A method for finding fault of secondary circuit of high-voltage electrical equipment

Abstract

The application provides a kind of high-voltage electrical equipment secondary circuit fault finding method, including determining the target secondary circuit associated when fault, and planning test point on target secondary circuit based on topology structure;After confirming that CT / VT has been installed on test point, specific frequency test signal is injected by external signal source, and based on fixed sampling frequency and total sampling time, current signal and voltage signal collected by CT / VT are periodically and synchronously acquired, and transmission delay time of time delay signal is further determined;Current signal and voltage signal on all test points are denoised and feature extraction is carried out, and combined with transmission delay time feature extraction, fault feature vector of each test point is constructed;Fault feature vector of each test point is imported into trained multi-classification diagnosis model, and fault type is obtained. By implementing the application, the problems of low efficiency, high safety hazard, poor universality and inaccurate fault point positioning in the prior art can be solved.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method for locating faults in the secondary circuits of high-voltage electrical equipment. Background Technology

[0002] As the "nerve center" of high-voltage electrical equipment, the secondary circuit undertakes core functions such as control command transmission, protection signal feedback, and operational status monitoring. Its reliability directly determines the safe and stable operation of the power system. In actual operation, due to its complex structure, dense wiring, long-term exposure to environmental corrosion (such as humidity and dust), and component aging (such as contact oxidation and coil degradation), the secondary circuit is prone to faults such as poor contact, line open / short circuit, and multiple grounding points, leading to serious consequences such as protection malfunctions, failure to operate, or equipment shutdown. Currently, the traditional method of comparing drawings with manual measurement is used to find faults in the secondary circuits of high-voltage electrical equipment. However, the above method has many shortcomings. The shortcomings are: (1) The comparison of drawings mainly relies on the experience of maintenance personnel to find faults, which makes it time-consuming (e.g., the average time exceeds 17 hours) and is prone to misjudgment due to inconsistencies between drawings and actual objects; (2) Manual measurement requires disconnecting the circuit or moving the terminal box because it uses conventional current / voltage measurement methods. Therefore, there is a risk of high-voltage safety hazards caused by open circuits in the secondary circuit, which seriously threatens the personal safety of maintenance personnel and the safety of equipment; (3) It can only be used for a single type of fault (e.g., only detecting multiple grounding points), which is not only poor in versatility, but also cannot achieve accurate location of the fault point. Therefore, there is an urgent need to design a new method for locating faults in the secondary circuits of high-voltage electrical equipment to solve the problems of low efficiency, high safety risks, poor versatility, and inaccurate fault location of existing technologies. Summary of the Invention

[0003] The technical problem to be solved by the embodiments of the present invention is to provide a method for finding faults in the secondary circuit of high-voltage electrical equipment, which can solve the problems of low efficiency, high safety risks, poor versatility and inaccurate fault location in the prior art.

[0004] To address the aforementioned technical problems, embodiments of the present invention provide a method for locating faults in the secondary circuit of high-voltage electrical equipment, the method comprising the following steps: Identify the target secondary circuit associated with a fault in the high-voltage electrical equipment, and based on the topology of the target secondary circuit, plan the test points for the current transformer to be installed on the target secondary circuit; wherein, the test points include the power input terminal, switch and / or knife switch button contacts, terminal block connection points, cable joints, relay auxiliary contacts, both ends of the relay coil, and the grounding N wire; After confirming that CT and VT transformers have been installed at all test points, a test signal of a specific frequency is injected into the target secondary circuit through an external signal source. Based on a fixed sampling frequency and total sampling duration, the current and voltage signals collected by the CT and VT transformers at each test point are periodically and synchronously acquired, and the transmission delay time of each current and voltage signal is further determined. Each current and voltage signal is superimposed with the test signal to form a composite signal carrying fault characteristics. The transmission delay time is used to characterize the difference between the time when the signal is first acquired and the first cycle sampling time. Noise reduction and feature extraction were performed on all current and voltage signals acquired at each test point. In addition, feature extraction was performed on the transmission delay time of each current and voltage signal to construct a fault feature vector for each test point. The fault feature vector of each test point includes voltage features determined by feature extraction of the voltage signal, current features determined by feature extraction of the current signal, impedance features jointly determined by the voltage and current features, and timing features determined by feature extraction of the transmission delay time. The fault feature vectors of each test point are imported into the pre-trained multi-class diagnostic model to obtain the fault type; wherein, the fault type includes contact / contact loose oxidation fault, multi-point grounding fault, line short circuit fault and line open circuit fault.

[0005] The VT current transformer is a miniature VT current transformer with a measurement range covering DC110V / 220V and AC220V, an accuracy class of 0.2, and a load impedance of ≤0.1Ω; the CT current transformer is a miniature CT current transformer with a range of 0.01A-5A, a transformation ratio of 1:1000, and a primary winding DC resistance of ≤0.1Ω.

[0006] The VT current transformer is connected to the corresponding test point via a piercing clamp; the CT current transformer is clamped onto the conductor of the target secondary circuit and close to the corresponding test point via an opening and closing clamp structure.

[0007] The test signal at the specific frequency is a sinusoidal signal with a frequency of 2kHz and an injection power of ≤5W; the fixed sampling frequency is 10kHz; and the total sampling duration is 3S.

[0008] The multi-class diagnostic model employs an enhanced causal Bayesian network, which integrates target secondary loop topology constraints and its relay protection logic. The target secondary loop topology constraints include the target secondary loop closed-loop logic and the initial states of the switches, disconnectors, and relay contacts on it.

[0009] The voltage characteristics include voltage drop abrupt change coefficient and voltage waveform distortion rate; the current characteristics include current shunt ratio deviation; the impedance characteristics include contact resistance value; and the timing characteristics include timing delay deviation. The contact resistance value is calculated based on Ohm's law R=U / I. The timing delay deviation is used to characterize the difference between the transmission delay time and a preset standard timing threshold.

[0010] The method further includes: Based on the fault feature vectors of each test point, two adjacent test points whose fault feature vector differences meet preset conditions are determined on the topology of the target secondary circuit. Combined with the preset distance between the two adjacent test points, the location of the fault point is located by a linear interpolation algorithm.

[0011] Specifically, the difference between two adjacent test points whose fault feature vector differences meet the preset conditions is that at least one feature in the fault feature vector of the two adjacent test points has a difference greater than the corresponding preset feature value.

[0012] Implementing the embodiments of the present invention has the following beneficial effects: 1. This invention achieves multi-parameter acquisition without disconnecting the circuit through the open / penetrating installation of VT transformers / CT transformers, completely avoiding the risk of open circuits in the secondary circuit and ensuring maintenance safety. It also adopts multi-dimensional fault feature fusion diagnosis, integrating four major categories of features: voltage, current, impedance, and time sequence, to construct a comprehensive fault feature vector to solve the problem of easy misjudgment in single-parameter diagnosis. Furthermore, it achieves accurate identification of fault types through a multi-classification diagnostic model based on enhanced causal Bayesian networks and incorporating secondary circuit topology constraints and relay protection logic, thereby solving the problems of low efficiency, high safety risks, and poor versatility of existing technologies. 2. This invention achieves centimeter-level fault location based on the characteristic abrupt gradient of adjacent test points, thereby solving the problem of inaccurate fault location in existing technologies. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0014] Figure 1 This is a flowchart of a method for locating faults in the secondary circuit of high-voltage electrical equipment, provided as an embodiment of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0016] like Figure 1 As shown in the figure, a method for locating faults in the secondary circuit of high-voltage electrical equipment is proposed in an embodiment of the present invention. The method includes the following steps: Step S1: Determine the target secondary circuit associated with the fault of the high-voltage electrical equipment, and based on the topology of the target secondary circuit, plan the test points of the current transformer to be installed on the target secondary circuit; wherein, the test points include the power input terminal, switch and / or knife switch button contacts, terminal block connection points, cable joints, relay auxiliary contacts, both ends of the relay coil, and the grounding N wire; The specific process is as follows: First, obtain the fault phenomena (such as protection failure to operate, indicator lights not turning on, and abnormal remote signaling) through the substation monitoring system. Then, compare the secondary circuit schematic diagram, sort out the circuit logic chain associated with the fault (such as control circuit, protection output circuit, and grounding circuit), and lock the target fault circuit, that is, the target secondary circuit.

[0017] Secondly, based on the topology of the target secondary circuit, test points for the current transformer to be installed are planned on the target secondary circuit; among them, test points include, but are not limited to, power input terminals, switch and / or knife switch button contacts, terminal block connection points, cable joints, relay auxiliary contacts, both ends of the relay coil, and grounding N line.

[0018] It should be noted that a fixed spacing is reserved between each test point, and the spacing does not exceed 1 meter, to ensure that no fault point is missed; in addition, test points are added in areas with dense connections and areas prone to aging during long-term operation (such as cable joints and terminal blocks).

[0019] Step S2: After confirming that CT and VT transformers have been installed at all test points, a test signal of a specific frequency is injected into the target secondary circuit through an external signal source. Based on a fixed sampling frequency and total sampling duration, the current and voltage signals collected by the CT and VT transformers at each test point are periodically and synchronously acquired, and the transmission delay time of each current and voltage signal is further determined. Each current and voltage signal is superimposed with the test signal to form a composite signal carrying fault characteristics. The transmission delay time is used to characterize the difference between the time when the signal is first acquired and the first cycle sampling time. The specific process is as follows: First, the VT transformer is selected as a miniature VT transformer, whose measurement range covers DC110V / 220V and AC220V, with an accuracy class of 0.2 and a load impedance of ≤0.1Ω; and the CT transformer is selected as a miniature CT transformer, with a range of 0.01A-5A, a transformation ratio of 1:1000, and a primary winding DC resistance of ≤0.1Ω.

[0020] Secondly, non-invasive installation methods are used to install CT and VT transformers. For example, the VT transformer is connected to the corresponding test point through a piercing clamp, and the CT transformer is clamped onto the conductor of the target secondary circuit and close to the corresponding test point through an opening and closing clamp structure. This eliminates the need to disconnect or modify the original wiring of the target secondary circuit, thus avoiding the risk of open circuit.

[0021] Next, confirm whether the CT transformer and VT transformer have been installed at all test points. If so, inject a test signal of a specific frequency (such as a 2kHz sinusoidal signal with an injection power of ≤5W) into the target secondary circuit through an external signal source to avoid interfering with the normal operation of the target secondary circuit. At the same time, the test signal is superimposed with the inherent current and voltage signals of the target secondary circuit to form a composite signal carrying fault characteristics and enhancing the fault characteristics.

[0022] Finally, a fixed sampling frequency of 10kHz and a total sampling duration of 3 seconds were set. Current and voltage signals collected by the CT and VT transformers at each test point were periodically and synchronously acquired. The presence of time delay was determined by analyzing the current and voltage signals collected at each test point over multiple sampling periods. If a time delay was found, the transmission delay time for each current and voltage signal was determined. The transmission delay time is the time difference between the time the signal is first acquired and the first sampling period. It should be noted that if the signal is acquired during the first sampling period, the transmission delay time is 0.

[0023] Understandably, when the test point is a contact of a switch, knife switch, or relay, its transmission delay time is used to characterize the release / closing time of the contact at that test point.

[0024] Step S3: Denoise and extract features from all current and voltage signals acquired at each test point. Combined with feature extraction of the transmission delay time of each current and voltage signal, construct the fault feature vector for each test point. The fault feature vector of each test point includes voltage features determined by feature extraction of the voltage signal, current features determined by feature extraction of the current signal, impedance features jointly determined by the voltage and current features, and timing features determined by feature extraction of the transmission delay time. The specific process is as follows: First, wavelet analysis is used to denoise all the current and voltage signals acquired at each test point in order to eliminate environmental interference and measurement noise.

[0025] Secondly, feature extraction is performed on both the denoised current and voltage signals, and the contact resistance value is calculated based on Ohm's law R=U / I. Among them, the extracted features of the voltage signal include, but are not limited to, voltage amplitude, voltage drop, voltage waveform distortion rate, and peak-to-valley difference; the extracted features of the current signal include, but are not limited to, current amplitude, current change rate, and current shunt ratio.

[0026] Then, the voltage drop abrupt change coefficient is calculated from the extracted features of the voltage signal, and combined with the voltage waveform distortion rate to form voltage features; the current shunt ratio deviation is extracted from the extracted features of the current signal to form current features; the contact resistivity that changes with time is determined based on the contact resistance value, and combined with the contact resistance value to form resistance features; the difference between the transmission delay time and the preset standard timing threshold is used to form timing features. It should be noted that voltage features, current features, impedance features, and timing features can be flexibly designed according to actual conditions, and will not be elaborated further here.

[0027] Finally, a fault feature vector is constructed by combining the voltage characteristics, current characteristics, impedance characteristics, and timing characteristics of the same test point.

[0028] Step S4: Import the fault feature vectors of each test point into the trained multi-class diagnostic model to obtain the fault type; wherein, the fault type includes contact / contact loosening and oxidation fault, multi-point grounding fault, line short circuit fault and line open circuit fault.

[0029] The specific process is as follows: First, a multi-class diagnostic model is constructed. This multi-class diagnostic model is constructed using an enhanced causal Bayesian network, and the target secondary loop topology constraints and its relay protection logic are integrated into the enhanced causal Bayesian network. The target secondary loop topology constraints include the target secondary loop closed-loop logic and the initial states (such as normally open / normally closed states) of the switches, disconnectors and relay contacts set on it.

[0030] Secondly, based on the training and testing sets of fault feature vectors formed from historical data, the multi-class diagnostic model is trained and tested to obtain a well-trained multi-class diagnostic model. It should be noted that the training and testing of the multi-class diagnostic model are implemented using conventional techniques in this field, which will not be elaborated upon here.

[0031] Finally, the fault feature vectors of each test point in step S3 are imported into the trained multi-class diagnostic model to obtain the fault type of the target secondary circuit. The fault types include contact / contact loosening and oxidation faults, multi-point grounding faults, line short-circuit faults, and line open-circuit faults.

[0032] In this embodiment of the invention, the method further includes: based on the fault feature vectors of each test point, determining two adjacent test points on the topology of the target secondary circuit whose fault feature vector differences meet preset conditions, and locating the fault point using a linear interpolation algorithm in conjunction with the preset distance between the determined two adjacent test points. Specifically, the two adjacent test points whose fault feature vector differences meet the preset conditions are defined as follows: at least one feature in the fault feature vectors of the two adjacent test points has a difference greater than a corresponding preset feature value. It should be noted that the preset feature values ​​corresponding to voltage features, current features, impedance features, and timing features are flexibly designed according to actual needs.

[0033] In one example, if the contact resistance value in the fault feature vector of two adjacent test points changes abruptly from the normal ≤3Ω to ≥20Ω, making the abrupt resistance value 17Ω greater than the preset threshold of 10Ω, then the condition is met.

[0034] Taking the secondary control circuit of a 110kV substation circuit breaker as an example, the application scenario of a high-voltage electrical equipment secondary circuit fault finding method in this embodiment of the invention is further explained as follows: (1) The circuit breaker remote control tripping command cannot be executed. The monitoring system displays "tripping circuit abnormal". It is initially judged that there is poor contact or line breakage in the secondary control circuit. Thus, the secondary control circuit is identified as the target secondary circuit to be found for the fault.

[0035] (2) On the secondary control circuit, select the power supply end (DC220V), the contact of the trip button, the two ends of the intermediate relay KA coil, the terminal block T1-T8, the circuit breaker auxiliary contact, the grounding N600 line, etc. as test points, and deploy miniature VT / CT on the selected test points. The test point spacing is 0.8-1 meter, and inject a sinusoidal signal with a specific frequency of 2kHz and a power of 3W as the test signal. Among them, the miniature CT adopts the opening and closing clamp type installation, and the miniature VT is connected through the piercing terminal clamp.

[0036] (3) Set the fixed sampling frequency to 10kHz and the total sampling time to 3S, periodically and synchronously collect the voltage and current signals at each test point, and calculate the contact resistance value based on the voltage and current signals at each test point, and determine the transmission delay time of the current and voltage signals at each test point.

[0037] Furthermore, based on the voltage signal, current signal, contact resistance value, and transmission delay time at each test point, a fault feature vector integrating four major categories of features—voltage, current, impedance, and timing—is constructed.

[0038] (4) Import the fault feature vectors at each test point into the trained multi-class diagnostic model to obtain the fault type of the secondary control loop as contact / contact loosening and oxidation fault.

[0039] For example, a multi-class diagnostic model found that the fault feature vector of a certain contact of the terminal block included a voltage drop of 26V (the voltage difference between the front voltage of 218V and the rear voltage of 192V), a contact resistance of 32Ω (far exceeding the normal threshold of 30Ω), and a time delay of 0.3 seconds (exceeding the standard of 0.2 seconds), and determined that the terminal block had poor contact due to contact oxidation.

[0040] (5) Based on the fault feature vectors of all terminals of the terminal block, the fault point is located between terminals T3 and T4 of the terminal block, 12 cm away from terminal T3, calculated by gradient algorithm.

[0041] (6) The maintenance personnel disassembled the terminal block and found that there was an oxide layer on the T3-T4 terminals. After grinding, the terminals were re-crimped and the circuit was restored to normal. The total time spent finding the fault was only 45 minutes, which is 97% shorter than the traditional method.

[0042] Implementing the embodiments of the present invention has the following beneficial effects: 1. This invention achieves multi-parameter acquisition without disconnecting the circuit through the open / penetrating installation of VT transformers / CT transformers, completely avoiding the risk of open circuits in the secondary circuit and ensuring maintenance safety. It also adopts multi-dimensional fault feature fusion diagnosis, integrating four major categories of features: voltage, current, impedance, and time sequence, to construct a comprehensive fault feature vector to solve the problem of easy misjudgment in single-parameter diagnosis. Furthermore, it achieves accurate identification of fault types through a multi-classification diagnostic model based on enhanced causal Bayesian networks and incorporating secondary circuit topology constraints and relay protection logic, thereby solving the problems of low efficiency, high safety risks, and poor versatility of existing technologies. 2. This invention achieves centimeter-level fault location based on the characteristic abrupt gradient of adjacent test points, thereby solving the problem of inaccurate fault location in existing technologies.

[0043] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, such as ROM / RAM, disk, optical disk, etc.

[0044] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A method for locating faults in the secondary circuit of high-voltage electrical equipment, characterized in that, The method includes the following steps: Identify the target secondary circuit associated with a fault in the high-voltage electrical equipment, and based on the topology of the target secondary circuit, plan the test points for the current transformer to be installed on the target secondary circuit; wherein, the test points include the power input terminal, switch and / or knife switch button contacts, terminal block connection points, cable joints, relay auxiliary contacts, both ends of the relay coil, and the grounding N wire; After confirming that CT and VT transformers have been installed at all test points, a test signal of a specific frequency is injected into the target secondary circuit through an external signal source. Based on a fixed sampling frequency and total sampling duration, the current and voltage signals collected by the CT and VT transformers at each test point are periodically and synchronously acquired, and the transmission delay time of each current and voltage signal is further determined. Each current and voltage signal is superimposed with the test signal to form a composite signal carrying fault characteristics. The transmission delay time is used to characterize the difference between the time when the signal is first acquired and the first cycle sampling time. Noise reduction and feature extraction were performed on all current and voltage signals acquired at each test point. In addition, feature extraction was performed on the transmission delay time of each current and voltage signal to construct a fault feature vector for each test point. The fault feature vector of each test point includes voltage features determined by feature extraction of the voltage signal, current features determined by feature extraction of the current signal, impedance features jointly determined by the voltage and current features, and timing features determined by feature extraction of the transmission delay time. The fault feature vectors of each test point are imported into the pre-trained multi-class diagnostic model to obtain the fault type; wherein, the fault type includes contact / contact loose oxidation fault, multi-point grounding fault, line short circuit fault and line open circuit fault.

2. The method for locating faults in the secondary circuit of high-voltage electrical equipment as described in claim 1, characterized in that, The VT transformer is a miniature VT transformer with a measurement range covering DC110V / 220V and AC220V, an accuracy class of 0.2, and a load impedance of ≤0.1Ω; the CT transformer is a miniature CT transformer with a range of 0.01A-5A, a transformation ratio of 1:1000, and a primary winding DC resistance of ≤0.1Ω.

3. The method for locating faults in the secondary circuit of high-voltage electrical equipment as described in claim 2, characterized in that, The VT current transformer is connected to the corresponding test point via a piercing clamp; the CT current transformer is clamped onto the conductor of the target secondary circuit and close to the corresponding test point via an opening and closing clamp structure.

4. The method for locating faults in the secondary circuit of high-voltage electrical equipment as described in claim 1, characterized in that, The test signal at the specific frequency is a sinusoidal signal with a frequency of 2kHz and an injection power of ≤5W; the fixed sampling frequency is 10kHz; and the total sampling duration is 3S.

5. The method for locating faults in the secondary circuit of high-voltage electrical equipment as described in claim 1, characterized in that, The multi-class diagnostic model employs an enhanced causal Bayesian network, which integrates target secondary loop topology constraints and its relay protection logic. The target secondary loop topology constraints include the target secondary loop closed-loop logic and the initial states of the switches, disconnectors, and relay contacts on it.

6. The method for locating faults in the secondary circuit of high-voltage electrical equipment as described in claim 1, characterized in that, The voltage characteristics include voltage drop abrupt change coefficient and voltage waveform distortion rate; the current characteristics include current shunt ratio deviation; the impedance characteristics include contact resistance value; the timing characteristics include timing delay deviation; wherein, the contact resistance value is calculated based on Ohm's law R=U / I; the timing delay deviation is used to characterize the difference between the transmission delay time and the preset standard timing threshold.

7. The method for locating faults in the secondary circuit of high-voltage electrical equipment as described in claim 1, characterized in that, The method further includes: Based on the fault feature vectors of each test point, two adjacent test points whose fault feature vector differences meet preset conditions are determined on the topology of the target secondary circuit. Combined with the preset distance between the two adjacent test points, the location of the fault point is located by a linear interpolation algorithm.

8. The method for locating faults in the secondary circuit of high-voltage electrical equipment as described in claim 7, characterized in that, Specifically, the difference between two adjacent test points whose fault feature vectors meet the preset conditions is that at least one feature in the fault feature vectors of the two adjacent test points has a difference greater than the corresponding preset feature value.

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