Dielectric loss measuring instrument
By combining a frequency converter control power supply and a current compensation reactor, the problem of measuring dielectric loss without removing the main transformer from the cable in the existing technology is solved, realizing an efficient and low-cost testing scheme, increasing the test voltage and obtaining accurate data through FFT calculation.
Patent Information
- Application Number
- CN202422017865.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-08-20
- Publication Date
- 2025-12-02
- Estimated Expiration
- 2034-08-20
AI Technical Summary
Existing dielectric loss testing instruments cannot test the main transformer without removing the cable, and adding an isolation break design is complex and costly.
The system employs a frequency converter, a step-up transformer, a reverse-connection current sampling unit, a measurement unit, a display unit, a standard capacitor, and a current compensation reactor. The test is conducted through current compensation, increasing the test voltage to 10kV, and combining this with FFT calculations to obtain accurate capacitance and dielectric loss values.
It enables dielectric loss measurement without removing cables or adding isolation breaks, reducing testing time and costs, and expanding the testing scope.
Smart Images
Figure CN223624330U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of testing equipment technology, and in particular to a dielectric loss measuring instrument. Background Technology
[0002] The high-voltage side of the transformer at the site is directly connected to both the oil-filled cable and the gas-insulated switchgear, without any isolation points. Therefore, if the gas-insulated switchgear and oil-filled cable on the high-voltage side of the transformer are not removed, the measurements of tgδ (dielectric loss value) and C (capacitance value) include the capacitance of both the gas-insulated switchgear and the oil-filled cable. Specifically, the capacitance of the gas-insulated switchgear is 1 nF, and the capacitance of the 500kV oil-filled cable is 100 nF. However, current dielectric loss testing instruments can only test 60 nF capacitance at 10kV, making it impossible to test the transformer without removing the cables. Utility Model Content
[0003] To address the aforementioned technical problems, the purpose of this application is to provide a dielectric loss measuring instrument, comprising:
[0004] Variable frequency control power supply is used to provide power supply voltage;
[0005] A step-up transformer, the input terminal of which is connected to the output terminal of the frequency converter control power supply, is used to step up the power supply voltage.
[0006] A reverse-connection current sampling unit has its input terminal connected to the output terminal of the step-up transformer, and its output terminal connected to the cable and the transformer respectively, for collecting the current passing through the transformer;
[0007] The measurement unit is isolated from the reverse-connection current sampling unit and is connected to the display unit, the cable and the transformer respectively, for collecting and processing test data;
[0008] The display unit has one end connected to the output terminal of the frequency converter control power supply and the other end connected to the test unit, and is used to display the test results;
[0009] A standard capacitor, one side of which is connected to the measuring unit and the other side of which is connected between the step-up transformer and the reverse-connection current sampling unit, is used to provide a reference value to the measuring unit;
[0010] The current compensation reactor has one side connected to the output terminal of the step-up transformer and the standard capacitor respectively via a high-voltage shielded wire, and the other side grounded, used to compensate for the current during testing.
[0011] As an optional embodiment, the input power supply of the frequency converter control power supply is AV220V.
[0012] As an optional embodiment, the output frequency of the variable frequency control power supply is 45Hz to 65Hz.
[0013] As an optional embodiment, the output voltage of the step-up transformer is 10kV, and the output current of the step-up transformer is 500mA.
[0014] As an optional embodiment, the current compensation reactor is connected in parallel with the standard capacitor to compensate for a current of 500mA.
[0015] As an optional embodiment, the capacitance value of the standard capacitor is 50pF ± 2%.
[0016] The beneficial effects of the embodiments of this application are as follows:
[0017] This application eliminates the need to remove the gas-insulated switchgear and cables on the high-voltage side of the main transformer during each test, and also eliminates the need to add an isolation break on the high-voltage side of the main transformer, significantly reducing the testing period and costs. By increasing the power supply and using a current-compensating reactor to compensate for the current, the voltage can be increased to 10kV for testing, expanding the testing range. Furthermore, by subtracting the capacitance of the gas-insulated switchgear and cables using FFT calculations, the capacitance and dielectric loss of the transformer can be calculated. Attached Figure Description
[0018] Figure 1 This is a structural block diagram of an embodiment of this application;
[0019] Figure 2 This is a test schematic diagram of an embodiment of this application. Detailed Implementation
[0020] Various embodiments and features of this application are described herein with reference to the accompanying drawings.
[0021] It should be understood that various modifications can be made to the embodiments described herein. Therefore, the above description should not be considered as limiting, but merely as an example of embodiments. Other modifications within the scope and spirit of this application will be apparent to those skilled in the art.
[0022] The accompanying drawings, which are included in and form part of this specification, illustrate embodiments of the present application and, together with the general description of the present application given above and the detailed description of the embodiments given below, serve to explain the principles of the present application.
[0023] These and other features of this application will become apparent from the following description of preferred forms of embodiments given as non-limiting examples, with reference to the accompanying drawings.
[0024] It should also be understood that although this application has been described with reference to some specific examples, those skilled in the art can certainly implement many other equivalent forms of this application.
[0025] The above and other aspects, features and advantages of this application will become more apparent when taken in conjunction with the accompanying drawings and in view of the following detailed description.
[0026] Specific embodiments of this application are described thereafter with reference to the accompanying drawings; however, it should be understood that the claimed embodiments are merely examples of this application, which can be implemented in various ways. Well-known and / or repeated functions and structures are not described in detail to avoid unnecessary or redundant details that could obscure the application. Therefore, the specific structural and functional details claimed herein are not intended to be limiting, but merely serve as the basis and representative basis for the claims to teach those skilled in the art to use this application in a variety of substantially any suitable detailed structures.
[0027] This specification may use the phrases “in one embodiment,” “in another embodiment,” “in yet another embodiment,” or “in other embodiments,” all of which may refer to one or more of the same or different embodiments according to this application.
[0028] Dielectric loss insulation testing can effectively detect overall moisture-induced deterioration and local defects in the insulation of electrical equipment, and is widely used in electrical manufacturing, electrical equipment installation, commissioning, and preventive testing.
[0029] The anti-interference precision dielectric loss measuring instrument is used for on-site anti-interference dielectric loss measurement or precision dielectric loss measurement in the laboratory. The instrument has an integrated structure, incorporating a dielectric loss bridge, frequency converter, test transformer, and standard capacitor. It employs 1Hz frequency conversion anti-interference and Fourier transform digital filtering technology, enabling fully automatic and intelligent measurement with highly stable data even under strong interference. Measurement results are displayed on a large LCD screen, and the instrument has a built-in micro printer for printing out test results.
[0030] The high-voltage side of the transformer at the site is directly connected to both the oil-filled cable and the gas-insulated switchgear, without any isolation points. Therefore, if the gas-insulated switchgear and oil-filled cable on the high-voltage side of the transformer are not removed, the measurements of tgδ (dielectric loss value) and C (capacitance value) include the capacitance of both the gas-insulated switchgear and the oil-filled cable. The capacitance of the gas-insulated switchgear is less than 1 nF, and the capacitance of the 500kV oil-filled cable is 100 nF. However, current dielectric loss testing instruments can only test 60 nF capacitance at 10kV, making it impossible to test the transformer without removing the cables.
[0031] The existing solutions are: removing the oil-filled cables and gas-insulated switchgear, which requires removal for each test, resulting in long removal and installation periods; and adding an isolation break on the high-voltage side of the main transformer, which has high design requirements and high costs.
[0032] To address the aforementioned problems, embodiments of this application provide a dielectric loss measuring instrument, such as... Figure 1 As shown, the dielectric loss measuring instrument includes a frequency converter control power supply, a step-up transformer, a reverse connection current sampling unit, a measurement unit, a display unit, a standard capacitor, and a current compensation reactor.
[0033] The variable frequency control power supply is used to provide the power supply voltage, wherein the input power supply of the variable frequency control power supply is AV220V. The output frequency of the variable frequency control power supply is 45Hz~65Hz, which reduces the impact of 50Hz power frequency interference and reduces the workload for measuring and calculating the capacitance and dielectric loss of the transformer.
[0034] The input terminal of the step-up transformer is connected to the output terminal of the frequency converter control power supply to boost the power supply voltage. The output voltage of the step-up transformer is 10kV, and the output current is 500mA.
[0035] The input terminal of the reverse connection current sampling unit is connected to the output terminal of the step-up transformer, and its output terminal is connected to both the cable and the transformer to collect the current passing through the transformer. The cable is an oil-filled cable. The output terminal of the reverse connection current sampling unit is connected to the high-voltage test core wire as the test power supply for the test object.
[0036] The measuring unit communicates in isolation from the reverse-connection current sampling unit and is connected to the display unit, the cable, and the transformer, respectively, for collecting and processing test data. One end of the display unit is connected to the output terminal of the frequency converter control power supply, and the other end is connected to the testing unit for displaying test results.
[0037] One side of the standard capacitor is connected to the measuring unit, and the other side is connected between the step-up transformer and the reverse-connection current sampling unit, providing a reference value to the measuring unit. The standard capacitor has a capacitance of 50pF ± 2% and a dielectric loss of less than 0.001%, used to compare the capacitance and dielectric loss values with the test sample.
[0038] The current-compensating reactor has one side connected to the output terminal of the step-up transformer and the standard capacitor via a high-voltage shielded wire, and the other side grounded, used to compensate for the current during testing. The current-compensating reactor and the standard capacitor are connected in parallel to compensate for a 500mA current. This application uses a current-compensating reactor to compensate for the current, eliminating the need for a high-power power supply and reducing the weight and size of the equipment required for testing.
[0039] Therefore, it is not necessary to remove the gas-insulated switchgear and cables on the high-voltage side of the main transformer during each test, nor is it necessary to add an isolation break on the high-voltage side of the main transformer, which greatly reduces the testing period and cost. By increasing the power supply and current compensation reactor, the voltage can be increased to 10kV for testing, thus expanding the testing range.
[0040] In this embodiment, the display unit controls the frequency converter power supply to output a voltage with a frequency of 45Hz-65Hz via communication, and then the voltage is stepped up to 10kV by the step-up transformer. The 10kV voltage is connected to the high-voltage shielded wire, the reverse connection current sampling unit, and the standard capacitor.
[0041] Specifically, the output of the frequency converter control power supply is connected to the input terminal of the step-up transformer. The sinusoidal voltage output by the frequency converter control power supply is stepped up to a 10kV test voltage through the step-up transformer. The 10kV voltage output is connected to the reverse connection current sampling unit. The first high-voltage output of the reverse connection current sampling unit is connected to the high-voltage shielding wire as a high-voltage shield for the test object, shielding stray capacitance to ensure reliable measurement data and reduce its adverse effects on the measurement. The second output is connected to the high-voltage core wire after passing through the reverse connection current sampling unit, serving as the test power supply for the test object. The third output is connected to the standard capacitor, and the tail end of the standard capacitor is connected to the measurement unit. Then, the capacitance value and dielectric loss value of the transformer are calculated.
[0042] The high-voltage shielded wire is connected to a current-compensating reactor, which can increase the test current I. L The reverse connection current sampling unit is connected to the test transformer and cable via a high-voltage core wire, and acquires the total test current I. 总 (I 总 =I L +I 测试仪 -I 标准 ).
[0043] The other end of the cable is connected to a measuring unit to obtain the cable's test current I. DL A standard capacitor is connected to the measuring unit to obtain the test current I of the standard capacitor. 标准 The total test current I is passed through. 总 and the test current I of the cable DLBased on this, the test current I of the transformer is calculated using the FFT (Fast Fourier Transform) algorithm. C I C and I 标准 The capacitance and dielectric loss of the transformer are calculated using the FFT (Fast Fourier Transform) algorithm.
[0044] In this method, a current compensation reactor is used to offset part of the capacitive current in the cable, thereby increasing the current testing range of the test transformer. For example... Figure 2 As shown, the cable is capacitive current I DL The transformer has capacitive current I. C The current compensation reactor is for inductive current I L When the two are connected in parallel, I C I DL with I L They cancel each other out, output current: I 测试仪 =|I DL +I C -I L |, that is, as long as the differential current is provided.
[0045] The dielectric loss measuring instrument can detect a 5A current in the transformer of the test sample, with a maximum output current of 0.5A at high voltage. Because the high-voltage shielding cable is connected to ground by a current compensation reactor, the compensation current I provided by the current compensation reactor... L It can offset most of I C To meet the maximum output current I when the instrument is under high voltage output 测试仪 =|I DL +I C -I L |≤0.5A, which can be less than the maximum output current of the transformer, making the test possible.
[0046] The current-compensating reactor is configured as a 64H / 12kV reactor. The dielectric loss measuring instrument uses an automatic dual-frequency conversion of 49 / 51Hz, which is close to 50Hz. Therefore, 50Hz can be used for calculation at 10kV / 50Hz. The calculation is as follows:
[0047] The compensation current I provided by the 64H / 12kV reactor L =High voltage / (2 * π * frequency * compensation inductance) = 10000 / (2 * 3.14 * 50 * 64) ≈ 0.498A ≈ 0.5A. The large compensation capacitor of the current compensation reactor is approximately 157nF. Two current compensation reactors can compensate approximately 2 * 157nF ≈ 314nF. Therefore, this scheme can measure a sample with a capacitance of 300nF under a 10kV test voltage.
[0048] During the test, after the measurement is started, the high voltage setpoint is sent from the display unit to the frequency converter control power supply. The frequency converter control power supply gradually adjusts the output to the setpoint. The measurement unit sends the measured high voltage to the frequency converter control power supply, forming negative feedback for closed-loop regulation, thereby achieving precise high voltage output.
[0049] The measuring unit reads the corresponding measurement data according to the settings, and then performs FFT calculations on all valid data to obtain the capacitance and dielectric loss values of the sample. After the measurement is completed, the display unit issues a voltage reduction command to control the frequency converter power supply to slowly reduce the voltage to zero.
[0050] For on-site transformer high-voltage bushing output testing, tgδ and C are measured. By measuring tgδ and C, technicians can assess the insulation status of the transformer high-voltage bushing, promptly identify potential insulation problems, thereby preventing faults and extending equipment life.
[0051] This application increases the test range by increasing the power supply and the compensation current of the reactor, and calculates the capacitance and dielectric loss of the transformer by subtracting the capacitance of the cable through FFT calculation.
[0052] In practical operation, this application allows for testing at up to 10kV without requiring the removal of gas-insulated switchgear and cables on the high-voltage side of the main transformer, significantly reducing testing time and costs. Furthermore, it can reduce cable capacitance C. DL With parameter shielding, the testing equipment has a larger capacity and can accurately measure the parameters of the main transformer, meeting national standards.
[0053] The above embodiments are merely exemplary embodiments of this application and are not intended to limit this application. The scope of protection of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent substitutions to this application within its substance and scope of protection, and such modifications or equivalent substitutions should also be considered to fall within the scope of protection of this application.
Claims
1. A dielectric loss measuring instrument, characterized in that, include: Variable frequency control power supply is used to provide power supply voltage; A step-up transformer, the input terminal of which is connected to the output terminal of the frequency converter control power supply, is used to step up the power supply voltage. A reverse-connection current sampling unit has its input terminal connected to the output terminal of the step-up transformer, and its output terminal connected to the cable and the transformer respectively, for collecting the current passing through the transformer; The measurement unit is isolated from the reverse-connection current sampling unit and is connected to the display unit, the cable and the transformer respectively, for collecting and processing test data; The display unit has one end connected to the output terminal of the frequency converter control power supply and the other end connected to the test unit, and is used to display the test results; A standard capacitor, one side of which is connected to the measuring unit and the other side of which is connected between the step-up transformer and the reverse-connection current sampling unit, is used to provide a reference value to the measuring unit; The current compensation reactor has one side connected to the output terminal of the step-up transformer and the standard capacitor respectively via a high-voltage shielded wire, and the other side grounded, used to compensate for the current during testing.
2. The dielectric loss measuring instrument according to claim 1, characterized in that, The input power of the frequency converter control power supply is AV220V.
3. The dielectric loss measuring instrument according to claim 1, characterized in that, The output frequency of the variable frequency control power supply is 45Hz to 65Hz.
4. The dielectric loss measuring instrument according to claim 1, characterized in that, The output voltage of the step-up transformer is 10kV, and the output current of the step-up transformer is 500mA.
5. The dielectric loss measuring instrument according to claim 1, characterized in that, The current compensation reactor is connected in parallel with the standard capacitor to compensate for a current of 500mA.
6. The dielectric loss measuring instrument according to claim 1, characterized in that, The capacitance of the standard capacitor is 50pF ± 2%.