Directly connected large capacity high voltage electrical equipment dielectric loss tester and testing method

Abstract

This invention specifically relates to a dielectric loss tester and method for direct-connected high-capacity high-voltage electrical equipment, belonging to the field of insulation performance measurement of high-voltage electrical equipment. The tester includes: a housing; a microcomputer control unit, a frequency converter, a boost unit, a sampling unit, and a standard capacitor disposed within the housing; and a reactor compensation unit disposed outside the housing, connected between the high-voltage shielded output terminal of the boost unit and ground. The reactor compensation unit provides an inductive compensation current opposite to the direction of the capacitive current of the equipment under test, to offset at least a portion of the capacitive current of the equipment under test, thereby maintaining the output current of the boost unit within its rated output range. This invention performs dielectric loss testing under a 10kV test voltage without removing external conductors and effectively shields the capacitive component of the connected high-voltage electrical equipment, thus accurately measuring the dielectric loss parameters of the direct-connected high-capacity high-voltage electrical equipment itself.

Description

Technical Field

[0001] This invention relates to the field of insulation performance measurement technology for high-voltage electrical equipment, specifically to a dielectric loss tester and method for direct-connected high-capacity high-voltage electrical equipment, used for accurate measurement of dielectric loss factor and capacitance of direct-connected high-capacity high-voltage electrical equipment. Background Technology

[0002] In power systems, dielectric loss parameters, including the dielectric loss factor (tgδ) and capacitance (C), are key parameters for evaluating the insulation condition of high-voltage electrical equipment. Currently, dielectric loss testers are used to test the dielectric loss of high-voltage electrical equipment. These instruments typically include a frequency converter, a boost unit, a sampling unit, and a microcomputer control unit. By applying high voltage and measuring the current flowing through the test sample, they calculate its dielectric loss factor (tgδ) and capacitance (C).

[0003] The main transformer is a typical large-capacity high-voltage electrical equipment. It is the core equipment in a substation that transforms electrical energy from one voltage level to another. The quality of its insulation performance directly determines the safe and stable operation of the entire power system. Therefore, it is crucial to conduct dielectric loss tests on the main transformer regularly.

[0004] In a "direct-connection" wiring structure for the main transformer, such as when the high-voltage side of the main transformer is directly connected to GIS and oil-filled cables without an isolation disconnect, the equivalent capacitance obtained from the measurement terminal will be much larger than the capacitance of the main transformer itself. For example, if... Figure 1 and 2 As shown, the high-voltage side of the main transformer of Unit 3 at Qin Er Plant is directly connected to the GIS and the 500kV oil-filled cable without an isolation port. If the GIS conductor on the high-voltage side of the main transformer is not removed, when measuring the dielectric loss factor (tgδ) and capacitance (C), the total equivalent capacitance is as high as 101.51nF, which exceeds the upper limit of the current instrument's range of 60nF. This is because the capacitance of the GIS (GIS1) on the main transformer side is 0.58nF, the capacitance of the GIS (GIS2) on the 500kV switchyard side is 0.58nF, the capacitance of the 500kV oil-filled cable (CDL) is 100nF, and the capacitance of the voltage transformer (CPT) on the 500kV switchyard side is 0.35nF.

[0005] Existing dielectric loss testers cannot meet the dielectric loss testing requirements of directly connected main transformers under a 10kV test voltage. For example, AI6000L, AI6000D, and AI6000E have a capacitance measurement range of 60pF-1200nF at a 0.5kV test voltage and 3pF-60nF at a 10kV test voltage. GD6000B has a capacitance measurement range of less than 300nF at a 1kV test voltage, less than 150nF at a 5kV test voltage, and less than 60nF at a 10kV test voltage. AI6000K, a fully automatic variable frequency dielectric loss tester, has a capacitance measurement range of 6pF-1000nF at a 0.5kV test voltage and 3pF-60nF at a 10kV test voltage.

[0006] Meanwhile, under the "direct connection" wiring structure of the main transformer, the existing dielectric loss tester measures the comprehensive dielectric loss factor (tgδ) and capacitance (C) of the main transformer and all its connected high-voltage electrical equipment. It cannot effectively shield the capacitive components of high-voltage electrical equipment such as CGIS1, CDL, CGIS2, and CPT, thus making it impossible to accurately obtain the insulation parameters of the high-voltage winding of the main transformer itself.

[0007] To address the aforementioned issues, the power plant attempted two solutions, but neither proved satisfactory. One was to remove the GIS conductor on the high-voltage side of the main transformer before each measurement. However, each removal required a 16-day construction period and a conservatively estimated cost of 800,000 yuan for SF6 gas recovery, external technical support, and the actual removal of the GIS conductor. The second solution was to implement a technical upgrade by adding an isolation break on the high-voltage side of the main transformer, but this was not feasible due to the lack of space in the original design. Therefore, in compact substation design, "accurate measurement without disconnection" remains a long-standing and unresolved technical challenge.

[0008] Therefore, there is an urgent need for a new dielectric loss tester that can directly test the dielectric loss of a direct-connected main transformer under a 10kV test voltage without removing the GIS conductor on the high-voltage side of the main transformer, and can effectively shield background capacitance interference and accurately measure the dielectric loss parameters of the main transformer itself. Summary of the Invention

[0009] The purpose of this invention is to solve the problem in the prior art that it is impossible to perform dielectric loss testing at a 10kV test voltage and accurately measure the dielectric loss parameters of a direct-connected main transformer without removing the high-voltage side GIS conductor, for a direct-connected main transformer without an isolation disconnect. This invention provides a dielectric loss measuring instrument for direct-connected large-capacity high-voltage electrical equipment that can perform dielectric loss testing at a 10kV test voltage without removing the high-voltage side GIS conductor of the direct-connected main transformer, and effectively shields the capacitive components of the connected CGIS1, CDL, CGIS2, and CPT, thereby accurately measuring the dielectric loss parameters of the direct-connected main transformer itself.

[0010] The dielectric loss measuring instrument for direct-connected high-capacity high-voltage electrical equipment provided by this invention is also applicable to other direct-connected high-capacity high-voltage electrical equipment without isolation breaks. It can perform dielectric loss tests under a 10kV test voltage without removing the external conductor, and effectively shield the capacitance component of the connected high-voltage electrical equipment, thereby accurately measuring the dielectric loss parameters of the direct-connected high-capacity high-voltage electrical equipment itself.

[0011] To achieve the above objectives, the present invention provides the following technical solution: A direct-connection high-capacity high-voltage electrical equipment dielectric loss tester includes: case; The microcomputer control unit, frequency converter, boost unit, sampling unit, and standard capacitor are housed within the casing. And a reactor compensation unit located outside the housing and connected between the high-voltage shielded output terminal of the boost unit and ground; The reactor compensation unit is used to provide an inductive compensation current that is opposite to the direction of the capacitive current of the device under test, so as to offset at least a portion of the capacitive current of the device under test, and keep the output current of the boost unit within its rated output range. The microcomputer control unit is connected to the input terminal of the frequency converter power supply unit and is used to control the frequency converter power supply unit to output an adjustable AC voltage. It is also connected to the output terminal of the sampling unit and is used to compare the amplitude ratio and phase difference of the two currents by Fourier transform based on the received current signals from the standard capacitor and the device under test, and to calculate the capacitance and dielectric damage factor of the device under test. The boost unit has its input terminal connected to the output terminal of the frequency converter power supply unit and is connected to the microcomputer control unit. It is used to boost the AC voltage output by the frequency converter power supply unit to the preset test voltage under the control of the microcomputer, and to apply the boosted test voltage to the device under test and the standard container simultaneously. The sampling unit is used to simultaneously acquire the current signal flowing through the standard capacitor and the device under test and send it to the microcomputer control unit. The capacitance value of a standard capacitor is a known and fixed high-precision value. When used in conjunction with a sampling unit, it forms the standard arm of a bridge measurement circuit, providing a benchmark for dielectric loss testing of the device under test.

[0012] As one possible implementation method, the sampling unit includes a reverse connection sampling unit and a normal connection sampling unit; the sampling unit provides two modes for users to choose from: normal connection sampling and reverse connection sampling. In positive sampling mode, the high voltage output terminal of the boost unit is connected to the high voltage terminal of the standard capacitor and the device under test, respectively. The low voltage terminal of the standard capacitor is connected to the first input terminal of the positive sampling unit, and the low voltage terminal of the device under test is connected to the second input terminal of the positive sampling unit. The positive sampling unit is used to synchronously acquire the current signal flowing through the standard capacitor and the device under test and send it to the microcomputer control unit. In reverse connection acquisition mode, the high voltage output terminal of the boost unit is connected to the high voltage input terminal of the reverse connection sampling unit, the current input terminal of the reverse connection sampling unit is connected to the high voltage terminal of the device under test, and the low voltage terminal of the device under test is grounded; the high voltage input terminal and the current input terminal of the reverse connection sampling unit are connected in series internally through a current sampling circuit; the reverse connection sampling unit integrates a standard capacitor branch, which is used to synchronously acquire the current signal flowing through the device under test and the standard capacitor, and send it to the microcomputer control unit through high voltage isolation transmission.

[0013] As one possible implementation method, the microcomputer control unit includes: The first microcomputer is connected to the input terminal of the frequency converter power supply unit and the second microcomputer respectively. It is used to communicate with the second microcomputer and receive measurement results; and to control the frequency converter power supply unit to output an adjustable AC voltage according to the control command. The second microcomputer is connected to the output terminals of the reverse sampling unit and the forward sampling unit, respectively, and is connected to the first microcomputer. It is used to compare the amplitude ratio and phase difference of the two currents by Fourier transform based on the received standard capacitor and the current signal of the device under test, calculate the capacitance and dielectric damage factor of the device under test as the measurement results, and send them to the first microcomputer.

[0014] As one possible implementation method, the microcomputer control unit also includes: The display unit, connected to the first microcomputer, is used to display the measurement results; The button unit is connected to the first microcomputer and is used to input test parameters by pressing the buttons. Based on the input test parameters, control commands are generated and sent to the first microcomputer.

[0015] As one possible approach, the first microcomputer is an ARM7 microcontroller, and the second microcomputer is an ARM Cortex M4 microcontroller.

[0016] As one possible approach, the reactor compensation unit includes one or more reactors connected in parallel; by selecting the inductive reactance value of the reactors and / or the number of reactors in operation, capacitive current compensation for devices under test with different capacities can be achieved.

[0017] As one possible approach, when two reactors with an inductance of 64H and a rated voltage of 12kV are connected in parallel, the maximum measurable capacitance of the tester under a test voltage of 10kV reaches 300nF.

[0018] As one possible approach, the variable frequency power supply unit outputs an AC voltage with an adjustable frequency in the range of 45Hz to 65Hz.

[0019] As one feasible approach, the tester suppresses the 50Hz power frequency and its harmonic interference on site by adopting a frequency conversion measurement method that deviates from the 50Hz power frequency. The preferred method is to use an automatic dual frequency conversion measurement method of 49Hz and 51Hz. The microcomputer control unit performs Fourier transform on the acquired signal to accurately extract the test frequency component and filter out the interference component. When there is power frequency interference with a frequency of 50Hz and an amplitude of 200% of the amplitude of the measured signal current, the accuracy of the tester in measuring capacitance reaches ±(reading × 1% + 1pF), and the accuracy in measuring dielectric loss factor can reach ±(reading × 1% + 0.00040).

[0020] To achieve the above objectives, in a second aspect, the present invention also provides a method for testing the dielectric loss of directly connected high-capacity high-voltage electrical equipment, using the aforementioned dielectric loss tester for directly connected high-capacity high-voltage electrical equipment, comprising the following steps: S1: Based on the estimated capacitance of the device under test, select the type and quantity of reactors in the reactor compensation unit, and connect them in parallel between the high-voltage shielded output terminal of the tester and ground; S2: The microcomputer control unit controls the frequency-adjustable AC voltage output of the frequency converter power supply unit, controls the boost unit to boost the AC voltage output by the frequency converter power supply unit to the preset test voltage, and applies the boosted test voltage synchronously to the device under test and the standard container. S3: During and after the voltage boosting process, the reactor compensation unit generates an inductive compensation current that is opposite to the direction of the capacitive current of the device under test, so as to offset part of the capacitive current of the device under test and keep the output current of the boost unit within the rated output range. S4: The sampling unit synchronously collects the current signal flowing through the standard capacitor and the device under test and sends it to the microcomputer control unit; S5: The microcomputer control unit compares the amplitude ratio and phase difference of the two currents by Fourier transform based on the received current signals from the standard capacitor and the device under test, and calculates the capacitance and dielectric failure factor of the device under test. S6: The microcomputer control unit outputs and displays the calculation results.

[0021] The working principle of the tester of this invention is as follows: Compensation Principle: The device under test (DUT) generates a capacitive current (IC) under the test voltage. The reactor (L) generates an inductive current (IL). According to Kirchhoff's Current Law, the total output current IT that the boost unit needs to provide is the vector difference between IC and IL, i.e., IT = |IC - IL|. By selecting a reactor with appropriate inductive reactance, making IL close to IC, IT can be significantly reduced, making it less than the maximum output current of the boost unit, thereby enabling the measurement of ultra-high capacity high-voltage electrical equipment.

[0022] Measurement Principle: The sampling unit, either directly or indirectly connected, simultaneously collects the current flowing through the device under test (DUT) and a standard capacitor. A second microcomputer compares the amplitude and phase difference of the two currents and uses digital signal processing algorithms to calculate the capacitance and dielectric loss factor of the DUT. The tester employs automatic dual-frequency conversion technology at 49Hz and 51Hz, effectively suppressing interference from the 50Hz power frequency and its harmonics, ensuring measurement accuracy.

[0023] Compared with the prior art, the present invention has the following beneficial technical effects: By employing reactor compensation technology, most of the capacitive current of the main transformer was effectively offset, thereby enabling the test capacitance to be increased to 300nF under a 10kV test voltage by connecting two reactors in parallel. This far exceeds the 60nF upper limit of existing portable instruments and solves the problem that direct-connected large-capacity equipment cannot be directly tested.

[0024] Through reactor compensation and subsequent signal processing, electrical shielding of additional capacitive components such as GIS and oil-filled cables is achieved, so that the measurement results mainly reflect the insulation parameters of the main transformer, thereby enabling accurate evaluation of the main transformer's performance.

[0025] The tester adopts integrated display and microcomputer control technology, integrating all operations, statuses and test results on the display unit, and supports exporting test results, which greatly facilitates on-site operation and data management.

[0026] By designing high-precision positive and negative sampling units and combining them with frequency conversion anti-interference technology, this invention achieves an accuracy of ±(reading × 1% + 1pF) in measuring capacitance and ±(reading × 1% + 0.00040) in measuring dielectric loss factor when there is power frequency interference of 50Hz and amplitude of 200% of the measured signal current amplitude, thus ensuring the accuracy of the test results. Attached Figure Description

[0027] Figure 1 A schematic diagram of the primary wiring of the high-voltage side of the main transformer of Unit 3 at Qin Er Plant; Figure 2 The equivalent circuit diagram of the high-voltage side of the main transformer of Unit 3 at Qin Er Factory; Figure 3 This is a schematic diagram of the structure of a direct-connection high-capacity high-voltage electrical equipment dielectric loss tester provided in an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating the principle of the dielectric loss testing method for direct-connected high-capacity high-voltage electrical equipment provided in an embodiment of the present invention.

[0028] In the diagram, C - equivalent capacitance of the device under test (DUT); IC - DUT current; L - reactor; IL - reactor current; T - boost unit; IT - boost unit output current (rated output current is 0.5A); S - high-voltage shielded output terminal of the boost unit (does not pass through the DUT current test circuit); A - reverse-connected DUT current test circuit, used to detect the capacitance and dielectric loss factor of the DUT; P - high-voltage panel. Detailed Implementation

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0030] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0031] In the description of this invention, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0032] The terms “first”, “second”, etc., are used merely to distinguish elements with similar properties, not to indicate or imply relative importance or a specific order.

[0033] The terms “include,” “comprising,” or any other variation thereof are intended to cover non-exclusive inclusion, which includes not only the elements listed but also other elements not expressly listed.

[0034] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and specific embodiments.

[0035] This embodiment provides a direct-connection high-capacity high-voltage electrical equipment dielectric loss tester, including: case; The microcomputer control unit, frequency converter, boost unit, sampling unit, and standard capacitor are housed within the casing. And a reactor compensation unit located outside the housing and connected between the high-voltage shielded output terminal of the boost unit and ground; The reactor compensation unit is used to provide an inductive compensation current that is opposite to the direction of the capacitive current of the device under test, so as to offset at least a portion of the capacitive current of the device under test, and keep the output current of the boost unit within its rated output range. The microcomputer control unit is connected to the input terminal of the frequency converter power supply unit and is used to control the frequency converter power supply unit to output an adjustable AC voltage. It is also connected to the output terminal of the sampling unit and is used to compare the amplitude ratio and phase difference of the two currents by Fourier transform based on the received current signals from the standard capacitor and the device under test, and to calculate the capacitance and dielectric damage factor of the device under test. The boost unit has its input terminal connected to the output terminal of the frequency converter power supply unit and is connected to the microcomputer control unit. It is used to boost the AC voltage output by the frequency converter power supply unit to the preset test voltage under the control of the microcomputer, and to apply the boosted test voltage to the device under test and the standard container simultaneously. The sampling unit is used to simultaneously acquire the current signal flowing through the standard capacitor and the device under test and send it to the microcomputer control unit. The capacitance value of a standard capacitor is a known and fixed high-precision value. When used in conjunction with a sampling unit, it forms the standard arm of a bridge measurement circuit, providing a benchmark for dielectric loss testing of the device under test.

[0036] In this embodiment, the sampling unit includes a reverse connection sampling unit and a normal connection sampling unit; the sampling unit provides two modes for the user to choose from: normal connection sampling and reverse connection sampling. In positive sampling mode, the high voltage output terminal of the boost unit is connected to the high voltage terminal of the standard capacitor and the device under test, respectively. The low voltage terminal of the standard capacitor is connected to the first input terminal of the positive sampling unit, and the low voltage terminal of the device under test is connected to the second input terminal of the positive sampling unit. The positive sampling unit is used to synchronously acquire the current signal flowing through the standard capacitor and the device under test and send it to the microcomputer control unit. In reverse connection acquisition mode, the high voltage output terminal of the boost unit is connected to the high voltage input terminal of the reverse connection sampling unit, the current input terminal of the reverse connection sampling unit is connected to the high voltage terminal of the device under test, and the low voltage terminal of the device under test is grounded; the high voltage input terminal and the current input terminal of the reverse connection sampling unit are connected in series internally through a current sampling circuit; the reverse connection sampling unit integrates a standard capacitor branch, which is used to synchronously acquire the current signal flowing through the device under test and the standard capacitor, and send it to the microcomputer control unit through high voltage isolation transmission.

[0037] In this embodiment, the microcomputer control unit includes: The first microcomputer is connected to the input terminal of the frequency converter power supply unit and the second microcomputer respectively. It is used to communicate with the second microcomputer and receive measurement results; and to control the frequency converter power supply unit to output an adjustable AC voltage according to the control command. The second microcomputer is connected to the output terminals of the reverse sampling unit and the forward sampling unit, respectively, and is connected to the first microcomputer. It is used to compare the amplitude ratio and phase difference of the two currents by Fourier transform based on the received standard capacitor and the current signal of the device under test, calculate the capacitance and dielectric damage factor of the device under test as the measurement results, and send them to the first microcomputer.

[0038] In this embodiment, the microcomputer control unit further includes: The display unit, connected to the first microcomputer, is used to display the measurement results; The button unit is connected to the first microcomputer and is used to input test parameters by pressing the buttons. Based on the input test parameters, control commands are generated and sent to the first microcomputer.

[0039] In this embodiment, the first microcomputer is an ARM7 microcontroller, and the second microcomputer is an ARM Cortex M4 microcontroller.

[0040] In this embodiment, the reactor compensation unit includes one or more reactors, which are connected in parallel. By selecting the inductive reactance value and / or the number of reactors in operation, capacitive current compensation for devices under test with different capacities can be achieved.

[0041] In this embodiment, when two reactors with an inductance of 64H and a rated voltage of 12kV are connected in parallel, the maximum measurable capacitance of the tester under a test voltage of 10kV reaches 300nF.

[0042] In this embodiment, the frequency converter power supply unit outputs an AC voltage with an adjustable frequency in the range of 45Hz to 65Hz.

[0043] In this embodiment, the tester uses a frequency conversion measurement method that deviates from the power frequency to suppress the power frequency and its harmonic interference on site; the microcomputer control unit performs Fourier transform on the acquired signal to accurately extract the test frequency component and filter out the interference component.

[0044] This embodiment also provides a method for testing the dielectric loss of directly connected high-capacity high-voltage electrical equipment. Using the aforementioned dielectric loss tester for directly connected high-capacity high-voltage electrical equipment, the dielectric loss parameters of the main transformer directly connected to GIS and oil-filled cables are measured, including the following steps: S1: Based on the estimated capacity of the main transformer, select two reactors with an inductance of 64H and a rated voltage of 12kV to be connected in parallel, and connect them in parallel between the high-voltage shielded output terminal of the tester and ground. S2: The user selects positive or negative sampling in the sampling unit; After selecting positive connection sampling, connect the high voltage output terminal of the boost unit to the high voltage terminal of the standard capacitor and the main transformer respectively, connect the low voltage terminal of the standard capacitor to the first input terminal of the positive connection sampling unit, and connect the low voltage terminal of the main transformer to the second input terminal of the positive connection sampling unit. After selecting reverse sampling, the high voltage output terminal of the boost unit is connected to the high voltage input terminal of the reverse sampling unit, the current input terminal of the reverse sampling unit is connected to the high voltage terminal of the device under test, and the low voltage terminal of the device under test is grounded. S3: Set the test voltage to 10kV and the test frequency to 49Hz and 51Hz automatic dual frequency conversion in the microcomputer control unit; the microcomputer control unit controls the frequency-adjustable AC voltage output by the frequency conversion power supply unit, controls the boost unit to boost the AC voltage output by the frequency conversion power supply unit to the preset test voltage, and applies the boosted test voltage synchronously to the device under test and the standard container. S4: During and after the voltage boosting process, the reactor compensation unit generates an inductive compensation current that is opposite to the direction of the capacitive current of the main transformer to offset part of the capacitive current of the main transformer, so that the output current of the boosting unit is maintained within the rated output range. S5: When positive sampling is selected in S2, this step involves the positive sampling unit synchronously acquiring the current signal flowing through the standard capacitor and the device under test and sending it to the microcomputer control unit. When reverse sampling is selected in S2, this step involves the reverse sampling unit synchronously acquiring the current signal flowing through the standard capacitor and the device under test and sending it to the microcomputer control unit. S6: The microcomputer control unit calculates the capacitance and dielectric failure factor of the device under test based on the received current signal from the standard capacitor and the device under test; S7: The microcomputer control unit outputs and displays the calculation results.

[0045] Without a reactor compensation unit, the test current range is 0-0.5A, and the test capacitance range is 0-150nF. After setting two reactors with an inductance of 64H and a rated voltage of 12kV in parallel, each reactor provides a compensation current of about 0.5A and a compensation capacitance of about 150nF. The test current range is increased to 0.5-1.0A, and the test capacitance range is increased to 150-300nF.

[0046] The sheath of the oil-filled cable is connected to the signal input terminal of the tester via the main transformer signal input line. The input resistance of this signal input terminal inside the tester is less than 2 ohms, and the maximum current flowing through the main transformer is 0.5A. Therefore, the voltage value generated at the signal input terminal is very low, less than 15V, and will not break down the cable sheath insulation.

[0047] The tester suppresses 50Hz power frequency interference by employing a frequency conversion measurement method that deviates from the 50Hz power frequency, preferably using an automatic dual-frequency conversion measurement method of 49Hz and 51Hz. Specifically, the first microcomputer controls the frequency conversion power supply unit to output a test voltage with a frequency deviating from the 50Hz power frequency, preferably a dual-frequency conversion test voltage of 49Hz and 51Hz. The response signal generated by the dual-frequency conversion test voltage applied to the device under test differs in frequency from the 50Hz power frequency interference signal in the field. After the sampling unit acquires this response signal, the second microcomputer extracts the signal component at this frequency conversion using digital signal processing technology. The invention filters out 50Hz and harmonic interference components. Since the frequencies of 49Hz and 51Hz are very close to the power frequency of 50Hz, the measured capacitance and dielectric loss factor can accurately reflect the true insulation state of the device under test at the power frequency. Experiments show that this technology enables the present invention to achieve capacitance measurement accuracy of ±(reading × 1% + 1pF) and dielectric loss factor measurement accuracy of ±(reading × 1% + 0.00040) when measuring standard samples with known parameters under power frequency interference with an amplitude of 200% of the measured signal current amplitude, with the tester operating in both positive and negative connection modes. This is attributed to the frequency conversion anti-interference technology and the dual-microcomputer digital signal processing architecture used in this invention to accurately extract the test frequency components and filter out interference components.

[0048] The direct-connection high-capacity high-voltage electrical equipment dielectric loss tester provided in this embodiment successfully solves the problem that existing technologies cannot measure the dielectric loss of high-capacity, high-interference electrical equipment without disconnection, through innovative reactor compensation technology and a precise sampling and control architecture.

[0049] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A direct-connection high-capacity high-voltage electrical equipment dielectric loss tester, characterized in that, include: case; The microcomputer control unit, frequency converter, boost unit, sampling unit, and standard capacitor are housed within the casing. And a reactor compensation unit located outside the housing and connected between the high-voltage shielded output terminal of the boost unit and ground; The reactor compensation unit is used to provide an inductive compensation current that is opposite to the direction of the capacitive current of the device under test, so as to offset at least a portion of the capacitive current of the device under test, and keep the output current of the boost unit within its rated output range. The microcomputer control unit is connected to the input terminal of the frequency converter power supply unit and is used to control the frequency-adjustable AC voltage output by the frequency converter power supply unit. It is connected to the output of the sampling unit and is used to compare the amplitude ratio and phase difference of the two currents by Fourier transform based on the received current signals from the standard capacitor and the device under test, and to calculate the capacitance and dielectric damage factor of the device under test. The boost unit has its input terminal connected to the output terminal of the frequency converter power supply unit and is connected to the microcomputer control unit. It is used to boost the AC voltage output by the frequency converter power supply unit to the preset test voltage under the control of the microcomputer, and to apply the boosted test voltage to the device under test and the standard container simultaneously. The sampling unit is used to simultaneously acquire the current signal flowing through the standard capacitor and the device under test and send it to the microcomputer control unit. The capacitance value of a standard capacitor is a known and fixed high-precision value. When used in conjunction with a sampling unit, it forms the standard arm of a bridge measurement circuit, providing a benchmark for dielectric loss testing of the device under test.

2. The direct-connection high-capacity high-voltage electrical equipment dielectric loss tester according to claim 1, characterized in that, The sampling unit includes a reverse connection sampling unit and a normal connection sampling unit; the sampling unit provides two modes for users to choose from: normal connection sampling and reverse connection sampling. In positive sampling mode, the high voltage output terminal of the boost unit is connected to the high voltage terminal of the standard capacitor and the device under test, respectively. The low voltage terminal of the standard capacitor is connected to the first input terminal of the positive sampling unit, and the low voltage terminal of the device under test is connected to the second input terminal of the positive sampling unit. The positive sampling unit is used to synchronously acquire the current signal flowing through the standard capacitor and the device under test and send it to the microcomputer control unit. In reverse connection acquisition mode, the high voltage output terminal of the boost unit is connected to the high voltage input terminal of the reverse connection sampling unit, the current input terminal of the reverse connection sampling unit is connected to the high voltage terminal of the device under test, and the low voltage terminal of the device under test is grounded; the high voltage input terminal and the current input terminal of the reverse connection sampling unit are connected in series internally through a current sampling circuit; the reverse connection sampling unit integrates a standard capacitor branch, which is used to synchronously acquire the current signal flowing through the device under test and the standard capacitor, and send it to the microcomputer control unit through high voltage isolation transmission.

3. The direct-connection high-capacity high-voltage electrical equipment dielectric loss tester according to claim 1, characterized in that, The microcomputer control unit includes: The first microcomputer is connected to the input terminal of the frequency converter power supply unit and the second microcomputer respectively. It is used to communicate with the second microcomputer and receive measurement results; and to control the frequency converter power supply unit to output an adjustable AC voltage according to the control command. The second microcomputer is connected to the output terminals of the reverse sampling unit and the forward sampling unit, respectively, and is connected to the first microcomputer. It is used to compare the amplitude ratio and phase difference of the two currents by Fourier transform based on the received standard capacitor and the current signal of the device under test, calculate the capacitance and dielectric damage factor of the device under test as the measurement results, and send them to the first microcomputer.

4. The direct-connection high-capacity high-voltage electrical equipment dielectric loss tester according to claim 3, characterized in that, The microcomputer control unit also includes: The display unit, connected to the first microcomputer, is used to display the measurement results; The button unit is connected to the first microcomputer and is used to input test parameters by pressing the buttons. Based on the input test parameters, control commands are generated and sent to the first microcomputer.

5. The direct-connection high-capacity high-voltage electrical equipment dielectric loss tester according to claim 3, characterized in that, The first microcomputer is an ARM7 microcontroller, and the second microcomputer is an ARM Cortex M4 microcontroller.

6. The direct-connection high-capacity high-voltage electrical equipment dielectric loss tester according to claim 1, characterized in that, The reactor compensation unit includes one or more reactors connected in parallel; by selecting the inductive reactance value and / or the number of reactors in operation, capacitive current compensation for equipment under test with different capacities can be achieved.

7. The direct-connection high-capacity high-voltage electrical equipment dielectric loss tester according to claim 6, characterized in that, When two reactors with an inductance of 64H and a rated voltage of 12kV are connected in parallel, the maximum measurable capacitance of the tester under a test voltage of 10kV reaches 300nF.

8. The direct-connection high-capacity high-voltage electrical equipment dielectric loss tester according to claim 1, characterized in that, The variable frequency power supply unit outputs an AC voltage with an adjustable frequency range of 45Hz to 65Hz.

9. The direct-connection high-capacity high-voltage electrical equipment dielectric loss tester according to claim 8, characterized in that, The tester suppresses the 50Hz power frequency and its harmonic interference on site by adopting a frequency conversion measurement method that deviates from the 50Hz power frequency. The preferred method is to use an automatic dual frequency conversion measurement method of 49Hz and 51Hz. The microcomputer control unit performs Fourier transform on the acquired signal to extract the test frequency component. When there is power frequency interference with a frequency of 50Hz and an amplitude of 200% of the amplitude of the measured signal current, the accuracy of the tester in measuring capacitance reaches ±(reading × 1% + 1pF), and the accuracy in measuring dielectric loss factor can reach ±(reading × 1% + 0.00040).

10. A method for testing the dielectric loss of directly connected high-capacity high-voltage electrical equipment, characterized in that, The application of the direct-connected high-capacity high-voltage electrical equipment dielectric loss tester according to any one of claims 1-9 includes the following steps: S1: Based on the estimated capacitance of the device under test, select the type and quantity of reactors in the reactor compensation unit, and connect them in parallel between the high-voltage shielded output terminal of the tester and ground; S2: The microcomputer control unit controls the frequency-adjustable AC voltage output of the frequency converter power supply unit, controls the boost unit to boost the AC voltage output by the frequency converter power supply unit to the preset test voltage, and applies the boosted test voltage synchronously to the device under test and the standard container. S3: During and after the voltage boosting process, the reactor compensation unit generates an inductive compensation current that is opposite to the direction of the capacitive current of the device under test, so as to offset part of the capacitive current of the device under test and keep the output current of the boost unit within the rated output range. S4: The sampling unit synchronously collects the current signal flowing through the standard capacitor and the device under test and sends it to the microcomputer control unit; S5: The microcomputer control unit compares the amplitude ratio and phase difference of the two currents by Fourier transform based on the received current signals from the standard capacitor and the device under test, and calculates the capacitance and dielectric failure factor of the device under test. S6: The microcomputer control unit outputs and displays the calculation results.

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