Method and system for measuring broadband high-voltage dielectric response of insulation of electrical equipment

Abstract

The present invention relates to a method and system for measuring the broadband high-voltage dielectric response of electrical equipment insulation, and belongs to the field of electric power technology. The method adopts the method of frequency segmentation and power supply complementation, and specifically includes: S1: determining measurement parameters; S2: determining the frequency segmentation point; S3: dividing the measured frequency range into two parts according to the frequency segmentation point, using a signal generator and a high-voltage amplifier as power supplies for the frequency points at and below the segmentation point, and using a capacitance variable frequency power supply and a high-frequency transformer as power supplies for the frequency band above the segmentation point; S4: measuring from the highest frequency point to the frequency segmentation point, and then replacing the power supply, measuring from the frequency segmentation point to the lowest frequency point; and using an oscilloscope to obtain the test voltage waveform and response current waveform of each frequency point; S5: based on the discrete time domain test voltage waveform and response current waveform, determine the dielectric characteristics of the insulation of the electrical equipment. The present invention can realize broadband measurement of the dielectric response characteristics of high-voltage and large-capacity electrical equipment.

Description

Technical Field

[0001] The invention belongs to the field of electric power technology and relates to a method and system for measuring the broadband high-voltage dielectric response of electrical equipment insulation. Background Art

[0002] At present, dielectric response methods based on dielectric relaxation theory are widely used in the diagnosis of insulation status of electrical equipment, mainly including frequency domain dielectric spectroscopy, recovery voltage method, and polarization and depolarization current method. Among them, frequency domain dielectric spectroscopy has become a research hotspot because it can reflect the dielectric insulation status within a wide frequency band.

[0003] The frequency domain dielectric response method is usually used to evaluate the insulation status of electrical equipment. Voltages of different frequencies are applied to both ends of the equipment insulation, and the response current is measured. Then, the dielectric parameters are further calculated based on the amplitude and phase relationship of the test voltage and the response current. The resistive current of the insulation of electrical equipment is extremely small under the voltage of the power frequency and above, and it is mainly capacitive. Assuming that the test voltage is U, the voltage angular frequency is ω, and the equipment insulation capacitance is C, the response current I and the test power capacity S are:

[0004] I=UωC (1)

[0005] S=UI=U 2 ωC (2)

[0006] It can be seen from formula (1) that the response current increases with the increase of the test voltage amplitude, angular frequency and equipment capacitance, while the output current amplitude of most power amplifiers is limited to less than 20mA. For some large-capacitance test products or electrical equipment (such as transformers, capacitors, large-capacitance bushings, capacitive voltage transformers, etc.), their dielectric response characteristics can only be measured at low frequency or low voltage. The use of high-frequency transformers can solve the problem of insufficient power supply capacity under high frequency and high voltage, but high-frequency transformers are usually only used at frequencies above the power frequency, which makes it difficult to reflect the characteristics of wide-band measurement of frequency-domain dielectric response and carry rich insulation status information.

[0007] It can be seen that the frequency domain dielectric response method can effectively evaluate the insulation state of electrical equipment. Although the existing dielectric response measurement is limited by the power supply capacity and is mostly measured at a low voltage of 200V peak, a small number of dielectric response instruments with power amplifiers can achieve high voltage measurement, but the measurement frequency band is relatively narrow. For actual power equipment, measuring dielectric response at low voltage has the following disadvantages: (1) For most high-voltage equipment, since its insulation is generally thick, the dielectric response current at low voltage is extremely small, which is very susceptible to electromagnetic interference in the environment, causing result deviation; (2) It is difficult to detect subtle defects in the dielectric during low-voltage measurement; (3) Many studies have shown that the dielectric response of the insulation of actual electrical equipment is voltage-dependent. The existing low-voltage measurement voltage is too different from the equipment operating voltage, and the measured dielectric parameters cannot reflect the insulation state of the equipment at the actual operating voltage. At the same time, the biggest advantage of the frequency domain dielectric response method over the time domain method is that the measurement frequency band is wide and carries rich insulation status information. However, the existing high-voltage narrowband measurement will lose the original advantages of the frequency domain dielectric response method. Specifically, there are the following disadvantages: (1) the frequency domain dielectric response measurement voltage is low, and the difference between the dielectric parameters and the actual operating voltage is too large; (2) the high-voltage frequency domain dielectric response measurement frequency band is narrow, which reflects insufficient insulation status information.

[0008] In the published Chinese patent "Electric Power Equipment High Voltage Time-Frequency Domain Dielectric Response Characteristics Measurement System and Method", a high voltage dielectric response measurement method suitable for electrical equipment insulation diagnosis is proposed, which uses a power amplifier to generate high voltage to measure the dielectric response characteristics of the equipment, but due to the equipment capacity limitation, it can only achieve a maximum of 70Hz. In the context of the new power system, the content of high-order harmonics in the system is increasing, and the harm of high-order harmonics to the insulation medium of the equipment cannot be ignored. Therefore, it is very important to extract the high-frequency dielectric response characteristics of the medium. Therefore, a broadband high-voltage dielectric response method is urgently needed to solve this problem. Summary of the invention

[0009] In view of this, the purpose of the present invention is to provide a method and system for measuring the wide-band, high-voltage dielectric response of electrical equipment insulation, which solves the problem of narrow measurement bandwidth of existing measurement methods due to power supply capacity limitations through frequency segmentation and power supply complementation, thereby realizing wide-band measurement of high-voltage dielectric parameters (wide-band dielectric parameters can fully reflect the insulation information of electrical equipment) and reducing measurement errors.

[0010] In order to achieve the above object, the present invention provides the following technical solutions:

[0011] A method for measuring the broadband high-voltage dielectric response of electrical equipment insulation is provided, which realizes broadband high-voltage dielectric response measurement in the mHz to kHz frequency band by adopting frequency segmentation and power supply complementation. The method specifically comprises the following steps:

[0012] S1: Determine the measurement parameters, including voltage effective value, frequency range and measurement frequency points, etc.;

[0013] S2: Determine the frequency segmentation point;

[0014] S3: The measured frequency range is divided into two parts according to the frequency segmentation point. The frequency points at and below the segmentation point use a signal generator and a high-voltage amplifier as the power supply, and the frequency band above the segmentation point uses a variable frequency power supply and a high-frequency transformer as the power supply;

[0015] S4: When measuring, start from the highest frequency point, measure from the highest frequency point to the frequency segmentation point, and use a variable frequency power supply and a high-frequency transformer as the power supply; when the frequency segmentation point is to be measured, replace the power supply with a signal generator and a high-voltage amplifier combined output voltage, and measure from the frequency segmentation point to the lowest frequency point in turn; and use an oscilloscope to obtain the test voltage waveform and response current waveform of each frequency point;

[0016] S5: The computer equipment determines the dielectric spectrum characteristics of the insulation of the electrical equipment based on the discrete time domain test voltage waveform and the response current waveform.

[0017] Further, in step S2, the frequency segmentation point is determined, specifically including: calculating the output frequency upper limit f of the high-voltage amplifier according to the voltage amplitude, the nameplate capacitance of the electrical equipment, and the output current constraint of the high-voltage amplifier. m , and take the nearest frequency point downward as the frequency segmentation point;

[0018]

[0019] Among them, I smax is the maximum continuous output current of the high-voltage amplifier, C is the nameplate capacitance of the electrical equipment, and U is the effective value of the measured voltage; the frequency segmentation point needs to be selected to be less than the upper limit of the output frequency f m , and the closest measurement frequency point.

[0020] Further, step S4 specifically includes the following steps:

[0021] S41: The measurement starts from the highest frequency point. The combined output voltage of the variable frequency power supply and the high frequency transformer acts on the high voltage electrode of the electrical equipment. The oscilloscope obtains the test voltage waveform through the high voltage probe. The end screen of the electrical equipment is connected to the ground potential through the sampling resistor. The oscilloscope obtains the response current waveform through the sampling resistor. 10 groups of voltage and current waveforms are collected continuously. The measurement of the first frequency point is completed in this way. Then the power is turned off and the high voltage electrode of the electrical equipment is short-circuited to the ground potential for 5 minutes. The measurement of the next frequency point begins.

[0022] S42: Repeat step S41 to measure from the highest frequency point to the frequency segmentation point in turn; when the frequency segmentation point is to be measured, the power supply is replaced with the combined output voltage of the signal generator and the high-voltage amplifier, and the oscilloscope obtains the test voltage waveform through the high-voltage probe; one end of the insulation of the electrical equipment is connected to the high-voltage amplifier, and the other end is connected to the ground potential through a sampling resistor, and the oscilloscope obtains the response current waveform through the sampling resistor; 10 groups of voltage and current waveforms are continuously collected; after each frequency point is measured, turn off the power supply, short-circuit the high-voltage electrode of the electrical equipment to the ground potential for 5 minutes, and start measuring the next frequency point; measure from the frequency segmentation point to the lowest frequency point in turn.

[0023] Further, in step S5, the dielectric spectrum characteristics of the insulation of the electrical equipment are determined, specifically including: the computer device synchronously performs Fourier transform on the 10 sets of test voltage waveforms and response current waveforms collected at each frequency point f, and extracts the amplitude U of the test voltage fundamental wave mi and phase θ Ui , the fundamental amplitude of the response current I mi and phase θ Ii ; Based on the above parameters, the dielectric spectrum characteristics are calculated as follows:

[0024]

[0025]

[0026]

[0027] Where C′ is the real part of the complex capacitance, C″ is the imaginary part of the complex capacitance, and tanδ is the dielectric loss factor.

[0028] The beneficial effects of the present invention are:

[0029] (1) The present invention solves the output current limitation of the high-voltage amplifier and the output frequency limitation of the high-frequency transformer by means of frequency segmentation and power supply complementation, and realizes the broadband measurement of the high-voltage dielectric response. The broadband dielectric parameters can fully reflect the insulation information of the electrical equipment.

[0030] (2) The test voltage used in the present invention is close to the actual operating voltage of the equipment, which can better reflect the insulation status of the equipment under actual operating conditions and improve the accuracy of insulation status assessment.

[0031] (3) The present invention collects the same set of data multiple times, extracts the fundamental frequency component by synchronous Fourier decomposition of voltage and current, calculates the dielectric parameters and takes the average value, thereby solving the problems of measurement error and randomness.

[0032] (4) The present invention improves the anti-interference capability of dielectric parameter measurement of high voltage and large capacitance equipment and improves the accuracy.

[0033] (5) The broadband high-voltage dielectric response method of the present invention is more sensitive to the diagnosis of equipment insulation status and can detect early and subtle insulation defects and deal with them early.

[0034] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0036] Figure 1 This is a flow chart of the method for measuring the broadband high-voltage dielectric response of electrical equipment insulation according to the present invention;

[0037] Figure 2 This is a schematic diagram of the structure of the dielectric response measurement system for electrical equipment;

[0038] Figure 3 It is the test voltage and response current waveform;

[0039] Figure 4 Calculation results of dielectric parameters of electrical equipment at different frequencies. DETAILED DESCRIPTION

[0040] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0041] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0042] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is 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 operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0043] See also Figure 1 to Figure 4 The present invention provides a method for measuring the broadband high-voltage dielectric response of insulation of electrical equipment. By adopting frequency segmentation and power supply complementation, broadband high-voltage dielectric response measurement in the millihertz to kilohertz frequency band can be achieved, which solves the shortcomings of low voltage or narrow frequency band in traditional dielectric response measurement and can accurately obtain dielectric response information of electrical equipment.

[0044] Figure 1 This is a flow chart of the method for measuring the broadband high-voltage dielectric response of electrical equipment insulation provided in this embodiment (taking the bushing as an example), which mainly includes the following steps:

[0045] (1) Determine the measurement parameters, including voltage effective value, frequency range, measurement frequency points, etc.

[0046] (2) Determine the frequency segmentation point. Based on the voltage amplitude, bushing nameplate capacitance, and output current constraint of the high-voltage amplifier in the first step, calculate the upper limit of the high-voltage amplifier output frequency f m , and take the nearest frequency point downward as the frequency segmentation point;

[0047]

[0048] In the formula, I smax is the maximum continuous output current of the high-voltage amplifier, C is the nameplate capacitance of the bushing, and U is the effective value of the measured voltage. The frequency segmentation point should be selected to be less than the upper limit of the output frequency f m The Matsusada AMP-20B20 high-voltage amplifier used in this embodiment has a maximum output current of ±20mA and can measure a maximum capacitance of 450pF at a power frequency of 10kV, which meets the dielectric response measurement requirements of most capacitive bushings.

[0049] (3) Divide the measured frequency range into two parts according to the frequency segmentation point calculated in step 2. The frequency points at and below the segmentation point use signal generators and high-voltage amplifiers as power supplies, and the frequency bands above the segmentation point use variable frequency power supplies and high-frequency transformers as power supplies. The two sets of power supply equipment complement each other. The measurement wiring diagram is as follows: Figure 2 As shown. When measuring, start from the highest frequency point. First, the variable frequency power supply and high frequency transformer combined output voltage acts on the central guide rod of the bushing. The oscilloscope obtains the waveform of the test voltage through the high-voltage probe. The end screen of the bushing is connected to the ground potential through the sampling resistor. The oscilloscope obtains the response current waveform through the sampling resistor. 10 groups of voltage and current waveforms are collected continuously. In this way, the measurement of the first frequency point is completed, and then the power supply is turned off, and the central guide rod of the bushing is short-circuited with the ground potential for 5 minutes. Start measuring the next frequency point.

[0050] (4) Repeat step (3) from the highest frequency point to the frequency segmentation point. When measuring the frequency segmentation point, the power supply should be replaced with the signal generator and high-voltage amplifier combined output voltage, and the oscilloscope obtains the waveform of the test voltage through the high-voltage probe; one end of the insulation of the electrical equipment is connected to the high-voltage amplifier, and the other end is connected to the ground potential through a sampling resistor, and the oscilloscope obtains the response current waveform through the sampling resistor; 10 sets of voltage and current waveforms are collected continuously; after each frequency point is measured, turn off the power supply, short-circuit the center guide rod of the bushing with the ground potential for 5 minutes, and start measuring the next frequency point; measure from the frequency segmentation point to the lowest frequency point in turn.

[0051] (4) The computer equipment determines the dielectric spectrum characteristics of the electrical equipment insulation based on the discrete time domain test voltage waveform and response current waveform. The computer equipment synchronously performs Fourier transform on the 10 sets of test voltage and response current waveforms collected at each frequency point, and extracts the amplitude U of the test voltage fundamental wave. mi and phase θ Ui , the fundamental amplitude of the response current I mi and phase θ Ii ; Based on the above parameters, the dielectric parameters are calculated as shown in the following formula;

[0052]

[0053]

[0054]

[0055] Where C′ is the real part of the complex capacitance, C″ is the imaginary part of the complex capacitance, and tanδ is the dielectric loss factor.

[0056] The present invention proposes to adopt the method of frequency segmentation and power supply complementation to realize the broadband measurement of high-voltage dielectric parameters of electrical equipment. The high-voltage amplifier is limited by capacity and cannot measure the high-frequency response of large-capacitance test products. The variable-frequency power supply can only output voltages at or above the industrial frequency. Through frequency segmentation, the advantages of two sets of power supplies can be utilized to realize high-voltage and broadband measurement of dielectric parameters of electrical equipment, solving the shortcomings of the original measurement method with narrow measurement bandwidth due to power supply capacity limitation. The broadband dielectric parameters can reflect more insulation information.

[0057] In the method of the present invention, the same group of data is collected multiple times, the voltage and current are synchronously Fourier decomposed to extract the fundamental frequency component, and the average value is taken after the dielectric parameters are calculated to solve the problems of measurement error and randomness.

[0058] Compared with the traditional measurement method, the measurement method proposed in the present invention has the following advantages: (1) the test voltage is higher, the response current is larger, and the anti-interference ability is stronger; (2) the high test voltage makes it easier to find subtle and initial defects in the insulation of electrical equipment and deal with them early; (3) the test voltage is close to the actual operating voltage of the equipment and can better reflect the insulation status of the equipment under actual operating conditions.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for measuring the broadband high-voltage dielectric response of electrical equipment insulation. It is characterized in that The high voltage, large capacity and wide frequency dielectric response characteristics of electrical equipment in the mHz to kHz frequency band are measured by adopting the test power supply frequency segmentation and power supply complementation method; the method specifically includes the following steps: S1: Determine the measurement parameters, including voltage effective value, frequency range and measurement frequency point; S2: Determine the frequency segmentation point, specifically including: Calculate the upper limit of the high-voltage amplifier output frequency f according to the voltage amplitude, the nameplate capacitance of the electrical equipment, and the output current constraint of the high-voltage amplifier m , and take the nearest frequency point downward as the frequency segmentation point; Among them, I smax is the maximum continuous output current of the high-voltage amplifier, C is the nameplate capacitance of the electrical equipment, and U is the effective value of the measured voltage; S3: The measured frequency range is divided into two parts according to the frequency segmentation point. The frequency points at and below the segmentation point use a signal generator and a high-voltage amplifier as the power supply, and the frequency band above the segmentation point uses a variable frequency power supply and a high-frequency transformer as the power supply; S4: When measuring, start from the highest frequency point, measure from the highest frequency point to the frequency segmentation point, and use a variable frequency power supply and a high-frequency transformer as the power supply; when the frequency segmentation point is to be measured, replace the power supply with a signal generator and a high-voltage amplifier combined output voltage, and measure from the frequency segmentation point to the lowest frequency point in turn; and use an oscilloscope to obtain the test voltage waveform and response current waveform of each frequency point; S5: Determine the dielectric spectrum characteristics of the insulation of the electrical equipment based on the discrete time domain test voltage waveform and the response current waveform.

2. The method for measuring the broadband high-voltage dielectric response of electrical equipment insulation according to claim 1, It is characterized in that Step S4 specifically includes the following steps: S41: The measurement starts from the highest frequency point. The combined output voltage of the variable frequency power supply and the high frequency transformer acts on the high voltage electrode of the electrical equipment. The oscilloscope obtains the test voltage waveform through the high voltage probe. The end screen of the electrical equipment is connected to the ground potential through the sampling resistor. The oscilloscope obtains the response current waveform through the sampling resistor. 10 groups of voltage and current waveforms are collected continuously. The measurement of the first frequency point is completed in this way. Then the power is turned off and the high voltage electrode of the electrical equipment is short-circuited to the ground potential for 5 minutes. The measurement of the next frequency point begins. S42: Repeat step S41 to measure from the highest frequency point to the frequency segmentation point in turn; when the frequency segmentation point is to be measured, the power supply is replaced with the combined output voltage of the signal generator and the high-voltage amplifier, and the oscilloscope obtains the test voltage waveform through the high-voltage probe; one end of the insulation of the electrical equipment is connected to the high-voltage amplifier, and the other end is connected to the ground potential through a sampling resistor, and the oscilloscope obtains the response current waveform through the sampling resistor; 10 groups of voltage and current waveforms are continuously collected; after each frequency point is measured, turn off the power supply, short-circuit the high-voltage electrode of the electrical equipment to the ground potential for 5 minutes, and start measuring the next frequency point; measure from the frequency segmentation point to the lowest frequency point in turn.

3. The method for measuring the broadband high-voltage dielectric response of electrical equipment insulation according to claim 1, It is characterized in that In step S5, the dielectric spectrum characteristics of the insulation of the electrical equipment are determined, specifically including: synchronously performing Fourier transform on the 10 sets of test voltage waveforms and response current waveforms collected at each frequency point f, and extracting the amplitude U of the test voltage fundamental wave mi and phase θ Ui , the fundamental amplitude of the response current I mi and phase θ Ii ; Based on the above parameters, the dielectric spectrum characteristics are calculated as follows: Among them, C ′ is the real part of the complex capacitance, C″ is the imaginary part of the complex capacitance, and tanδ is the dielectric loss factor.

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