A new type of lobular magnetic shielding partial discharge detection device and detection method

Abstract

The application discloses a novel lung lobe-shaped magnetic shielding partial discharge detection device and a detection method. The device comprises an isolation transformer, a bushing, a detection electrode and a partial discharge instrument. A single-phase power supply is connected with a reactor in parallel, and then connected with an input end of the isolation transformer. One end of an output end of the isolation transformer is connected with the bushing, and then connected with the detection electrode. The other end of the output end of the isolation transformer is grounded. A grounding end of a to-be-detected lung lobe-shaped magnetic shielding is grounded, and the grounding end of the to-be-detected lung lobe-shaped magnetic shielding is connected with the partial discharge instrument. The to-be-detected lung lobe-shaped magnetic shielding and the detection electrode are correspondingly arranged to form an equivalent capacitor and are coupled and connected. The application can be used to determine whether there is a defect in the lung lobe-shaped magnetic shielding by performing a partial discharge test on the lung lobe-shaped magnetic shielding before the lung lobe-shaped magnetic shielding is assembled into a transformer. The application has the characteristics of high test efficiency and low applied voltage, and greatly improves the first-time pass rate of the transformer product provided with the lung lobe-shaped magnetic shielding.

Description

Technical Field

[0001] This invention relates to the field of transformer testing technology, specifically to a novel lung-shaped magnetically shielded partial discharge detection device and method. Background Technology

[0002] Lung-shaped magnetic shielding is named for the lung-like shape of its internal silicon steel sheets. It is a shielding component that protects against magnetic leakage at the ends of transformer coils. High-permeability silicon steel sheets are used as the leakage magnetic shielding material. Due to its large arrangement area, lung-shaped shielding offers excellent shielding performance and is currently widely used in large-capacity transformers.

[0003] The lobe-shaped magnetic shield is filled with high-permeability silicon steel sheets. To fix the silicon steel sheets, epoxy casting is required during the production process. Epoxy casting is carried out in an atmospheric environment, which can lead to defects such as air bubbles. Since the lobe-shaped magnetic shield is installed in the high-electric-field area of ​​a transformer, defects in the shield can affect the transformer's performance, causing partial discharge (PD).

[0004] Internal defects in the lobe-shaped magnetic shield cannot be detected through visual inspection. Currently, they can only be discovered during factory testing after installation on the transformer. Once a defect is found, due to the structural characteristics of the lobe-shaped magnetic shield, the only solution is rework by lifting the shield, removing the coils, and replacing the entire lobe-shaped magnetic shield. The frequent need for transformer rework due to defects in the lobe-shaped magnetic shield severely impacts production efficiency.

[0005] In view of the above-mentioned defects, the inventors of this invention have finally obtained this invention after a long period of research and practice. Summary of the Invention

[0006] To address the aforementioned technical deficiencies, the present invention provides a novel lung-shaped magnetic shielding partial discharge detection device, comprising an isolation transformer, a bushing, a detection electrode, and a partial discharge instrument. A single-phase power supply is connected in parallel with a reactor and then led out to the input terminal of the isolation transformer. One end of the output terminal of the isolation transformer is connected to the bushing and then to the detection electrode. The other end of the output terminal of the isolation transformer is grounded. The grounding terminal of the lung-shaped magnetic shield under test is led out and grounded, and the grounding terminal of the lung-shaped magnetic shield under test is connected to the partial discharge instrument. The lung-shaped magnetic shield under test and the detection electrode are correspondingly configured to form an equivalent capacitance for coupling connection.

[0007] Preferably, the grounding terminal of the lung lobe-shaped magnetic shield to be tested is connected to the partial discharge instrument in sequence via a ring CT scanner and a detection impedance.

[0008] Preferably, the detection electrode and the lung lobe-shaped magnetic shield to be tested are stacked, with a detection electrode disposed between each of the two lung lobe-shaped magnetic shields to be tested, and adjacent detection electrodes do not share the lung lobe-shaped magnetic shield to be tested.

[0009] Preferably, the device also includes an oil tank, with the sleeve disposed at the top of the oil tank, the detection electrode and the lung-shaped magnetic shield to be tested both disposed inside the oil tank, a bottom pad disposed at the bottom of the oil tank, the lung-shaped magnetic shield to be tested being disposed at the bottom of the bottom pad, and a support pad disposed between the detection electrode, the bottom of the oil tank, and adjacent detection electrodes.

[0010] Preferably, the edges of the detection electrodes are rounded.

[0011] Preferably, the surface of the detection electrode is covered with insulating paperboard, and the edge of the detection electrode is surrounded by an edge electrode.

[0012] Preferably, the detection electrodes are connected to each other by a connecting wire through a first terminal, and an electrode wire is then led out from the first terminal and connected to the sleeve.

[0013] Preferably, each of the lung lobe-shaped magnetic shields is provided with two symmetrical leaf electrodes, and each leaf electrode is provided with a grounding plate. The grounding plate is connected to a second terminal fixed on the oil tank through a shielding wire. The second terminal is connected in sequence to the ring CT, the detection impedance and the partial discharge instrument.

[0014] Preferably, a novel lobe-shaped magnetically shielded partial discharge detection method, employing the aforementioned novel lobe-shaped magnetically shielded partial discharge detection device, includes the following steps:

[0015] S1, Before partial discharge detection, the lung-shaped magnetic shielding wire to be tested is placed in the new lung-shaped magnetic shielding partial discharge detection device, and transformer oil is injected into the oil tank through vacuum oil injection.

[0016] S2, the voltage is gradually increased through the single-phase power supply until it reaches the predetermined voltage, and the waveform change on the partial discharge instrument is observed. When the partial discharge instrument detects that the partial discharge value is greater than the detection threshold, the lung lobe-shaped magnetic shield under test has a defect.

[0017] Preferably, before partial discharge detection, the electric field of the lung-shaped magnetic shield under test inside the transformer is simulated and calculated through three-dimensional modeling to obtain the maximum field strength on the surface of the lung-shaped magnetic shield inside the transformer, i.e., the simulated field strength; then, the electric field of the lung-shaped magnetic shield under partial discharge detection is simulated and calculated. The maximum field strength on the surface of the lung-shaped magnetic shield under partial discharge detection is consistent with the simulated field strength, and the maximum voltage required to be applied by the single-phase power supply under partial discharge detection is calculated, i.e., the predetermined voltage, and the detection threshold is 100pC.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: the present invention allows for the determination of whether there are internal defects in the lung-shaped magnetic shield by conducting a partial discharge test on the lung-shaped magnetic shield separately before it is assembled into the transformer; it has the characteristics of high testing efficiency and low applied voltage, which greatly improves the first-pass yield of transformer products equipped with lung-shaped magnetic shield. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the circuit structure of the novel lobe-shaped magnetically shielded partial discharge detection device;

[0020] Figure 2 This is a front view of the structure of the novel lobe-shaped magnetically shielded partial discharge detection device;

[0021] Figure 3 This is a top view of the structure of the novel lobe-shaped magnetically shielded partial discharge detection device;

[0022] Figure 4 This is a side view of the structure of the novel lobe-shaped magnetically shielded partial discharge detection device;

[0023] Figure 5 This is a top view of the internal structure of the novel lobe-shaped magnetically shielded partial discharge detection device;

[0024] Figure 6 The waveform of the partial discharge instrument when the novel lobe-shaped magnetically shielded partial discharge detection device detects a defect is shown in the diagram.

[0025] Figure 7 The waveform of the partial discharge instrument is shown when no defect is detected by the novel lung-shaped magnetic shielded partial discharge detection device.

[0026] The numbers in the image represent:

[0027] 1-Isolation transformer; 2-Bushing; 3-Detection electrode; 4-Partial discharge instrument; 5-Lung-shaped magnetic shield; 6-Single-phase power supply; 7-Reactor; 8-Circular CT; 9-Detection impedance; 10-Oil tank; 11-Bottom pad; 12-Support pad; 13-Insulating cardboard; 14-Edge electrode; 15-First terminal; 16-Grounding piece; 17-Second terminal; 18-Insulating support; 19-Rising seat; 20-Oil pipe; 21-Oil conservator; 22-Gas connection pipe; 23-Cover plate; 24-Oil inlet; 25-Oil return port. Detailed Implementation

[0028] The above-mentioned and other technical features and advantages of the present invention will be described in more detail below with reference to the accompanying drawings.

[0029] Example 1

[0030] like Figure 1 As shown, Figure 1 This is a schematic diagram of the circuit structure of the novel lung-shaped magnetically shielded partial discharge detection device.

[0031] The novel lung-shaped magnetic shielded partial discharge detection device of this invention includes an isolation transformer 1, a bushing 2, a detection electrode 3, and a partial discharge instrument 4. A single-phase power supply 6 is connected in parallel with a reactor 7, which is then led out and connected to the input terminal of the isolation transformer 1. One end of the output terminal of the isolation transformer 1 is connected to the bushing 2 and then to the detection electrode 3. The other end of the output terminal of the isolation transformer 1 is grounded. The grounding terminal of the lung-shaped magnetic shield 5 under test is led out and grounded, and the grounding terminal of the lung-shaped magnetic shield 5 under test is connected to the partial discharge instrument 4. The lung-shaped magnetic shield 5 under test and the detection electrode 3 are correspondingly configured to form an equivalent capacitance for coupling connection. The reactor 7 is used to adjust the test circuit current, and the isolation transformer 1 is used to isolate external signal interference.

[0032] Preferably, the grounding terminal of the lung lobe-shaped magnetic shield 5 to be tested is connected to the partial discharge instrument 4 in sequence through the ring CT 8 and the detection impedance 9.

[0033] like Figures 2 to 5 As shown, Figure 2 This is a front view of the structure of the novel lobe-shaped magnetically shielded partial discharge detection device; Figure 3 This is a top view of the structure of the novel lobe-shaped magnetically shielded partial discharge detection device; Figure 4 This is a side view of the structure of the novel lobe-shaped magnetically shielded partial discharge detection device; Figure 5 This is a top view of the internal structure of the novel lung-shaped magnetically shielded partial discharge detection device.

[0034] Generally, the detection electrode 3 and the lung lobe-shaped magnetic shield 5 to be tested are stacked, and a detection electrode 3 is provided between each of the two lung lobe-shaped magnetic shields 5 to be tested, and adjacent detection electrodes 3 do not share the lung lobe-shaped magnetic shield 5 to be tested.

[0035] The novel lobe-shaped magnetic shielded partial discharge detection device of the present invention further includes an oil tank 10. The sleeve 2 is disposed at the top of the oil tank 10. The detection electrode 3 and the lobe-shaped magnetic shield 5 to be tested are both disposed inside the oil tank 10. A bottom pad 11 is disposed at the bottom of the oil tank 10. The lobe-shaped magnetic shield 5 to be tested, which is located at the bottom, is disposed on the bottom pad 11. Support pads 12 are disposed between the detection electrode 3 and the bottom of the oil tank 10 and between adjacent detection electrodes 3 to stably support the placement of the detection electrode 3 in the oil tank 10 and prevent the detection electrode 3 from sagging and deforming.

[0036] Specifically, a lung-shaped magnetic shield is stacked on top of the bottom pad 11, and a detection electrode 3 is stacked on top of the lung-shaped magnetic shield. Another lung-shaped magnetic shield is then stacked on top of the detection electrode 3, followed by another lung-shaped magnetic shield, and then another detection electrode 3. Finally, another lung-shaped magnetic shield is stacked, forming a configuration where one detection electrode 3 is sandwiched between every two lung-shaped magnetic shields. The number of lung-shaped magnetic shields can be increased, and correspondingly, the number of detection electrodes 3 should also be increased. Since the detection electrodes 3 are at the same potential, multiple lung-shaped magnetic shields can be tested simultaneously.

[0037] The edges of the detection electrodes 3 are all rounded to reduce the electric field strength on the surface of the detection electrodes 3. The placement of the detection electrodes 3 is designed according to the overlap position of the lobe-shaped magnetic shield with the high-voltage coil in the transformer to ensure that the electric field strength of the lobe-shaped magnetic shield during testing is consistent with that during transformer testing.

[0038] The distance between the lobe-shaped magnetic shield and the detection electrode 3 is very small, so that the electric field value during factory testing can be achieved with a very small voltage. For example, in this embodiment, when a 55kV power frequency voltage is applied, the electric field strength on the surface of the lobe-shaped magnetic shield can be achieved when the coil end voltage is 395kV during transformer testing. The number of lobe-shaped magnetic shields and the detection electrode 3 can be increased as needed. This embodiment only illustrates the case of four lobe-shaped magnetic shields and two detection electrodes 3.

[0039] The surface of the detection electrode 3 is covered with insulating paperboard 13 to reduce the electric field strength on the surface during the test. The edge of the detection electrode 3 is surrounded by an edge electrode 14 to mitigate the electric field strength at the edge of the detection electrode 3.

[0040] The detection electrode 3 has a connecting hole drilled at its corner for obtaining a potential. The detection electrodes 3 are connected to each other by a connecting wire through a first terminal 15, and an electrode wire is then led out from the first terminal 15 and connected to the sleeve 2. During the test, voltage is applied through the sleeve 2.

[0041] Each of the aforementioned lobe-shaped magnetic shields is provided with two symmetrical leaf electrodes, and each leaf electrode is provided with a grounding plate 16. The grounding plate 16 is connected to a second terminal 17 fixed on the oil tank 10 via a shielded wire. The second terminal 17 is sequentially connected to the annular CT 8, the detection impedance 9, and the partial discharge instrument 4. During the test, the partial discharge waveform signal displayed on the partial discharge instrument 4 can be used to determine whether there is a defect in each lobe-shaped magnetic shield.

[0042] An insulating support 18 is fixedly installed inside the oil tank 10. The insulating support 18 supports the connecting wire, the electrode wire and the shielding wire.

[0043] This invention allows for the determination of internal defects in the lobed magnetic shield by conducting a partial discharge test on the lobed magnetic shield separately before it is assembled into the transformer. It features high testing efficiency and low applied voltage, greatly improving the first-pass yield of transformer products equipped with lobed magnetic shields.

[0044] Example 2

[0045] A riser seat 19 is fixedly installed on the outer side of the top of the oil tank 10. The sleeve 2 is fixedly installed above the riser seat 19. The top of the oil tank 10 is fixedly connected to the oil conservator 21 through an oil pipe 20. The oil pipe 20 is connected to the top of the riser seat 19 through a vent pipe 22. The oil conservator 21 and the oil pipe 20 are used to adjust the oil level inside the oil tank 10 to adapt to changes in oil level at different temperatures. The vent pipe 22 is used to discharge the gas at the top of the riser seat 19.

[0046] The second terminal 17 is fixedly connected to one side of the oil tank 10 via a cover plate 23, which facilitates the installation and removal of the second terminal 17.

[0047] The top of the oil tank 10 is provided with an oil inlet 24, and the bottom of the oil tank 10 is provided with an oil return outlet 25. Both the oil inlet 24 and the oil return outlet 25 are connected to an external oil supply system. The oil inlet 24 and the oil return outlet 25 are used to inject and flow out the transformer oil in the oil tank 10 to simulate the state of the transformer during operation.

[0048] Example 3

[0049] The novel lobe-shaped magnetically shielded partial discharge detection method of the present invention, employing the novel lobe-shaped magnetically shielded partial discharge detection device, includes the following steps:

[0050] S1. Before partial discharge detection, the lung-shaped magnetic shield 5 to be tested is wired into the new lung-shaped magnetic shield partial discharge detection device, and transformer oil is injected into the oil tank 10 through vacuum oil injection to simulate the state of the transformer inside operation.

[0051] S2, the voltage is gradually increased through the single-phase power supply 6 until it reaches the predetermined voltage, and the waveform change on the partial discharge instrument 4 is observed. When the partial discharge instrument 4 detects that the partial discharge value is greater than the detection threshold, the lung lobe-shaped magnetic shield 5 under test has a defect.

[0052] Before partial discharge (PD) testing, a 3D model is used to simulate the electric field of the lung-shaped magnetic shield inside the transformer, yielding the maximum electric field strength on the surface of the lung-shaped magnetic shield within the transformer, i.e., the simulated field strength. Then, the electric field of the lung-shaped magnetic shield under PD testing conditions is simulated. The maximum electric field strength on the surface of the lung-shaped magnetic shield under PD testing conditions is consistent with the simulated field strength, allowing the calculation of the maximum voltage required to be applied by the single-phase power supply under PD testing conditions, i.e., the predetermined voltage. Because the distance between the electrodes and the lung-shaped magnetic shield is small, a relatively small voltage is sufficient to maximize the electric field strength on the surface of the lung-shaped magnetic shield.

[0053] Generally, the predetermined voltage is set to 55kV, and the detection threshold is 100pC.

[0054] Specifically, such as Figure 6 The image shows the partial discharge (PD) signals of the two internal silicon steel sheets (the two leaf electrodes) on the left and right sides of a lung-shaped magnetic shield. These PD signals were measured when a voltage of 55kV was applied, at which point the electric field strength on the lung-shaped magnetic shield reached the value required for transformer testing. The PD value in the left image is 34.94pC, and in the right image it is 1259.49pC. The PD waveforms are clear and free of interference, typical of bubble discharge in adhesive. The PD value in the left image is less than 100pC, meeting the transformer test acceptance standards, while the PD value in the right image is much greater than 100pC, failing to meet the requirements. Therefore, this lung-shaped magnetic shield cannot be installed on a transformer.

[0055] like Figure 7 As shown, the partial discharge signal of the silicon steel sheet inside another lung-shaped magnetic shield is 6.38pC in the left image and 5.16pC in the right image. The partial discharge value is much less than 100pC, so the partial discharge of the lung-shaped magnetic shield meets the requirements, indicating that there are no internal defects and it can be used in transformers.

[0056] This invention employs an equivalent field strength method to detect defects in the lobe-shaped magnetic shielding under a relatively low test voltage. It features high testing efficiency and low applied voltage, significantly improving the first-pass yield of transformer products equipped with lobe-shaped magnetic shielding.

[0057] The above description is merely a preferred embodiment of the present invention and is illustrative rather than restrictive. Those skilled in the art will understand that many changes, modifications, and even equivalents can be made within the spirit and scope defined by the claims of the present invention, all of which will fall within the protection scope of the present invention.

Claims

1. A novel lobe-shaped magnetically shielded partial discharge detection device, characterized in that, The system includes an isolation transformer, a bushing, detection electrodes, and a partial discharge instrument. A single-phase power supply parallel reactor is led out and connected to the input terminal of the isolation transformer. One end of the output terminal of the isolation transformer is connected to the bushing and then to the detection electrode. The other end of the output terminal of the isolation transformer is grounded. The grounding terminal of the lung lobe-shaped magnetic shield under test is led out and grounded, and the grounding terminal of the lung lobe-shaped magnetic shield under test is connected to the partial discharge instrument. The lung lobe-shaped magnetic shield under test and the detection electrode are correspondingly configured to form an equivalent capacitance for coupling connection.

2. The novel lobe-shaped magnetically shielded partial discharge detection device as described in claim 1, characterized in that, The grounding terminal of the lung lobe-shaped magnetic shield to be tested is connected to the partial discharge instrument in sequence via a ring CT and a detection impedance.

3. The novel lobe-shaped magnetically shielded partial discharge detection device as described in claim 2, characterized in that, The detection electrode and the lung lobe-shaped magnetic shield to be tested are stacked in a layered manner, with a detection electrode disposed between each of the two lung lobe-shaped magnetic shields to be tested, and adjacent detection electrodes do not share the lung lobe-shaped magnetic shield to be tested.

4. The novel lobe-shaped magnetically shielded partial discharge detection device as described in claim 3, characterized in that, It also includes an oil tank, the sleeve is disposed at the top of the oil tank, the detection electrode and the lung lobe-shaped magnetic shield to be tested are both disposed inside the oil tank, a bottom pad is disposed at the bottom of the oil tank, the lung lobe-shaped magnetic shield to be tested at the bottom is disposed on the bottom pad, and a support pad is disposed between the detection electrode, the bottom of the oil tank and the adjacent detection electrode.

5. The novel lobe-shaped magnetically shielded partial discharge detection device as described in claim 4, characterized in that, The edges of the detection electrodes are all rounded.

6. The novel lobe-shaped magnetically shielded partial discharge detection device as described in claim 4, characterized in that, The surface of the detection electrode is covered with insulating cardboard, and the edge of the detection electrode is surrounded by an edge electrode.

7. The novel lobe-shaped magnetically shielded partial discharge detection device as described in claim 4, characterized in that, The detection electrodes are connected to each other by a connecting wire through a first terminal, and an electrode wire is then led out from the first terminal and connected to the sleeve.

8. The novel lobe-shaped magnetically shielded partial discharge detection device as described in claim 7, characterized in that, Each of the lung-shaped magnetic shields is provided with two symmetrical leaf electrodes. Each leaf electrode is provided with a grounding plate. The grounding plate is connected to a second terminal fixed on the oil tank through a shielding wire. The second terminal is connected in sequence to the ring CT, the detection impedance and the partial discharge instrument.

9. A novel method for detecting partial discharge using a lobe-shaped magnetically shielded system, employing the novel lobe-shaped magnetically shielded partial discharge detection device as described in claim 8, characterized in that... Including the following steps: S1, Before partial discharge detection, the lung-shaped magnetic shielding wire to be tested is placed in the new lung-shaped magnetic shielding partial discharge detection device, and transformer oil is injected into the oil tank through vacuum oil injection. S2, the voltage is gradually increased through the single-phase power supply until it reaches a predetermined voltage, and the waveform change on the partial discharge instrument is observed. When the partial discharge value detected by the partial discharge instrument is greater than the detection threshold, the lung lobe-shaped magnetic shield under test has a defect.

10. The novel lung lobe-shaped magnetically shielded partial discharge detection method as described in claim 9, characterized in that, Before partial discharge testing, the electric field of the lung-shaped magnetic shield under test inside the transformer is simulated and calculated using 3D modeling to obtain the maximum electric field strength on the surface of the lung-shaped magnetic shield inside the transformer, i.e., the simulated electric field strength. Then, the electric field of the lung-shaped magnetic shield under partial discharge testing is simulated and calculated. The maximum electric field strength on the surface of the lung-shaped magnetic shield under partial discharge testing is consistent with the simulated electric field strength. The maximum voltage required to be applied by the single-phase power supply under partial discharge testing is calculated, i.e., the predetermined voltage. The detection threshold is 100pC.

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