Test system for partial discharge test of transformer
By using different filter combinations in the transformer partial discharge test system to filter out low-frequency and high-frequency interference, the problem of severe interference in transformer partial discharge tests is solved, and high-precision discharge quantity measurement is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- SUZHOU HUADIAN ELECTRIC CO LTD
- Filing Date
- 2023-09-26
- Publication Date
- 2026-04-24
AI Technical Summary
In transformer partial discharge tests, there is severe interference from signals. Existing technical solutions are greatly affected by test conditions and environment, making it difficult to effectively suppress interference, resulting in inaccurate test results or the inability to conduct the test.
The first and second low-pass filters are combined to filter out low-frequency and high-frequency harmonic interference, respectively. By setting LC and LCL filters, combined with iron-core and coreless inductors, the harmonics of ground grid and spatial interference are filtered out, thereby improving the test conditions.
It effectively reduces background noise in the test, ensures the accuracy of the test results, meets the requirements of partial discharge test, and achieves discharge quantity measurement below 20pC.
Smart Images
Figure CN224163763U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of high-voltage testing technology for electrical equipment in power system distribution networks, specifically to a test system for partial discharge testing of transformers. Background Technology
[0002] Partial discharge, also known as partial discharge, refers to the non-penetrating discharge phenomenon that occurs in electrical equipment (such as transformers) under the influence of voltage, occurring in the air gaps, oil films, or conductor edges within the insulation structure.
[0003] The insulation structure of electrical equipment (such as transformers) is complex, and there are many reasons for partial discharge. For example, improper design may result in excessively high electric field strength in localized areas; manufacturing defects may introduce air bubbles into the insulation; mechanical vibration and thermal expansion and contraction can cause localized cracking and air bubble formation, all of which can lead to partial discharge even at lower applied voltages. Partial discharge in electrical equipment can continue to develop, causing insulation aging. Therefore, conducting partial discharge experiments on large power transformers and measuring their parameters can effectively and promptly identify defects in the transformer's manufacturing and installation processes, playing a crucial role in ensuring the safe operation of power transformers.
[0004] Interference signals are often present during transformer partial discharge tests, commonly including power supply interference, spatial electromagnetic field interference, test equipment interference, ground grid interference, and floating potential interference. The waveform detected at the test site may be the result of multiple interferences acting together. These interferences have a significant impact on the test results, potentially making square wave verification impossible or even completely drowning out the transformer's own partial discharge signal. Therefore, suppressing interference in transformer partial discharge tests is particularly important.
[0005] Existing partial discharge test interference elimination schemes are related to actual test conditions and environment, and are greatly affected by human factors. For example, if the transformer is subjected to partial discharge test after oil filling or oil replenishment, attention should be paid to letting it stand for more than 24 hours in accordance with the test procedures or manufacturer requirements (following the stricter standards) to allow internal air bubbles to fully escape or dissolve. The test can only be carried out after all the vent holes of the transformer are vented. Before the test, the iron core, clamps, and the grounding of the end screen terminals of each winding bushing of the transformer should be carefully checked, etc.
[0006] Therefore, it is necessary to find an interference scheme for transformer partial discharge testing that is not affected by actual test conditions, environment, or human factors. Utility Model Content
[0007] To address the aforementioned problems, this invention provides a testing system for partial discharge testing of transformers, effectively solving the problem of electromagnetic interference in the space environment and grounding grid.
[0008] The technical solution is as follows: a test system for partial discharge testing of a transformer, comprising the following components connected in series:
[0009] Power supply, used for supplying power;
[0010] An excitation transformer, the primary side of which is connected to the power supply;
[0011] A test transformer, wherein the primary side of the test transformer is connected to the secondary side of the excitation transformer;
[0012] A bushing capacitor is connected to the secondary side of the test transformer.
[0013] The detection impedance is connected to the secondary side of the test transformer and is connected in series with the bushing capacitor.
[0014] A partial discharge meter, wherein the partial discharge meter is connected in parallel across the detection impedance;
[0015] Its features are:
[0016] A first low-pass filter is provided between the power supply and the primary side of the excitation transformer;
[0017] A second low-pass filter is provided between the secondary side of the excitation transformer and the primary side of the test transformer.
[0018] Furthermore, the first low-pass filter and the second low-pass filter have different filtering frequency bands.
[0019] Furthermore, the first low-pass filter includes two LC filters: inductor L1 and capacitor C1 form one LC filter, and inductor L2 and capacitor C2 form another LC filter. Inductor L1 is connected between the power supply and the primary side of the excitation transformer, and inductor L1 is connected to capacitor C1 and then grounded. Inductor L2 is connected between the power supply and the primary side of the excitation transformer, and inductor L2 is connected to capacitor C2 and then grounded.
[0020] Furthermore, the second low-pass filter includes two LCL filters. Inductor L3, capacitor C3, and inductor L4 form one LCL filter, and inductor L5, capacitor C4, and inductor L6 form the other LCL filter. Inductors L3 and L4, connected in series, are connected between the secondary side of the excitation transformer and the primary side of the test transformer. Inductors L3 and L4 are connected to ground via capacitor C3. Inductors L5 and L6, connected in series, are connected between the secondary side of the excitation transformer and the primary side of the test transformer. Inductors L5 and L6 are connected to ground via capacitor C4.
[0021] Furthermore, the frequency at which the first low-pass filter filters out harmonics is lower than the frequency at which the second low-pass filter filters out harmonics.
[0022] Furthermore, the inductor of the first low-pass filter is an iron-core reactor with an inductance value on the order of mH, and the capacitor is a power filter capacitor with a capacitance value on the order of uF. The passband cutoff frequency is within 1KHz.
[0023] Furthermore, the inductor of the second low-pass filter is a coreless high-frequency inductor with an inductance value on the order of mH, and the capacitor is a power filter capacitor with a capacitance value on the order of nF. The passband cutoff frequency is within 10KHz.
[0024] The partial discharge test system of this invention, by setting a first low-pass filter and a second low-pass filter, can effectively filter out and improve the harmonics of ground grid and space interference, thereby achieving the test conditions for partial discharge. Attached Figure Description
[0025] Figure 1 This is a schematic diagram of a transformer partial discharge test system according to an embodiment;
[0026] Figure 2 This is the partial discharge value of a three-phase transformer without a filter.
[0027] Figure 3 The partial discharge value of the three-phase transformer after adding the filter;
[0028] Figure 4 The images show the frequency response curves of the filter and the improved filter. Detailed Implementation Plan
[0029] Potential problems in the two current partial discharge tests of transformers:
[0030] 1. Transformer partial discharge test: The test scenario is complex. Due to the presence of a large number of operating electrical equipment around the site, there are discharge phenomena, harmonics, vibrations, eddy currents, noise, etc., which generate currents to the ground and pollute the ground. The on-site partial discharge test requires the discharge quantity to be below 100pC, but the test background may have exceeded 100pC. The on-site conditions for partial discharge test cannot be met, so the test cannot be carried out.
[0031] 2. For transformer factory testing, the test site has a shielded room with a good test background. However, due to the aging of the ground wire, the operation of other equipment often interferes with the partial discharge test. The test input line voltage waveform is not clean. When introduced into the test chamber, it will generate spatial radiation, which will interfere with the partial discharge test. The factory test requirement for the test chamber is within 20pC, but if the background of the test chamber is not good, it will reach more than 20pC, which cannot meet the conditions for partial discharge test.
[0032] In this embodiment, solutions are proposed to address potential problems in two types of partial discharge tests. Based on the requirements of transformer testing, a test system for transformer partial discharge testing is designed to filter out and improve harmonics from ground grid and spatial interference, thereby achieving the test conditions for partial discharge.
[0033] See Figure 1 This utility model provides a test system for partial discharge testing of a transformer in an embodiment, comprising the following components connected in series:
[0034] Power supply 1 is used for power supply, and power supply 1 can be a frequency converter.
[0035] Excitation transformer 2, the primary side of excitation transformer 2 is connected to power supply 1;
[0036] Test transformer 3, the primary side of test transformer 3 is connected to the secondary side of excitation transformer 2;
[0037] Bushing capacitor 4 is connected to the secondary side of test transformer 3.
[0038] The detection impedance 5 and detection impedance 4 are connected to the secondary side of the test transformer 3 and are connected in series with the bushing capacitor 4.
[0039] Partial discharge instrument 6 is connected in parallel across the detection impedance 5;
[0040] A first low-pass filter 7 is provided between the power supply 1 and the primary side of the excitation transformer 2;
[0041] A second low-pass filter 8 is provided between the secondary side of the excitation transformer 2 and the primary side of the test transformer 3.
[0042] In practice, the first low-pass filter and the second low-pass filter have different filtering frequency bands. The first low-pass filter 7 can filter out the lower frequency harmonic components in the harmonic interference, while the second low-pass filter 8 can filter out the higher frequency harmonic components in the harmonic interference.
[0043] Specifically, in the embodiment, the first low-pass filter 7 includes two LC filters. Inductor L1 and capacitor C1 form one LC filter, and inductor L2 and capacitor C2 form another LC filter. Inductor L1 is connected between the power supply and the primary side of the excitation transformer, and inductor L1 is connected to capacitor C1 and then grounded. Inductor L2 is connected between the power supply and the primary side of the excitation transformer, and inductor L2 is connected to capacitor C2 and then grounded.
[0044] Specifically, in this embodiment, the second low-pass filter includes two LCL filters. Inductor L3, capacitor C3, and inductor L4 form one LCL filter, and inductor L5, capacitor C4, and inductor L6 form the other LCL filter. Inductors L3 and L4, connected in series, are connected between the secondary side of the excitation transformer and the primary side of the test transformer. Inductors L3 and L4 are connected to ground via capacitor C3. Similarly, inductors L5 and L6, also connected in series, are connected between the secondary side of the excitation transformer and the primary side of the test transformer. Inductors L5 and L6 are connected to ground via capacitor C4.
[0045] In one specific embodiment, the inductor of the first low-pass filter is a coreless reactor with an inductance value on the order of mH, and the capacitor is a power filter capacitor with a capacitance value on the order of uF, and the passband cutoff frequency is within 1KHz; the inductor of the second low-pass filter is a coreless high-frequency inductor with an inductance value on the order of mH, and the capacitor is a power filter capacitor with a capacitance value on the order of nF, and the passband cutoff frequency is within 10KHz.
[0046] The following section provides a detailed description of the use of the partial discharge test system described in the embodiments for conducting partial discharge tests on a power transformer of model ODFS-400000 / 500. The frequency range of the partial discharge test is 40KHz to 300KHz.
[0047] In this example, a frequency converter is used for power supply. The output voltage is converted into a high-voltage AC voltage that is close to a sine wave by the first low-pass filter. L1 and L2 are iron-core reactors, which only have a smoothing effect on the frequency voltage within 400Hz and a suppression effect on the frequency voltage above 400Hz, which meets the requirements of the partial discharge test for the frequency converter in the frequency range of 30 to 300Hz.
[0048] The signal from the first low-pass filter is boosted by the excitation transformer 2 to meet the input voltage requirements of the test transformer. To achieve the requirement of a low partial discharge of less than 20pC, the excitation transformer 2 is a dry-type isolation transformer with an iron core, which has a good blocking effect on high frequencies.
[0049] The output high voltage then passes through a second low-pass filter to filter out high-frequency carrier signals. L3-L6 are high-frequency inductors, and C3-C4 are non-inductive high-frequency absorption capacitors. The filter smooths frequencies below 10kHz and suppresses frequencies above 10kHz, attenuating the voltage to over 30dB. The output voltage is then connected to the test transformer for partial discharge testing.
[0050] Test results are as follows Figure 2 , Figure 3 , Figure 2 This is the partial discharge value of a three-phase transformer without a filter. Figure 3The partial discharge readings of the three-phase transformer after adding a filter are compared. Figure 2 and Figure 3 The discharge amount was significantly reduced. The test data is shown in Table 1. The test system for partial discharge test achieved the design effect.
[0051] Table 1
[0052]
[0053]
[0054] In the embodiments of the present invention, further improvements are made based on the above embodiments by using parallel connection of inductor and resistor, parallel connection of capacitor and resistor, etc., which can improve the resonance phenomenon caused by the inclusion of inductor L and capacitor in the circuit. Figure 4 The two curves A and B in the figure are the frequency response curves of the filter before and after the improvement, respectively. It can be seen from the curves that curve A has a peak at around 40KHz, while curve B is flatter.
[0055] In this embodiment, the first low-pass filter can filter out low-frequency interference and shape the voltage waveform, while the second low-pass filter can filter out high-frequency interference signals. Users can select filters of different frequency bands according to their needs to improve the background of the field use environment, suppress high-frequency interference on the circuit, and meet the partial discharge test conditions. At the same time, in order to solve the problem of poor frequency response curve characteristics caused by the resonant frequency of the LC filter, the inductor, capacitor and resistor are connected in series and parallel to make the frequency response curve achieve a monotonically decreasing effect.
[0056] It will be apparent to those skilled in the art that this invention is not limited to the details of the exemplary embodiments described above, and that it can be implemented in other specific forms without departing from the spirit or essential characteristics of this invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of this invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this invention.
Claims
1. A test system for partial discharge testing of a transformer, comprising: Power supply, used for supplying power; An excitation transformer, the primary side of which is connected to the power supply; A test transformer, wherein the primary side of the test transformer is connected to the secondary side of the excitation transformer; A bushing capacitor is connected to the secondary side of the test transformer. The detection impedance is connected to the secondary side of the test transformer and is connected in series with the bushing capacitor. A partial discharge meter, wherein the partial discharge meter is connected in parallel across the detection impedance; Its features are: A first low-pass filter is provided between the power supply and the primary side of the excitation transformer; A second low-pass filter is provided between the secondary side of the excitation transformer and the primary side of the test transformer.
2. The partial discharge test system for a transformer of claim 1, wherein: The first low-pass filter and the second low-pass filter have different filtering frequency bands.
3. The partial discharge test system for a transformer of claim 1, wherein: The first low-pass filter includes two LC filters. Inductor L1 and capacitor C1 form one LC filter, and inductor L2 and capacitor C2 form the other LC filter. Inductor L1 is connected between the power supply and the primary side of the excitation transformer, and inductor L1 is connected to capacitor C1 and then grounded. Inductor L2 is connected between the power supply and the primary side of the excitation transformer, and inductor L2 is connected to capacitor C2 and then grounded.
4. The partial discharge test system for a transformer of claim 3, wherein: The second low-pass filter includes two LCL filters. Inductor L3, capacitor C3, and inductor L4 form one LCL filter, and inductor L5, capacitor C4, and inductor L6 form the other LCL filter. Inductors L3 and L4, connected in series, are connected between the secondary side of the excitation transformer and the primary side of the test transformer. Inductors L3 and L4 are connected to ground via capacitor C3. Inductors L5 and L6, connected in series, are connected between the secondary side of the excitation transformer and the primary side of the test transformer. Inductors L5 and L6 are connected to ground via capacitor C4.
5. The partial discharge test system for a transformer of claim 2, wherein: The first low-pass filter removes harmonics at a frequency lower than that of the second low-pass filter.
6. The partial discharge test system for a transformer of claim 3, wherein: The inductor of the first low-pass filter is an iron-core reactor with an inductance value on the order of mH, and the capacitor is a power filter capacitor with a capacitance value on the order of uF. The passband cutoff frequency is within 1KHz.
7. The partial discharge test system for a transformer of claim 4, wherein: The inductor of the second low-pass filter is a coreless high-frequency inductor with an inductance value in the mH range, and the capacitor is a power filter capacitor with a capacitance value in the nF range. The passband cutoff frequency is within 10KHz.
8. The partial discharge test system for a transformer of claim 1, wherein: The excitation transformer is a dry-type isolation transformer.
9. The partial discharge test system for a transformer of claim 4, wherein: For the inductors in the first and second low-pass filters, resistors are connected in parallel; for the capacitors in the first and second low-pass filters, resistors are connected in parallel.