Method and system for positioning internal partial discharge source of power transformer

Abstract

The invention discloses a method and system for positioning an internal partial discharge source of a power transformer, and the method comprises the steps: 1), obtaining an ultrasonic signal generated by the discharge of the internal partial discharge source of the power transformer, and obtaining the relative time delay of the ultrasonic signal reaching a preset position around an oil tank wall of the power transformer; 2) obtaining an optimization function for solving the actual position of the partial discharge source according to the size of the oil tank and the relative time delay, and taking the optimization function as a target function of a preset partial discharge source positioning model; and 3) selecting a swarm intelligent particle swarm algorithm as an optimization tool, solving the target function of the preset local discharge source positioning model, and performing iterative optimization on the possible local discharge source position to obtain the optimal discharge source position as the actual position of the local discharge source in the power transformer. The method has the advantages of real-time performance, accuracy, high efficiency and the like.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of transformers, and in particular to a method and system for locating a local discharge source inside a power transformer. Background Art

[0002] As an important power transmission and transformation equipment in the power system, power transformers play the role of voltage conversion and electric energy distribution in the power system. Ensuring their normal operation is the premise for improving the safety and stability of the power system. Transformer failures are of various types, which can be roughly divided into three categories: conductor failure, mechanical failure and insulation failure. Among them, insulation failure accounts for the highest proportion. The statistical results of transformer failures by the International Conference on Large Electric Systems (CIGRE) in 2015 show that the proportion of failures caused by windings and insulation is as high as 41%.

[0003] Transformers work under high voltage and high current environment for a long time. Because of the extremely uneven internal insulation, solid, liquid and gas often coexist. This makes it very easy for some weak insulation areas to break down and cause partial discharge inside the transformer. Partial discharge is the main cause of transformer insulation degradation. Long-term and high-intensity partial discharge will have a serious impact on the insulation performance of the transformer. At the same time, as partial discharge continues to develop, the scale of insulation damage will continue to expand, and may even lead to the complete loss of transformer insulation performance, greatly shortening its operating life cycle.

[0004] The transformer partial discharge power outage test method currently commonly used in maintenance sites can usually only determine whether there is a partial discharge signal inside the main transformer and the phase where the discharge signal is located, but cannot determine the specific location of the partial discharge source. During the on-site lifting cover overhaul of the transformer, due to the limitations of the main transformer structure, it is difficult to find the local fault point inside the winding on site, unless the main transformer is returned to the factory for disassembly and search, but this will also greatly increase the power outage time of the main transformer and affect the power supply reliability. In addition, the power outage of the main transformer for maintenance is risky. The power outage of the main transformer will not only seriously affect the reliability of power supply, but also greatly increase the risk of the power grid. Taking a 110kV substation as an example, if there are two 110kV main transformers in the substation, when one of them is shut down for maintenance, if the other is affected by other uncontrollable factors and trips and powers off, it will directly cause a level 6 power grid event, greatly reducing the reliability of power grid operation. Summary of the invention

[0005] In view of the technical problems existing in the prior art, the present invention provides a method and system for locating a local discharge source inside a power transformer with high positioning accuracy.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0007] A method for locating a local discharge source inside a power transformer comprises the following steps:

[0008] 1) Obtaining an ultrasonic signal generated by the discharge of a local discharge source inside the power transformer, and then obtaining a relative time delay of the ultrasonic signal reaching a predetermined position around the oil tank wall of the power transformer;

[0009] 2) obtaining an optimization function for solving the actual position of the local discharge source according to the oil tank size and the relative time delay, and using the optimization function as the objective function of the preset local discharge source positioning model;

[0010] 3) Select the swarm intelligence particle swarm algorithm as the optimization tool, solve the objective function of the preset local discharge source location model, iteratively optimize the possible local discharge source locations, and obtain the optimal discharge source location as the actual location of the local discharge source inside the power transformer.

[0011] Preferably, in step 1), a group of ultrasonic sensors are arranged on the oil tank walls around the power transformer to collect ultrasonic signals generated during internal partial discharge, and the ultrasonic sensors are installed on the side walls of the transformer; one group of ultrasonic sensors serves as a reference sensor, and the other three groups of ultrasonic sensors serve as measurement sensors.

[0012] Preferably, in step 2), the preset local discharge source location model is specifically:

[0013] The transformer is equivalent to a cube, and a spatial rectangular coordinate system is established with a vertex of the cube as the origin, where P represents the local discharge source inside the transformer, S 1 , S 2 , S 3 Respectively represent three groups of measurement sensors; S 0 is the reference sensor; the position of the discharge source P is (x s ,y s , z s ), S 1 -S 3 The position of (x i ,y i , z i , i=1, 2, 3), S 0 The position of (x 0 ,y 0 , z 0 );

[0014] Sensor S 1 , S 2 , S 3 With reference sensor S 0 The relative distance difference to the discharge source point P is:

[0015]

[0016] In formula (1), i = 1, 2, 3, and the ultrasonic wave reaches the sensor S 1 , S 2 , S 3 The time of arrival at the reference sensor S 0 The time difference is τ i , i = 1, 2, 3, assuming that the speed of ultrasonic wave propagation in oil is v, then it is obvious that the following formula holds true:

[0017] Δl i ≈τ i v(2) According to formula (2), the actual position of the local discharge source will make the function value of the following formula (3) very small:

[0018]

[0019] Formula (3) is used as the preset local discharge source location model.

[0020] Preferably, the optimization function is:

[0021]

[0022] In formula (4), x l ,y w , z h They represent the length, width and height of the transformer respectively; v represents the propagation speed of ultrasonic waves in the transformer.

[0023] Preferably, in step 3), in the swarm intelligence particle swarm optimization algorithm, particles search for the position of the optimal solution in space by continuously iterative flight, and the speed and position of the particles are updated in each iteration according to the following formula:

[0024]

[0025] where c 1 、c 2 represents the learning factor of the particle; r 1 、r 2 are two random numbers; v and x represent the velocity and position of the particle; ω is the inertia weight; and Represents the individual extreme value of the particle and the global extreme value of the population during the kth iteration.

[0026] The present invention also discloses a local discharge source positioning system inside a power transformer, comprising:

[0027] The partial discharge signal acquisition module is used to acquire the ultrasonic signal generated by the discharge of the partial discharge source inside the power transformer, and then obtain the relative time delay of the ultrasonic signal reaching the predetermined position around the oil tank wall of the power transformer;

[0028] A partial discharge signal processing module, used to obtain an optimization function for solving the actual position of the partial discharge source according to the oil tank size and the relative time delay, and use the optimization function as the objective function of the preset partial discharge source positioning model;

[0029] The partial discharge signal analysis module is used to select the swarm intelligence particle swarm optimization algorithm as the optimization tool, solve the objective function of the preset partial discharge source positioning model, iteratively optimize the possible partial discharge source positions, and obtain the optimal discharge source position as the actual position of the partial discharge source inside the power transformer.

[0030] Preferably, the partial discharge signal acquisition module includes multiple groups of ultrasonic sensors, which are respectively installed on the oil tank walls around the power transformer; one group of ultrasonic sensors is used as a reference sensor, and the other three groups of ultrasonic sensors are used as measurement sensors.

[0031] Preferably, the partial discharge signal processing module comprises a partial discharge monitoring IED, which is divided into a three-section structure of upper, middle and lower sections, wherein the bottom section is a power supply unit, the middle section is a signal filtering unit and the upper section is a signal acquisition and processing unit.

[0032] Preferably, the bottom layer includes a system power filter, an AC / DC switching power supply and an AC / DC power board; the middle layer consists of a fixed gain amplifier, a bandpass filter and a programmable amplifier; the upper layer consists of an FPGA signal acquisition scanning processing module and an industrial frequency signal trigger module.

[0033] Preferably, it also includes a display unit, wherein the interface of the display unit is divided into three parts, namely: a data input and output area, a graphic output area and a control panel area;

[0034] The data input and output area is used to input the size of the transformer, the installation position of the ultrasonic sensor, the relative delay data of each sensor relative to the reference sensor, and output the calculated spatial position of the local discharge source inside the tested transformer;

[0035] The graphic output area is used to dynamically display the process of locating the internal discharge source of the transformer in the form of a visual image;

[0036] The control panel area is used to clear data, perform calculations, and exit a program.

[0037] Compared with the prior art, the advantages of the present invention are:

[0038] Starting from the ultrasonic signal generated by partial discharge, the present invention realizes the online monitoring and positioning of the discharge source signal inside the transformer by establishing a discharge source positioning model based on ultrasonic signals, proposing a model solving algorithm, and designing a comprehensive software system integrating the model and the method. The present invention is of great significance for the effective online monitoring and precise positioning of the partial discharge signal appearing inside the operating transformer: it can not only effectively judge the health status and aging degree of the main transformer insulation, and provide an effective basis for transformer fault diagnosis; it can also reduce the number of main transformer power outages caused by data misjudgment and improve the reliability of power supply of the power grid.

[0039] The method of online monitoring of discharge source signals of the present invention avoids the grid risk caused by frequent power outages of the main transformer and improves the power supply reliability of the power system; the discharge source online monitoring function ensures that operation and maintenance personnel can timely discover the insulation degradation phenomenon inside the main transformer, so as to formulate maintenance strategies in advance and extend the healthy life cycle of the main transformer; the high-precision discharge source positioning and image visualization function can help maintenance personnel accurately and quickly find the defect location to eliminate the fault, ensure timely power restoration of the main transformer, and reduce the economic losses and grid risks caused by power outages of the main transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a diagram showing an embodiment of the local discharge source locating method of the present invention in a specific application.

[0041] Figure 2 It is a schematic diagram of the transformer local discharge source positioning model of the present invention.

[0042] Figure 3 This is a schematic diagram of the transformer local discharge source positioning principle of the present invention.

[0043] Figure 4 It is a flow chart of a method for locating a local discharge source in an embodiment of the present invention.

[0044] Figure 5 It is a structural diagram of a partial discharge source locating system in an embodiment of the present invention.

[0045] Figure 6 This is an interface diagram of the transformer partial discharge ultrasonic positioning software system in the present invention. DETAILED DESCRIPTION

[0046] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0047] like Figure 1 , Figure 3 and Figure 4 As shown, the method for locating the local discharge source inside the power transformer according to the embodiment of the present invention comprises the steps of:

[0048] 1) Obtaining an ultrasonic signal generated by the discharge of a local discharge source inside the power transformer, and then obtaining a relative time delay of the ultrasonic signal reaching a predetermined position around the oil tank wall of the power transformer;

[0049] 2) According to the tank size and relative time delay, an optimization function for solving the actual position of the local discharge source is obtained, and the optimization function is used as the objective function of the preset local discharge source positioning model;

[0050] 3) Select the swarm intelligence particle swarm algorithm as the optimization tool, solve the objective function of the preset local discharge source location model, iteratively optimize the possible local discharge source locations, and obtain the optimal discharge source location as the actual location of the local discharge source inside the power transformer.

[0051] In step 1), a group of ultrasonic sensors are arranged on the oil tank walls around the power transformer to collect ultrasonic signals generated during internal partial discharge. The ultrasonic sensors are installed on the side walls of the transformer; one group of ultrasonic sensors is used as a reference sensor, and the other three groups of ultrasonic sensors are used as measurement sensors.

[0052] At present, most of the transformers on site are cubic structures. Therefore, when establishing the model in step 2), the transformer can be equivalent to a cube, and a spatial rectangular coordinate system is established with one vertex of the cube as the origin. The specific structure is as follows: Figure 2 As shown. Where P represents the local discharge source inside the transformer, S 1 , S 2 , S 3 Respectively represent sensors 1, 2, and 3; S 0 is the reference sensor for sensors 1, 2, and 3. The location of the discharge source P is (x s ,y s , z s ), sensor S 1 To S 3 The position of (x i ,y i , z i , i = 1, 2, 3), reference sensor S 0 The position of (x 0 ,y 0 , z 0 ).

[0053] according to Figure 2 From the geometric information in the sensor S 1 , S 2 , S 3 With reference sensor S 0 The relative distance difference to the discharge source point P is:

[0054]

[0055] In formula (1), i = 1, 2, 3, and the ultrasonic wave reaches the sensor S 1 , S 2 , S 3 The time of arrival at the reference sensor S 0 The time difference is τ i (i=1, 2, 3), assuming that the speed of ultrasonic wave propagation in oil is v, then the following equation is obviously established:

[0056] Δl i ≈τ i v(2) According to formula (2), the actual position of the local discharge source will make the function value of the following formula (3) very small.

[0057]

[0058] Formula (3) is a nonlinear equation, which is very difficult to solve directly. To simplify the calculation, it is equivalent to a constrained optimization problem:

[0059]

[0060] In formula (4), x l ,y w , z h They represent the length, width and height of the transformer respectively; v represents the propagation speed of ultrasonic waves in the transformer.

[0061] Therefore, the actual location of the local discharge source can be obtained by simply solving the optimization function (4).

[0062] In step 3), the Particle Swarm Optimization (PSO) algorithm is a search algorithm based on random initial solutions. The algorithm has the advantages of simple implementation and fast calculation speed. The algorithm takes "swarm" and "evolution" as the basic concepts and regards each solution as a particle in the search space. Each particle has a certain speed, and its size is dynamically adjusted according to its own historical experience and population experience. Particles search for the location of the optimal solution in space by continuously iterating flight. The speed and position of the particles are updated according to the following formula for each iteration:

[0063]

[0064]

[0065] In the above formula, c 1 、c 2 represents the learning factor of the particle; r 1 、r 2 are two random numbers; v and x represent the velocity and position of the particle; ω is the inertia weight; and It represents the individual extreme value and the global extreme value of the population in the kth iteration of the particle. According to the particle velocity update formula, the moving direction of the particle in the next iteration = inertia direction + individual optimal direction + group optimal direction. That is, the particle swarm optimization algorithm is used to find the minimum value of the optimization equation (4). In this algorithm, each "particle" represents a possible discharge position, and the goal of the algorithm is to find a position that minimizes the error of equation (4) among all possible discharge positions.

[0066] Starting from the ultrasonic signal generated by partial discharge, the present invention realizes the online monitoring and positioning of the discharge source signal inside the transformer by establishing a discharge source positioning model based on ultrasonic signals, proposing a model solving algorithm, and designing a comprehensive software system integrating the model and the method. The present invention is of great significance for the effective online monitoring and precise positioning of the partial discharge signal appearing inside the operating transformer: it can not only effectively judge the health status and aging degree of the main transformer insulation, and provide an effective basis for transformer fault diagnosis; it can also reduce the number of main transformer power outages caused by data misjudgment and improve the reliability of power supply of the power grid.

[0067] The method of online monitoring of discharge source signals of the present invention avoids the grid risk caused by frequent power outages of the main transformer and improves the power supply reliability of the power system; the discharge source online monitoring function ensures that operation and maintenance personnel can timely discover the insulation degradation phenomenon inside the main transformer, so as to formulate maintenance strategies in advance and extend the healthy life cycle of the main transformer; the high-precision discharge source positioning and image visualization function can help maintenance personnel accurately and quickly find the defect location to eliminate the fault, ensure timely power restoration of the main transformer, and reduce the economic losses and grid risks caused by power outages of the main transformer.

[0068] like Figure 5 As shown, an embodiment of the present invention further provides a local discharge source locating system inside a power transformer, comprising:

[0069] The partial discharge signal acquisition module is used to acquire the ultrasonic signal generated by the discharge of the partial discharge source inside the power transformer, and then obtain the relative time delay of the ultrasonic signal reaching the predetermined position around the oil tank wall of the power transformer;

[0070] A partial discharge signal processing module, used to obtain an optimization function for solving the actual position of the partial discharge source according to the oil tank size and the relative time delay, and use the optimization function as the objective function of the preset partial discharge source positioning model;

[0071] The partial discharge signal analysis module is used to select the swarm intelligence particle swarm algorithm as an optimization tool, solve the objective function of the preset partial discharge source positioning model, iteratively optimize the possible partial discharge source positions, and obtain the optimal discharge source position as the actual position of the partial discharge source inside the power transformer.

[0072] Specifically, the partial discharge signal acquisition module includes a partial discharge ultrasonic signal acquisition module and a partial discharge monitoring IED module. The partial discharge ultrasonic signal acquisition module is composed of four groups of ultrasonic sensors: a group of ultrasonic sensors are arranged on the oil tank walls around the main transformer to collect the ultrasonic signals generated by the internal partial discharge. The ultrasonic sensors are installed on the side walls of the transformer and are installed in an adsorption manner, which effectively ensures that the ultrasonic sensor monitoring achieves global coverage. The sensor uses piezoelectric ceramic sensitive elements with temperature stability and a sensitivity of up to 67dB. The frequency bandwidth covers the acoustic emission signal frequency of common metal materials.

[0073] Sensor parameters: 1) Frequency range: 100kHz~400kHz; 2) Sensor sensitivity: 67dB; 3) Impedance matching: 50Ω; 4) Installation method: adsorption installation; 5) Output connector: M5; 6) Resonant frequency: 150kHz; 7) Working temperature: -20℃~70℃.

[0074] The main function of the partial discharge monitoring IED (Intelligent Electronic Device) module is to process the partial discharge signal received by the ultrasonic sensor, analyze the insulation status of the equipment under test based on the expert database, and send the analysis results to the background. The transformer partial discharge monitoring IED module can analyze the local discharge characteristic quantities, including basic parameters such as the maximum discharge amount and discharge phase, discharge number, and average discharge amount. The above-mentioned partial discharge monitoring IED module is a conventional device, such as the equipment produced by Jiangsu Jiuchuang Electric Technology Co., Ltd., model: JC-OM400B-01AE.

[0075] The partial discharge signal processing module and the partial discharge signal analysis module are both located in the online monitoring platform. The data processed by the field monitoring unit is uploaded to the main processor unit through optical fiber. The main processor unit analyzes the signal waveforms from the four groups of ultrasonic sensors to obtain the relative delays of three of the sensors relative to the reference sensor, which serves as the basis for subsequent discharge source location. In addition, the partial discharge historical measurement data stored on the main processor unit can be queried by staff and remote management systems.

[0076] In addition, it also includes a transformer partial discharge source positioning software system. The software interface of the discharge source positioning system is divided into three parts: data input and output area, graphic output area and control panel area. The functions of each part are as follows: the data input and output area is used to input data such as the size of the transformer, the installation position of the ultrasonic sensor, the relative delay of each sensor relative to the reference sensor, and output the calculated spatial position of the partial discharge source inside the tested transformer; the graphic output area dynamically displays the process of the algorithm locating the internal discharge source of the transformer in the form of a visual image; the control panel area is used to realize data clearing, calculation and program exit.

[0077] During normal operation, the system can monitor and record the status of the transformer online at any time, and use the diagnostic system to analyze and judge the operating status of the equipment. When the transformer is abnormal, the system quickly collects and processes fault data, and completes online calculation, storage, statistics, alarm, analysis report and data remote transmission functions.

[0078] In specific applications, when the transformer is abnormal and needs to locate the internal discharge source, first Figure 2 A discharge source positioning model for the corresponding transformer is established, and four sets of sensors are arranged on the oil tank walls around the transformer to receive the ultrasonic signals generated by the discharge. Figure 5 The detected signal shown in the figure is filtered, RF preamplifier and detector, and then sampled, stored, digitally processed and analyzed by the high-speed data acquisition module to obtain the relative time delay of each sensor relative to the reference sensor. Finally, the transformer size, sensor position, relative time delay and other information are input into the Figure 6 In the positioning software system shown, the specific location of the discharge source can be obtained.

[0079] The present invention uses the ultrasonic signal generated when partial discharge occurs inside the transformer as a characteristic signal, and receives the signal by installing an ultrasonic sensor on each oil tank wall around the transformer. At the same time, the acquired signal waveform is filtered, subjected to a radio frequency preamplifier and a detector, and then sampled, stored, digitally processed and analyzed by a high-speed data acquisition module. Finally, the analyzed discharge amount and the relative time delay of each sensor are brought into the established discharge source positioning model, and solved by an intelligent optimization algorithm to realize online monitoring and positioning of the discharge source inside the transformer.

[0080] The present invention realizes online monitoring and precise positioning of the local discharge source inside the transformer by adopting advanced ultrasonic signal processing technology, and solves the problems of traditional power outage partial discharge test methods that are time-consuming, costly and inaccurate in positioning.

[0081] The present invention can collect ultrasonic signals inside the transformer in real time, and accurately identify the characteristic signals generated by partial discharge through high-speed signal processing and analysis algorithms. Compared with traditional methods, this system does not require power outage operation, greatly shortens the detection cycle, reduces operation and maintenance costs, and improves the reliability and safety of the power system. In terms of precise positioning, this system achieves three-dimensional spatial positioning of the discharge source through theoretical modeling and optimization algorithm solution. This not only improves the accuracy of fault diagnosis, but also provides strong technical support for subsequent maintenance work.

[0082] In terms of online monitoring of the main transformer, this system can monitor the operating status of the transformer in real time and promptly discover potential safety hazards. Through long-term data accumulation and analysis, this system can also evaluate the health status of the transformer and provide a scientific basis for the maintenance and management of the transformer.

[0083] In addition, this system can also be combined with the existing fault diagnosis system to achieve information sharing and complementarity, further improving the accuracy and efficiency of fault diagnosis. By timely discovering and handling partial discharge problems, this system can effectively extend the service life of the transformer and improve the overall economic benefits of the power system.

[0084] In summary, the online monitoring and positioning system of local discharge sources inside transformers based on ultrasonic signals has the characteristics of real-time, accuracy, and high efficiency, and has important application value and promotion prospects in power systems.

[0085] In the description of the present invention, it should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0086] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0087] In the present invention, unless otherwise clearly specified and limited, the terms "assemble", "connect", "connect", "fix" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0088] The above are only preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims

1. A method for locating a local discharge source inside a power transformer, characterized in that: Includes steps: 1) Obtaining an ultrasonic signal generated by the discharge of a local discharge source inside the power transformer, and then obtaining a relative time delay of the ultrasonic signal reaching a predetermined position around the oil tank wall of the power transformer; 2) obtaining an optimization function for solving the actual position of the local discharge source according to the oil tank size and the relative time delay, and using the optimization function as the objective function of the preset local discharge source positioning model; 3) Select the swarm intelligence particle swarm algorithm as the optimization tool, solve the objective function of the preset local discharge source location model, iteratively optimize the possible local discharge source locations, and obtain the optimal discharge source location as the actual location of the local discharge source inside the power transformer.

2. The method for locating the local discharge source inside the power transformer according to claim 1, characterized in that: In step 1), a group of ultrasonic sensors are arranged on the oil tank walls around the power transformer to collect ultrasonic signals generated during internal partial discharge. The ultrasonic sensors are installed on the side walls of the transformer; one group of ultrasonic sensors is used as a reference sensor, and the other three groups of ultrasonic sensors are used as measurement sensors.

3. The method for locating the local discharge source inside the power transformer according to claim 2, characterized in that: In step 2), the preset local discharge source location model is specifically: The transformer is equivalent to a cube, and a spatial rectangular coordinate system is established with a vertex of the cube as the origin, where P represents the local discharge source inside the transformer, S1, S2, and S3 represent three groups of measurement sensors respectively; S0 is the reference sensor; the position of the discharge source P is (x s ,y s , z s ), the position of S1-S3 is (x i ,y i , z i , i=1, 2, 3), the position of S0 is (x0, y0, z0); The relative distance difference between sensors S1, S2, S3 and reference sensor S0 to the discharge source point P is: In formula (1), i = 1, 2, 3, and the time difference between the time when the ultrasonic wave reaches the sensors S1, S2, S3 and the time when it reaches the reference sensor S0 is τ i , i = 1, 2, 3, assuming that the speed of ultrasonic wave propagation in oil is v, then it is obvious that the following formula holds true: Δl i ≈τ i v(2) According to formula (2), the actual location of the local discharge source will make the function value of the following formula (3) very small: Formula (3) is used as the preset local discharge source location model.

4. The method for locating the local discharge source inside the power transformer according to claim 3, characterized in that: The optimization function is: In formula (4), x l ,y w , z h They represent the length, width and height of the transformer respectively; v represents the propagation speed of ultrasonic waves in the transformer.

5. The method for locating the local discharge source inside the power transformer according to claim 4, characterized in that: In step 3), in the swarm intelligence particle swarm optimization algorithm, particles continuously iterate to find the position of the optimal solution in space. The speed and position of the particles are updated according to the following formula in each iteration: Where c1 and c2 represent the learning factors of the particle; r1 and r2 are two random numbers; v and x represent the velocity and position of the particle; ω is the inertia weight; and Represents the individual extreme value of the particle and the global extreme value of the population during the kth iteration.

6. A local discharge source location system inside a power transformer, characterized in that: include: The partial discharge signal acquisition module is used to acquire the ultrasonic signal generated by the discharge of the partial discharge source inside the power transformer, and then obtain the relative time delay of the ultrasonic signal reaching the predetermined position around the oil tank wall of the power transformer; A partial discharge signal processing module, used to obtain an optimization function for solving the actual position of the partial discharge source according to the oil tank size and the relative time delay, and use the optimization function as the objective function of the preset partial discharge source positioning model; The partial discharge signal analysis module is used to select the swarm intelligence particle swarm optimization algorithm as the optimization tool, solve the objective function of the preset partial discharge source positioning model, iteratively optimize the possible partial discharge source positions, and obtain the optimal discharge source position as the actual position of the partial discharge source inside the power transformer.

7. The local discharge source location system inside a power transformer according to claim 6, characterized in that: The partial discharge signal acquisition module includes multiple groups of ultrasonic sensors, which are respectively installed on the oil tank walls around the power transformer; one group of ultrasonic sensors is used as a reference sensor, and the other three groups of ultrasonic sensors are used as measurement sensors.

8. The local discharge source location system inside a power transformer according to claim 6 or 7, characterized in that: The partial discharge signal processing module comprises a partial discharge monitoring IED, which is divided into a three-stage structure of upper, middle and lower sections, wherein the bottom section is a power supply unit, the middle section is a signal filtering unit and the upper section is a signal acquisition and processing unit.

9. The local discharge source location system inside a power transformer according to claim 8, characterized in that: The bottom layer includes a system power filter, an AC / DC switching power supply and an AC / DC power board; the middle layer consists of a fixed gain amplifier, a bandpass filter and a programmable amplifier; the upper layer consists of an FPGA signal acquisition scanning processing module and an industrial frequency signal trigger module.

10. The local discharge source location system inside a power transformer according to claim 6 or 7, characterized in that: It also includes a display unit, wherein the interface of the display unit is divided into three parts: a data input and output area, a graphic output area and a control panel area; The data input and output area is used to input the size of the transformer, the installation position of the ultrasonic sensor, the relative delay data of each sensor relative to the reference sensor, and output the calculated spatial position of the local discharge source inside the tested transformer; The graphic output area is used to dynamically display the process of locating the internal discharge source of the transformer in the form of a visual image; The control panel area is used to clear data, perform calculations, and exit a program.

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