaining the information on the main stray current sources, the operation module will divide the obtained sine wave amplitude A i by the reference amplitude A to obtain the coefficient λ characterizing the waveform attenuation degree i .

[0040] Step 6: Through the DC leakage fitting function f(λ) of the subway line k obtain the approximate straight-line distance d between the DC leakage location and the substation i .

[0041] Step 7: Output the distance information d i and the frequency information f i to the display module, and accurately locate the stray current leakage line section based on these two data

[0042] A subway DC bias magnetic recognition system of the present invention is as Figure 4 shown. The system consists of the following modules: a signal wave generation module, a fast Fourier transform module 4, a matching module 3, an operation module 2, and a display module 1. The fast Fourier transform module 4, the matching module 3, the operation module 2, and the display module 1 are included in the microcomputer system. The signal wave generation module consists of a sine wave generator 12 and a DC wave generator 13, where the amplitude of the generated DC signal is slightly larger than the amplitude of the sine signal. The working current is obtained by the pantograph from the catenary 10, flows through the working grounding shaft 18, and returns to the traction substation from the rail 16. According to the generation mechanism of DC leakage, two waveform generators are connected before the grounding resistance 17 of the working grounding shaft, and a unidirectional conducting diode 14 is connected in series before the connection point. The sine wave and DC wave generated by the two waveform generators are superimposed to show a DC waveform with a constant direction. After this waveform is injected into the working grounding shaft 18, it is discharged to the rail 16 together with the working current. The series-connected diode 14 prevents the injected signal wave from flowing back into the subway power supply circuit in the reverse direction, thereby protecting the on-vehicle VVVF inverter from interference and ensuring the normal operation of the subway vehicle. After the signal wave is mixed with the working current, it leaks to the ground, is conducted through the ground to the neutral grounding point of the power transformer 8, and flows into the neutral grounding wire 7. A current transformer is set on the neutral grounding wire 7 to take current from the neutral line. After taking the current, it is filtered by the EMI filter 6 to remove interference, and then transmitted to the microcomputer system through the current sensor 5. The fast Fourier transform module 4 decomposes the current signal. According to the Fourier transform formula, a periodic signal that satisfies the Dirichlet conditions can be decomposed into a series of sine waves and a DC component with different frequencies and amplitudes, that is:

[0043]

[0044] where,

[0045]

[0046]

[0047] The frequency and amplitude data of a series of waveforms obtained after decomposition are sent to the matching module 3 for calculation and pairing. After the pairing is completed, they are sent to the operation module 2 for calculating the attenuation coefficient of the amplitude. The obtained attenuation coefficient is brought into the fitting function to obtain the approximate linear distance data of the DC leakage location from the substation, so as to accurately identify and locate the subway line and distance of the DC leakage.

[0048] The hardware block diagram of the present invention is as Figure 5 shown. The subway vehicle waveform injection platform consists of an on-vehicle sine wave generation module, an on-vehicle DC wave generation module, a waveform data acquisition module, a waveform modulation / demodulation superposition module, and a waveform injection module. The microcomputer Fourier transform matching platform consists of a waveform amplitude acquisition module, a module for preprocessing and storing waveform specific frequency data, a fast Fourier transform module, and a waveform decomposition and data matching module. Among them, the frequency data of the specific waveform generated by the sine wave generator have been pre-stored in the system. The waveform coefficient processing platform consists of a waveform sending device, a waveform data sending module, a pre-stored analog DC leakage fitting function, and a data operation module. Among them, the fitting function has been pre-stored in the system. After the fast Fourier decomposition module decomposes the current signal of the neutral grounding wire, the data matching module will match the decomposed frequency data, compare it with the pre-stored frequency data. The successfully matched frequency data will be sent to the data operation module together with the amplitude data of the sine wave corresponding to the frequency waveform. The data operation module will divide the amplitude of this frequency by the amplitude at the time of injection to obtain an amplitude attenuation coefficient λ. This coefficient characterizes the attenuation degree of the current leaked from a certain subway line to the neutral grounding point of the transformer. The data operation module brings this coefficient into the fitting function to obtain the approximate linear distance between the leakage location and the substation. Finally, the display module will transmit the obtained frequency and distance data to the display for display. From the display, it can be read which subway lines have DC leakage affecting the power transformer of the substation and the distance between the leakage location and the substation. Among them, the solution method of the fitting function is as follows: For any subway line, a trial sine signal y with an amplitude of A is applied at a certain point on the track, and then the amplitude A' of y1 is detected at the neutral grounding point of the power transformer of the substation. Divide A' by A to obtain the attenuation coefficient λ1, and record the linear distance d1 from the trial point to the substation. Then repeat the above process at certain intervals along the track to obtain a set of λ i and d i data. Using matlab, the approximate relationship between the distance d from the trial point to the substation and the attenuation coefficient λ is fitted as:

[0049] d = f(λ)

[0050] Each subway line of the present invention is injected with a sine wave of a specific frequency, such as Figure 6 As shown, each subway line will be injected with a sine wave of a specific frequency. After being superimposed with the DC wave, it is discharged to the rail together with the working current, leaked to the ground through the rail, and then transmitted to the neutral grounding point of the power transformer. The frequency data injected into each subway line is pre-stored in the microcomputer system for comparison with the frequency data obtained by Fourier decomposition.

Claims

1. An analysis and positioning method for the impact of a subway DC traction power supply system on a grid substation, characterized in that, It includes the following steps: Step 1: Install a sine wave generator and a DC wave generator on the train to form a sine wave y with a frequency of f i , an amplitude of A Ai and a DC wave y with an amplitude of D Di ; At the same time, the traction current leaks to the ground through the leakage point at the connection between the rail and the ground together with the working current after superposition, thus forming stray current; Step 2: The stray current propagates through the ground to the neutral grounding wire of the substation transformer. The current sensor obtains the stray current from the ground and the remaining interference signal waves from the neutral grounding wire of the transformer, and after being processed by the EMI filter, the interference signal waves are filtered out; Step 3: After being filtered by the EMI filter, the stray current enters the microcomputer Fourier transform matching platform for processing. First, it is decomposed by the fast Fourier transform module through Fourier transform, and a series of sine waves with a frequency of f i , an amplitude of A i are obtained; Step 4: After obtaining a series of sine waves with a frequency of f i and an amplitude of A i , the waveform data is sent to the matching module for processing. The matching module stores the frequencies of the specific signals injected by the trains on each subway line. The microcomputer system matches the frequency of the specific signal in the stray current obtained from the grounding end of the transformer with the stored signal frequencies to screen out the subway line data with matching values, thereby obtaining the source of the main stray current; Step 5: After obtaining the information on the main sources of stray current, the operation module will divide the obtained sine wave amplitude A i by the reference amplitude A to obtain the coefficient λ i ; Step 6: Obtain the approximate linear distance d between the DC leakage location and the substation through the DC leakage fitting function f(λ) of the subway line k i ;​ Step 7: Distance information d i and frequency information f i are output to the display module, and the stray current leakage line section is accurately located according to these two data.

2. The analysis and positioning method for the impact of a subway DC traction power supply system on a grid substation according to claim 1, wherein In the said Step 1, to prevent the sine wave and DC wave generated by the on-vehicle sine wave generator and DC wave generator from affecting the VVVF inverter box of the train, a diode is installed behind the VVVF inverter box to prevent the sine wave and DC wave from flowing in.

3. A subway DC bias identification system using the analysis and location method for the impact of the subway DC traction power supply system described in claim 1 on the grid substation, characterized in that, A signal wave generation module composed of a sine wave generator (12) and a DC wave generator (13) leaks to the ground through the working grounding shaft (18), conducts through the ground to the neutral grounding point of the power transformer (8) and flows into the neutral grounding wire (7). A current transformer is set on the neutral grounding wire (7) to take current from the neutral wire. After taking the current, the interference is filtered out by the EMI filter (6), and then transmitted to the microcomputer system through the current sensor (5). The current signal is decomposed by the fast Fourier transform module (4). The frequency and amplitude data of a series of waveforms obtained after decomposition are sent to the matching module (3) for calculation and pairing. After the pairing is completed, it is sent to the operation module (2) for calculating the attenuation coefficient of the amplitude. The obtained attenuation coefficient is brought into the fitting function to obtain the approximate straight-line distance data of the DC leakage location from the substation, so as to accurately identify and locate the subway line and distance of the DC leakage.

Images