A test method and platform for testing the insulation performance of a capacitive voltage transformer

Abstract

The application discloses a test method and platform for testing the insulation performance of a capacitive voltage transformer, a test loop is constructed by connecting a high-voltage test transformer, a current-limiting inductor, a measured capacitive voltage transformer, an isolation switch and a coupling capacitor in series, a high-frequency decay oscillation transient process generated by multiple reignitions of the contact of the isolation switch when operating the coupling capacitor is utilized, and the laboratory reproduction of the switching condition of the series compensation platform is realized; through two-stage processes of low-voltage debugging and rated-voltage formal testing, the safety of parameter setting is ensured, and the effective testing of the cumulative damage effect is realized; through real-time acquisition of transient response parameters to monitor the breakdown event and immediately stop operation when the breakdown event occurs, the instant perception of the insulation state and the protection of the equipment in the testing process are realized; through quantitative comparison and judgment of the insulation state parameters before and after the test, definite qualified judgment basis is provided for the grid connection of the series compensation platform side CVT, and the technical blank of the special testing in the field is filled.

Description

Technical Field

[0001] This application relates to the field of high-voltage electrical equipment technology, and in particular to a test method and platform for evaluating the insulation performance of capacitive voltage transformers. Background Technology

[0002] Capacitive voltage transformers (CVTs) are widely used voltage measurement devices in high-voltage transmission lines. Their function is to convert voltage signals from high-voltage lines into low-voltage signals usable by relay protection devices and measuring instruments. Ultra-high-voltage (UHV) transmission lines typically have large transmission capacities and long transmission distances. To improve transmission capacity and system stability, fixed series compensation devices (FSCs) are commonly used. In a series compensation system, disconnect switches and circuit breakers are used to switch between various operating modes of the compensation platform. The CVT is installed on the compensation platform side to monitor the voltage of the line and the compensation platform, and to provide voltage signals to relay protection devices. Therefore, the operational reliability of the CVT on the compensation platform side directly affects the safe and stable operation of the series compensation system and the flexible and reliable operation of UHV substations.

[0003] In power systems, the opening and closing of disconnecting switches are routine operations. However, unlike circuit breakers, disconnecting switches lack arc-extinguishing devices, and their contacts move relatively slowly. Under certain operating conditions, repeated breakdowns can occur between the contacts, resulting in transient overvoltages and currents. The amplitude, frequency, and waveform characteristics of these transients are closely related to the equipment type, circuit parameters, and layout. Normally, the transient overvoltages and currents generated by disconnecting switches in air-insulated switchgear (AIS) have lower frequencies than those in gas-insulated switchgear (GIS). However, when the circuit layout is compact and the operated capacitor is large, AIS can also generate high-amplitude, high-frequency transient overvoltages and currents.

[0004] In UHV series compensation projects, the capacitance to ground of the compensation platform typically reaches several thousand picofarads. The capacitance of the CVT installed on the compensation platform side is generally 5000pF or 10000pF, and the CVT is only about 20 meters away from the compensation platform. This circuit structure determines that high-frequency, high-amplitude pulse voltages and pulse currents will be generated during the operation of the disconnecting switch. Practical engineering experience shows that when the series compensation platform is switched on and off using a disconnecting switch, the rapid transient process caused by repeated breakdown between the disconnecting switch contacts will trigger high-amplitude, high-steepness, and high-frequency pulse currents. When these pulse currents flow through the adjacent CVT, they can cause insulation faults in the CVT. Such faults have occurred multiple times during the system commissioning phase of UHV substations, seriously affecting the energized switching of the series compensation platform and the flexible and reliable operation of the UHV substation.

[0005] Currently, in the insulation performance testing of CVTs before they are put into service, laboratories typically use an impulse voltage generator to apply a standard impulse waveform to the high-voltage terminals of the CVT. However, this testing method has significant limitations. First, the applied transient waveform is a preset standard waveform, which differs fundamentally from the actual high-frequency damped oscillation waveform in the field. Furthermore, existing engineering cases have shown that some CVTs, even after passing the standard impulse test, still experienced insulation failures in the field. Second, the number of impulses applied by this method is limited, making it difficult to simulate the cumulative impact effect of multiple reignitions in the field. More importantly, this testing method is not specifically designed for CVTs on the series compensation platform side under disconnector switching conditions, and cannot effectively simulate the transient stress conditions experienced by CVTs in actual operation.

[0006] It is evident that existing technologies lack a CVT insulation performance testing scheme capable of effectively simulating the actual transient operating conditions of the disconnecting switch switching series compensation platform under laboratory conditions. The CVT on the series compensation platform side lacks a dedicated testing test equivalent to actual field conditions before grid connection, resulting in a technological gap in verifying its insulation withstand capability. This technological gap has posed a substantial constraint on the safe commissioning and reliable operation of UHV series compensation projects.

[0007] Therefore, there is an urgent need to provide a CVT insulation performance assessment method and platform that can realistically simulate the transient operating conditions of series compensation platform switching under laboratory conditions, can apply a large number of transient impacts in a short time, and has flexible adjustable transient stress parameters, so as to fill the technical gap in the special assessment test of CVT before grid connection on the series compensation platform side. Summary of the Invention

[0008] The embodiments of this disclosure provide a test method and platform for evaluating the insulation performance of capacitive voltage transformers, thereby at least solving the technical problem in the prior art of lacking a special evaluation test scheme equivalent to the actual field working conditions before the CVT on the series compensation platform is connected to the grid.

[0009] According to one aspect of the present disclosure, a test method for assessing the insulation performance of a capacitive voltage transformer is provided, comprising: acquiring initial insulation state parameters of the capacitive voltage transformer under test; constructing a test circuit, the test circuit including a high-voltage test transformer, a current-limiting inductor, the capacitive voltage transformer under test, a disconnecting switch, and a coupling capacitor for simulating the capacitance to ground of a series compensation platform, connected in series; operating the disconnecting switch at a first voltage lower than a target test voltage, acquiring a first transient response parameter generated in the test circuit due to the operation of the disconnecting switch, adjusting the circuit parameters of the test circuit according to the first transient response parameter until the first transient response parameter meets preset test conditions; and raising the output voltage of the high-voltage test transformer to the target test voltage. While keeping the circuit parameters unchanged, the disconnecting switch is operated at a preset operating frequency. The second transient response parameter of the test circuit is simultaneously acquired and recorded during the operation. Based on the second transient response parameter, the test capacitor voltage transformer is monitored for breakdown events during the assessment. If a breakdown event occurs, the operation is stopped; if no breakdown event occurs, the operation continues until the preset number of operations is reached. If a breakdown event occurs, the test capacitor voltage transformer is determined to have failed the insulation performance assessment. If no breakdown event occurs, the final insulation state parameter of the test capacitor voltage transformer is obtained. Based on the comparison between the initial insulation state parameter and the final insulation state parameter, it is determined whether the test capacitor voltage transformer has passed the insulation performance assessment.

[0010] According to another aspect of the present disclosure, a test platform for evaluating the insulation performance of a capacitive voltage transformer is also provided, comprising: a high-voltage test transformer for providing a test voltage to a test circuit; a current-limiting inductor, the first end of which is connected to the output terminal of the high-voltage test transformer; a capacitive voltage transformer under test, the high-voltage input terminal of which is connected to the second terminal of the current-limiting inductor; a disconnecting switch, the first terminal of which is connected to the low-voltage output terminal of the capacitive voltage transformer under test; a coupling capacitor, the high-voltage terminal of which is connected to the second terminal of the disconnecting switch, the low-voltage terminal of which is grounded, the coupling capacitor being used to simulate the capacitance to ground of the series compensation platform; a measurement unit for acquiring transient response parameters generated in the test circuit due to the operation of the disconnecting switch; and a control unit, the control unit being connected to the high-voltage test transformer, the disconnecting switch, and the measurement unit respectively, the control unit being used to execute the above-described test method for evaluating the insulation performance of a capacitive voltage transformer.

[0011] This application obtains the initial insulation state parameters of the tested capacitive voltage transformer, providing a quantitative comparison benchmark for judging the insulation performance degradation after subsequent testing. By constructing a test circuit consisting of a high-voltage test transformer, a current-limiting inductor, the tested capacitive voltage transformer, a disconnecting switch, and a coupling capacitor connected in series, and operating the disconnecting switch to switch the coupling capacitor, the application utilizes the high-frequency damped oscillation transient process generated by repeated breakdowns between the disconnecting switch contacts to achieve laboratory reproduction of the actual operating conditions of the series compensation platform switching. By operating the disconnecting switch at a first voltage lower than the target test voltage and acquiring the first transient response parameter, and adjusting the circuit parameters according to the first transient response parameter until the preset test conditions are met, the application achieves pre-tuning of the circuit transient characteristics under low voltage and safe conditions, avoiding potential damage to the tested CVT and high-voltage test transformer that might be caused by direct debugging at rated voltage. Furthermore, by raising the output voltage of the high-voltage test transformer to the target test voltage and... Under the condition of keeping the circuit parameters unchanged, the formal test is carried out according to the preset operating frequency and preset number of tests, so that the CVT under test is subjected to a large number of transient impacts equivalent to the actual field conditions at the rated voltage. By synchronously collecting and recording the second transient response parameter during the formal test, and monitoring whether the CVT under test has a breakdown event in real time based on the second transient response parameter, the operation is stopped immediately when a breakdown event occurs. This realizes the real-time perception of the insulation status of the CVT during the test and the effective protection of the test equipment, which solves the problem that the existing test methods cannot perceive the insulation status of the CVT in real time during the test. By obtaining the final insulation status parameter after the test and comparing it with the initial insulation status parameter, the degree of insulation performance degradation of the CVT is quantitatively determined. This provides a clear basis for judging whether the insulation performance of the CVT on the series compensation platform side is qualified before entering the grid, thus effectively filling the technical gap of special test equivalent to the actual field conditions before the CVT on the series compensation platform side enters the grid. Attached Figure Description

[0012] The accompanying drawings, which are included to provide a further understanding of this disclosure and form part of this application, illustrate exemplary embodiments of this disclosure and are used to explain this disclosure, but do not constitute an undue limitation of this disclosure. In the drawings: Figure 1 This is a flowchart of the test method for assessing the insulation performance of a capacitive voltage transformer according to Embodiment 1 of this application; Figure 2 This is a schematic diagram of the layout of the test circuit according to Embodiment 1 of this application; Figure 3 This is a schematic diagram of the voltage and current measurement position according to Embodiment 1 of this application. Detailed Implementation

[0013] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0014] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0015] Example 1 According to the first aspect of this embodiment, a test method for evaluating the insulation performance of a capacitive voltage transformer is provided. Figure 1 A flowchart illustrating the method is shown below. (Refer to...) Figure 1 As shown, the method includes: Step 1: Obtain the initial insulation state parameters of the capacitive voltage transformer under test; In this embodiment, before conducting the test, the initial insulation state parameters of the CVT under test are first obtained. These insulation state parameters characterize the initial state of the CVT's insulation performance and serve as a benchmark for comparing the degree of insulation performance degradation after subsequent evaluation. Specifically, before the test begins, the dielectric loss, capacitance, and error of the high-voltage and medium-voltage capacitors of the CVT under test are measured and recorded. Dielectric loss reflects the loss characteristics of the CVT's insulating dielectric under AC voltage and is a key parameter for determining whether the insulation is damp or aged. Capacitance reflects the integrity of the CVT's capacitor elements; when a component breaks down in a capacitor unit, the capacitance changes accordingly. Error (including ratio error and phase error) reflects the accuracy of the CVT's voltage conversion; its changes can indirectly reflect the state changes of the internal electromagnetic units or capacitive voltage dividers.

[0016] Therefore, by obtaining the initial insulation state parameters of the CVT under test before the test, a quantitative comparison benchmark is provided for whether the insulation performance of the CVT has deteriorated and whether the degree of deterioration is within the allowable range after the subsequent test.

[0017] Step 2: Construct a test circuit, which includes a high-voltage test transformer, a current-limiting inductor, the capacitive voltage transformer under test, a disconnecting switch, and a coupling capacitor for simulating the capacitance to ground of the series compensation platform, connected in series in sequence. In this embodiment, according to Figure 2 The layout diagram shown illustrates the construction of the test loop. Figure 2 In this circuit, a high-voltage test transformer, a current-limiting inductor, a capacitive voltage transformer (CVT) under test, a disconnecting switch, and a coupling capacitor (C1) are arranged sequentially and connected in series via high-voltage conductors. The output terminal of the high-voltage test transformer is connected to one end of the current-limiting inductor, and the other end of the current-limiting inductor is connected to the high-voltage input terminal of the CVT under test. The low-voltage output terminal of the CVT under test is connected to one end of the disconnecting switch, and the other end of the disconnecting switch is connected to the high-voltage terminal of the coupling capacitor. The low-voltage terminal of the coupling capacitor is grounded. The CVT under test is used to connect to the CVT under test; that is, the high-voltage terminal of the CVT under test is connected to the high-voltage input terminal of the CVT under test, and the low-voltage terminal of the CVT under test is connected to the low-voltage output terminal of the CVT under test. The high-voltage test transformer provides the test voltage for the entire test circuit. The current-limiting inductor is connected in series between the high-voltage test transformer and the CVT under test to limit the transient current flowing into the high-voltage test transformer from the test circuit. The disconnecting switch is a switching device without an arc-extinguishing device, and its contacts can undergo multiple repeated breakdowns during opening and closing operations. The coupling capacitor is used to simulate the capacitance to ground of the series compensation platform.

[0018] Thus, a test circuit capable of simulating the actual operating conditions of the series compensation platform switching was constructed. This circuit switches the coupling capacitor by operating the disconnecting switch, which can generate transient overvoltage and pulse current with high frequency damping oscillation in the test circuit and apply them to the CVT under test connected to the capacitive voltage transformer under test.

[0019] Step 3: Operate the disconnecting switch at a first voltage lower than the target test voltage, collect the first transient response parameter generated in the test circuit due to the operation of the disconnecting switch, and adjust the circuit parameters of the test circuit according to the first transient response parameter until the first transient response parameter meets the preset test conditions. In this embodiment, a target test voltage needs to be set, which is the rated voltage of the CVT under test. Then, the output voltage of the high-voltage test transformer is adjusted to a first voltage lower than the target test voltage. The first voltage is set lower than the target test voltage to ensure that even if the circuit parameters are improperly set during commissioning, it will not damage the CVT under test or the high-voltage test transformer. At the first voltage, the disconnecting switch is operated to perform one opening or closing operation. During the operation of the disconnecting switch, multiple repeated breakdowns occur between its contacts, generating transient overvoltages and pulse currents in the test circuit. During this operation, a measurement unit is used to collect the first transient response parameters generated in the test circuit due to the operation of the disconnecting switch. The first transient response parameters include the pulse current flowing through the current-limiting inductor, the pulse current flowing through the CVT under test, the transient overvoltage on the primary side of the CVT under test, and the transient overvoltage on the intermediate voltage side of the CVT under test.

[0020] After acquiring the first transient response parameter, it is compared with preset test conditions. The preset test conditions refer to pre-defined conditions used to characterize the transient response parameter reaching the target assessment level, including one or more of the preset target ranges for pulse current amplitude, transient overvoltage amplitude, and transient overvoltage frequency. If the first transient response parameter does not meet the preset test conditions, the loop parameters of the test circuit are adjusted according to the deviation direction of the first transient response parameter relative to the preset test conditions. The loop parameters include one or more of the current-limiting parameters of the current-limiting inductor, the capacitance value of the coupling capacitor, and the relative positions of the various devices. After adjusting the loop parameters, the isolating switch is operated again under the first voltage to acquire a new first transient response parameter, and the preset test conditions are re-evaluated. This process is repeated until the first transient response parameter meets the preset test conditions.

[0021] Therefore, under safe voltage conditions below the target test voltage, the transient response characteristics of the test circuit are tuned to meet the preset test conditions through closed-loop debugging. This ensures that the transient stress applied to the CVT under test can accurately reach the target test level during the subsequent formal test at the rated voltage, while avoiding the damage to equipment and personnel that may be caused by directly applying high voltage under parameter mismatch.

[0022] Step 4: Increase the output voltage of the high-voltage test transformer to the target test voltage. While keeping the circuit parameters unchanged, operate the disconnect switch at the preset operating frequency. Simultaneously collect and record the second transient response parameter of the test circuit during the operation. Monitor whether the tested capacitive voltage transformer experiences a breakdown event during the test based on the second transient response parameter. If a breakdown event occurs, stop the operation. If no breakdown event occurs, continue the operation until the preset number of tests is reached. In this embodiment, after confirming in step 3 that the first transient response parameter meets the preset test conditions, the output voltage of the high-voltage test transformer is increased from the first voltage to the target test voltage. During and after the voltage increase, the circuit parameters determined in step 3 remain unchanged. After reaching the target test voltage, the disconnecting switch is operated at a preset operating frequency until all operations are completed. The preset operating frequency refers to the time interval between two adjacent disconnecting switch operations, for example, once every 5 minutes. Its setting needs to consider the decay time of the transient process in the test circuit after each operation and the heat dissipation requirements of the operating mechanism itself. Furthermore, the number of disconnecting switch operations needs to effectively simulate the number of disconnecting switch operations in the field for effective CVT evaluation. The recommended design principle for the number of disconnecting switch operations is the sum of the number of disconnecting switch operations during system commissioning and the actual number of operations per year during the operation of the series disconnecting switches. The recommended number of operations is 20-60 times.

[0023] During each operation of the disconnect switch, the measurement unit synchronously acquires and records the second transient response parameter of the test circuit. The second transient response parameter includes at least the same type of physical quantity as the first transient response parameter, namely, the pulse current flowing through the current-limiting inductor, the pulse current flowing through the CVT under test, the transient overvoltage on the primary side of the CVT under test, and the transient overvoltage on the intermediate voltage side of the CVT under test. Synchronous acquisition means that all acquisition channels of the measurement unit are activated at the same time to ensure accurate phase and time relationships between the parameters. Recording refers to saving the acquired waveform data of the second transient response parameter to a storage device.

[0024] While operating the disconnect switch and collecting the second transient response parameter each time, the test CVT is monitored in real time based on the second transient response parameter to see if a breakdown event occurs during the assessment process. Figure 3 A schematic diagram showing the voltage and current measurement locations in this embodiment is provided. (Reference) Figure 3As shown, the acquisition of the first and second transient response parameters is achieved through multiple measurement points arranged in the test circuit. Specifically, the first measurement point is located on the high-voltage conductor between the current-limiting inductor and the CVT under test, used to acquire the pulse current I1 flowing through the current-limiting inductor; the second measurement point is located on the high-voltage conductor between the CVT under test and the disconnecting switch, used to acquire the pulse current I2 flowing through the CVT under test; the third measurement point is located at the high-voltage input terminal of the CVT under test, used to acquire the transient overvoltage U1 on the primary side of the CVT under test; and the fourth measurement point is located at the low-voltage output terminal of the CVT under test, used to acquire the transient overvoltage U2 on the medium-voltage side of the CVT under test. Each measurement point inputs signals to an oscilloscope or data acquisition card via sensors, and all channels are synchronously triggered using the same trigger signal.

[0025] If a breakdown event is detected during any disconnector operation in the assessment process, subsequent disconnector operations should be stopped immediately to prevent further damage to the already broken CVT during subsequent operations. If no breakdown event is detected in any of the completed disconnector operations, the disconnector should continue to be operated at the preset operating frequency until the preset number of operations is reached. The preset number of assessments refers to the total number of disconnector operations required in the formal assessment phase, and its value should be sufficient to simulate the cumulative transient impact effect caused to the CVT by the disconnector on the field series compensation platform during system debugging and operation.

[0026] Thus, under the condition of keeping the circuit parameters constant, multiple transient impacts equivalent to the actual working conditions on the CVT under test are applied at the rated voltage. At the same time, the waveform characteristics of the second transient response parameter are monitored in real time to realize the instant perception and judgment of the insulation status of the CVT during the test. The test is automatically stopped when a breakdown occurs to ensure safety.

[0027] Step 5: If the breakdown event occurs, the tested capacitive voltage transformer is determined to have failed the insulation performance test; if the breakdown event does not occur, the final insulation state parameter of the tested capacitive voltage transformer is obtained, and the test is determined to have passed the insulation performance test based on the comparison between the initial insulation state parameter and the final insulation state parameter.

[0028] In this embodiment, after the assessment is completed, the judgment stage begins. The judgment logic is as follows: First, it is determined whether a breakdown event occurred during the formal assessment process in step 4. If a breakdown event occurred, the tested CVT is directly judged to have failed the insulation performance assessment, and no further insulation state parameter measurement and comparison is required. If no breakdown event occurred, the final insulation state parameters of the tested CVT are obtained after the assessment is completed. The method for obtaining the final insulation state parameters is the same as the method for obtaining the initial insulation state parameters in step 1, that is, using the same measuring equipment and the same measuring conditions, the dielectric loss, capacitance, and error of the high-voltage capacitor and medium-voltage capacitor of the tested CVT are measured respectively, and the measurement results are recorded. After obtaining the final insulation state parameters, they are compared item by item with the initial insulation state parameters recorded in step 1, and the test CVT is judged to have passed the insulation performance assessment based on the comparison results.

[0029] Thus, by combining the veto power of a breakdown event with a quantitative comparison of insulation status parameters, a two-level judgment logic is achieved to objectively and quantitatively determine whether the insulation performance of the tested CVT is qualified, providing clear assessment conclusions and judgment criteria for the grid connection of CVTs on the series compensation platform side.

[0030] As described in the background section, existing technologies lack a CVT insulation performance testing scheme that can effectively simulate the actual transient operating conditions of the disconnecting switch switching series compensation platform under laboratory conditions. The CVT on the series compensation platform side lacks a dedicated testing test equivalent to actual field conditions before grid connection, resulting in a technological gap in verifying its insulation withstand capability. This technological gap has posed a substantial constraint on the safe commissioning and reliable operation of UHV series compensation projects.

[0031] In view of this, this application obtains the initial insulation state parameters of the tested capacitive voltage transformer, providing a quantitative comparison benchmark for judging the insulation performance degradation after subsequent testing; by constructing a test circuit consisting of a high-voltage test transformer, a current-limiting inductor, the tested capacitive voltage transformer, a disconnecting switch, and a coupling capacitor connected in series, and operating the disconnecting switch to switch the coupling capacitor, the laboratory reproduction of the actual operating condition of the series compensation platform switching is achieved by utilizing the high-frequency damped oscillation transient process generated by repeated breakdown between the disconnecting switch contacts; by operating the disconnecting switch at a first voltage lower than the target test voltage and collecting the first transient response parameter, and adjusting the circuit parameters according to the first transient response parameter until the preset test conditions are met, the pre-tuning of the circuit transient characteristics under low voltage and safe conditions is achieved, avoiding the damage that may be caused to the tested CVT and high-voltage test transformer by direct debugging at the rated voltage; by raising the output voltage of the high-voltage test transformer to the target test voltage... Under the condition of keeping the circuit parameters unchanged, the formal test was carried out according to the preset operating frequency and preset number of tests, so that the CVT under test was subjected to a large number of transient impacts equivalent to the actual field conditions at the rated voltage. By synchronously collecting and recording the second transient response parameter during the formal test, and monitoring whether the CVT under test has a breakdown event in real time based on the second transient response parameter, the operation was stopped immediately when a breakdown event occurred. This achieved real-time perception of the insulation status of the CVT during the test and effective protection of the test equipment, solving the problem that the existing test methods could not perceive the insulation status of the CVT in real time during the test. By obtaining the final insulation status parameter after the test and comparing it with the initial insulation status parameter, the degree of insulation performance degradation of the CVT was quantitatively determined, providing a clear judgment basis for whether the insulation performance of the CVT on the series compensation platform side is qualified before entering the grid. This effectively filled the technical gap of special test equivalent to the actual field conditions before the CVT on the series compensation platform side enters the grid.

[0032] Optionally, the operation of constructing the test circuit includes: connecting the output terminal of the high-voltage test transformer to one end of the current-limiting inductor; connecting the other end of the current-limiting inductor to the high-voltage input terminal of the capacitive voltage transformer under test; connecting the low-voltage output terminal of the capacitive voltage transformer under test to one end of the disconnecting switch; connecting the other end of the disconnecting switch to the high-voltage terminal of the coupling capacitor; grounding the low-voltage terminal of the coupling capacitor; and the high-voltage test transformer and the capacitive voltage transformer under test each having a grounded reference terminal.

[0033] In this embodiment, according to Figure 2 The layout diagram shown illustrates the construction of the test loop. Figure 2In this test circuit, the high-voltage test transformer, current-limiting inductor, test position (connected to the capacitive voltage transformer under test), disconnecting switch, and coupling capacitor are arranged sequentially in the same direction and connected in series via high-voltage conductors. Specifically, the output terminal of the high-voltage test transformer is connected to one end of the current-limiting inductor via a high-voltage conductor, and the other end of the current-limiting inductor is connected to the high-voltage input terminal of the test position via a high-voltage conductor. The test position is used to connect the capacitive voltage transformer under test; that is, the high-voltage terminal of the capacitive voltage transformer under test is connected to the high-voltage input terminal of the test position, and the low-voltage terminal of the capacitive voltage transformer under test is connected to the low-voltage output terminal of the test position. The low-voltage output terminal of the test position is connected to one end of the disconnecting switch via a high-voltage conductor. The other end of the disconnecting switch is connected to the high-voltage terminal of the coupling capacitor via a high-voltage conductor. The low-voltage terminal of the coupling capacitor is grounded. Simultaneously, both the high-voltage test transformer and the capacitive voltage transformer under test have grounded reference terminals, with the reference terminal of the high-voltage test transformer grounded and the low-voltage terminal (i.e., the medium-voltage side reference terminal) of the capacitive voltage transformer under test grounded. The high-voltage test transformer provides power to the entire test circuit, and its output voltage can be adjusted according to test requirements. A current-limiting inductor is installed on the high-voltage line between the high-voltage test transformer and the capacitive voltage transformer under test. It serves as a surge shield to prevent transient overvoltages generated by the operation of the disconnecting switch from affecting the insulation of the high-voltage test transformer. The capacitive voltage transformer under test is the test object and is connected in series in the test circuit. The disconnecting switch is located between the capacitive voltage transformer under test and the coupling capacitor. The coupling capacitor is used to simulate the series compensation platform's capacitance to ground.

[0034] Therefore, during the operation of the disconnecting switch to switch the coupling capacitor, the multiple reignitions between the disconnecting switch contacts will generate multiple transient overvoltages in the test circuit and form a resonant circuit between the CVT and the coupling capacitor. The pulse current of several kA will test the insulation performance of the CVT.

[0035] Optionally, the operation of adjusting the loop parameters of the test circuit according to the first transient response parameter includes: adjusting the current limiting parameter of the current limiting inductor according to the deviation direction of the first transient response parameter relative to the preset test conditions; if the first transient response parameter still does not meet the preset test conditions after adjusting the current limiting parameter of the current limiting inductor, then adjusting the capacitance value of the coupling capacitor according to the deviation direction of the first transient response parameter relative to the preset test conditions; if the first transient response parameter still does not meet the preset test conditions after adjusting the current limiting parameter of the current limiting inductor and the capacitance value of the coupling capacitor, then adjusting the relative positions of the devices in the test circuit.

[0036] In this embodiment, after the first transient response parameter is acquired, since this parameter is obtained at a first voltage lower than the target test voltage, and the preset test conditions correspond to the target value at the target test voltage (i.e., rated voltage), the acquired first transient response parameter needs to be converted to the rated voltage according to the voltage ratio before being compared with the preset test conditions. Specifically, the conversion factor is the ratio of the target test voltage to the first voltage. For example, when the first voltage is 50kV and the target test voltage is 1000kV, the conversion factor is 20 times. During the conversion, the amplitudes of transient overvoltage and pulse current are amplified according to the above ratio, while the frequency characteristics remain unchanged.

[0037] The calculated first transient response parameter is compared with the preset test conditions to determine whether the amplitude and frequency of the pulse current flowing through the tested capacitive voltage transformer meet the test requirements. If not, the current-limiting parameter of the current-limiting inductor is adjusted according to the deviation direction of the first transient response parameter relative to the preset test conditions. The value of the current-limiting inductor is closely related to the amplitude and frequency of the pulse current flowing into the high-voltage test transformer. The larger the inductance value, the smaller the pulse current amplitude and the lower the frequency; conversely, the smaller the inductance value, the larger the pulse current amplitude and the higher the frequency. After adjusting the current-limiting inductor, the disconnecting switch is operated again under the first voltage, the first transient response parameter is collected again, and converted to the rated voltage according to the same ratio. The amplitude and frequency of the pulse current flowing through the tested capacitive voltage transformer are then re-determined to determine whether they meet the test requirements.

[0038] If adjusting the current-limiting parameters of the current-limiting inductor does not yet meet the preset test conditions, the capacitance of the coupling capacitor should be further adjusted. The capacitance of the coupling capacitor is closely related to the amplitude and frequency of the pulse current flowing through the capacitive voltage transformer under test. A larger capacitance results in a larger pulse current amplitude and lower frequency, while a smaller capacitance results in a smaller pulse current amplitude and higher frequency. After adjusting the coupling capacitor, operate the disconnecting switch again at the first voltage, collect the first transient response parameters, and convert them to the rated voltage for judgment until the test requirements are met.

[0039] If, after adjusting the current-limiting parameters of the current-limiting inductor and the capacitance value of the coupling capacitor, the calculated first transient response parameters still do not meet the preset test conditions, then the relative positions of the devices in the test circuit should be adjusted. The relative positions of the devices affect the amplitude and frequency of transient overvoltages and pulse currents. The closer the relative positions, the higher the amplitude and frequency of transient overvoltages and pulse currents. This is mainly due to the suppressive effect of the inductive characteristics of the wires between the devices during the transient process on transient overvoltages.

[0040] Therefore, by gradually adjusting the circuit parameters of the test circuit according to the priority order of first limiting inductor, then coupling capacitor, and finally equipment spacing, and repeatedly performing closed-loop debugging of "operating disconnect switch → collecting first transient response parameter → proportional conversion → adjusting circuit parameters → re-verification" at a lower voltage, the first transient response parameter after conversion to rated voltage finally meets the preset test conditions, providing accurate circuit parameter configuration for subsequent formal assessment at rated voltage.

[0041] Optionally, adjusting the current-limiting parameter of the current-limiting inductor according to the deviation direction of the first transient response parameter relative to the preset test conditions includes: decreasing the current-limiting parameter of the current-limiting inductor when the pulse current amplitude in the first transient response parameter is lower than the preset amplitude target value corresponding to the current-limiting inductor; increasing the current-limiting parameter of the current-limiting inductor when the pulse current amplitude in the first transient response parameter is higher than the preset amplitude target value corresponding to the current-limiting inductor; increasing the current-limiting parameter of the current-limiting inductor when the transient overvoltage frequency in the first transient response parameter is higher than the preset frequency target value corresponding to the current-limiting inductor; and decreasing the current-limiting parameter of the current-limiting inductor when the transient overvoltage frequency in the first transient response parameter is lower than the preset frequency target value corresponding to the current-limiting inductor.

[0042] In this embodiment, after the first transient response parameter is converted to the rated voltage, it is compared with the preset test conditions. If it is determined that the preset test conditions are not met, the current limiting parameter of the current limiting inductor is adjusted according to the direction of deviation. Specifically, when the converted pulse current amplitude is lower than the preset amplitude target value corresponding to the current limiting inductor, it indicates that the current current limiting inductor's suppression effect on the pulse current is too strong. It is necessary to reduce the inductance value of the current limiting inductor to reduce its current limiting effect on the pulse current, so that the pulse current amplitude flowing through the CVT under test increases to the target range. When the converted pulse current amplitude is higher than the preset amplitude target value corresponding to the current limiting inductor, it indicates that the current current limiting inductor's suppression effect on the pulse current is insufficient. It is necessary to increase the inductance value of the current limiting inductor to enhance its current limiting effect on the pulse current, so that the pulse current amplitude flowing through the CVT under test decreases to the target range. The larger the inductance value of the current-limiting inductor, the stronger its suppression effect on pulse current, the smaller the pulse current amplitude, and the lower the frequency; conversely, the smaller the inductance value of the current-limiting inductor, the larger the pulse current amplitude and the higher the frequency.

[0043] When the converted transient overvoltage frequency is higher than the preset target frequency value corresponding to the current-limiting inductor, the inductance value of the current-limiting inductor needs to be increased to lower the resonant frequency; when the converted transient overvoltage frequency is lower than the preset target frequency value corresponding to the current-limiting inductor, the inductance value of the current-limiting inductor needs to be decreased to increase the resonant frequency. This is because the current-limiting inductor and coupling capacitor in the test circuit form an LC resonant circuit, and the resonant frequency is inversely proportional to the inductance value. Increasing the inductance value decreases the frequency, and decreasing the inductance value increases the frequency. After adjusting the current-limiting inductor according to the above rules, the isolating switch is operated again under the first voltage, new first transient response parameters are collected and converted to the rated voltage, and the preset test conditions are re-evaluated.

[0044] Therefore, by determining the direction of adjustment of the current-limiting inductor parameter by the deviation direction of the pulse current amplitude and transient overvoltage frequency from their respective preset target values, the precise and data-driven adjustment of the current-limiting inductor parameter is achieved, avoiding blind trial and error and improving the efficiency of circuit parameter debugging.

[0045] Optionally, adjusting the capacitance value of the coupling capacitor according to the deviation direction of the first transient response parameter relative to the preset test conditions includes: increasing the capacitance value of the coupling capacitor when the pulse current amplitude in the first transient response parameter is lower than the preset amplitude target value corresponding to the coupling capacitor; decreasing the capacitance value of the coupling capacitor when the pulse current amplitude in the first transient response parameter is higher than the preset amplitude target value corresponding to the coupling capacitor; increasing the capacitance value of the coupling capacitor when the transient overvoltage frequency in the first transient response parameter is higher than the preset frequency target value corresponding to the coupling capacitor; and decreasing the capacitance value of the coupling capacitor when the transient overvoltage frequency in the first transient response parameter is lower than the preset frequency target value corresponding to the coupling capacitor.

[0046] In this embodiment, when the calculated first transient response parameter still does not meet the preset test conditions, the capacitance value of the coupling capacitor is adjusted according to the deviation direction. The coupling capacitor is used to simulate the capacitance to ground of the series compensation platform, and its capacitance value is closely related to the amplitude and frequency of the pulse current flowing through the CVT under test. Specifically, when the calculated pulse current amplitude is lower than the preset amplitude target value corresponding to the coupling capacitor, it indicates that the current capacitance value of the coupling capacitor is too small and insufficient to provide enough discharge charge. The capacitance value of the coupling capacitor needs to be increased to increase the pulse current amplitude flowing through the CVT under test. When the calculated pulse current amplitude is higher than the preset amplitude target value corresponding to the coupling capacitor, it indicates that the current capacitance value of the coupling capacitor is too large, and the stored charge is too high, resulting in an excessively high pulse current amplitude. The capacitance value of the coupling capacitor needs to be decreased to reduce the pulse current amplitude flowing through the CVT under test. The larger the capacitance of the coupling capacitor, the more charge it stores, and the larger the amplitude and lower the frequency of the pulse current flowing through the CVT under test during discharge; conversely, the smaller the capacitance of the coupling capacitor, the smaller the amplitude and higher the frequency of the pulse current flowing through the CVT under test.

[0047] When the converted transient overvoltage frequency is higher than the preset target frequency value corresponding to the coupling capacitor, the capacitance of the coupling capacitor needs to be increased to lower the resonant frequency; when the converted transient overvoltage frequency is lower than the preset target frequency value corresponding to the coupling capacitor, the capacitance of the coupling capacitor needs to be decreased to increase the resonant frequency. This is because the current-limiting inductor and the coupling capacitor in the test circuit form an LC resonant circuit, and the resonant frequency is inversely proportional to the square root of the capacitance value. Increasing the capacitance value decreases the frequency, and decreasing the capacitance value increases the frequency. After adjusting the coupling capacitor, the isolating switch is operated again under the first voltage, new first transient response parameters are collected and converted to the rated voltage, and the preset test conditions are re-evaluated.

[0048] Therefore, by determining the direction of increase or decrease of the coupling capacitor value based on the deviation direction of the pulse current amplitude and transient overvoltage frequency from their respective preset target values, the precise and data-driven adjustment of the coupling capacitor value is achieved. Combined with the adjustment of the current-limiting inductor, the transient response characteristics of the test circuit can flexibly adapt to the CVT test requirements of different voltage levels and structural types.

[0049] Optionally, adjusting the relative positions of the devices in the test circuit includes: when the pulse current amplitude in the first transient response parameter is lower than the preset amplitude target value corresponding to the device spacing, shortening the distance between the disconnecting switch and the coupling capacitor, and / or shortening the distance between the capacitive voltage transformer under test and the disconnecting switch; when the pulse current amplitude in the first transient response parameter is higher than the preset amplitude target value corresponding to the device spacing, increasing the distance between the disconnecting switch and the coupling capacitor, and / or increasing the distance between the capacitive voltage transformer under test and the disconnecting switch; when the transient overvoltage frequency in the first transient response parameter is higher than the preset frequency target value corresponding to the device spacing, increasing the distance between the disconnecting switch and the coupling capacitor, and / or increasing the distance between the capacitive voltage transformer under test and the disconnecting switch; when the transient overvoltage frequency in the first transient response parameter is lower than the preset frequency target value corresponding to the device spacing, shortening the distance between the disconnecting switch and the coupling capacitor, and / or shortening the distance between the capacitive voltage transformer under test and the disconnecting switch.

[0050] In this embodiment, if the calculated first transient response parameter still does not meet the preset test conditions after adjusting the current-limiting parameter of the current-limiting inductor and the capacitance value of the coupling capacitor, the relative positions of the devices in the test circuit are adjusted. The relative positions of the devices affect the amplitude and frequency of transient overvoltage and pulse current. The closer the relative positions, the higher the amplitude and frequency of transient overvoltage and pulse current. This is mainly due to the inductive characteristics of the wires between the devices during the transient process, which suppresses transient overvoltage. The closer the distance, the shorter the wire length, the smaller the line inductance, and the weaker the suppression effect on transient high-frequency components.

[0051] Specifically, when the calculated pulse current amplitude is lower than the preset target amplitude value corresponding to the equipment spacing, it indicates that the current equipment spacing is too large, resulting in excessive suppression of transient processes by the line inductance. It is necessary to shorten the distance between the disconnecting switch and the coupling capacitor, and / or shorten the distance between the tested capacitive voltage transformer and the disconnecting switch to reduce line inductance, thereby reducing the suppression effect on transient overvoltages and pulse currents, and thus increasing the pulse current amplitude flowing through the tested CVT. When the calculated pulse current amplitude is higher than the preset target amplitude value corresponding to the equipment spacing, it indicates that the current equipment spacing is too small, the line inductance is insufficient, and the suppression effect on transient processes is too weak. It is necessary to increase the distance between the disconnecting switch and the coupling capacitor, and / or increase the distance between the tested capacitive voltage transformer and the disconnecting switch to increase line inductance, thereby enhancing the suppression effect on transient overvoltages and pulse currents, and thus reducing the pulse current amplitude flowing through the tested CVT.

[0052] When the converted transient overvoltage frequency is higher than the preset frequency target value corresponding to the equipment spacing, it is necessary to increase the distance between the disconnecting switch and the coupling capacitor, and / or increase the distance between the measured capacitive voltage transformer and the disconnecting switch to increase the line inductance and reduce the resonant frequency; when the converted transient overvoltage frequency is lower than the preset frequency target value corresponding to the equipment spacing, it is necessary to shorten the distance between the disconnecting switch and the coupling capacitor, and / or shorten the distance between the measured capacitive voltage transformer and the disconnecting switch to reduce the line inductance and increase the resonant frequency.

[0053] In this embodiment, a distance of 10m to 20m is recommended between the disconnecting switch and the coupling capacitor to simulate the actual distance between the disconnecting switch and the series compensation platform on site. A distance of 15m to 50m is recommended between the tested capacitive voltage transformer and the disconnecting switch; the closer the distance, the more stringent the CVT test. A distance of 10m to 100m is recommended between the tested capacitive voltage transformer and the high-voltage test transformer; the farther the distance, the more stringent the CVT test. If, due to site constraints, the distance between the high-voltage test transformer and the tested capacitive voltage transformer cannot meet the above requirements, a current-limiting inductor can be connected in series between the tested capacitive voltage transformer and the high-voltage test transformer to effectively increase the line length. The larger the current-limiting inductor value, the longer the simulated line; calculations are performed at 1μH per meter. After adjusting the relative positions of the equipment, the disconnecting switch is operated again under the first voltage, new first transient response parameters are collected and converted to the rated voltage, and the preset test conditions are re-evaluated.

[0054] Therefore, when the adjustment of the current-limiting inductor and coupling capacitor still cannot meet the requirements, the relative positions of the devices in the test circuit are further adjusted to change the suppression effect of the distributed inductance of the line on the transient process. With the adjustment of the current-limiting inductor and coupling capacitor, flexible and precise adjustment of the amplitude and frequency of transient overvoltage and pulse current is achieved, so that the test circuit can adapt to different site conditions and different CVT assessment requirements.

[0055] Optionally, the inductance value of the current-limiting inductor is 20μH to 500μH.

[0056] In this embodiment, the current-limiting inductor uses an air-core copper coil. The inductance value of the current-limiting inductor is selected within the above-mentioned range based on the actual debugging results of the test circuit. The value of the current-limiting inductor is closely related to the amplitude and frequency of the pulse current flowing into the high-voltage test transformer: the larger the inductance value, the smaller the pulse current amplitude and the lower the frequency, resulting in stronger protection for the high-voltage test transformer; the smaller the inductance value, the larger the pulse current amplitude and the higher the frequency, resulting in more stringent testing of the CVT. The current-limiting inductor is set in the range of 20μH to 500μH, which can effectively suppress the transient current flowing into the high-voltage test transformer, protecting the insulation of the high-voltage test transformer from the impact damage of transient overvoltage, while not excessively suppressing the pulse current flowing through the CVT under test, thus ensuring the effectiveness of the test.

[0057] In addition, the current-limiting inductor is designed as an air-core copper coil, with the coil diameter and number of turns following the formula. The design is carried out, where N is the number of coil turns and S is the coil diameter; l The circumference of the coil; Permeability of free space is a fundamental physical constant in electromagnetism. The diameter of the copper coil is designed according to the amplitude of the pulse current to ensure that the coil conductor has sufficient current-carrying capacity and thermal stability when a pulse current of several kA flows through it, thus avoiding overheating damage to the coil due to current heating effects. Therefore, by selecting the current-limiting inductance value within the above range, the high-frequency transient overvoltage generated by the operation of the disconnecting switch can be effectively blocked from propagating to the high-voltage test transformer side during the formal assessment process. This protects the insulation safety of the high-voltage test transformer while ensuring that the pulse current flowing through the CVT under test has sufficient amplitude and frequency characteristics, thus achieving effective assessment of the CVT's insulation performance.

[0058] Optionally, the capacitance of the coupling capacitor is 2nF to 8nF, and the rated voltage of the coupling capacitor is greater than or equal to the rated voltage of the capacitive voltage transformer under test.

[0059] In this embodiment, a coupling capacitor is used to simulate the capacitance to ground of the series compensation platform. The capacitance value of the coupling capacitor is selected within the aforementioned range based on the actual debugging results of the test circuit. The capacitance value of the coupling capacitor is closely related to the amplitude and frequency of the pulse current flowing through the CVT under test: the larger the capacitance value, the larger the amplitude and lower the frequency of the pulse current flowing through the CVT under test; the smaller the capacitance value, the smaller the amplitude and higher the frequency of the pulse current flowing through the CVT under test. The capacitance value of the coupling capacitor is set in the range of 2nF to 8nF, which can effectively simulate the actual value range of the capacitance to ground of the series compensation platform (usually several thousand pF), so that the transient process characteristics generated by the test circuit match the actual working conditions on site. At the same time, the rated voltage of the coupling capacitor must be greater than or equal to the rated voltage of the CVT under test to ensure that the coupling capacitor can withstand the target test voltage without self-insulation breakdown during the formal test at the rated voltage, ensuring the safety and effectiveness of the test process.

[0060] Therefore, by selecting the capacitance value of the coupling capacitor within the above range, the test circuit can truly simulate the electrical characteristics of the series compensation platform to ground capacitance, ensuring that the frequency and amplitude characteristics of the transient overvoltage and pulse current generated by the operation of the disconnecting switch are equivalent to the actual working conditions on site. At the same time, the rated voltage matching design ensures the insulation reliability of the coupling capacitor itself during the test process.

[0061] Optionally, the operation of determining whether the tested capacitive voltage transformer passes the insulation performance test based on the comparison result of the initial insulation state parameter and the final insulation state parameter includes: comparing the error change of the tested capacitive voltage transformer; if the error does not exceed half of the corresponding error limit of its accuracy class and meets the corresponding accuracy class requirements, then the item is deemed qualified; comparing the capacitance change of the tested capacitive voltage transformer; if the capacitance change value does not exceed the change equivalent to the breakdown of a series element, then the item is deemed qualified; comparing the dielectric loss factor change of the tested capacitive voltage transformer; if the dielectric loss factor does not exceed 0.0015, then the item is deemed qualified; comparing the partial discharge quantity change of the tested capacitive voltage transformer; if the partial discharge quantity does not exceed 5pC, then the item is deemed qualified; if all of the above items are qualified, then the tested capacitive voltage transformer is deemed to have passed the insulation performance test.

[0062] In this embodiment, when no breakdown event occurs after the test, the final insulation state parameters of the tested capacitive voltage transformer are obtained, and the final insulation state parameters are compared item by item with the initial insulation state parameters recorded in step 1. The following four criteria are used for judgment: First, compare the error variation of the tested capacitive voltage transformer. The errors include ratio error (ratio error) and phase error (phase displacement error), which are the core accuracy indicators of the CVT as a voltage measurement device. Compare the error value measured after assessment with the initial error value measured before assessment. If the error variation does not exceed half of the error limit corresponding to the accuracy class of the CVT, and the absolute value of the error after assessment still meets the requirements of the corresponding accuracy class, this item is determined to be qualified. For example, for a 0.2 class CVT, its ratio error limit is ±0.2%, so the variation of the ratio error after assessment shall not exceed ±0.1%, and the absolute value of the ratio error after assessment shall still be within the range of ±0.2%. The error variation can reflect whether performance degradation has occurred in the internal electromagnetic unit or capacitive voltage divider of the CVT after a transient shock.

[0063] Second, compare the capacitance variation of the tested capacitive voltage transformer. The capacitances include the capacitance values of the high-voltage capacitor C1 and the medium-voltage capacitor C2. Compare the capacitance value measured after assessment with the initial capacitance value measured before assessment. If the capacitance variation does not exceed the variation equivalent to that caused by breakdown of one series element, this item is determined to be qualified. The capacitive voltage divider of the CVT is composed of multiple capacitive elements connected in series. When one of the elements breaks down, the total capacitance of the series branch will increase stepwise, and the variation is equal to the equivalent capacitance increment after the element is short-circuited. Taking whether the capacitance variation exceeds the variation corresponding to breakdown of one series element as the criterion can effectively judge whether breakdown or damage has occurred to the internal capacitive elements of the CVT during the transient shock process.

[0064] Third, compare the dielectric loss factor variation of the tested capacitive voltage transformer. The dielectric loss factor is a parameter reflecting the ratio of active loss to reactive loss of the CVT insulating medium under the action of alternating voltage, and its value directly reflects the degree of insulation degradation such as moisture and aging of the insulating medium. Compare the dielectric loss factor value measured after assessment with the initial value measured before assessment. If the dielectric loss factor after assessment does not exceed 0.0015, this item is determined to be qualified. An increase in the dielectric loss factor means that new defects have appeared inside the insulating medium or existing defects have intensified, and exceeding the limit of 0.0015 indicates that the insulation performance no longer meets the operation requirements.

[0065] Fourth, compare the partial discharge magnitude variation of the tested capacitive voltage transformer. Compare the partial discharge magnitude measured after assessment with the initial value measured before assessment. If the partial discharge magnitude after assessment does not exceed 5pC, this item is determined to be qualified. Partial discharge is a phenomenon that discharge occurs in a local area inside the insulation, and its discharge magnitude directly reflects whether there are defects (such as bubbles, impurities, delamination, etc.) inside the insulation. An increase in the partial discharge magnitude after assessment indicates that the transient shock may have introduced new local defects inside the insulation.

[0066] If all four criteria above are met, the tested capacitive voltage transformer is deemed to have passed the insulation performance test; if any one criterion fails, the insulation performance test is deemed to have failed. This is because insulation performance is a comprehensive indicator with multiple dimensions, and any degradation of any key parameter exceeding the allowable range means that the insulation reliability of the CVT can no longer meet the operational requirements.

[0067] Thus, by comparing and judging each of the above four quantitative indicators, a comprehensive, objective, and quantitative assessment of the degree of insulation performance degradation of the tested CVT was achieved, providing a clear basis for determining whether the insulation performance of the CVT on the series compensation platform side is qualified before it enters the grid.

[0068] In summary, this application provides a test method and platform for evaluating the insulation performance of capacitive voltage transformers (CVTs). By constructing a test circuit consisting of a high-voltage test transformer, a current-limiting inductor, the CVT under test, a disconnecting switch, and a coupling capacitor connected in series, and utilizing the high-frequency decaying oscillation transient process generated by multiple reignitions between contacts during disconnecting switch operation of the coupling capacitor, the actual operating conditions of the series compensation platform switching are reproduced in the laboratory. The two-stage test process of low-voltage commissioning and rated voltage formal testing ensures the safety of the circuit parameter setting process and effectively assesses the cumulative damage effect of CVT insulation. Real-time acquisition of transient response parameters and monitoring of breakdown events, with immediate cessation of operation upon breakdown, enables immediate perception of the CVT insulation status during the testing process and effective protection of the test equipment. Quantitative comparison of insulation status parameters before and after the test provides a clear basis for determining whether the insulation performance of the CVT on the series compensation platform side is qualified before grid connection, thus effectively filling the technical gap in specialized testing equivalent to actual field operating conditions for the CVT on the series compensation platform side before grid connection.

[0069] Compared with the closest prior art, the present invention has the following advantages: 1) Realistic Reproduction of Test Conditions. In existing technologies, the laboratory uses an impulse voltage generator to apply standard operating impulses and standard lightning impulse waveforms to the high-voltage terminals of the CVT. Fifteen standard operating impulses, fifteen standard lightning impulses, and three interruption overvoltages are applied according to standard requirements. However, the test waveforms of this method are preset standard waveforms, which are fundamentally different from the actual transient waveforms in the field. Field operating experience shows that even after passing the above standard impulse test, the CVT still experiences insulation faults during the operation of the series compensation platform disconnecting switch, indicating that existing test methods fail to realistically simulate actual transient conditions in the field. In contrast, the test circuit of this invention utilizes the high-frequency damped oscillation transient process generated by the disconnecting switch switching coupling capacitor, fundamentally reproducing the actual transient conditions of the series compensation platform switching, effectively solving the technical dilemma of passing laboratory tests but experiencing faults in the field.

[0070] 2) Effective Assessment of Cumulative Damage Effects. In existing technologies, impulse voltage generators require discharge and recharge after each impulse, taking approximately 10 minutes per cycle. Furthermore, limitations such as equipment heating prevent the continuous application of numerous impulses; therefore, standard methods apply only a limited number of impulses (a total of 33). However, during a single operation of a disconnecting switch, multiple reignitions occur between the contacts (approximately 10 times per power frequency cycle), generating thousands of transient impulses in just 3-7 seconds per operation. The test circuit of this invention operates the disconnecting switch at a preset operating frequency up to a preset number of assessment cycles (e.g., 20-60 times). Each operation includes multiple reignition transient processes, resulting in tens of thousands of transient overvoltages applied to the CVT high-voltage end and pulse currents flowing through the CVT, effectively assessing the cumulative damage effects on CVT insulation.

[0071] 3) Flexible and adjustable transient stress. This invention allows for adjustment of the inductance value of the current-limiting inductor, the capacitance value of the coupling capacitor, and the relative positions of the various devices according to test requirements. This enables flexible adjustment of the amplitude and frequency of transient overvoltages and pulse currents, allowing the test circuit to adapt to the CVT testing requirements of different voltage levels and structural types. Its flexibility and applicability are significantly better than existing test circuits.

[0072] It should be noted that, for the sake of simplicity, the foregoing method embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, as some steps may be performed in other orders or simultaneously according to this application. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily essential to this application.

[0073] Example 2 This embodiment proposes a test platform for evaluating the insulation performance of a capacitive voltage transformer, comprising: a high-voltage test transformer for providing test voltage to the test circuit; a current-limiting inductor, the first end of which is connected to the output terminal of the high-voltage test transformer; a capacitive voltage transformer under test, the high-voltage input terminal of which is connected to the second terminal of the current-limiting inductor; a disconnecting switch, the first terminal of which is connected to the low-voltage output terminal of the capacitive voltage transformer under test; a coupling capacitor, the high-voltage terminal of which is connected to the second terminal of the disconnecting switch, and the low-voltage terminal of which is grounded, the coupling capacitor being used to simulate the capacitance to ground of the series compensation platform; a measurement unit for acquiring transient response parameters generated in the test circuit due to the operation of the disconnecting switch; and a control unit, which is connected to the high-voltage test transformer, the disconnecting switch, and the measurement unit respectively, the control unit being used to execute the test method for evaluating the insulation performance of the capacitive voltage transformer described in Embodiment 1 above.

[0074] It should be noted that the test platform for evaluating the insulation performance of capacitive voltage transformers provided in this embodiment can realize all the functions and steps in the above method embodiments, solve the same technical problems, and achieve the same technical effects. The similarities will not be repeated here.

[0075] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0076] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0077] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A test method for evaluating the insulation performance of a capacitive voltage transformer, characterized in that, include: Obtain the initial insulation state parameters of the capacitive voltage transformer under test; A test circuit is constructed, comprising a high-voltage test transformer, a current-limiting inductor, the capacitive voltage transformer under test, a disconnecting switch, and a coupling capacitor for simulating the capacitance to ground of the series compensation platform, all connected in series. The disconnecting switch is operated at a first voltage lower than the target test voltage. The first transient response parameter generated in the test circuit due to the operation of the disconnecting switch is collected. The circuit parameters of the test circuit are adjusted according to the first transient response parameter until the first transient response parameter meets the preset test conditions. The output voltage of the high-voltage test transformer is increased to the target test voltage. While keeping the circuit parameters unchanged, the disconnecting switch is operated at a preset operating frequency. The second transient response parameter of the test circuit is collected and recorded synchronously during the operation. The test capacitor voltage transformer under test is monitored for breakdown during the test based on the second transient response parameter. If a breakdown event occurs, the operation is stopped. If no breakdown event occurs, the operation continues until the preset number of tests is reached. If the breakdown event occurs, the tested capacitive voltage transformer is determined to have failed the insulation performance test; if the breakdown event does not occur, the final insulation state parameter of the tested capacitive voltage transformer is obtained, and the test result is used to determine whether the tested capacitive voltage transformer has passed the insulation performance test based on the comparison between the initial insulation state parameter and the final insulation state parameter.

2. The method according to claim 1, characterized in that, The steps for constructing a test loop include: Connect the output terminal of the high-voltage test transformer to one end of the current-limiting inductor; Connect the other end of the current-limiting inductor to the high-voltage input terminal of the capacitive voltage transformer under test; Connect the low-voltage output terminal of the capacitive voltage transformer under test to one end of the disconnect switch; Connect the other end of the disconnecting switch to the high-voltage end of the coupling capacitor; Ground the low-voltage end of the coupling capacitor; The high-voltage test transformer and the tested capacitive voltage transformer each have a grounded reference terminal.

3. The method according to claim 1, characterized in that, The operation of adjusting the loop parameters of the test loop according to the first transient response parameter includes: The current limiting parameter of the current limiting inductor is adjusted according to the deviation direction of the first transient response parameter relative to the preset test conditions. If the first transient response parameter still does not meet the preset test conditions after adjusting the current limiting parameter of the current limiting inductor, the capacitance value of the coupling capacitor is adjusted according to the deviation direction of the first transient response parameter relative to the preset test conditions. If the first transient response parameter still does not meet the preset test conditions after adjusting the current limiting parameter of the current limiting inductor and the capacitance value of the coupling capacitor, then the relative positions of the devices in the test circuit are adjusted.

4. The method according to claim 3, characterized in that, The operation of adjusting the current-limiting parameter of the current-limiting inductor according to the deviation direction of the first transient response parameter relative to the preset test conditions includes: When the amplitude of the pulse current in the first transient response parameter is lower than the preset amplitude target value corresponding to the current limiting inductor, the current limiting parameter of the current limiting inductor is reduced. When the amplitude of the pulse current in the first transient response parameter is higher than the preset amplitude target value corresponding to the current limiting inductor, the current limiting parameter of the current limiting inductor is increased; When the transient overvoltage frequency in the first transient response parameter is higher than the preset frequency target value corresponding to the current limiting inductor, the current limiting parameter of the current limiting inductor is increased. When the transient overvoltage frequency in the first transient response parameter is lower than the preset frequency target value corresponding to the current limiting inductor, the current limiting parameter of the current limiting inductor is reduced.

5. The method according to claim 3, characterized in that, The operation of adjusting the capacitance value of the coupling capacitor according to the deviation direction of the first transient response parameter relative to the preset test conditions includes: When the amplitude of the pulse current in the first transient response parameter is lower than the preset amplitude target value corresponding to the coupling capacitor, the capacitance value of the coupling capacitor is increased. When the amplitude of the pulse current in the first transient response parameter is higher than the preset amplitude target value corresponding to the coupling capacitor, the capacitance value of the coupling capacitor is reduced. When the transient overvoltage frequency in the first transient response parameter is higher than the preset frequency target value corresponding to the coupling capacitor, the capacitance value of the coupling capacitor is increased. When the transient overvoltage frequency in the first transient response parameter is lower than the preset frequency target value corresponding to the coupling capacitor, the capacitance value of the coupling capacitor is reduced.

6. The method according to claim 3, characterized in that, The operation of adjusting the relative positions of the devices in the test loop includes: When the amplitude of the pulse current in the first transient response parameter is lower than the preset amplitude target value corresponding to the device spacing, the distance between the disconnecting switch and the coupling capacitor is shortened, and / or the distance between the measured capacitive voltage transformer and the disconnecting switch is shortened; When the amplitude of the pulse current in the first transient response parameter is higher than the preset amplitude target value corresponding to the device spacing, the distance between the disconnecting switch and the coupling capacitor is increased, and / or the distance between the measured capacitive voltage transformer and the disconnecting switch is increased; When the transient overvoltage frequency in the first transient response parameter is higher than the preset frequency target value corresponding to the equipment spacing, the distance between the disconnecting switch and the coupling capacitor is increased, and / or the distance between the measured capacitive voltage transformer and the disconnecting switch is increased; When the transient overvoltage frequency in the first transient response parameter is lower than the preset frequency target value corresponding to the device spacing, the distance between the disconnecting switch and the coupling capacitor is shortened, and / or the distance between the measured capacitive voltage transformer and the disconnecting switch is shortened.

7. The method according to claim 3, characterized in that, The inductance value of the current-limiting inductor is 20μH to 500μH.

8. The method according to claim 3, characterized in that, The capacitance of the coupling capacitor is 2nF to 8nF, and the rated voltage of the coupling capacitor is greater than or equal to the rated voltage of the capacitive voltage transformer under test.

9. The method according to claim 1, characterized in that, The operation of judging whether the tested capacitive voltage transformer passes the insulation performance assessment according to the comparison result between the initial insulation state parameter and the final insulation state parameter includes: Compare the error change of the tested capacitive voltage transformer, and if the error does not exceed half of the corresponding error limit of its accuracy class and meets the corresponding accuracy class requirements, this item is judged to be qualified; Compare the capacitance change of the tested capacitive voltage transformer, and if the capacitance change value does not exceed the change amount equivalent to that caused by breakdown of one series element, this item is judged to be qualified; Compare the dielectric loss factor change of the tested capacitive voltage transformer, and if the dielectric loss factor does not exceed 0.0015, this item is judged to be qualified; Compare the partial discharge capacity change of the tested capacitive voltage transformer, and if the partial discharge capacity does not exceed 5pC, this item is judged to be qualified; If all the above items are qualified, it is judged that the tested capacitive voltage transformer passes the insulation performance assessment.

10. A test platform for evaluating the insulation performance of a capacitive voltage transformer, characterized in that, includes: a high-voltage test transformer, configured to provide a test voltage for a test loop; a current-limiting inductor, wherein a first end of the current-limiting inductor is connected to an output end of the high-voltage test transformer; a tested capacitive voltage transformer, wherein a high-voltage input end of the tested capacitive voltage transformer is connected to a second end of the current-limiting inductor; a disconnector, wherein a first end of the disconnector is connected to a low-voltage output end of the tested capacitive voltage transformer; a coupling capacitor, wherein a high-voltage end of the coupling capacitor is connected to a second end of the disconnector, a low-voltage end of the coupling capacitor is grounded, and the coupling capacitor is configured to simulate the capacitance to ground of a series compensation platform; a measurement unit, configured to collect transient response parameters generated in the test loop due to operation of the disconnector; a control unit, wherein the control unit is respectively connected to the high-voltage test transformer, the disconnector and the measurement unit, and the control unit is configured to execute the test method for assessing the insulation performance of a capacitive voltage transformer according to any one of claims 1 to 9.

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