An anti-interference online monitoring method for partial discharge of high-voltage transformer bushings

Abstract

The present invention relates to an anti-interference online monitoring method for partial discharge of high-voltage transformer bushings. In addition to the high-frequency current sensor on the transformer end screen grounding, another high-frequency current sensor is installed at the transformer core grounding wire. The system can synchronously collect two signals. Through the time domain comparison algorithm of the two signals, the transformer partial discharge signal can be effectively filtered out, and only the bushing partial discharge signal is retained, thereby achieving the purpose of monitoring the partial discharge of the high-voltage transformer bushing.

Description

Technical Field

[0001] The invention belongs to the technical field of insulation monitoring of large-scale high-voltage transformer bushings, and in particular relates to an online high-voltage transformer bushing partial discharge monitoring method. Background Art

[0002] Transformers play a crucial role in power transmission. Transformers of different voltage levels can be combined to connect power grids of varying voltages, forming a complex and extensive power network that enables long-distance transmission of electrical energy. The transformer bushing is the most critical component at the transformer busbar input and output interfaces, and its performance directly impacts the transformer's proper operation.

[0003] At present, the testing of high-voltage transformer bushings is still mainly in the offline detection stage. That is, when the transformer is shut down for maintenance, the bushings are tested together with the routine inspection and testing of the high-voltage transformer. Online monitoring still mainly focuses on the transformer as the main monitoring object, mainly including: main transformer oil chromatography, partial discharge, core grounding current, oil temperature and oil pressure monitoring, which are relatively mature monitoring systems. The monitoring of bushings mainly includes leakage current, bushing dielectric loss and capacitance monitoring, which are more common, while online monitoring of partial discharge of high-voltage transformer bushings is less common.

[0004] Currently, there are several main methods for online monitoring of partial discharge of high-voltage transformer bodies and transformer bushings, depending on the location and method of coupling partial discharge signals: first, a high-frequency current sensor (HFCT) is used to pass through the end-screen grounding wire to couple the bushing partial discharge signal; second, the high-voltage bushing is used as a coupling capacitor, and a sampling capacitor or inductor is connected in series with the end-screen grounding wire to couple the bushing partial discharge signal; third, an ultrasonic or geomagnetic wave sensor is installed on the outside of the bushing's raised seat to couple the bushing partial discharge signal; fourth, a long-distance non-contact ultra-high frequency sensor is used to couple the bushing partial discharge signal by receiving ultra-high frequency electromagnetic waves in space. The first two methods primarily monitor partial discharge (PD) in the transformer itself, not in the transformer bushing. The third method uses ultrasonic and geomagnetic wave sensors to couple the bushing PD signal at the bushing riser. This method, however, only measures the PD qualitatively, not quantitatively. Furthermore, the transformer is significantly affected by its own vibration during operation, leading to inaccurate measurements. The fourth method, the ultra-high frequency (UHF) method, suffers from the fact that the transformer bushing is an external device, completely exposed to the outside world and therefore susceptible to interference from high-frequency electromagnetic waves from mobile phones, base stations, and other sources, resulting in significant measurement errors. Therefore, it is currently impossible to accurately detect transformer bushing PD signals. Summary of the Invention

[0005] The purpose of the present invention is to provide an effective anti-interference monitoring method for online monitoring of partial discharge of high-voltage transformer bushings: by utilizing high-speed synchronous acquisition of high-frequency current pulse signals of the bushing end screen grounding wire and the transformer core grounding wire, and using the corresponding time domain pulse filtering method of the two signals, the transformer partial discharge pulse interference can be effectively separated and filtered out, thereby achieving the purpose of monitoring partial discharge of the bushing.

[0006] The technical solution adopted by the present invention to achieve the above-mentioned object is: an anti-interference high-voltage transformer bushing partial discharge online monitoring method, which comprises: providing a first current sensor at the transformer end screen grounding and a second current sensor at the transformer core grounding, collecting and processing signals from the two current sensors to obtain bushing discharge signals, thereby realizing real-time detection of bushing partial discharge, and comprising the following steps:

[0007] Simultaneously collect signals from two current sensors; wherein the first current sensor collects signals from the transformer bushing, and the second current sensor collects signals from the transformer core;

[0008] According to the pulse position of the transformer core signal, the corresponding transformer bushing signal position is found, and the transformer core signal is filtered out to obtain the bushing partial discharge signal.

[0009] The transformer core signal and the transformer bushing signal have the same pulse position in the time domain.

[0010] The signals of the two current sensors are synchronized.

[0011] An anti-interference high-voltage transformer bushing partial discharge online monitoring system, comprising:

[0012] The first current sensor is located at the grounding point of the transformer end screen and is used for the transformer bushing signal;

[0013] The second current sensor is provided at the grounding position of the transformer core and is used to collect the transformer core signal;

[0014] The acquisition unit is used to receive signals from the first current sensor and the second current sensor, find the corresponding transformer bushing signal position according to the pulse position of the transformer core signal, and filter the transformer core signal to obtain the bushing partial discharge signal.

[0015] The length of the connection line between the first current sensor and the acquisition unit is equal to the length of the connection line between the second current sensor and the acquisition unit.

[0016] The first current sensor and the second current sensor are high-frequency current sensors.

[0017] The first current sensor and the second current sensor are of the same model.

[0018] The present invention has the following beneficial effects and advantages:

[0019] The present invention uses HFCT to obtain partial discharge signals. The partial discharge signal of the transformer body can be regarded as an interference signal. This method can filter out the transformer body discharge signal. Because the partial discharge of the transformer body is 1 to 2 orders of magnitude greater than the partial discharge of the transformer bushing, and the two discharge mechanisms are similar, the characteristics of the discharge statistical spectrum formed are also very similar. Therefore, by adding a high-frequency current sensor signal of the transformer core grounding wire, the two signals are synchronously collected at high speed. Through the time domain comparison algorithm of the two channels, the partial discharge signal of the transformer body can be effectively filtered out, achieving the purpose of monitoring the partial discharge of the high-voltage transformer bushing. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Structure diagram of the transformer bushing partial discharge online monitoring system.

[0021] Among them, 1 transformer bushing, 2 end screen grounding interface, 3 bushing seat, 4 iron core, 5 transformer body, 6 winding, 7 iron core grounding wire, 8 transformer shell grounding wire, 9 end screen grounding wire, 10 high-frequency current sensor, 11 cable, 12 acquisition unit, 13 optical fiber line, 14 host;

[0022] Figure 2 Schematic diagram of the anti-interference method for online monitoring of partial discharge in transformer bushings.

[0023] Figure 3 When the simulated discharge source discharges simultaneously in the transformer body and the bushing, the system tests a time domain pulse diagram.

[0024] Figure 4a The discharge spectrum of the transformer end screen grounding wire sensor signal when partial discharge is generated only at the transformer bushing.

[0025] Figure 4b The discharge spectrum of the transformer core grounding wire sensor signal when partial discharge occurs only at the transformer bushing.

[0026] Figure 5a When partial discharge occurs simultaneously due to defects in the transformer bushing and body, the transformer end screen grounding wire sensor obtains the discharge statistics and discharge spectrum after the time domain algorithm.

[0027] Figure 5b When partial discharge occurs simultaneously due to defects in the transformer bushing and body, the transformer core grounding wire sensor obtains the discharge statistics and discharge spectrum after the time domain algorithm. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0029] The present invention utilizes HFCT to extract partial discharge signals at the bushing end screen grounding wire and can separate the transformer body partial discharge and bushing partial discharge signals, thereby filtering out transformer body discharge while retaining transformer bushing discharge. In a high-voltage transformer bushing partial discharge monitoring system, the transformer body partial discharge signal can be considered an interference signal and must be filtered out using a specific method. Furthermore, because the transformer body partial discharge is one to two orders of magnitude greater than the transformer bushing partial discharge, and the two discharge mechanisms are similar, the characteristics of the resulting discharge statistical spectrum are also very similar. Therefore, completely filtering out transformer body partial discharge is particularly difficult.

[0030] This patent proposes an anti-interference online monitoring method for partial discharge of high-voltage transformer bushings, that is, an anti-interference method that can effectively filter out partial discharge of the transformer body when testing partial discharge of the transformer bushing. The specific approach is to add a high-frequency current sensor signal of the transformer core grounding wire on the basis of the first monitoring method, so that the two signals can be collected synchronously at high speed. Through the time domain comparison algorithm of the two channels, the partial discharge signal of the transformer body can be effectively filtered out.

[0031] There are many anti-interference methods for transformer bushing partial discharge monitoring, and different methods are suitable for different interferences. These mainly include: using threshold filtering to filter out baseband noise; using software and hardware filtering to filter out fixed-frequency interference signals; and using time-domain windowing to filter out periodic pulse interference. However, the transformer body discharge signal can also be transmitted through the bushing to the end screen grounding point. Therefore, the partial discharge signal coupled at the end screen is the result of the time domain superposition of the bushing partial discharge and the transformer body partial discharge. However, separating the two signals is extremely difficult, whether from the single-pulse discharge pulse characteristics, frequency characteristics, transmission characteristics, or the final statistical discharge spectrum characteristics. The apparent discharge charge of the transformer body is much greater than the apparent discharge charge of the transformer bushing. Therefore, it is difficult to separate the two signals that have been superimposed in the time domain using only the transformer bushing end screen grounding line signal.

[0032] In addition to the high-frequency current sensor on the transformer end screen grounding, another high-frequency current sensor is installed at the transformer core grounding wire to couple the partial discharge signal of the transformer body. Since the bushing discharge signal amplitude is small (the bushing factory partial discharge is generally tens of picoules), it is transmitted to the core grounding through the transformer bus and winding coil, and the signal transmission attenuation is large. Therefore, the high-frequency current sensor installed at the transformer core grounding wire is basically unable to couple to the bushing partial discharge signal, while the transformer body partial discharge signal can be coupled to both the end screen grounding wire and the core grounding wire. This system can synchronize the two signals. Acquisition, through the time domain comparison algorithm of the two signals, that is, the transformer bushing sensor signal and the transformer core signal are collected at the same time. When the bushing has discharge, due to the small discharge amount, only the transformer bushing sensor is coupled at this time; when there is discharge inside the transformer, the transformer bushing sensor and the transformer core sensor are coupled to the signal at the same time. Since the two signals are collected at the same time, the positions of the two pulses in the time domain are consistent. Therefore, the corresponding transformer bushing signal position can be found according to the pulse position of the transformer core signal and filtered out, thereby achieving the purpose of filtering out the internal discharge of the transformer and retaining the bushing partial discharge signal.

[0033] The system structure of the present invention is as follows: Figure 1 As shown, two through-hole high-frequency current sensors 10 pass through the end screen grounding wire 9 and the core grounding wire 7 respectively, and are connected to the acquisition unit 12 through a high-frequency coaxial cable 11. The acquisition unit 12 is connected to the test host 14 through an optical fiber line 13. The storage, calculation, processing and display of the final test data are all completed on the test host 14, thus forming an online monitoring system for partial discharge of transformer bushings.

[0034] like Figure 1 As shown, the transformer is composed of a transformer body 5 consisting of an iron core 4, a winding 6 and other components. A bushing seat 3 is provided at the upper end of the transformer body 5, and a transformer bushing 1 is connected to the bushing seat 3. The bottom of the transformer bushing 1 has an end screen grounding interface 2, which is connected to an end screen grounding wire 9. The end screen grounding wire 9 is grounded through a transformer casing grounding wire 8. The transformer iron core 4 is single-ended grounded through the iron core grounding wire 7, thus forming a transformer connection structure.

[0035] like Figure 2As shown in the figure, the transformer winding is connected to the high-voltage busbar through a bushing. The outer layer of the transformer bushing is grounded via the end-screen grounding wire, and the transformer core is grounded via the grounding wire. When a partial discharge occurs in the transformer, due to the large discharge amount, one discharge signal (1) will be transmitted along the busbar to the bushing. Due to its high frequency, it can be transmitted to the end-screen grounding wire through the capacitance of the transformer bushing, thereby being coupled by the HFCT at the end-screen grounding wire. The other signal will be transmitted along the transformer core grounding wire and coupled by the HFCT at the core grounding wire. The two signals are collected simultaneously by the high-speed acquisition module, so the pulses are essentially coincident at the time of occurrence. This characteristic can be used to filter out partial discharges generated by the transformer. When a partial discharge occurs in the transformer bushing, due to the small discharge amount, it can only be directly transmitted to the end-screen grounding wire through capacitance. However, the inductance, interturn capacitance, and distributed capacitance of the transformer winding severely attenuate the signal, making it difficult to couple to the partial discharge signal caused by the bushing discharge at the core grounding wire. Therefore, by comparing the two signals, the transformer partial discharge signal can be completely filtered out, and only the bushing partial discharge signal is retained, which increases the system's anti-interference ability, truly monitors the transformer bushing partial discharge amount, and objectively reflects the transformer bushing insulation status.

[0036] An anti-interference online monitoring method for partial discharge of high-voltage transformer bushings is implemented by the following steps:

[0037] Step 1: Reference Figure 1 ,Will Figure 1 Connect the system using the connection method in the figure, use two pulse generators simulating partial discharge to input discharge pulses at the transformer body and transformer bushing positions respectively, to simulate partial discharge occurring at the two positions, and use the system test to check the system's anti-interference ability.

[0038] Step 2: First, connect the simulated discharge pulse source to the transformer winding 6 to simulate the inter-turn discharge defect of the transformer. The discharge amount is 200pC and the pulse is input continuously. Then, connect the simulated discharge pulse source to the transformer bushing to simulate the partial discharge generated by the transformer bushing. The discharge amount is 20pC. Finally, according to Figure 1 Connect the transformer bushing partial discharge online monitoring system and start the system to test the anti-interference method described in this patent, such as Figure 3As shown in the figure, the waveform (a) of the end-screen grounding wire sensor clearly shows the superposition of two periodic pulse waves: one is the transformer body partial discharge pulse wave, which has a larger amplitude and an average amplitude of 1.3V, while the transformer bushing partial discharge pulse wave has a smaller amplitude and an average amplitude of 0.2V. This shows that the end-screen grounding wire can simultaneously receive partial discharge signals from the transformer body and the transformer bushing. The waveform (b) of the core grounding wire sensor shows that only one pulse signal exists. A time domain comparison with the waveform (a) of the end-screen grounding wire sensor shows that the time point of the pulse coincides with the time point when the end-screen grounding wire sensor couples to the transformer body partial discharge pulse. Because the system is synchronously collected, the signal coupled at this time is the partial discharge signal of the transformer body. The transmission paths of partial discharge pulses in transformers vary, resulting in different distributed impedances. The transmission impedance of high-frequency pulse signals through the core grounding conductor is greater than the impedance of the transformer bushing end screen grounding conductor. Therefore, the amplitude of the partial discharge signal through the core grounding conductor is smaller than that of the transformer bushing end screen grounding conductor. Therefore, during factory partial discharge testing and routine maintenance partial discharge testing on transformers, partial discharge signals are typically obtained from the transformer bushing end screen grounding conductor. The waveform (c) after time-domain pulse comparison and filtering shows that the partial discharge signal from the transformer body has been completely filtered out, retaining only the partial discharge signal from the transformer bushing. Therefore, laboratory simulated discharge experiments demonstrate that this method effectively filters out partial discharge signals caused by the transformer body, retaining only the partial discharge signal from the transformer bushing, achieving true monitoring of transformer bushing partial discharge.

[0039] The process of this method is verified through actual transformer pressure test:

[0040] The present invention proposes an anti-interference online monitoring method for partial discharge of high-voltage transformer bushings, which is verified by actual transformer pressure. Figure 1 Connect all components of the monitoring system as shown, confirming that all connections are correct, ensuring that the coaxial lines from the two high-frequency current sensors 10 to the acquisition unit 12 are of equal length, and minimizing the time error between the two paths. Next, artificially create defects at different locations in the actual transformer and apply pressure to induce partial discharge. Finally, test data from the monitoring system verifies the feasibility of this method.

[0041] First, place a metal wire inside the transformer bushing to simulate the suspended discharge caused by metal foreign matter inside the bushing. Then assemble the entire transformer and slowly apply pressure to maintain continuous discharge inside the bushing. Test the signals of the two channels and form discharge spectra respectively, as shown in the following figure. Figure 4a-4b As shown, Figure 4aThe transformer end screen grounding wire sensor signal discharge spectrum shows a clear discharge signal, and the discharge points are concentrated in symmetrical phases, which is consistent with the internal discharge characteristics of power equipment. This shows that this discharge signal comes from inside the transformer bushing, and the discharge amount is 5.92pC. Figure 4b It can be seen that the signals are basically baseband interference signals, and there is no obvious discharge signal. This shows that the discharge signal generated by the transformer bushing is severely attenuated by the transformer body and is difficult to couple out on the core grounding wire.

[0042] Next, a metal burr is made in the transformer winding to simulate the inter-turn discharge of the transformer body. After the entire transformer is reassembled, the monitoring system is connected and the voltage is slowly increased to the same level so that the two defects have obvious discharge signals. The system test is started and the two-way signal time domain filtering algorithm proposed in this patent is applied to obtain the following results: Figure 5a-5b The waveform shown in the figure shows the transformer core grounding wire sensor signal discharge spectrum. Figure 5b It can be seen that the transformer body has a large discharge signal, the discharge amount is 55.92pC, and the discharge characteristics are consistent with the internal discharge signal characteristics of the power equipment, indicating that this discharge is generated by the transformer body. Figure 5a As shown in the figure, there is still an obvious discharge signal, and the discharge amount is 5.22pC, which is consistent with the discharge amount when only the defect is made on the transformer bushing. It is also only a partial discharge signal of the transformer bushing. Therefore, it shows that the time domain comparison filtering algorithm proposed in this patent can effectively filter out the partial discharge signal generated by the transformer body, so its result is not interfered by the discharge signal generated by the transformer body.

[0043] Finally, by Figure 5a-5b It can be clearly seen that the algorithm proposed in this patent has completely filtered out the transformer body discharge and retained the partial discharge signal of the transformer bushing.

[0044] It can be seen from this that the anti-interference online monitoring method for partial discharge of high-voltage transformer bushings involved in this patent can effectively separate the partial discharge signals of the transformer bushing and the partial discharge signals of the transformer body, and filter them out. Using the algorithm of this patent, the system misjudgment can be effectively reduced and the insulation status of the transformer bushing can be truly reflected.

Claims

1. An anti-interference online monitoring method for partial discharge of high-voltage transformer bushings, characterized in that: By setting a first current sensor at the transformer end screen grounding and a second current sensor at the transformer core grounding, collecting and processing the signals of the two current sensors, obtaining the bushing discharge signal and thus realizing real-time detection of bushing partial discharge, the method includes the following steps: Simultaneously collect signals from two current sensors; wherein the first current sensor collects signals from the transformer bushing, and the second current sensor collects signals from the transformer core; The transformer bushing signal and the transformer core signal are collected simultaneously. When the bushing discharges, only the first current sensor is coupled due to the small discharge amount. When the transformer discharges inside, the second current sensor and the first current sensor are coupled to the signal at the same time. Since the two signals are collected simultaneously, the positions of the two pulses are consistent in the time domain. According to the pulse position of the transformer core signal, the corresponding transformer bushing signal position is found, and the transformer core signal is filtered out to obtain the bushing partial discharge signal; The transformer core signal and the transformer bushing signal have the same pulse position in the time domain.

2. The anti-interference monitoring system of the high-voltage transformer bushing partial discharge online monitoring method according to claim 1 is characterized in that: include: The first current sensor is located at the grounding point of the transformer end screen and is used to collect the transformer bushing signal; The second current sensor is provided at the grounding position of the transformer core and is used to collect the transformer core signal; An acquisition unit is configured to receive signals from the first current sensor and the second current sensor, find the corresponding transformer bushing signal position according to the pulse position of the transformer core signal, and filter out the transformer core signal to obtain a bushing partial discharge signal; Receiving signals from the first current sensor and the second current sensor, specifically: the transformer body winding is connected to the high-voltage busbar through the bushing, the outer layer of the transformer bushing is grounded through the end-screen grounding wire, and the transformer core is grounded through the grounding wire. When partial discharge occurs in the transformer, due to the large discharge amount, one path of the discharge signal will be transmitted along the busbar to the bushing. Due to the high signal frequency, it is transmitted to the end-screen grounding wire through the capacitance of the transformer bushing, and thus is coupled to the second current sensor at the end-screen grounding wire; the other path will be transmitted along the transformer core grounding wire, and thus is coupled to the first current sensor at the core grounding point; the connection between the first current sensor and the acquisition unit is equal in length to the connection between the second current sensor and the acquisition unit; The method of finding the corresponding transformer bushing signal position according to the pulse position of the transformer core signal and filtering the transformer core signal to obtain the bushing partial discharge signal includes: when the bushing has discharge, since the discharge amount is small, only the first current sensor is coupled to the transformer bushing signal; When there is discharge inside the transformer, the second current sensor and the first current sensor are coupled to the signal at the same time. Since the two signals are collected at the same time, the positions of the pulses corresponding to the two signals are consistent in the time domain. Based on the pulse time domain position of the transformer core signal, the corresponding transformer bushing signal position is found, and the transformer core signal is filtered out to obtain the bushing partial discharge signal. The transformer core signal and the transformer bushing signal have the same pulse position in the time domain.

3. The anti-interference monitoring system for high-voltage transformer bushing partial discharge online monitoring method according to claim 2, characterized in that: The first current sensor and the second current sensor are high-frequency current sensors.

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