TDR and passive transient analysis fused power transmission cable fault diagnosis system

Abstract

The invention discloses a TDR and passive transient analysis fused power transmission cable fault diagnosis system, and belongs to the technical field of power system fault diagnosis and intelligent diagnosis. The method comprises the following steps: firstly, constructing a pulse injection and signal acquisition integrated device at the end part of a cable, acquiring three-phase voltage and current transient signals, and forming increments before and after a fault; and further constructing an incident wave and a reflected wave at a port, extracting a high-frequency detail component by adopting wavelet decomposition, enhancing wave head features in combination with a TEO energy operator, and analyzing a fault type. And judging a grounding fault, a high-resistance fault or a low-resistance fault. If the fault is a low-resistance fault, passive distance measurement is adopted, and if the fault is a high-resistance fault, the active distance measurement device generates pulse distance measurement. According to the high-resistance and low-resistance self-adaptive distance measurement method, the wave head detectability and the distance measurement stability can be improved under the conditions of different fault impedances and different fault types, and the reliability of cable fault positioning is improved.

Description

Technical Field

[0001] This invention relates to the field of cable fault detection and location technology, and in particular to a power transmission cable fault diagnosis system that integrates TDR and passive transient analysis. Background Technology

[0002] With the rapid development of power systems, communication systems, and industrial automation systems, various types of power cables and communication cables are widely used in power transmission networks, rail transit, mining engineering, and large industrial facilities. Cables are usually laid underground, in tunnels, or inside complex structures, and operate under high voltage, high load, and complex environmental conditions for a long time. They are susceptible to aging, moisture, mechanical damage, and construction damage, which can lead to faults such as open circuits, short circuits, and impedance changes.

[0003] Currently, commonly used cable fault detection and location methods mainly include the DC bridge method, pulse reflection method, traveling wave method, and active time domain reflection ranging (TDR) method. Among them, the TDR method injects a high-speed pulse signal into the cable and analyzes the time characteristics of the pulse propagation and reflection in the cable. It can calculate the fault distance based on the time difference between the reflected signal and the incident signal. It has the advantages of being non-destructive, easy to operate, and having high positioning accuracy, and is widely used in the field of cable fault detection.

[0004] However, in practical engineering applications, traditional TDR cable fault detection methods still have certain limitations. When a cable experiences a short circuit fault, the amplitude of the reflected wave is relatively small and is easily superimposed with the oscillations caused by the line distribution parameters, making it difficult to accurately determine the arrival time of the reflected wave.

[0005] To address existing shortcomings, this invention proposes a power transmission cable fault diagnosis system that integrates TDR (Transient Dynamic Reflection) and passive transient analysis. By jointly analyzing the reflection characteristics generated by actively injected pulse signals and the transient signals of cable faults, and introducing signal processing techniques such as time-frequency analysis and energy operators, a comprehensive judgment of cable location and fault type can be achieved, thereby improving the accuracy of fault location. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention provides a power transmission cable fault diagnosis system that integrates TDR and passive transient analysis. The system consists of two parts: an active pulse generation and monitoring pulse device and a device-based cable fault location method. The active pulse generation and monitoring pulse device is composed of an active pulse generation device and a monitoring pulse device.

[0007] Furthermore, the active pulse generating device consists of a threshold reference module, a comparison and rectification module, a pulse generating module, and a status indication module.

[0008] Furthermore, the threshold reference module is composed of voltage divider resistors.

[0009] Furthermore, the comparison rectifier module consists of a comparator and a resistor.

[0010] Furthermore, the pulse generation module is composed of a 555 timer.

[0011] Furthermore, the status indication module consists of an alarm.

[0012] Furthermore, the monitoring pulse device consists of a front-end wavefront extraction module, a rectifier output module, a comparison amplification module, and an enable control module.

[0013] Furthermore, the front-end wavefront extraction module consists of an operational amplifier, capacitors, and resistors.

[0014] Furthermore, the rectifier output module consists of diodes, resistors, and capacitors.

[0015] Furthermore, the comparison amplification module consists of operational amplifiers and transistors.

[0016] Furthermore, the enable control module consists of resistors, switches, and transistors.

[0017] Furthermore, the cable fault location method generally includes the following nine steps:

[0018] Step 1: Construct a faulty transmission cable and use a data acquisition module to collect transient voltage and current signals at the cable port, as well as the instantaneous three-phase voltage signals at the cable port before the fault. With three-phase instantaneous current signal and three-phase instantaneous voltage signals after the fault With three-phase instantaneous current signal And collect.

[0019] Step 2: Construct fault transient voltage and current increments from the acquired three-phase instantaneous voltage and current signals using the incremental method, and calculate the fault transient voltage and current increments. The simulated components are calculated as shown in equation (1).

[0020] (1)

[0021] In the formula, It is a time variable; , These represent the transient voltage and current increments during the fault.

[0022] Furthermore, the calculation The simulated components are shown in equation (2).

[0023] (2)

[0024] In the formula, For voltage , Zero-sequence mode components; For current , Zero-sequence mode components.

[0025] Step 3: Construct incident and reflected waves at the fault point, extract high-frequency components d1 using wavelet transform, and then use TEO to enhance the energy of the components extracted by wavelet transform and superimpose them.

[0026] Furthermore, the formulas for the incident wave and the reflected wave are constructed as shown in equation (3).

[0027] (3)

[0028] In the formula, For incident traveling wave; To reflect traveling waves; This is the voltage signal corresponding to the mode; This is the current signal corresponding to the mode; The characteristic impedance of a cable is usually approximated by the unit length parameter, as shown in equation (4).

[0029] (4)

[0030] Furthermore, the component d1 extracted by the TEO wavelet transform is enhanced with energy, as shown in Equation (5).

[0031] (5)

[0032] In the formula, It is a discrete sequence signal; The discrete sampling point number; The energy operator is used; further, the incident and reflected channel energies are fused to construct a wavefront detection energy sequence.

[0033] Furthermore, the high-frequency components are superimposed to obtain the energy sequence E(t), the specific form of which is shown in equation (6).

[0034] (6)

[0035] In the formula, (t) represents the energy sequence; For incident wave A layer of detail components is obtained by trisectioning wavelets; To reflect waves A layer of detail components obtained by wavelet decomposition; , This is the TEO energy sequence corresponding to the detail components.

[0036] Step 4: Determine the type of fault in the power transmission cable.

[0037] Furthermore, the specific steps for determining the fault type of the power transmission cable in step 4 are as follows.

[0038] Step 4.1: Determine if there is a grounding fault, based on zero-sequence component. The significance of the saturation is used to determine whether the ground is grounded. When a ground fault occurs, the zero-sequence component increases significantly. The calculation is shown in equation (7).

[0039] (7)

[0040] In the formula, The zero-order significance index; It is the zero-sequence current mode component; for , Modal current components; This is the root mean square operation; To prevent extremely small positive numbers with a denominator of zero; The grounding detection threshold.

[0041] Step 4.2: Determine if it is a single-phase / two-phase / three-phase fault. Calculate the amplitude characteristics of the three-phase current increment. If only one phase increases significantly, it is determined to be a single-phase fault; if both phases increase significantly at the same time, it is determined to be a two-phase fault; if both phases increase significantly at the same time and the amplitudes are close ( If the value is 0, it is determined to be a three-phase fault; the calculation formula is shown in equation (8).

[0042] (8)

[0043] In the formula, This represents the amplitude characteristics of the three-phase incremental current. These are the three-phase incremental current components; This is an imbalance factor used to distinguish between symmetric and asymmetric faults. , This is for finding the maximum or minimum value.

[0044] Step 4.3: Determine whether it is a high-resistance fault or a low-resistance fault. The larger the fault resistance, the smaller the reflection amplitude and transient current peak value. The calculation is shown in Equation (9).

[0045] (9)

[0046] In the formula, represents the reflection intensity index; To reflect traveling waves; For incident traveling wave; The current-to-voltage ratio is a key indicator. , This refers to incremental current or voltage. The threshold value is the resistance level. It is a very small positive number.

[0047] Step 5: Autonomous optimal fault location based on active pulse ranging for high-impedance faults and passive ranging for low-impedance faults.

[0048] Furthermore, if the fault is high impedance, the waveform under natural transient conditions is weak and the wavefront is not obvious, so active pulse ranging is used.

[0049] Furthermore, the active pulse ranging is initiated by an active pulse generating device that outputs a pulse waveform to the cable port. and collect port responses. The echo arrival time is obtained by matched filtering. And calculate the fault distance, the calculation formula is shown in equation (10).

[0050] (10)

[0051] In the formula, The pulse waveform output by the device; The reflected pulse signal acquired at the port; This is the cross-correlation function between the pulse waveform and the response signal; For time delay variables; To estimate the round-trip time delay of the obtained echo;

[0052] Step 6: Based on the adaptive threshold of E(t) and the wavefront arrival time of the protected area, candidate time differences are identified.

[0053] Furthermore, an adaptive threshold strategy is employed on the energy sequence E(t) to determine the first arrival wavefront time. The threshold can be set as the peak ratio, and the calculation formula is shown in equation (11).

[0054] (11)

[0055] In the formula, k is the threshold coefficient.

[0056] Step 7: To avoid misidentifying the same wavefront as a second-arriving wavefront, a protection zone is set up. Only Then search for the second significant peak as The calculation formula is shown in equation (12).

[0057] (12)

[0058] In the formula, For minimum interval constraints, The maximum interval constraint can provide conditions for the accuracy of distance measurement through constraint conditions.

[0059] Step 8: Combine TDR ranging and passive ranging to output the fault distance. The ranging formula is shown in equation (13).

[0060] (13)

[0061] In the formula, The fault distance is obtained through passive ranging. For the propagation speed of the traveling wave, satisfying ; The first arrival wavefront time (the first significant wavefront detected by the port); This is the second arrival time of the wavefront; The time difference between the two arrivals corresponds to the round-trip propagation time of the traveling wave.

[0062] Step 9: Repeat steps 1 and 8 above to collect multiple sets of data to verify the accuracy of the power transmission cable fault diagnosis system.

[0063] The beneficial effects of adopting the above technical solution are as follows: This invention provides a power transmission cable fault diagnosis system that integrates TDR and passive transient analysis. The system consists of two parts: an active pulse generation and monitoring device, and a cable fault location method based on the device. The active pulse generation and monitoring device comprises an active pulse generation device and a monitoring pulse device. Based on the constructed active pulse generation and monitoring device, pulses of different frequencies can be rapidly emitted through voltage changes, and the reflected pulse wavefronts at fault points can be accurately monitored. Based on the cable fault location method constructed by the device, the instantaneous voltage and current signals of the three phases before and after the fault at the cable port are collected, a fault transient increment is constructed, and the incident traveling wave component and the reflected traveling wave component are obtained. Then, wavelet decomposition and energy operator methods are used... This system enhances wavefront characteristics, suppresses distributed parameter oscillations and background noise, and achieves stable identification of the arrival time of reflected wavefronts. It determines the cable fault type by collecting three-phase instantaneous voltage and current signals and adaptively selects the ranging method based on the fault's equivalent impedance: for low-resistance faults, passive ranging is performed using the obvious wavefront characteristics of the fault's natural transient traveling wave; for high-resistance faults, an active pulse generator is activated to inject pulses into the cable and collect echoes, calculating the fault distance using the echo time difference. This approach accommodates various fault conditions, including high and low resistance, expanding its applicability. Simultaneously, by setting wavefront criteria and time interval constraints, the system reduces the probability of false detections and missed detections, improving ranging accuracy and positioning reliability. Ultimately, it obtains the fault distance, reducing the scope of manual line inspections and power outage time, thereby improving the efficiency of power transmission cable fault handling and maintenance support. Attached Figure Description

[0064] Figure 1 This is a flowchart illustrating the overall steps of a power transmission cable fault diagnosis system that integrates TDR and passive transient analysis according to the present invention.

[0065] Figure 2 This invention relates to an active ranging pulse generation device.

[0066] Figure 3 This invention relates to a device for detecting reflected pulses.

[0067] Figure 4 The embodiment of this invention outputs an 800Hz result graph.

[0068] Figure 5 The embodiment of this invention outputs a 1000Hz result graph.

[0069] Figure 6 This is a schematic diagram of a power transmission cable simulating a fault, as presented in this invention.

[0070] Figure 7 The embodiment of the present invention provides a diagram showing the construction results of incident and reflected waves.

[0071] Figure 8 The wavelet transform extraction result diagram of the embodiment of the present invention.

[0072] Figure 9 Statistical fault result diagram of an embodiment of the present invention. Detailed Implementation

[0073] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0074] This invention takes the fault diagnosis process of a 100-kilometer-long power transmission cable with a fault point at 50 kilometers as an example. A power transmission cable fault diagnosis system that integrates TDR and passive transient analysis consists of two parts: an active pulse generation and monitoring pulse device and a device-based cable fault and ranging method. The active pulse generation and monitoring pulse device consists of an active pulse generation device and a monitoring pulse device.

[0075] Furthermore, the active pulse generating device comprises a threshold reference module, a comparison and rectification module, a pulse generating module, and a status indication module, and its circuit structure is as follows: Figure 2 As shown.

[0076] Furthermore, in this embodiment, the threshold reference module is composed of a voltage divider resistor R4, which outputs a reference voltage Vref under the supply voltage VCC to determine whether the cable has a low resistance fault or a high resistance fault. The two ends of the voltage divider resistor R4 are connected to the supply voltage VCC and the ground wire, respectively, and the voltage divider node of R4 is connected to the comparison rectifier module.

[0077] Furthermore, in this embodiment, the comparison rectification module consists of two comparators, U1A and U2A. In this embodiment, the comparator chip type is LM339AD. The input terminal of U1A is connected to the analog voltage node R4 and VSS1, where VSS1 is 0.8V. The power supply terminals are connected to VDD and VDDS, where VDD and VDDS are 12V and -12V, respectively. VDD is connected to the output terminal of U1A through resistor R3. The input terminal of U2A is connected to the analog voltage node R4 and VSS, where VSS is 3.5V. The power supply terminals are connected to VDD and VDDS, where VDD and VDDS are 12V and -12V, respectively. VDD is connected to the output terminal of U1A through resistor R10. The output terminals of U1A and U2A are connected to the pulse generation module.

[0078] Furthermore, in this embodiment, the pulse generation module consists of 555 timers A1 and A2. In this embodiment, the 555 timer chip type is 555_VIRTUAL. The VCC pin of 555 timer A1 is connected to VCC, and the GND pin is connected to ground. The RST pin of 555 timer A1 is connected to the analog voltage node of the voltage divider resistor R4. The DIS pin of 555 timer A1 is connected in series with resistor R1 and then back to the VCC pin. The DIS pin is connected in series with resistor R2 and then back to the THR pin. The THR pin is connected to the TRI pin. The TRI pin is connected in series with capacitor C1 and then back to the ground pin. The CON pin is connected to the ground pin. Capacitor C3 is connected in series back to the ground pin; the VCC pin of 555 timer A2 is connected to VCC, and the GND pin is connected to ground; the RST pin of 555 timer A2 is connected to the analog voltage node of voltage divider resistor R4; the DIS pin of 555 timer A2 is connected in series with resistor R8 and then back to the VCC pin; the DIS pin is connected in series with resistor R9 and then back to the THR pin; the THR pin is connected to the TRI pin; the TRI pin is connected in series with capacitor C2 and then back to the ground pin; the CON pin is connected in series with capacitor C4 and then back to the ground pin; the OUT pins of 555 timers A1 and A2 are respectively connected to the status indicator module. Figure 4 To output the 800Hz result diagram for this embodiment, when the analog voltage of the voltage divider resistor R4 is less than 0.8V, the 555 timer outputs an 800Hz pulse as shown in Figure 4. Figure 5 The output of this embodiment is a 1000Hz result diagram. When the analog voltage of the voltage divider resistor R4 is greater than 3.5, the 555 timer outputs a Hz pulse as shown in Figure 5.

[0079] Furthermore, in this embodiment, the status indication module consists of alarms LS3 and LS1. The alarm model is BUZZER. The two ends of the buzzer LS3 are connected to VCC and the collector of transistor Q1. The base of transistor Q1 is connected in series with R16 and back to the OUT pin of 555 timer A1. The emitter of transistor Q1 is connected to ground.

[0080] Furthermore, the monitoring pulse device consists of a front-end wavefront extraction module, a rectifier output module, a comparison amplification module, and an enable control module, and its circuit structure is as follows: Figure 3 As shown.

[0081] Furthermore, the front-end wavefront extraction module is composed of an operational amplifier U1, a diode D1, a resistor R1A, and a capacitor C1. The positive power supply terminal of the operational amplifier U1 is connected to VCC, and the negative power supply terminal is connected to VEE; VCC is 12V, and VEE is -12V. The non-inverting input terminal of the operational amplifier U1 is connected to an AC signal source V2. The inverting input terminal of the operational amplifier U1 is connected to its output terminal through a feedback network, which specifically includes a resistor R1A, a diode D1, and a capacitor C1. One end of the resistor R1A is connected to the output terminal of the operational amplifier U1, and the other end is connected to the inverting input terminal. The anode of the diode D1 is connected to the inverting input terminal, and the cathode is connected to the output terminal. The capacitor C1 is connected in parallel across the diode D1.

[0082] Furthermore, the rectifier output module consists of diode D2, diode D3, resistor R2A, and capacitor C2. The anode of diode D2 is connected to the output terminal of operational amplifier U1, and the cathode is connected to the anode of diode D3. The cathode of diode D3 is connected to one end of capacitor C2, and the other end of capacitor C2 is grounded. One end of resistor R2A is connected to the connection node of diodes D2 and D3, and the other end is connected to the power supply node.

[0083] Furthermore, the comparison amplification module consists of an operational amplifier U2 and transistors Q1 and Q2, wherein the positive power supply terminal of the operational amplifier U2 is connected to VCC and the negative power supply terminal is connected to VEE; the non-inverting input terminal of the operational amplifier U2 is connected to the output terminal of the rectifier output module; the inverting input terminal of the operational amplifier U2 is connected to the reference potential; and the output terminal of the operational amplifier U2 is connected to the oscilloscope XSC7.

[0084] Furthermore, the enable control module consists of a resistor R3A, a switch S1, and the control terminals of transistors Q1 and Q2. The switch S1 is a manually controlled switch, with one end connected to the power supply VCC and the other end connected to the base control node of transistors Q1 and Q2. One end of the resistor R3A is connected to the switch S1, and the other end is connected to the base of transistors Q1 and Q2.

[0085] Furthermore, according to Figure 1 The six steps shown demonstrate the cable fault location method, explained in detail below.

[0086] Step 1: Construct the faulted transmission cable as shown in Figure 6. Use the acquisition module to collect transient voltage and current signals at the cable port, and collect the instantaneous three-phase voltage signals at the cable port before the fault. With three-phase instantaneous current signal and three-phase instantaneous voltage signals after the fault With three-phase instantaneous current signal And collect.

[0087] Step 2: Construct fault transient voltage and current increments from the acquired three-phase instantaneous voltage and current signals using the incremental method, and calculate the fault transient voltage and current increments. The simulated components are calculated as shown in equation (1).

[0088] (1)

[0089] In the formula, For time variables; , These represent the transient voltage and current increments during the fault.

[0090] Furthermore, the calculation The simulated components are shown in equation (2).

[0091] (2)

[0092] In the formula, For voltage , Zero-sequence mode components; For current , Zero-sequence mode components;

[0093] Step 3: Construct incident and reflected waves at the fault point, extract high-frequency components d1 using wavelet transform, and then use TEO to enhance the energy of the components extracted by wavelet transform and superimpose them.

[0094] Furthermore, the formulas for the incident wave and the reflected wave are constructed as shown in equation (3). Figure 7 The resulting diagram of incident and reflected waves for this embodiment is shown below. Figure 7 The waveform shown is the incident wave above the fault point separation and the reflected wave below.

[0095] (3)

[0096] In the formula, For incident traveling wave; To reflect traveling waves; This is the voltage signal corresponding to the mode; This is the current signal corresponding to the mode; The characteristic impedance of a cable is usually approximated by the unit length parameter, as shown in equation (4).

[0097] (4)

[0098] Furthermore, the component d1 extracted by the TEO wavelet transform is enhanced with energy, as shown in Equation (5).

[0099] (5)

[0100] In the formula, It is a discrete sequence signal; The discrete sampling point number; The energy operator is used; further, the incident and reflected channel energies are fused to construct a wavefront detection energy sequence.

[0101] Furthermore, the high-frequency components are superimposed to obtain the energy sequence E(t), the specific form of which is shown in equation (6). Figure 8 This is a waveform image of the wavelet transform extraction result in this embodiment, as shown below. Figure 8 The high-frequency component is obtained by performing wavelet transform on the incident wavefront.

[0102] (6)

[0103] In the formula, (t) represents the energy sequence; For incident wave A layer of detail components is obtained by trisectioning wavelets; To reflect waves A layer of detail components obtained by wavelet decomposition; , This is the TEO energy sequence corresponding to the detail components.

[0104] Step 4: Determine the type of fault in the power transmission cable.

[0105] Furthermore, the specific steps for determining the fault type of the power transmission cable in step 4 are as follows.

[0106] Step 4.1: Determine if there is a grounding fault, based on zero-sequence component. The significance of the saturation is used to determine whether the ground is grounded. When a ground fault occurs, the zero-sequence component increases significantly. The calculation is shown in equation (7).

[0107] (7)

[0108] In the formula, The zero-order significance index; It is the zero-sequence current mode component; for , Modal current components; This is the root mean square operation; To prevent extremely small positive numbers with a denominator of zero; The grounding detection threshold.

[0109] Step 4.2: Determine if it is a single-phase / two-phase / three-phase fault. Calculate the amplitude characteristics of the three-phase current increment. If only one phase increases significantly, it is determined to be a single-phase fault; if both phases increase significantly at the same time, it is determined to be a two-phase fault; if both phases increase significantly at the same time and the amplitudes are close ( If the value is 0, it is determined to be a three-phase fault; the calculation formula is shown in equation (8).

[0110] (8)

[0111] In the formula, This represents the amplitude characteristics of the three-phase incremental current. These are the three-phase incremental current components; This is an imbalance factor used to distinguish between symmetric and asymmetric faults. , This is for finding the maximum or minimum value.

[0112] Step 4.3: Determine whether it is a high-resistance fault or a low-resistance fault. The larger the fault resistance, the smaller the reflection amplitude and transient current peak value. The calculation is shown in Equation (9).

[0113] (9)

[0114] In the formula, represents the reflection intensity index; To reflect traveling waves; For incident traveling wave; The current-to-voltage ratio is a key indicator. , This refers to incremental current or voltage. The threshold value is the resistance level. It is a very small positive number.

[0115] Step 5: Autonomous optimal fault location based on active pulse ranging for high-impedance faults and passive ranging for low-impedance faults.

[0116] Furthermore: If the fault is high impedance, the waveform under natural transient conditions will be weak and the wavefront will not be obvious, so active pulse ranging will be used.

[0117] Furthermore, the active pulse ranging is initiated by an active pulse generating device that outputs a pulse waveform to the cable port. and collect port responses. The echo arrival time is obtained by matched filtering. And calculate the fault distance, the calculation formula is shown in equation (10).

[0118] (10)

[0119] In the formula, The pulse waveform output by the device; The reflected pulse signal acquired at the port; This is the cross-correlation function between the pulse waveform and the response signal; For time delay variables; To estimate the round-trip time delay of the obtained echo;

[0120] Step 6: Based on the adaptive threshold of E(t) and the wavefront arrival time of the protected area, candidate time differences are identified.

[0121] Furthermore, an adaptive threshold strategy is employed on the energy sequence E(t) to determine the first arrival wavefront time. The threshold can be set as the peak ratio, and the calculation formula is shown in equation (11).

[0122] (11)

[0123] In the formula, k is the threshold coefficient.

[0124] Step 7: To avoid misidentifying the same wavefront as a second-arriving wavefront, a protection zone is set up. Only Then search for the second significant peak as The calculation formula is shown in equation (12).

[0125] (12)

[0126] In the formula, For minimum interval constraints, The maximum interval constraint can provide conditions for the accuracy of distance measurement through constraint conditions.

[0127] Step 8: Combine TDR ranging and passive ranging to output the fault distance. The ranging formula is shown in equation (13).

[0128] (13)

[0129] In the formula, The fault distance is obtained through passive ranging. For the propagation speed of the traveling wave, satisfying ; The first arrival wavefront time (the first significant wavefront detected by the port); This is the second arrival time of the wavefront; The time difference between the two arrivals corresponds to the round-trip propagation time of the traveling wave.

[0130] Step 9: Repeat steps 1 and 8 above to collect multiple sets of data to verify the accuracy of the power transmission cable fault diagnosis system. Furthermore, Figure 9The statistical fault result diagram of this embodiment can accurately analyze whether it is a high-resistance or low-resistance fault in terms of monitoring fault type, and quickly determine whether it is a ground fault or a fault in a certain phase; in terms of measuring fault points, the error is less than 0.5%.

[0131] Although the present invention has been disclosed above with reference to preferred embodiments, these are not intended to limit the invention. Any person skilled in the art can make various changes or modifications without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention should be defined by the scope of the claims of this application.

Claims

1. A fault diagnosis system for power transmission cables that integrates TDR and passive transient analysis, characterized in that, The system consists of two parts: an active pulse generation and monitoring device and a device-based cable fault and ranging method. Furthermore, the active pulse generating device consists of a threshold reference module, a comparison and rectification module, a pulse generating module, and a status indication module; Furthermore, the threshold reference module is composed of voltage divider resistors; Furthermore, the comparator rectifier module consists of a comparator and resistors; Furthermore, the pulse generation module is composed of a 555 timer; Furthermore, the status indication module consists of an alarm. Furthermore, the monitoring pulse device consists of a front-end wavefront extraction module, a rectifier output module, a comparison amplification module, and an enable control module; Furthermore, the front-end wavefront extraction module consists of an operational amplifier, capacitors, and resistors; Furthermore, the rectifier output module consists of diodes, resistors, and capacitors; Furthermore, the comparison amplification module consists of operational amplifiers and transistors; Furthermore, the enable control module consists of resistors, switches, and transistors.

2. The power transmission cable fault diagnosis system integrating TDR and passive transient analysis according to claim 1, characterized in that, The cable fault location method includes the following 6 steps: Step 1: Construct a faulty transmission cable, and use a data acquisition module to collect transient voltage and current signals at the cable port, as well as the instantaneous three-phase voltage signals at the cable port before the fault. With three-phase instantaneous current signal and three-phase instantaneous voltage signals after the fault With three-phase instantaneous current signal And collect; Step 2: Construct fault transient voltage and current increments from the acquired three-phase instantaneous voltage and current signals using the incremental method, and calculate the fault transient voltage and current increments. The simulated components are calculated as shown in equation (1); （1） In the formula, It is a time variable; , For fault transient voltage and current increments; The above calculation The simulated components are shown in equation (2); （2） In the formula, For voltage , Zero-sequence mode components; For current , Zero-sequence mode components; Step 3: Construct incident and reflected waves at the fault point, extract high-frequency components d1 using wavelet transform, and then perform energy enhancement and superposition on the components extracted by wavelet transform using TEO. The above formulas for incident and reflected waves are shown in equation (3); （3） In the formula, For incident traveling wave; To reflect traveling waves; This is the voltage signal corresponding to the mode; This is the current signal corresponding to the mode; The characteristic impedance of a cable is usually approximated by the unit length parameter, as shown in equation (4). （4） In step 3 above, TEO performs energy enhancement on the component d1 extracted by wavelet transform, and its specific form is shown in equation (5). （5） In the formula, It is a discrete sequence signal; The discrete sampling point number; The energy operator is used; further, the incident and reflected channel energies are fused to construct a wavefront detection energy sequence; The energy sequence E(t) obtained by superimposing the high-frequency components in step 3 above is shown in Equation (6). （6） In the formula, (t) represents the energy sequence; For incident wave A layer of detail components is obtained by trisectioning wavelets; To reflect waves A layer of detail components obtained by wavelet decomposition; , For the corresponding detail components, the TEO energy sequence; Step 4: Determine the type of fault in the power transmission cable; Step 5: Autonomous optimal fault location based on active pulse ranging for high-impedance faults and passive ranging for low-impedance faults. If the above is a high-impedance fault, the waveform under natural transient is weak and the wavefront is not obvious, so active pulse ranging is used. Step 5 above, active pulse ranging, involves the active pulse generator outputting a pulse waveform, which is then activated to output a pulse waveform to the cable port. and collect port responses. The echo arrival time is obtained by matched filtering. And calculate the fault distance, the calculation formula is shown in equation (7); （7） In the formula, The pulse waveform output by the device; The reflected pulse signal acquired at the port; This is the cross-correlation function between the pulse waveform and the response signal; For time delay variables; To estimate the round-trip time delay of the obtained echo; Step 6: Based on the adaptive threshold of E(t) and the wavefront arrival time of the protected area, candidate time differences are identified; An adaptive threshold strategy is used to determine the first arrival wavefront time on the energy sequence E(t) mentioned above. The threshold can be set as the peak ratio, and the calculation formula is shown in equation (8). （8） In the formula, k is the threshold coefficient; Step 7: To avoid misidentifying the same wavefront as a second-arriving wavefront, a protection zone is set up. Only Then search for the second significant peak as The calculation formula is shown in equation (9); （9） In the formula, For minimum interval constraints, The maximum interval constraint can provide conditions for the accuracy of distance measurement through constraint conditions; Step 8: Integrate TDR ranging and passive ranging to output the fault distance. The ranging formula is shown in equation (10). （10） In the formula, The fault distance is obtained through passive ranging. For the propagation speed of the traveling wave, satisfying ; The first arrival wavefront time (the first significant wavefront detected by the port); This is the second arrival time of the wavefront; The time difference between the two arrivals corresponds to the round-trip propagation time of the traveling wave. Step 9: Repeat steps 1 and 8 above to collect multiple sets of data to verify the accuracy of the power transmission cable fault diagnosis system.

3. The power transmission cable fault diagnosis system integrating TDR and passive transient analysis according to claim 2, characterized in that, The specific steps for determining the fault type of the power transmission cable using wavelet transform in step 4 are as follows: Step 4.1: Determine if there is a grounding fault, based on zero-sequence component. The significance of the saturation is used to determine whether the ground is grounded. When a ground fault occurs, the zero-sequence component increases significantly. The calculation is shown in Equation (11). （11） In the formula, The zero-order significance index; It is the zero-sequence current mode component; for , Modal current components; This is the root mean square operation; To prevent extremely small positive numbers with a denominator of zero; Grounding detection threshold; Step 4.2: Determine if it is a single-phase / two-phase / three-phase fault. Calculate the amplitude characteristics of the three-phase current increment. If only one phase increases significantly, it is determined to be a single-phase fault; if both phases increase significantly at the same time, it is determined to be a two-phase fault; if both phases increase significantly at the same time and the amplitudes are close ( If the value is 0, it is determined to be a three-phase fault; the calculation formula is shown in equation (12); （12） In the formula, The amplitude characteristics of the three-phase incremental current; These are the three-phase incremental current components; This is an imbalance factor used to distinguish between symmetric and asymmetric faults. , To perform the maximum or minimum operation; Step 4.3: Determine whether it is a high-resistance fault or a low-resistance fault. The larger the fault resistance, the smaller the reflection amplitude and the peak value of the transient current. The calculation is shown in Equation (13). （13） In the formula, represents the reflection intensity index; To reflect traveling waves; For incident traveling wave; The current-to-voltage ratio is a key indicator. , This refers to incremental current or voltage. The threshold value is the resistance level. It is a very small positive number.

Images