A system and method for testing charge of oil-paper insulation under polarity-reversing electric field

Abstract

The present application relates to the technical field of charge test of oil-paper insulation of converter transformer, and particularly relates to a system and method for charge test of oil-paper insulation under polarity-reversed electric field, determining the number of time points for charge distribution analysis within the polarity-reversed time, determining the pulse period and pulse number of a test pulse signal triggered by an arbitrary pulse signal based on the principle of the electrical voice pulse method, testing the space charge of an oil-paper insulation sample under polarity-reversed electric field, triggering the collection of the space charge waveform and polarization voltage amplitude at the rising edge of the test pulse signal in the polarity-reversed process, applying different temperature fields to the oil-paper insulation sample under polarity-reversed electric field, and repeatedly testing the space charge. The measurement of the charge waveform at any number of time points in the reversal process is realized, the problem of rapid measurement of the charge waveform in the reversal process is solved, and the real-time recording of the charge transient characteristics is ensured.

Description

Technical Field

[0001] This invention relates to the field of converter transformer oil-paper insulation charge testing technology, specifically to an oil-paper insulation charge testing system and method under a polarity reversal electric field. Background Technology

[0002] As a core component of DC transmission, the safety of converter transformers is crucial for the stable operation of DC transmission. However, with the development of high-voltage DC transmission, insulation problems in converter transformers have become increasingly apparent, with more than half of converter transformer failures occurring on the valve side. Compared to traditional AC transformers, the valve side of a converter transformer, in addition to AC electric fields, also bears harmonic electric fields, DC electric fields, and polarity reversal electric fields. Especially under polarity reversal electric fields, the amplitude and polarity of the electric field change rapidly in a short period of time, causing transient processes in the insulation and making it more prone to insulation failure. As the main insulation form for valve-side windings, oil-paper insulation needs to be studied for its insulation characteristics under polarity reversal voltage.

[0003] Among various insulation characteristics, space charge and partial discharge have long been considered important causes of insulation degradation and even failure. During the long-term operation of converter transformers, space charge accumulates in the internal oil-paper insulation. During polarity reversal, this space charge becomes trapped within the insulation, distorting the local electric field after the reversal and thus exacerbating discharge, enhancing insulation degradation, and even leading to insulation failure. Therefore, to deeply understand the degradation mechanism of converter transformers, studying the characteristics of charge trapping under polarity reversal conditions and its impact on discharge is of significant scientific importance and engineering application value.

[0004] Current space charge experimental research only focuses on the charge accumulation characteristics under DC before and after polarity reversal. Due to limitations in testing technology, it is difficult to conduct relevant research on the reversal process, and it is impossible to test the charge transient process during polarity reversal. The dynamic characteristics of oil paper charge during polarity reversal are still unclear. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a system for testing the charge on oil-paper insulation under a polarity-reversed electric field, comprising:

[0006] Function generator: By changing the rise time of the control signal through an arbitrary waveform generator and changing the RC time constant, a voltage output signal with the required rise time can be generated.

[0007] Test pulse matching circuit: Generates a sequence of pulses with a time interval Δt based on the signal rise time. Any pulse signal of the sequence of pulses triggers the generation of several test pulse signals with the same period. The test pulse signals are used to trigger the high-voltage pulse power supply.

[0008] High-voltage pulse power supply: used to load test pulse signals to generate rapid test pulses, and to achieve precise matching of polarity reversal voltages;

[0009] Polarization voltage power supply: used to receive voltage output signals and generate polarization reversal voltage;

[0010] Charge testing unit: Apply test pulses to the oil-paper insulation sample under polarity reversal electric field to excite the oil-paper insulation to generate charge acoustic wave signals;

[0011] Temperature regulator: used to apply an adjustable temperature field to oil-paper insulating samples under a polarity reversal electric field;

[0012] Oscilloscope: Used to acquire the synchronization signal of space charge and polarization voltage, and to store the space charge waveform and the corresponding polarization voltage amplitude during polarity reversal.

[0013] The test pulse matching circuit is composed of a first pulse triggering circuit, a second pulse triggering circuit, and an opto-isolator connected in sequence; the first pulse triggering circuit is used to generate a sequence of pulses with a certain time interval Δt; the second pulse triggering circuit generates a number of test pulse signals with the same period based on any pulse signal of the sequence of pulses; the opto-isolator is used to perform opto-isolation to shield electromagnetic interference.

[0014] The polarization voltage power supply includes a power amplifier for amplifying the voltage output signal received from the function generator.

[0015] In one specific implementation, the charge testing unit applies a fast test pulse and a polarity reversal voltage, which are coupled to the high-voltage electrode of the charge testing unit through a numerically matched capacitor and resistor; the charge testing unit is also provided with a ground electrode, which is grounded.

[0016] The oscilloscope uses sequential sampling, which is triggered by the rising edge of a sequence of pulses. The sequential sampling storage depth of the oscilloscope is set to be greater than or equal to the number of test pulse signals within the polarity reversal time.

[0017] Another aspect of the present invention provides a method for testing the charge on oil-paper insulation under a polarity-reversed electric field, the method comprising the following steps:

[0018] Determine the number of time points during which charge distribution analysis needs to be performed within the polarity reversal time, and calculate the time interval Δt of the sequence pulses based on the polarization voltage polarity reversal time.

[0019] Based on the principle of electroacoustic pulse method, the pulse period and number of pulses of the test pulse signal triggered by any pulse signal are determined according to the test time interval of the sequence pulse;

[0020] Based on the dynamic characteristics of oil-paper insulation, the equivalent resistance and equivalent capacitance of oil-paper insulation are obtained, and the voltage division equation under the polarity reversal electric field is used to determine the polarization voltage.

[0021] A test pulse signal is applied to generate a fast test pulse. The fast test is coupled with the polarization voltage to test the space charge of the oil-paper insulation sample under the polarity reversal electric field.

[0022] During the polarity reversal process, the space charge waveform and polarization voltage amplitude at the rising edge of the test pulse signal are collected, and these values ​​are measured and stored in real time.

[0023] Different temperature fields were applied to the oil-paper insulation sample under the polarity reversal electric field, and the space charge test was repeated.

[0024] The determination of the polarization voltage includes establishing an equivalent circuit for the oil-paper insulation based on the oil-paper insulation structure model; obtaining the equivalent resistance and equivalent capacitance with dielectric constant based on the equivalent circuit; calculating the voltage divider equation for the oil-paper insulation under the polarity reversal electric field based on the obtained equivalent resistance and equivalent capacitance; and determining the expression for the polarity reversal polarization voltage based on the voltage divider equation.

[0025] In a specific implementation, the polarity reversal electric field begins at the moment corresponding to the first test pulse signal, which begins to excite the oil-paper insulation sample to generate charge acoustic wave signals.

[0026] The method for testing the charge of oil-paper insulation under a polarity reversal electric field also includes summing and averaging the measured space charge waveform and polarization voltage amplitude to obtain the charge distribution and corresponding polarization voltage amplitude at each time point during the polarization reversal process.

[0027] Beneficial effects: This invention solves the problem of real-time matching between space charge waveform and polarization electric field by designing a test pulse matching circuit. Furthermore, by adjusting the time interval of the output sequence pulses through the test pulse matching circuit, and based on the electroacoustic pulse method, it realizes the measurement of charge waveforms at any multiple time points during polarity reversal, solving the problem of rapid charge waveform measurement during reversal and ensuring the real-time recording of charge transient characteristics. At the same time, by using a temperature regulator to simulate the temperature data of the converter transformer during actual operation, it realizes rapid and accurate measurement of charge dynamic characteristics during polarity reversal of oil-paper insulation. Attached Figure Description

[0028] Figure 1 Flowchart of the method for testing the charge on oil-paper insulation under a polarity-reversed electric field;

[0029] Figure 2 This is a schematic diagram of the system structure of the present invention;

[0030] Figure 3 This is a structural model of the oil-paper insulation of the present invention;

[0031] Figure 4 This is the equivalent circuit diagram of the oil-paper insulation of the present invention;

[0032] Figure 5 This is a schematic diagram illustrating the matching between the test pulse and the polarity reversal voltage.

[0033] Figure 6 The graph shows the measured data and post-processed data from the oscilloscope. Detailed Implementation

[0034] The preferred embodiments are described in detail below with reference to the accompanying drawings.

[0035] Example

[0036] See Figure 2 The oil-paper insulation charge testing system under a polarity-reversed electric field of this application includes a function generator, a polarization voltage power supply, a test pulse matching circuit, a high-voltage pulse power supply, a charge testing unit, a temperature regulator, and an oscilloscope. The output terminal of the function generator is connected to both the test pulse matching circuit and the polarization voltage power supply. The output terminal of the test pulse matching circuit is connected to the input terminal of the high-voltage pulse power supply. The output terminals of the high-voltage pulse power supply and the polarization voltage power supply are respectively coupled to the high-voltage electrode of the charge testing unit by numerically matched capacitors and resistors. The charge testing unit is equipped with a grounding electrode, which is grounded. The temperature regulator is connected to the charge testing unit and can apply an adjustable temperature field to the oil-paper insulation sample of the charge testing unit.

[0037] Meanwhile, the acquisition channels of the oscilloscope are connected to the charge testing unit, the test pulse matching circuit, and the function generator, respectively.

[0038] The function generator uses the AFG31000 series arbitrary wave function generator, which controls the rise time of the signal by changing the RC time constant to generate a voltage output signal with the required rise time.

[0039] The test pulse matching circuit consists of a first pulse trigger circuit, a second pulse trigger circuit, and an opto-isolator connected in sequence. The first and second pulse trigger circuits are composed of a zero-crossing comparator circuit and a converter connected in sequence. The first pulse trigger circuit generates a sequence of pulses with a certain time interval Δt. The second pulse trigger circuit generates several test pulse signals with the same period based on any pulse signal from the sequence of pulses. The opto-isolator is used for opto-isolation and shielding against electromagnetic interference, preventing electromagnetic interference signals caused by the operation of the high-voltage pulse power supply from backflowing into the test pulse matching circuit and causing false triggering. The test pulse signal triggers the high-voltage pulse power supply switch through the opto-isolator, and finally outputs a fast test pulse to be applied to the charge testing unit.

[0040] The high-voltage pulse power supply is used to load the test pulse signal to generate a fast test pulse, and the same polarity reverse polarization voltage is used for precise matching.

[0041] The polarization voltage power supply includes a power amplifier, which can receive the voltage output signal from the function generator and amplify it to generate a polarity reversal voltage.

[0042] The high-voltage electrode of the charge testing unit applies a rapid test pulse and a polarity reversal voltage, and uses the test pulse to excite the oil paper insulation to generate a charge acoustic signal.

[0043] The oscilloscope used is the LeCroy HD06054, which employs sequential sampling. It uses the rising edge of a sequence of pulses as the trigger signal for acquisition, and the oscilloscope channels acquire the space charge signal and voltage output signal at that moment respectively. At the same time, the oscilloscope's sequential sampling storage depth is set to be greater than or equal to the number of test pulse signals within the polarity reversal time, which can store the space charge waveform and the corresponding polarization voltage amplitude during the polarity reversal process.

[0044] In this embodiment, see Figure 1 The present application provides a method for testing the charge on oil-paper insulation under a polarity-reversed electric field, which includes the following steps:

[0045] (1) Determine the number of time points during which charge distribution analysis needs to be performed within the polarity reversal time, and calculate the time interval Δt of the sequence pulses based on the polarization voltage polarity reversal time;

[0046] Given It is a reversal of the time interval. It is the set of positive real numbers, H is a positive integer, and it determines the number of time points during the polarity reversal time that require charge distribution analysis, denoted by T. pr Taking 60s as an example, assuming that the charge distribution at 7 time points needs to be analyzed, and that all time points are evenly divided into the entire polarity reversal time, the test time interval Δt = 10s can be calculated.

[0047] (2) Based on the principle of electroacoustic pulse method, determine the pulse period and number of pulses of the test pulse signal triggered by any pulse signal according to the test time interval of the sequence pulse;

[0048] Based on the principle of the electroacoustic pulse method, each rising edge of the test pulse can excite the charge acoustic wave signal at that moment. Therefore, using the rising edge of the sequence pulse as the trigger signal of the oscilloscope triggers the oscilloscope to acquire the space charge signal at that moment, which can realize the reversal of the time interval T. pr Acquisition of time point charge signals within the time frame.

[0049] The noise error can be effectively eliminated by averaging 100 sets of charge data within 0.5s. Therefore, a second set of pulse triggering circuits is used to generate 100 test pulse signals within 0.5s for each pulse in the sequence pulse.

[0050] (3) Based on the dynamic characteristics of oil paper insulation, the equivalent resistance and equivalent capacitance of oil paper insulation are obtained, and the voltage division equation under the polarity reversal electric field is used to determine the polarization voltage.

[0051] like Figure 3-4 As shown, based on the oil-paper insulation structure model, an equivalent circuit for oil-paper insulation is established. The thicknesses of the transformer oil and the insulating paperboard are given as d1 and d2, respectively, the dielectric constants of the transformer oil and the insulating paperboard are ε1 and ε2, respectively, and the resistance values ​​of the transformer oil and the insulating paperboard are r1 and r2, respectively.

[0052] Based on the equivalent circuit of oil-paper insulation, the following equivalent resistances R1 and R2 and equivalent capacitances C1 and C2 with dielectric constants are obtained, where the equivalent capacitances of transformer oil and insulating paperboard are respectively expressed by the following equations:

[0053] C1 = ε1d1, C2 = ε2d2.

[0054] The equivalent resistances of the transformer oil and the insulating paperboard are R1 = r1 and R2 = r2, respectively.

[0055] Based on the obtained equivalent capacitance and equivalent resistance, the voltage division E1(t) and E2(t) of the transformer oil and insulating paperboard under the polarity reversal electric field are calculated. The calculation equations are as follows:

[0056]

[0057] Based on the voltage divider equations for transformer oil and insulating paperboard, the expression for the polarity reversal voltage is determined as follows:

[0058]

[0059] (4) Load the test pulse signal to generate a fast test pulse, couple the fast test with the polarization voltage, and test the space charge of the oil paper insulation sample under the polarity reversal electric field;

[0060] The function generator controls the rise time of the signal by changing the RC time constant, generating a polarization voltage output signal, which is then applied to the polarization voltage power supply. Simultaneously, the voltage output signal is acquired by the test pulse matching circuit and, after passing through the first set of pulse triggering circuits, outputs a sequence of pulses with an interval of Δt. Each pulse in the sequence triggers the second set of pulse triggering circuits to generate 100 test pulse signals with a period of 0.005s. Finally, these signals are applied to the high-voltage pulse power supply through an opto-isolator. The high-voltage pulse power supply generates a fast test pulse corresponding to its frequency. The polarization voltage power supply receives the output signal from the function generator, amplifies it through an internal power amplifier, and generates a polarity reversal polarization voltage. The charge testing unit receives the fast test pulse and the polarity reversal polarization voltage, which are applied to the high-voltage electrodes of the charge testing unit via numerically matched capacitors and resistors, respectively, generating a polarization reversal electric field. The start of the polarization electric field reversal corresponds to the first test pulse signal, initiating the excitation of the sample to generate a charge acoustic wave signal.

[0061] (5) Trigger the acquisition of the space charge waveform and polarization voltage amplitude at the rising edge of the test pulse signal during the polarity reversal process, and measure and store the above values ​​in real time.

[0062] The test pulse matching circuit output signal, i.e., the rising edge of the test pulse signal triggers the oscilloscope to acquire the space charge waveform at that moment, and at the same time triggers the oscilloscope to acquire the polarization voltage amplitude at that moment, so as to realize the real-time continuous measurement and storage of the space charge waveform and its corresponding polarization voltage amplitude during the polarity reversal process.

[0063] (6) Apply different temperature fields to the oil-paper insulation sample under the polarity reversal electric field and repeat the space charge test;

[0064] The temperature of the oil-paper insulation sample in the charge testing unit is controlled by a temperature regulator. Different temperature values ​​are adjusted to place it in different temperature fields to simulate the temperature data of the converter transformer during actual operation. Based on different temperature values, steps one to five are repeated to obtain the space charge signal of the oil-paper insulation sample at different temperatures and time points.

[0065] (7) Perform noise reduction and mean averaging on the acquired signals to obtain valid values.

[0066] By averaging 100 sets of charge data at each test interval to obtain the effective value, noise errors can be effectively eliminated. Matlab software is used to sum and average the acquired space charge waveforms and polarization voltage amplitudes to obtain the charge distribution and corresponding polarization voltage amplitude at each time point during the reversal process.

[0067] like Figure 5 As shown in the figure, the prior art and the present invention illustrate the matching trigger diagram of the test pulse and polarity reversal voltage during the reversal process. The former is the matching trigger diagram of the prior art test pulse and polarization voltage, which only realizes the change of charge distribution under DC electric field before and after polarity reversal, and does not clearly understand the dynamic characteristics of the gradual change of charge during polarity reversal. The latter is the matching trigger diagram of the present invention test pulse and polarization voltage, which realizes the matching of the test pulse and polarity reversal voltage during the reversal process by designing a test pulse matching circuit, and at the same time realizes the measurement of space charge waveform at any number of time points during polarity reversal.

[0068] refer to Figure 6 The image shows the measured data before and after charge testing when the reversal time is 30 seconds and the number of time points for analyzing charge distribution is 60. The upper image shows the polarization voltage and charge signals measured by 6000 rapid pulse triggers before processing. Only the polarization voltage amplitude and the upper and lower limits of the charge signal at that moment can be read from this image. After averaging every 100 waveforms, the polarization voltage and charge signal images at each 0.5-second time point are obtained below. Each image can read the polarization voltage amplitude and the charge distribution information inside the sample at that moment. This invention only selects the charge distribution at a few key time points for display.

[0069] It should be noted that the exemplary embodiments mentioned in this invention describe methods or systems based on a series of steps or apparatus. However, this invention is not limited to the order of the steps described above; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0070] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations, additions, or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A system for testing the charge on oil-paper insulation under a polarity-reversed electric field, characterized in that, The system includes: Function generator: By changing the rise time of the control signal through an arbitrary waveform generator and changing the RC time constant, a voltage output signal with the required rise time can be generated. Test pulse matching circuit: Generates a sequence of pulses with a time interval Δt based on the signal rise time. Any pulse signal of the sequence of pulses triggers the generation of several test pulse signals with the same period. The test pulse signals are used to trigger the high-voltage pulse power supply. High-voltage pulse power supply: used to load test pulse signals to generate rapid test pulses, and to achieve precise matching of polarity reversal voltages; Polarization voltage power supply: used to receive voltage output signals and generate polarization reversal voltage; Charge testing unit: Apply test pulses to the oil-paper insulation sample under polarity reversal electric field to excite the oil-paper insulation to generate charge acoustic wave signals; Temperature regulator: used to apply an adjustable temperature field to oil-paper insulating samples under a polarity reversal electric field; Oscilloscope: Used to acquire the synchronization signal of space charge and polarization voltage, and to store the space charge waveform and the corresponding polarization voltage amplitude during polarity reversal.

2. The oil-paper insulation charge testing system under a polarity reversal electric field according to claim 1, characterized in that, The test pulse matching circuit is composed of a first pulse trigger circuit, a second pulse trigger circuit, and an opto-isolator connected in sequence; the first pulse trigger circuit is used to generate a sequence of pulses with a certain time interval Δt. The second pulse triggering circuit generates several test pulse signals with the same period based on any pulse signal of the sequence pulse; The opto-isolator is used for opto-isolation and shielding against electromagnetic interference.

3. The oil-paper insulation charge testing system under a polarity reversal electric field according to claim 1, characterized in that, The polarization voltage power supply includes a power amplifier for receiving the voltage output signal from the function generator and amplifying it.

4. The oil-paper insulation charge testing system under a polarity reversal electric field according to claim 1, characterized in that, The charge testing unit applies a fast test pulse and a polarity reversal voltage, which are coupled to the high-voltage electrode of the charge testing unit through numerically matched capacitors and resistors.

5. The oil-paper insulation charge testing system under a polarity reversal electric field according to claim 4, characterized in that, The charge testing unit is also equipped with a grounding electrode, which is grounded.

6. The oil-paper insulation charge testing system under a polarity reversal electric field according to claim 1, characterized in that, The oscilloscope uses sequential sampling, which is triggered by the rising edge of a sequence of pulses. The sequential sampling storage depth of the oscilloscope is set to be greater than or equal to the number of test pulse signals within the polarity reversal time.

7. A method for testing the charge on oil-paper insulation under a polarity-reversed electric field, characterized in that, The method includes the following steps: Determine the number of time points during which charge distribution analysis needs to be performed within the polarity reversal time, and calculate the time interval Δt of the sequence pulses based on the polarization voltage polarity reversal time. Based on the principle of electroacoustic pulse method, the pulse period and number of pulses of the test pulse signal triggered by any pulse signal are determined according to the test time interval of the sequence pulse; Based on the dynamic characteristics of oil-paper insulation, the equivalent resistance and equivalent capacitance of oil-paper insulation are obtained, and the voltage division equation under the polarity reversal electric field is used to determine the polarization voltage. A test pulse signal is applied to generate a fast test pulse. The fast test is coupled with the polarization voltage to test the space charge of the oil-paper insulation sample under the polarity reversal electric field. During the polarity reversal process, the space charge waveform and polarization voltage amplitude at the rising edge of the test pulse signal are collected, and these values ​​are measured and stored in real time. Different temperature fields were applied to the oil-paper insulation sample under the polarity reversal electric field, and the space charge test was repeated.

8. The method for testing the charge on oil-paper insulation under a polarity-reversed electric field according to claim 7, characterized in that, The determination of polarization voltage includes establishing an equivalent circuit for oil-paper insulation based on an oil-paper insulation structure model; obtaining the equivalent resistance and equivalent capacitance with dielectric constant based on the equivalent circuit; and calculating the voltage divider equation for oil-paper insulation under a polarity reversal electric field based on the obtained equivalent resistance and equivalent capacitance. Based on the voltage divider equation, determine the expression for the polarity reversal voltage.

9. The method for testing the charge on oil-paper insulation under a polarity-reversed electric field according to claim 7, characterized in that, The polarity reversal electric field begins at the moment corresponding to the first test pulse signal, which begins to excite the oil-paper insulation sample to generate charge acoustic signals.

10. The method for testing the charge on oil-paper insulation under a polarity-reversed electric field according to claim 7, characterized in that, It also includes summing and averaging the measured space charge waveform and polarization voltage amplitude to obtain the charge distribution and corresponding polarization voltage amplitude at each time point during the polarization reversal process.

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