Multi-point grounding online monitoring device and fault monitoring method

Abstract

The invention relates to the technical field of grounding detection and maintenance, in particular to a multipoint grounding online monitoring device and a fault monitoring method. The current detection unit is used for detecting current signals in the grounding wire and the zero line grounding wire; the signal processing unit is used for filtering the current signal output by the current detection unit; the control unit determines the presence of a multi-point ground fault. If the amplitude of the grounding wire current signal exceeds a preset threshold value, a multi-point grounding fault exists; if the current signal has an abnormal frequency component, a multi-point grounding fault exists; current signals have phase differences, and multi-point grounding faults exist. And an unbalanced load resistor is connected, and if no current is detected in the grounding wire, a multi-point grounding fault exists. On-line monitoring of PT multipoint grounding faults is achieved under the condition that system operation is not affected. Manual inspection is replaced, PT multipoint grounding faults are found and alarmed in time, the working efficiency and safety are improved, two detection methods of a zero line current method and an unbalanced load current method are provided, and the requirements of different scenes are met.

Description

Technical Field

[0001] The invention relates to the technical field of grounding detection and maintenance, in particular to a multi-point grounding online monitoring device and a fault monitoring method. Background Art

[0002] Voltage transformer (PT) is an important measuring device in the power system. The multi-point grounding problem of its secondary circuit will cause distortion of measurement data, affect the correct operation of relay protection devices, and even cause safety accidents. Therefore, monitoring and locating multi-point grounding faults of PT is crucial to ensure the safe and stable operation of the power grid.

[0003] The existing multi-point grounding fault detection method requires untying the N600 grounding wire for measurement, which is cumbersome and has potential safety hazards. The current N600 current needs to be measured regularly every six months, and a measurement must be carried out when new equipment is put into operation. Manual inspections are inefficient and cannot be monitored in real time, and it is easy to miss the time when a fault occurs. Therefore, there is a need for a multi-point grounding online monitoring device and fault monitoring method that can realize PT multi-point grounding fault detection without affecting system operation, replace manual inspections, promptly detect and alarm PT multi-point grounding faults, and improve work efficiency and safety to meet the needs of the existing environment.

[0004] After installing the N600 single-point grounding detection and alarm device in the substation, the number of N600 current measurements by personnel in the jurisdiction area can be reduced by more than 500 times, effectively optimizing human resources and saving costs. At the same time, the secondary remote operation and maintenance capabilities are enhanced, which meets the development trend requirements of the power grid. Summary of the invention

[0005] The purpose of this section is to summarize some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract of the specification and the title of the invention of this application to avoid blurring the purpose of this section, the abstract of the specification and the title of the invention, and such simplifications or omissions cannot be used to limit the scope of the present invention.

[0006] In view of the above-mentioned prior art, the existing multi-point grounding fault detection method requires untying the N600 grounding wire for measurement, which is cumbersome to operate and has safety hazards. It mainly relies on manual inspection, which is inefficient and cannot be monitored in real time, and it is easy to miss the time when the fault occurs.

[0007] Therefore, the technical problem to be solved by the present invention is to design a multi-point grounding online monitoring device and fault monitoring method that can realize PT multi-point grounding fault detection without affecting the system operation, replace manual inspection, timely discover and alarm PT multi-point grounding faults, improve work efficiency and safety to meet the needs of the existing environment.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: a multi-point grounding online monitoring device, comprising:

[0009] Current detection unit, detects the current signal in the N600 grounding wire and the PT neutral grounding wire;

[0010] A signal processing unit, which amplifies and filters the current signal output by the current detection unit and converts it into a digital signal;

[0011] The control unit determines the existence of a multi-point grounding fault according to the processed current signal.

[0012] As an improvement of the present invention,

[0013] The control unit includes a microcontroller that executes data processing and fault determination algorithms;

[0014] The alarm unit is electrically connected to the control unit, and the alarm unit includes an audible and visual alarm to send out audible and visual alarm information.

[0015] The communication unit is electrically connected to the control unit, and the communication unit includes a wireless communication module to transmit the monitoring data to the remote monitoring center.

[0016] As an improvement of the present invention,

[0017] The control unit is electrically connected to the fault locating unit, and locates the fault branch according to the characteristic signal and the current analysis result.

[0018] A fault monitoring method,

[0019] When it is determined that there is a multi-point grounding fault,

[0020] The control unit transmits a signal according to the signal processing unit;

[0021] If the current signal amplitude of the N600 grounding wire and the PT neutral grounding wire exceeds the preset threshold, there is a multi-point grounding fault;

[0022] If the current signals of the N600 grounding wire and the PT neutral grounding wire have abnormal frequency components, there is a multi-point grounding fault;

[0023] If there is a phase difference between the current signals of the N600 grounding wire and the PT neutral grounding wire, there is a multi-point grounding fault.

[0024] When an unbalanced load resistor is connected and no current is detected in the N600 grounding wire, there is a multi-point grounding fault.

[0025] As an improvement of the present invention,

[0026] When judging the current signal amplitude,

[0027] Set preset thresholds based on voltage level and transformer capacity;

[0028] If the current signal amplitude of the N600 grounding wire and the PT neutral grounding wire is lower than the preset threshold, there is no multi-point grounding fault;

[0029] If the current signal amplitude of the N600 grounding wire and the PT neutral grounding wire is higher than the preset threshold, there is a multi-point grounding fault.

[0030] As an improvement of the present invention,

[0031] When judging abnormal frequency,

[0032] The standard frequency is set to 60Hz, and the abnormal frequency is the frequency of non-standard frequency and integer multiple harmonics;

[0033] Perform fast Fourier transform (FFT) on the ground wire current signal to obtain the signal spectrum, and observe the signal spectrum to find abnormal frequencies;

[0034] If there is no abnormal frequency, there is no multi-point grounding fault;

[0035] If abnormal frequency occurs, there are multiple ground faults.

[0036] As an improvement of the present invention,

[0037] When judging that the current signal phase difference exists,

[0038] Set the phase difference threshold (Δφ>Δφ_max, Δφ<Δφ_min);

[0039] If the phase difference fluctuation range suddenly increases, there is a multi-point grounding fault;

[0040] If the phase difference fluctuates periodically, it means that there is additional current movement, and there are multiple ground faults;

[0041] If the phase difference shows a monotonically increasing or decreasing trend, it means that the ground wire is aging and the insulation performance is deteriorating, and there are multiple grounding faults.

[0042] A fault monitoring method,

[0043] When judging that there is current in the N600 grounding wire,

[0044] Connect an unbalanced load resistor to detect the unbalanced load current in the N600 grounding wire;

[0045] If the unbalanced load current does not exist, then there is a multi-point grounding fault in the PT, and the current is shunted back to the PT neutral point through the fault point, and does not flow through the N600 grounding wire;

[0046] If unbalanced load current exists, there is no multi-point grounding fault.

[0047] As an improvement of the present invention,

[0048] When conducting reliable grounding detection,

[0049] Send digital signals and transmit them through the loop formed by the grounding of the N line.

[0050] If the received and sent signal values ​​are the same, the grounding is reliable;

[0051] If the received and sent signal values ​​are inconsistent, there is a ground fault.

[0052] The beneficial effects of the present invention are: online monitoring of PT multi-point grounding faults is realized without affecting the operation of the system. Instead of manual inspection, PT multi-point grounding faults can be discovered and warned in time, and work efficiency and safety can be improved. Two detection methods, the neutral line current method and the unbalanced load current method, are provided to meet the needs of different scenarios. The unbalanced load current method is not affected by the potential difference between the grounding fault point and the N600 grounding point, and has high detection sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0054] Figure 1 It is a structural planning diagram of the multi-point grounding online monitoring device in the present invention.

[0055] Figure 2 This is a flow chart of signal filtering in the multi-point grounding online monitoring device of the present invention.

[0056] Figure 3 This is a working principle diagram of the neutral line current method in the multi-point grounding online monitoring device of the present invention.

[0057] Figure 4 This is a working principle diagram of the unbalanced load current method in the multi-point grounding online monitoring device of the present invention.

[0058] Figure 5 It is a schematic diagram of the reliable grounding detection principle in the multi-point grounding online monitoring device of the present invention. DETAILED DESCRIPTION

[0059] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0060] Example 1

[0061] Reference Figures 1-2 , this embodiment provides a multi-point grounding online monitoring device.

[0062] The current detection unit includes a Hall sensor, a signal conditioning circuit and an A / D converter. The Hall sensor is used to detect the current signal in the N600 grounding wire and the PT neutral grounding wire.

[0063] Install the Hall sensor near the N600 ground wire and the PT neutral ground wire, and ensure that the distance between the sensor and the ground wire does not exceed 5mm. To improve the detection accuracy, the sensor should be placed parallel to the ground wire. The signal conditioning circuit and A / D converter are installed in the device housing and connected to the sensor through a shielded cable.

[0064] When there is a current signal in the N600 grounding wire or the PT neutral grounding wire, the Hall sensor converts it into a voltage signal, and the signal processing unit amplifies the voltage signal by 100 times. The amplified signal passes through a low-pass filter with a cutoff frequency of 1kHz to remove high-frequency interference. The filtered signal is input to the A / D converter and converted into a digital signal.

[0065] The amplifier circuit in the signal processing unit uses the operational amplifier LM358 to amplify the current signal 100 times to meet the subsequent processing requirements. The filter circuit uses a second-order active low-pass filter with a cut-off frequency of 1000Hz to effectively remove high-frequency interference.

[0066] The control unit includes a microprocessor, a comparison circuit and an alarm circuit. The microprocessor analyzes the digital signal output by the signal processing unit, the comparison circuit is used to set the fault threshold, and the alarm circuit sounds an alarm when a fault is detected. The comparison circuit uses a voltage comparator LM393, and sets the fault threshold to 100mA. When the current signal exceeds 100mA, the comparator outputs a high level. Alarm circuit: When the comparator outputs a high level, the alarm circuit is triggered. The alarm circuit uses a buzzer and an LED indicator to emit an audible and visual alarm.

[0067] The present invention realizes accurate identification of multi-point grounding faults by detecting, processing and judging current signals in the N600 grounding wire and the PT neutral grounding wire.

[0068] Example 2

[0069] Reference Figures 1-2 This embodiment is based on the previous embodiment, and is different from the previous embodiment in that:

[0070] The core of the control unit is a microcontroller. The present invention can adopt an STM32F407 series microcontroller, which has a high-performance ARM Cortex-M4 core and can execute complex data processing and fault judgment algorithms.

[0071] The control unit also includes a data processing module, which is responsible for further processing the digital signal output by the signal processing unit, such as mean filtering, fast Fourier transform (FFT), etc., to extract the characteristics of the current signal. Based on the characteristics of the current signal, it is determined whether there is a multi-point grounding fault through a preset algorithm.

[0072] After the microcontroller is powered on, the system is initialized first. The microcontroller periodically obtains the digital value of the current signal from the signal processing unit, performs mean filtering and FFT analysis on the collected data, extracts the characteristic parameters of the current signal, and executes the fault judgment algorithm based on the characteristic parameters. If the judgment result is a fault, the alarm unit is activated.

[0073] The communication unit includes a wireless communication module. In this embodiment, the Wi-Fi module ESP8266 is used. The module supports the TCP / IP protocol and can transmit the monitoring data to the remote monitoring center through the wireless network. The control unit encapsulates the processed current signal data and the fault judgment result into a data packet, and the wireless communication module establishes a connection with the remote monitoring center according to the preset network parameters. The encapsulated data packet is sent to the remote monitoring center through the Wi-Fi network. After the monitoring center receives the data, it sends a confirmation signal back to the communication unit to complete a data transmission process.

[0074] The fault location unit includes a current sensor array and a location algorithm. The current sensor array is installed on each branch to detect the current signal of each branch. The location algorithm determines the specific branch where the fault occurs based on the characteristic signal and the current analysis results. The current sensor array collects the current signal of each branch and sends the data to the control unit.

[0075] The control unit analyzes the current signals of each branch and identifies abnormal signals. The positioning algorithm determines the specific branch where the fault occurs based on the characteristics of the abnormal signal, such as current size and phase difference. The control unit notifies the operator and the remote monitoring center of the fault location results through the alarm unit and communication unit.

[0076] Example 3

[0077] Reference Figures 1 to 5 This embodiment is based on the previous embodiment, and is different from the previous embodiment in that:

[0078] The control unit periodically receives amplified and filtered current signals from the signal processing unit, which have been converted into digital signals for processing by the microcontroller. The preset threshold is determined through experiments and theoretical calculations based on the voltage level and transformer capacity. For example, the preset threshold of the current signal amplitude of the N600 grounding wire and the PT neutral grounding wire is set to 1mA.

[0079] In the power system, the standard power frequency is 50Hz or 60Hz, depending on the power system standard in the area. The detection of abnormal frequency is achieved through the FFT (Fast Fourier Transform) algorithm, which is able to convert the time domain signal into the frequency domain signal, thereby revealing the frequency components of the signal. By performing FFT analysis on the current signal, we can identify the frequency components of non-standard frequencies and their non-integer harmonics, which are usually indications of ground faults. For example, if a frequency component of 150Hz is detected, this may indicate that there is a ground fault in the system.

[0080] The detection of phase difference is an important means to determine the health status of the grounding system. The change of phase difference means the change of current path, which is a typical feature of grounding fault. A sudden increase in the fluctuation range of phase difference indicates the existence of multi-point grounding faults; periodic fluctuations in phase difference indicate additional current movement and the existence of multi-point grounding faults; a monotonically increasing or decreasing trend in phase difference indicates that the ground wire is aging, the insulation performance is degraded, and there are multi-point grounding faults.

[0081] In the power system, N600 grounding wire is usually used for neutral point grounding. By connecting the unbalanced load resistor, a specific test condition is artificially created to detect whether there is unbalanced load current in the N600 grounding wire. If no current is detected in the N600 grounding wire, it indicates that there is a multi-point grounding fault in the PT neutral line, and the current returns through other paths, bypassing the N600 grounding wire.

[0082] In reliable grounding detection, the integrity of the grounding system can be determined by comparing the transmitted and received digital signals. This method is similar to the return loss test in the communication system, which is used to detect the loss of the signal on the transmission path. If the values ​​are inconsistent, this may indicate that there are problems such as breakpoints, poor contact or impedance mismatch in the grounding system.

[0083] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A multi-point grounding online monitoring device, characterized in that: include, Current detection unit, detects the current signal in the N600 grounding wire and the PT neutral grounding wire; A signal processing unit, which amplifies and filters the current signal output by the current detection unit and converts it into a digital signal; The control unit determines the existence of a multi-point grounding fault according to the processed current signal.

2. The multi-point grounding online monitoring device according to claim 1 is characterized in that: The control unit includes a microcontroller that executes data processing and fault determination algorithms; The alarm unit is electrically connected to the control unit, and the alarm unit includes an audible and visual alarm to send out audible and visual alarm information. The communication unit is electrically connected to the control unit, and the communication unit includes a wireless communication module to transmit the monitoring data to the remote monitoring center.

3. The multi-point grounding online monitoring device according to claim 2 is characterized in that: The control unit is electrically connected to the fault locating unit, and locates the fault branch according to the characteristic signal and the current analysis result.

4. A fault monitoring method, characterized in that: The invention comprises the multi-point grounding online monitoring device as claimed in claim 2, and When it is determined that there is a multi-point grounding fault, The control unit transmits a signal according to the signal processing unit; If the current signal amplitude of the N600 grounding wire and the PT neutral grounding wire exceeds the preset threshold, there is a multi-point grounding fault; If the current signals of the N600 grounding wire and the PT neutral grounding wire have abnormal frequency components, there is a multi-point grounding fault; If there is a phase difference between the current signals of the N600 grounding wire and the PT neutral grounding wire, there is a multi-point grounding fault. When an unbalanced load resistor is connected and no current is detected in the N600 grounding wire, there is a multi-point grounding fault.

5. The fault monitoring method according to claim 4, characterized in that: When judging the current signal amplitude, Set preset thresholds based on voltage level and transformer capacity; If the current signal amplitude of the N600 grounding wire and the PT neutral grounding wire is lower than the preset threshold, there is no multi-point grounding fault; If the current signal amplitude of the N600 grounding wire and the PT neutral grounding wire is higher than the preset threshold, there is a multi-point grounding fault.

6. The fault monitoring method according to claim 4, characterized in that: When judging abnormal frequency, The standard frequency is set to 60Hz, and the abnormal frequency is the frequency of non-standard frequency and integer multiple harmonics; Perform fast Fourier transform (FFT) on the ground wire current signal to obtain the signal spectrum, and observe the signal spectrum to find abnormal frequencies; If there is no abnormal frequency, there is no multi-point grounding fault; If abnormal frequency occurs, there are multiple ground faults.

7. The fault monitoring method according to claim 5 or 6, characterized in that: When judging that the current signal phase difference exists, Set the phase difference threshold (Δφ>Δφ_max, Δφ<Δφ_min); If the phase difference fluctuation range suddenly increases, there is a multi-point grounding fault; If the phase difference fluctuates periodically, it means that there is additional current movement, and there are multiple ground faults; If the phase difference shows a monotonically increasing or decreasing trend, it means that the ground wire is aging and the insulation performance is deteriorating, and there are multiple grounding faults.

8. The fault monitoring method according to claim 7, characterized in that: When judging that there is current in the N600 grounding wire, Connect an unbalanced load resistor to detect the unbalanced load current in the N600 grounding wire; If the unbalanced load current does not exist, then there is a multi-point grounding fault in the PT, and the current is shunted back to the PT neutral point through the fault point, and does not flow through the N600 grounding wire; If unbalanced load current exists, there is no multi-point grounding fault.

9. The fault monitoring method according to claim 8, characterized in that: When conducting reliable grounding detection, Send digital signals and transmit them through the loop formed by the grounding of the N line. If the received and sent signal values ​​are the same, the grounding is reliable; If the received and sent signal values ​​are inconsistent, there is a ground fault.

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