Method and system for detecting capacitance and dielectric loss of transformer in non-disconnection state

Abstract

The invention discloses a method and a system for detecting capacitance and dielectric loss of a transformer in a non-disconnection state, and relates to the technical field of electric power detection, and the method comprises the following steps: collecting multi-point voltage time domain data of the transformer in a non-power-failure state; the initial frequency corresponding to the position with the minimum spectral line amplitude in the preset frequency range is obtained through calculation by adopting an FFT transformation optimization algorithm; controlling the program-controlled high-voltage alternating current power supply to generate high-voltage alternating current with initial frequency, and connecting the high-voltage alternating current to the transformer; collecting a current sequence and a high-voltage output voltage sequence of a transformer bushing branch; calculating and correcting the voltage amplitude of the spectral line position corresponding to the initial frequency and the current amplitude of each branch to be measured of the transformer by adopting an FFT (Fast Fourier Transform) optimization algorithm; and subtracting the voltage initial phase angle from the current initial phase angle to obtain a current phase angle. The pilot frequency measurement technology is adopted for measurement, the current spatial frequency is staggered, and the influence of the induced voltage on the measurement result can be eliminated.

Description

Technical Field

[0001] The present invention relates to the technical field of power detection, and more particularly to a method and system for detecting transformer capacitance and dielectric loss without disconnecting the wiring. Background Art

[0002] The winding capacitance of a transformer is one of the important items in the routine test items of the transformer to judge its health status. However, when conducting this test item, it is necessary to remove the three-side leads connecting the high, medium and low voltage sides of the transformer.

[0003] For outdoor transformers above 220kV, the bushing lead joints are located at a high altitude, often requiring the assistance of an aerial work platform. The work process is cumbersome and complex, and frequent removal and installation of the leads may also result in poor contact. For indoor transformers of 220kV and above, aerial work platforms are inaccessible, requiring testers to climb to the top of the bushing and manually remove and install the leads repeatedly, significantly increasing the safety risk of falling from heights. The investment of significant manpower, material resources, and large-scale mechanical equipment significantly increases the risk and cost of transformer testing, and significantly reduces maintenance efficiency. Removing the leads for high-voltage testing not only reduces work efficiency and prolongs power outages, but also poses a safety hazard. However, existing dielectric loss testers typically require the removal of transformer leads for testing. Currently, there is no system that can complete dielectric loss and capacitance testing without removing the transformer leads.

[0004] Therefore, how to research and design a method and system for detecting transformer capacitance and dielectric loss without disconnecting the wires that can overcome the above-mentioned defects is a problem that we urgently need to solve. Summary of the Invention

[0005] To address the deficiencies in the prior art, the present invention aims to provide a method and system for detecting transformer capacitance and dielectric loss without removing the wiring. During the measurement of the transformer without removing the wiring, surrounding live equipment will induce voltage in the measurement system, and this induced voltage may be as high as thousands of volts. The present invention adopts a different-frequency measurement technology for measurement. By designing a variable-frequency high-voltage voltage source as an excitation source, the current spatial frequency is staggered, and power is supplied to the equivalent capacitance of the transformer winding to be measured, thereby eliminating the influence of the induced voltage on the measurement results.

[0006] The above technical objectives of the present invention are achieved through the following technical solutions:

[0007] In a first aspect, a method for detecting transformer capacitance and dielectric loss without disconnecting the wiring is provided, comprising the following steps:

[0008] Collect multi-point voltage time domain data of the transformer when it is not powered off;

[0009] Based on multi-point voltage time domain data, the FFT transformation optimization algorithm is used to calculate the initial frequency corresponding to the position with the minimum spectral line amplitude within the preset frequency range;

[0010] Control the programmable high-voltage AC power source to generate high-voltage AC power of the initial frequency, and connect the high-voltage AC power to the transformer;

[0011] After the transformer is connected to the high-voltage AC power, the current sequence of the transformer bushing branch and the high-voltage output voltage sequence are collected;

[0012] Based on the current sequence and high-voltage output voltage sequence, the FFT transformation optimization algorithm is used to calculate and correct the voltage amplitude of the spectrum line position corresponding to the initial frequency and the current amplitude of each branch to be measured of the transformer;

[0013] The initial voltage phase angle and the initial current phase angle are calculated based on the complex number property, and the current phase angle is obtained by subtracting the initial voltage phase angle from the initial current phase angle.

[0014] The capacitance and / or dielectric loss of the transformer are calculated based on the current phase angle.

[0015] Furthermore, the calculation process of the FFT transformation optimization algorithm is specifically as follows:

[0016] The voltage sequence collected is U (i) , the current sequence is I (i) , i∈0,1,2…N-1;

[0017] After setting the Hanning window to N / 2 points and performing self-convolution, we get a window sequence W of N-1 points. 1(i) ;

[0018] Will I (i) Sequence and W 1(i) After multiplication, we get sequence I h ;

[0019] Will U (i) Sequence and W 1(i) After multiplication, we get the sequence U h ;

[0020] Will I h and U h Perform FFT transformation to obtain complex frequency domain CI k and complex sequence CU k , remove the mirror part, k∈0,1,2,…N / 2-1;

[0021] Through the N-point Hanning window W d The sequence multiplied by the current and voltage sequence is directly transformed by FFT to obtain the complex frequency domain DI k and the complex sequence DU k ;

[0022] According to the complex frequency domain CI k , complex sequence CU k , complex frequency domain DI k and the complex sequence DU k The corrected amplitude and / or frequency is calculated.

[0023] Furthermore, the calculation formula of the corrected amplitude is specifically:

[0024] A m =D m 2 / C m ;

[0025] Among them, A m represents the amplitude of the corrected spectral line position m; D m represents the amplitude of the spectral line position m calculated by FFT after adding the Hanning window; C m Represents the Hanning window self-convolution window W 1(i) The amplitude of the spectral line position m is then calculated by FFT.

[0026] Furthermore, the frequency calculation formula after correction is specifically:

[0027]

[0028] f m =ω m / (2π)

[0029] Among them, ω m represents the angular frequency of the corrected spectral line position m; Indicates CI k or CU k The phase of the spectral line to be corrected; λ m Indicates DI k or DU k The phase of the spectrum line that needs to be corrected; N represents the number of points in the voltage time domain data; f m represents the frequency of the corrected spectral line position m.

[0030] Furthermore, the number of points of the voltage time domain data is 4096 or 8192 points.

[0031] Furthermore, the preset frequency range is within 50 Hz±5 Hz.

[0032] Furthermore, the capacitance calculation formula of the transformer is specifically as follows:

[0033]

[0034] Where, C represents the capacitance of the transformer; θIa represents the current phase angle; f min Represents the initial frequency; Ia represents the current amplitude of each branch of the transformer to be measured; Ua represents the voltage amplitude at the spectrum position corresponding to the initial frequency; R represents the equivalent resistance of the capacitor in parallel.

[0035] Furthermore, the transformer dielectric loss calculation formula is specifically as follows:

[0036] loss=tan(90-θ Ia );

[0037] Among them, loss represents the dielectric loss of the transformer; θ Ia Indicates the current phase angle.

[0038] In the second aspect, a system for detecting transformer capacitance and dielectric loss without disconnecting the wiring is provided, comprising a programmable high-voltage AC power supply, a communication module, and a detection and analysis module;

[0039] The detection and analysis module is used to implement a method for detecting transformer capacitance and dielectric loss without disconnecting the wiring as described in any one of the first aspects.

[0040] Furthermore, the programmable high-voltage AC power supply includes a programmable inverter unit and a step-up transformer;

[0041] The detection and analysis module includes a high voltage and current acquisition unit, a processor unit, a storage unit and a display unit;

[0042] The program-controlled inverter unit is connected to the processor unit via a communication module to obtain control instructions from the processor unit;

[0043] The high-voltage voltage and current acquisition unit uses high-voltage resistor voltage division to obtain a low-voltage signal for ADC acquisition, and uses a high-precision current transformer to collect current and convert it into a signal for ADC acquisition.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. The present invention provides a method for detecting transformer capacitance and dielectric loss without removing the wiring. During the measurement process of the transformer without removing the wiring, surrounding live equipment will induce voltage in the measurement system. This induced voltage may be as high as thousands of volts. The present invention adopts a different-frequency measurement technology for measurement. By designing a variable-frequency high-voltage voltage source as the excitation source, staggering the current spatial frequency, and supplying power to the equivalent capacitance of the transformer winding to be measured, the influence of the induced voltage on the measurement results can be eliminated.

[0046] 2. The FFT transform optimization algorithm adopted by the present invention can automatically identify the electromagnetic environment with the least interference, control the boost system to automatically match the frequency of the electromagnetic environment with the least interference, and achieve an adaptive effect on the electromagnetic environment;

[0047] 3. The present invention can automatically calculate the dielectric loss and capacitance using a single device without removing the wires, and the operation process is simple and convenient. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0049] Figure 1 This is a flowchart of Example 1 of the present invention;

[0050] Figure 2 is a system block diagram in Example 2 of the present invention;

[0051] Figure 3 2 is a connection diagram of the detection device in Example 2 of the present invention. DETAILED DESCRIPTION

[0052] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0053] It should be noted that when a component is referred to as being “fixed to” or “disposed on” another component, it can be directly on the other component or indirectly on the other component. When a component is referred to as being “connected to” another component, it can be directly or indirectly connected to the other component.

[0054] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0055] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0056] Example 1: A method for detecting transformer capacitance and dielectric loss without disconnecting the wires, such as Figure 1 As shown, the following steps are included:

[0057] S1: Collect multi-point voltage time domain data of the transformer when it is not powered off;

[0058] S2: Based on the multi-point voltage time domain data, the FFT transform optimization algorithm is used to calculate the initial frequency corresponding to the position with the minimum spectral line amplitude within the preset frequency range;

[0059] S3: Control the programmable high-voltage AC power supply to generate high-voltage AC power of the initial frequency, and connect the high-voltage AC power to the transformer;

[0060] S4: After the transformer is connected to the high-voltage AC power, the current sequence of the transformer bushing branch and the high-voltage output voltage sequence are collected;

[0061] S5: Based on the current sequence and the high-voltage output voltage sequence, the FFT transformation optimization algorithm is used to calculate and correct the voltage amplitude at the spectral line position corresponding to the initial frequency and the current amplitude of each branch to be measured of the transformer;

[0062] S6: Calculate the initial voltage phase angle and the initial current phase angle according to the complex number property, and obtain the current phase angle by subtracting the initial voltage phase angle from the initial current phase angle;

[0063] S7: Calculate the capacitance and / or dielectric loss of the transformer based on the current phase angle.

[0064] It should be noted that the high-voltage AC power generated by the programmable high-voltage AC power supply needs to wait for a time t2, generally 2-5 seconds. After the high-voltage AC power stabilizes, the high-voltage output relay is controlled to connect the external measurement circuit to achieve high-voltage output.

[0065] Furthermore, the present invention uses the voltage phase angle as the initial angle of 0 when calculating the current phase angle. The fundamental complex angle of a variable obtained by the FFT is relative to this initial phase angle. Within a given FFT solution, the difference between the fundamental angles of all reference variables and the voltage angle is used as the angle difference. Clearly, the voltage angle relative to its own angle difference is 0 degrees.

[0066] In this embodiment, the sampling rate is Fs, and the calculation process of the FFT transformation optimization algorithm is as follows: the collected voltage sequence is U (i) , the current sequence is I (i) , i∈0,1,2…N-1; set the Hanning window to N / 2 points and perform self-convolution to obtain the window sequence W of N-1 points 1(i) ; will I (i) Sequence and W 1(i) After multiplication, we get sequence I h ;Change U (i) Sequence and W 1(i) After multiplication, we get the sequence U h ; will I h and U h Perform FFT transformation to obtain complex frequency domain CI k and complex sequence CU k , remove the mirror part, k∈0,1,2,…N / 2-1; through the N-point Hanning window W d The sequence multiplied by the current and voltage sequence is directly transformed by FFT to obtain the complex frequency domain DI k and the complex sequence DU k ; According to the complex frequency domain CI k , complex sequence CU k , complex frequency domain DI k and the complex sequence DU k The corrected amplitude and / or frequency is calculated.

[0067] For example, the formula for calculating the amplitude after correction is:

[0068] A m =D m 2 / C m ;

[0069] Among them, A m represents the amplitude of the corrected spectral line position m; D m represents the amplitude of the spectral line position m calculated by FFT after adding the Hanning window; C m Represents the Hanning window self-convolution window W 1(i) The amplitude of the spectral line position m is then calculated by FFT.

[0070] For another example, the frequency calculation formula after correction is:

[0071]

[0072] Among them, ω m represents the angular frequency of the corrected spectral line position m; Indicates CI k or CU kThe phase of the spectral line to be corrected; λ m Indicates DI k or DU k The phase of the spectrum line that needs to be corrected; N represents the number of points in the voltage time domain data; f m represents the frequency of the corrected spectral line position m.

[0073] It should be noted that the number of points of the voltage time domain data can be set as needed, for example, the number of points is 4096 or 8192 points.

[0074] In this embodiment, the preset frequency range is within 50 Hz±5 Hz.

[0075] The specific calculation formula for the transformer capacitance is:

[0076]

[0077] Where, C represents the capacitance of the transformer; θ Ia represents the current phase angle; f min Represents the initial frequency; Ia represents the current amplitude of each branch of the transformer to be measured; Ua represents the voltage amplitude at the spectrum position corresponding to the initial frequency; R represents the equivalent resistance of the capacitor in parallel.

[0078] The transformer dielectric loss calculation formula is as follows:

[0079] loss=tan(90-θ Ia );

[0080] Among them, loss represents the dielectric loss of the transformer; θ Ia Indicates the current phase angle.

[0081] Example 2: A system for detecting transformer capacitance and dielectric loss without removing the wires, comprising a programmable high-voltage AC power supply, a communication module, and a detection and analysis module; wherein the detection and analysis module is used to implement a method for detecting transformer capacitance and dielectric loss without removing the wires as described in any one of the first aspects.

[0082] like Figure 2 As shown, the programmable high-voltage AC power supply includes a programmable inverter unit and a step-up transformer; the detection and analysis module includes a high-voltage voltage and current acquisition unit, a processor unit, a storage unit and a display unit; wherein the programmable inverter unit is connected to the processor unit through a communication module to obtain control instructions sent by the processor unit; the high-voltage voltage and current acquisition unit uses high-voltage resistor voltage division to obtain a low-voltage signal for ADC acquisition, and uses a high-precision current transformer to collect current and convert it into a signal for ADC acquisition.

[0083] In addition, the processor unit can also be connected to some human-computer interaction interfaces, such as a keyboard module.

[0084] The present invention can integrate the programmable high voltage AC power supply, the communication module and the detection and analysis module into a set of detection devices, which can be connected to the transformer detection position by leading out the detection line, such as Figure 3 As shown. The detection device connects the output high-voltage AC power to the transformer, respectively, at the high-voltage bushing lead positions of phases A, B, C, and 0. The output voltage U is obtained through the high-voltage voltage divider resistor, and the current I entering the transformer of phases A, B, C, and 0 is obtained through the high-voltage transformer. A , I B , I C and I0.

[0085] In order to avoid excessive wiring in the device, I A , I B , I C and I0 are collected through the current transformer and then enter the internal processing module, U, I A , I B , I C and I0 are discretely quantized by the internal ADC and become corresponding U, I A , I B , I C The discrete sequence of U and I0 can be solved by the FFT transformation optimization algorithm to obtain the capacitance and dielectric loss information corresponding to U and Ix (x∈A,B,C,0), and finally displayed on the display or transmitted to other devices through communication equipment for processing.

[0086] Working principle: During the measurement of the transformer without removing the wires, the surrounding live equipment will induce a voltage in the measurement system. This induced voltage may be as high as thousands of volts. The present invention adopts a different-frequency measurement technology for measurement. By designing a high-voltage voltage source with a variable frequency as an excitation source, staggering the current spatial frequency, and supplying power to the equivalent capacitance of the transformer winding to be measured, the influence of the induced voltage on the measurement result can be eliminated. In addition, the FFT transformation optimization algorithm adopted by the present invention can automatically identify the electromagnetic environment with the least interference, control the boost system to automatically match the frequency of the electromagnetic environment with the least interference, and achieve an adaptive effect on the electromagnetic environment. In addition, the present invention can automatically calculate the dielectric loss and capacitance using a single set of devices without removing the wires, and the operation process is simple and convenient.

[0087] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0088] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0089] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0090] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0091] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for detecting transformer capacitance and dielectric loss without disconnecting the wires, characterized in that: The following steps are involved: Collect multi-point voltage time domain data of the transformer when it is not powered off; Based on multi-point voltage time domain data, the FFT transformation optimization algorithm is used to calculate the initial frequency corresponding to the position with the minimum spectral line amplitude within the preset frequency range; Control the program-controlled high-voltage AC power source to generate high-voltage AC power of the initial frequency, and connect the high-voltage AC power to the transformer; After the transformer is connected to high-voltage AC power, the current sequence of the transformer bushing branch and the high-voltage output voltage sequence are collected; Based on the current sequence and the high-voltage output voltage sequence, the FFT transformation optimization algorithm is used to calculate and correct the voltage amplitude at the spectral line position corresponding to the initial frequency and the current amplitude of each branch to be tested of the transformer; The initial voltage phase angle and the initial current phase angle are calculated according to the complex number property, and the current phase angle is obtained by subtracting the initial voltage phase angle from the initial current phase angle; The capacitance and / or dielectric loss of the transformer is calculated based on the current phase angle.

2. The method for detecting transformer capacitance and dielectric loss without disconnecting the wires according to claim 1 is characterized in that: The calculation process of the FFT transformation optimization algorithm is specifically as follows: The voltage sequence collected is U (i) , the current sequence is I (i) , i∈0,1,2…N-1; After setting the Hanning window to N / 2 points and performing self-convolution, we get a window sequence W of N-1 points. 1(i) ; Will I (i) Sequence and W 1(i) After multiplication, we get sequence I h ; Will U (i) Sequence and W 1(i) After multiplication, we get the sequence U h ; Will I h and U h Perform FFT transformation to obtain complex frequency domain CI k and complex sequence CU k , remove the mirror part, k∈0,1,2,…N / 2-1; Through the N-point Hanning window W d The sequence multiplied by the current and voltage sequence is directly transformed by FFT to obtain the complex frequency domain DI k and the complex sequence DU k ; According to the complex frequency domain CI k , complex sequence CU k , Complex frequency domain DI k and the complex sequence DU k The corrected amplitude and / or frequency is calculated.

3. The method for detecting transformer capacitance and dielectric loss without disconnecting the wires according to claim 2 is characterized in that: The corrected amplitude calculation formula is specifically: A m =|D m | 2 / |C m |; Among them, A m represents the amplitude of the corrected spectral line position m; D m represents the amplitude of the spectral line position m calculated by FFT after adding the Hanning window; C m Represents the Hanning window self-convolution window W 1(i) The amplitude of the spectral line position m is then calculated by FFT.

4. The method for detecting transformer capacitance and dielectric loss without disconnecting the wires according to claim 2 is characterized in that: The corrected frequency calculation formula is specifically: Among them, ω m represents the angular frequency of the corrected spectral line position m; Indicates CI k or CU k The phase of the spectral line to be corrected; λ m Indicates DI k or DU k The phase of the spectrum line that needs to be corrected; N represents the number of points in the voltage time domain data; f m represents the frequency of the corrected spectral line position m.

5. The method for detecting transformer capacitance and dielectric loss without disconnecting the wires according to claim 1 is characterized in that: The number of points of the voltage time domain data is 4096 or 8192 points.

6. The method for detecting transformer capacitance and dielectric loss without disconnecting the wires according to claim 1 is characterized in that: The preset frequency range is within 50 Hz±5 Hz.

7. The method for detecting transformer capacitance and dielectric loss without disconnecting the wires according to claim 1 is characterized in that: The capacitance calculation formula of the transformer is specifically: Where, C represents the capacitance of the transformer; θ Ia represents the current phase angle; f min Represents the initial frequency; Ia represents the current amplitude of each branch of the transformer to be measured; Ua represents the voltage amplitude of the spectrum line position corresponding to the initial frequency; R represents the equivalent resistance of the capacitor in parallel.

8. The method for detecting transformer capacitance and dielectric loss without disconnecting the wires according to claim 1 is characterized in that: The dielectric loss calculation formula of the transformer is specifically: loss=tan(90-θ Ia ); Among them, loss represents the dielectric loss of the transformer; θ Ia Represents the current phase angle.

9. A detection system for transformer capacitance and dielectric loss without disconnecting the wires, characterized in that: It includes a program-controlled high-voltage AC power supply, a communication module and a detection and analysis module; The detection and analysis module is used to implement a method for detecting transformer capacitance and dielectric loss without disconnecting the wiring as described in any one of claims 1 to 7.

10. A detection system for transformer capacitance and dielectric loss without disconnecting the wires according to claim 9, characterized in that: The program-controlled high-voltage AC power supply includes a program-controlled inverter unit and a step-up transformer; The detection and analysis module includes a high voltage and current acquisition unit, a processor unit, a storage unit and a display unit; The program-controlled inverter unit is connected to the processor unit via a communication module to obtain control instructions sent by the processor unit; The high voltage and current acquisition unit uses high voltage resistor voltage division to obtain low voltage signals for ADC acquisition, and uses a high precision current transformer to acquire current and convert it into a signal for ADC acquisition.

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