Power frequency interference resistant FRA online monitoring sensor

Abstract

The invention relates to an FRA online monitoring sensor capable of resisting power frequency interference. The FRA online monitoring sensor comprises a shielding shell, an annular iron core and a balance coil. A containing cavity is defined by the shielding shell, the balance coil is wound on the annular iron core, the balance coil and the annular iron core jointly form a body, the body is contained in the containing cavity, and the size error of the annular iron core is controlled within a preset range; a grounding bolt is arranged at the bottom end of the shielding shell, the grounding bolt is matched with the root of a sleeve of the transformer to be monitored, the grounding bolt is used for being screwed on the root of the sleeve of the transformer to be monitored, and the grounding bolt is connected with a grounding grid of the transformer to be monitored through a copper woven belt; and by arranging the shielding shell, the anti-interference capability is improved, and the winding state can be accurately monitored.

Description

Technical Field

[0001] This invention relates to the field of online monitoring technology for power equipment, and in particular to an FRA online monitoring sensor that is resistant to power frequency interference. Background Technology

[0002] Currently, transformers are core power transmission and transformation equipment in power systems, and the structural integrity of their windings directly determines their operational safety and reliability. If the windings deform due to factors such as short circuits or vibrations (e.g., displacement, bending, inter-turn short circuits), it will gradually lead to insulation aging and increased partial discharge, which in severe cases can cause equipment failure and shutdown, resulting in significant economic losses and the risk of power outages.

[0003] Traditional winding monitoring relies on offline FRA detection, which requires power outages and cannot track winding status in real time, making it difficult to meet the "uninterrupted power supply or minimal power outages" operation and maintenance requirements of power systems. Existing online monitoring solutions, however, suffer from the following core technical problems with FRA online monitoring sensors:

[0004] Weak anti-interference capability: Power system sites have complex electromagnetic environments such as power frequency magnetic fields, high frequency communication interference, and corona discharge. Traditional sensors do not have a dedicated shielding design, and external interference is easy to intrude, resulting in low signal-to-noise ratio and high false alarm rate of monitoring signals, and inability to accurately identify winding partial discharge signals.

[0005] Insufficient high-frequency performance: The partial discharge signal corresponding to winding deformation is concentrated in the 1kHz to 10MHz frequency band. Traditional sensors have problems such as low transmission impedance (<5mV / mA) and narrow 6dB bandwidth (<2MHz), making it difficult to capture weak high-frequency partial discharge signals of 50pC level, resulting in early missed detection of winding deformation.

[0006] Poor resistance to power frequency saturation: When the transformer is running at full load, the power frequency current can reach 2500A. The toroidal core of traditional sensors is prone to magnetic saturation (saturation occurs when the power frequency current is less than 1000A), which causes signal distortion or even failure, making it impossible to monitor normally under full load conditions.

[0007] Low processing and testing efficiency: Traditional sensors rely on manual processing, resulting in large errors in the size of the toroidal core (±1mm), deviations in the number of coil turns (±5%), and poor performance consistency (pass rate <60%). Testing requires manual circuit setup, data recording, and manual calculation, with a single unit test taking more than 4 hours, making it difficult to meet the needs of mass production and engineering applications.

[0008] Poor environmental and standard compatibility: Traditional sensor housings have low protection levels (mostly below IP54), making them prone to damage in substation environments with high temperature, high humidity, and strong vibration; they lack standardized installation interfaces at the root of 10kV / 110kV bushings, making installation complex and incompatible; at the same time, they do not meet the insulation and mechanical performance requirements of the power industry standard DL / T 1498.1-2016, posing safety hazards. Summary of the Invention

[0009] To address the shortcomings of existing technologies, the purpose of this invention is to provide an online monitoring sensor for FRA that is resistant to power frequency interference. Its advantages include improved anti-interference capability and accurate identification of winding partial discharge signals. At the same time, it improves the high-frequency signal detection sensitivity, processing and testing efficiency, and adaptability. In addition, it solves the technical problem of "magnetic saturation under high power frequency current" and ensures stable performance under complex working conditions.

[0010] The above-mentioned objective of this invention is achieved through the following technical solution: an FRA online monitoring sensor resistant to power frequency interference, comprising a shielding shell, a toroidal core, and a balancing coil; the shielding shell is configured to form an accommodating cavity, the balancing coil is wound on the toroidal core, the balancing coil and the toroidal core together constitute the body, the body is housed within the accommodating cavity, and the dimensional error of the toroidal core is controlled within a preset range; a grounding bolt is provided at the bottom end of the shielding shell, the grounding bolt is adapted to the bushing root of the transformer to be monitored, the grounding bolt is used to screw into the bushing root of the transformer to be monitored, and the grounding bolt is connected to the grounding grid of the transformer to be monitored through a copper braided strip.

[0011] Preferably, in the FRA online monitoring sensor for resisting power frequency interference provided by the present invention, the annular iron core is made of nanocrystalline alloy material.

[0012] Preferably, in the FRA online monitoring sensor for resisting power frequency interference provided by the present invention, the surface of the annular iron core is treated with resin curing.

[0013] Preferably, the FRA online monitoring sensor for resisting power frequency interference provided by the present invention includes a shielding housing comprising a metal shell and an anti-corrosion layer, wherein the metal shell is configured to form an accommodating cavity, and the anti-corrosion layer is disposed on the outer surface of the metal shell.

[0014] Preferably, the FRA online monitoring sensor for resisting power frequency interference provided by the present invention includes an aluminum alloy body and a stainless steel foil layer in the metal housing. The stainless steel foil layer is disposed on the inner surface of the aluminum alloy body, and the anti-corrosion layer is sprayed on the outer surface of the aluminum alloy body.

[0015] Preferably, the FRA online monitoring sensor for resisting power frequency interference provided by the present invention includes an anti-corrosion layer comprising an oxide layer, a fine sand layer, and an anti-ultraviolet coating. The oxide layer is formed by black oxidation treatment of the outer surface of the metal shell, and fine sand is sprayed onto the oxide layer to form the fine sand layer. The anti-ultraviolet coating is sprayed onto the fine sand layer.

[0016] Preferably, in the FRA online monitoring sensor for resisting power frequency interference provided by the present invention, the thickness of the anti-ultraviolet coating ranges from 5 to 8 μm.

[0017] Preferably, in the FRA online monitoring sensor for resisting power frequency interference provided by the present invention, the gap between the balancing coil and the toroidal core is in the range of 0.1 to 0.2 mm.

[0018] Preferably, the FRA online monitoring sensor for resisting power frequency interference provided by the present invention uses epoxy resin potting compound to encapsulate and fix the balance coil onto the annular iron core.

[0019] Preferably, in the FRA online monitoring sensor for resisting power frequency interference provided by the present invention, the lead wire of the balanced coil is a shielded cable.

[0020] In summary, the beneficial technical effects of this invention are as follows: The FRA online monitoring sensor for resisting power frequency interference provided in this application includes a shielding shell, a toroidal core, and a balancing coil; the shielding shell is configured to form an accommodating cavity, and the balancing coil is wound on the toroidal core. The balancing coil and the toroidal core together constitute the body, which is housed within the accommodating cavity. The dimensional error of the toroidal core is controlled within a preset range; a grounding bolt is provided at the bottom of the shielding shell, which is adapted to the bushing root of the transformer to be monitored. The grounding bolt is used to screw onto the bushing root of the transformer to be monitored, and the grounding bolt is connected to the grounding grid of the transformer to be monitored through a copper braided strip; by setting the shielding shell, the anti-interference capability is improved, and the winding status can be accurately monitored. Attached Figure Description

[0021] Figure 1 This is a top view of the FRA online monitoring sensor with anti-power frequency interference provided in an embodiment of the present invention.

[0022] Figure 2 This is a front view of the FRA online monitoring sensor for resisting power frequency interference provided in an embodiment of the present invention.

[0023] Figure 3 This is a side view of the FRA online monitoring sensor with anti-power frequency interference provided in an embodiment of the present invention.

[0024] Figure 4 This is a cross-sectional view of the FRA online monitoring sensor for resisting power frequency interference provided in an embodiment of the present invention.

[0025] Figure 5 This is a front view of the toroidal core in the FRA online monitoring sensor for resisting power frequency interference provided in this embodiment of the invention.

[0026] Figure 6 This is a top view of the toroidal iron core in the FRA online monitoring sensor for resisting power frequency interference provided in an embodiment of the present invention.

[0027] In the diagram, 1 is the FRA online monitoring sensor; 11 is the shielding housing; 111 is the grounding bolt; and 12 is the toroidal iron core. Detailed Implementation

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

[0029] Reference Figures 1 to 6 The present invention discloses an online monitoring sensor 1 for FRA that resists power frequency interference, which has reciprocity between response function and excitation function.

[0030] During on-site installation, two FRA online monitoring sensors can be installed on the bushing of the transformer to be monitored. The two FRA online monitoring sensors are used to send excitation signals and receive response signals, respectively.

[0031] Specifically, the FRA online monitoring sensor 1 provided in this embodiment adopts the response-excitation reciprocity principle, that is, the FRA online monitoring sensor 1 has the functions of high-frequency partial discharge signal detection (response mode) and high-frequency excitation signal output (excitation mode). In response mode, the winding partial discharge signal in the frequency band of 1kHz to 10MHz is captured by electromagnetic induction, and in excitation mode, the distortion-free high-frequency signal is output to the FRA measurement circuit through non-contact coupling, realizing the integration of "monitoring-verification".

[0032] The FRA online monitoring sensor 1 for resisting power frequency interference provided in this embodiment includes a shielding shell 11, a toroidal core 12, and a balancing coil. The shielding shell 11 forms an accommodating cavity, and the balancing coil is wound on the toroidal core 12. The balancing coil and the toroidal core 12 together constitute the body, which is housed in the accommodating cavity. The dimensional error of the toroidal core is controlled within a preset range. A grounding bolt 111 is provided at the bottom of the shielding shell 11. The grounding bolt 111 is adapted to the bushing root of the transformer to be monitored. The grounding bolt 111 is used to screw onto the bushing root of the transformer to be monitored. The grounding bolt 111 is connected to the grounding grid of the transformer to be monitored through a copper braided strip. By setting the shielding shell 11 and the grounding bolt 111, external electromagnetic interference is suppressed through the triple action of "absorption-reflection-grounding conduction", which improves the anti-interference capability and enables accurate monitoring of the winding status.

[0033] Specifically, the balance coil is wound onto the toroidal iron core 12, which is machined by a CNC machine tool, using a winding machine. The dimensional error of the toroidal iron core is controlled within ±0.5mm.

[0034] In this embodiment, the annular iron core 12 is made of nanocrystalline alloy. The shielding shell is annular in shape, and the accommodating cavity is adapted to the body.

[0035] For example, the outer dimensions of the toroidal core 12 are an outer diameter of φ350mm and an inner diameter of φ.

[0036] With a diameter of 290mm and a thickness of 30mm, and a dimensional error controlled within ±0.5mm, the toroidal core 12 was precisely machined to ensure a uniform magnetic circuit and prevent saturation caused by excessive local magnetic reluctance. The toroidal core 12 was precision machined using a CNC lathe, with dimensional errors controlled within ±0.5mm.

[0037] The surface of the toroidal core 12 is treated with resin curing, which enhances the insulation and mechanical strength of the toroidal core 12.

[0038] The performance of the toroidal core 12 after processing was verified: 100A, 200A and 400A currents were applied by a power frequency current source, and the secondary voltage waveforms were collected by an oscilloscope. Under the 100A condition, the secondary voltages Vrms = 0.2227V and Vp = 0.391V, with no signal distortion, proving that it is not saturated.

[0039] Specifically, the balancing coil is wound with enameled copper wire, and the number of turns is optimized according to the transmission impedance requirements. The balancing coil uses a fully automatic winding machine to ensure winding uniformity, reduce signal distortion caused by inter-turn capacitance, and avoid inter-turn short circuits.

[0040] In this embodiment, the lead wires of the balancing coil are made of shielded cable, which reduces signal interference.

[0041] During use, the balancing coil is coaxially wound onto the toroidal core 12, and the gap between the balancing coil and the toroidal core 12 is controlled within the range of 0.1 to 0.2 mm. The balancing coil is encapsulated and fixed onto the toroidal core 12 using epoxy resin potting compound.

[0042] When the shielding coil is wound in two layers on the toroidal iron core 12, interlayer insulation is achieved between the two layers of shielding coil using a polyimide film.

[0043] Specifically, grounding bolt 111 is compatible with the root of the 10kV / 110kV bushing.

[0044] In this embodiment, there are 4 grounding bolts 111.

[0045] During installation, the grounding bolt 111 is screwed onto the bushing root of the transformer to be monitored. The grounding bolt 111 is sealed to the bushing root through a silicone rubber sealing ring, thereby improving the waterproof performance to IP65 waterproof and dustproof performance.

[0046] The temperature resistance range of the silicone rubber sealing ring is -40 to 120℃.

[0047] Specifically, grounding bolt 111 is made of copper braided tape (cross-sectional area ≥ 10mm²). 2 Connect to the grounding grid of the transformer to be monitored, wherein the grounding resistance is ≤1Ω.

[0048] The shielding shell 11 has a coupling window (not shown in the figure), and a polytetrafluoroethylene insulating sheet is provided on the coupling window to achieve "differentiated shielding".

[0049] Specifically, the coupling window provides a dedicated, controllable channel for high-frequency monitoring signals, minimizing attenuation of high-frequency signals in specific frequency bands, thus allowing signals to pass through effectively, while the shielding housing maintains good shielding against most other interference frequencies.

[0050] By setting a polytetrafluoroethylene (PTFE) insulating sheet on the coupling window, the PTFE insulating sheet has extremely high dielectric strength, which can reliably isolate the high voltage inside and outside the FRA online monitoring sensor, ensuring safety. In addition, the PTFE insulating sheet has very low dielectric loss and stable dielectric constant at high frequencies, which means that when high-frequency signals pass through it, the additional attenuation and phase distortion are very small and will not significantly affect the accuracy of the monitoring signal.

[0051] Furthermore, in this embodiment, the shielding housing 11 includes a metal shell and an anti-corrosion layer. The metal shell is arranged to form an accommodating cavity, and the anti-corrosion layer is sprayed on the outer surface of the metal shell; this arrangement improves the anti-interference capability.

[0052] The metal shell consists of an aluminum alloy body and a stainless steel foil layer. The stainless steel foil layer is located on the inner surface of the aluminum alloy body, and the anti-corrosion layer is located on the outer surface of the aluminum alloy body. By setting the aluminum alloy body, the aluminum alloy has both lightweight and high electromagnetic shielding performance.

[0053] In this embodiment, the anti-corrosion layer includes an oxide layer, a fine sand layer, and an anti-ultraviolet coating. The outer surface of the metal shell is blackened to form an oxide layer. Fine sand is sprayed onto the oxide layer to form a fine sand layer. The anti-ultraviolet coating is sprayed onto the fine sand layer. With this configuration, the shielding shell 11 improves its corrosion resistance and anti-ultraviolet capability.

[0054] The thickness of the UV-protective coating ranges from 5 to 8 μm.

[0055] Specifically, the metal casing is machined as a whole using a CNC lathe to ensure the dimensional accuracy of the interface. After machining, sharp corners and burrs are removed, and the edges and corners are rounded (rounded radius ≥ 2mm). Then, the machined metal casing undergoes surface treatment, which involves first performing a black anodizing treatment to form an oxide layer, then spraying fine sand to form a fine sand layer, and finally spraying an anti-UV coating.

[0056] The test process for the FRA online monitoring sensor 1 with anti-power frequency interference provided in this embodiment is as follows: (I) The test to solve the problem of "low sensitivity of high frequency signal detection" and improve the partial discharge signal capture capability is as follows:

[0057] 1. Experimental conditions and methods:

[0058] ① Transmission impedance test: Excited by a 100Vpp sinusoidal signal, the frequency band of 3MHz to 30MHz is adjusted in 1MHz steps. The output terminal of the FRA online monitoring sensor 1 is set with a 50Ω load and connected to an oscilloscope through a 1-meter 50Ω coaxial cable. The output voltage V2(f) of the sensor and the voltage V1(f) across the 50Ω non-inductive resistor R0 are measured simultaneously. The transmission impedance is calculated according to the formula Z(f)=R0×[V2(f) / V1(f)].

[0059] ② Frequency response test: 0.5MHz~50MHz frequency band, the signal generator outputs a constant sinusoidal current of 5mA~10mA, the oscilloscope monitors the voltage of R0 to keep the current stable, and records the frequency corresponding to the maximum output of the FRA online monitoring sensor 1 and the upper and lower limits of the 6dB bandwidth.

[0060] ③ Sensitivity test: The steep pulse generator outputs 10pC, 20pC, and 50pC apparent charge (pulse rise time ≤ 5ns, decay time ≥ 200ns), and the injected capacitor C0 = 100pF. The signal-to-noise ratio of the sensor to different partial discharge levels is then tested.

[0061] 2. Experimental Data and Results:

[0062] ① Transmission impedance: The transmission impedances of the two FRA online monitoring sensors are 14.02mV / mA ​​and 13.86mV / mA, respectively, both far exceeding the requirement of ">5mV / mA". This is more than 4 times higher than that of traditional sensors (usually <3mV / mA), which can convert a weak 1mA high-frequency current signal into a clear voltage signal of ≥13.86mV.

[0063] ② Frequency response: The maximum output frequency is concentrated in 3MHz~30MHz (meets design requirements); the 6dB bandwidth reaches 32MHz (covering 0.5MHz~32.5MHz), far exceeding the industry standard of "≥2MHz", which is 6 times higher than that of traditional sensors (6dB bandwidth <5MHz), and can fully cover the typical frequency band of transformer high-frequency partial discharge signal from 1kHz to 10MHz.

[0064] ③ Sensitivity: The signal-to-noise ratios for 10pC, 20pC, and 50pC partial discharge signals are 1.8:1, 1.9:1, and 2.2:1, respectively, with the 50pC signal having a signal-to-noise ratio ≥2:1 (meets the requirements). This is more than twice as sensitive as traditional sensors (minimum measurable partial discharge >100pC), and can identify minute deformations of transformer windings less than 0.1mm in advance (traditional sensors require deformations of more than 0.5mm to detect).

[0065] Compared with the prior art, traditional sensors have large transmission impedance fluctuations (deviation ±30%) in the 3MHz to 10MHz frequency band, and the narrow 6dB bandwidth causes the loss of some high-frequency partial discharge signals. The FRA online monitoring sensor 1 provided in this application has a transmission impedance stability deviation of <±5%, and the 6dB bandwidth covers the entire monitoring frequency band, significantly improving the monitoring accuracy.

[0066] The experiment shows that the FRA online monitoring sensor 1 provided in this application has a transmission impedance that far exceeds the design requirement of 5mV / mA ​​in the 1kHz to 10MHz frequency band, and a 6dB bandwidth that meets the requirements for wide-band signal acquisition. It can accurately detect weak partial discharge signals at the 50pC level, solve the problem of insufficient high-frequency sensitivity of traditional sensors, and provide data support for early deformation monitoring of transformer windings.

[0067] (II) The test to solve the problem of "magnetic saturation under high power frequency current" and ensure stable performance under complex operating conditions is as follows:

[0068] (1) Test subjects:

[0069] An FRA online monitoring sensor is constructed using a 16-turn standard coil wound in two groups, with a balanced coil wound on the toroidal core 12.

[0070] (2) Experimental conditions and methods

[0071] Power frequency current source: Adjusted by a voltage regulator, 75V corresponds to 500A power frequency current and 150V corresponds to 1000A power frequency current. The balancing coil was short-circuited during the test.

[0072] High-frequency signal source: The signal generator outputs a high-frequency signal with an adjustable frequency of 1kHz to 10MHz and an adjustable peak-to-peak value of 1V to 20V, which is injected into the sensor through a 1Ω resistor;

[0073] Test circuit: Construct a composite circuit of "power frequency current source + high frequency current source + sensor + oscilloscope (2.5GSa / s sampling rate)", connect the oscilloscope to a standard coil, and synchronously acquire the waveforms and Vpp values ​​of the input and output signals;

[0074] Test variables:

[0075] Variable 1: The high-frequency signal voltage is fixed at 20V, and the frequency is adjusted sequentially to 1kHz, 50kHz, 100kHz, 500kHz, 1MHz, 5MHz, and 10MHz;

[0076] Variable 2: With the high-frequency signal frequency fixed at 50kHz, the voltage is adjusted sequentially to 10V, 15V, and 20V.

[0077] (3) Experimental data and results

[0078] ①500A power frequency current condition:

[0079] Frequency variable test: When the input Vpp of a 50kHz high-frequency signal is 296mV, the output Vpp is 426mV (no signal attenuation and enhanced due to coil coupling); when the input Vpp of a 10MHz high-frequency signal is 388mV, the output Vpp is 8.575mV, with an attenuation rate of only 2.21%; the waveform in the full frequency band from 1kHz to 10MHz is uninterrupted and undistorted, and the measured value of the power frequency current is 495~501A (deviation ≤1.2%).

[0080] Voltage variable test: With a 10V input, the output voltage amplitude is 209.72mV; with a 15V input, it is 313.6mV; with a 20V input, it is 411.6mV. The output voltage is linearly positively correlated with the input voltage (R). 2 =0.998), with no nonlinear deviation caused by saturation;

[0081] ②1000A power frequency current condition:

[0082] Frequency variable test: When the input Vpp of a 50kHz high-frequency signal is 300mV, the output Vpp is 408.66mV; when the input Vpp of a 10MHz high-frequency signal is 398mV, the output Vpp is 9.114mV, with an attenuation rate of 2.29%; the measured value of the power frequency current is 982~998A (deviation ≤1.8%), and the waveform stability is consistent with the 500A operating condition.

[0083] Voltage variable test: Output 206.78mV with 10V input, 308.7mV with 15V input, 422mV with 20V input, linear correlation R 2 =0.997, no signal distortion;

[0084] Compared with the prior art: traditional FRA sensors usually experience core saturation at 300A power frequency current, the attenuation rate of 10MHz high-frequency signal exceeds 40%, and the linear deviation between output and input is >10%. The FRA online monitoring sensor 1 provided in this application still maintains low attenuation and high linearity at 1000A power frequency, and the anti-saturation capability is improved by more than 3 times.

[0085] The experiment shows that the FRA online monitoring sensor 1 provided in this application, through the balanced coil anti-magnetic flux saturation design and standard coil grouping winding optimization, achieves no saturation phenomenon under 500A~1000A power frequency current, a high frequency signal transmission attenuation rate of ≤3.38% from 1kHz to 10MHz, and a linear correlation between output and input voltage of ≥0.997. It solves the pain points of weak power frequency current tolerance and high frequency signal distortion of traditional sensors, and can meet the high frequency partial discharge monitoring requirements of 10kV~110kV transformers operating at full load.

[0086] (III) The experiment aimed at addressing the problem of "weak external electromagnetic interference suppression capability" and reducing the false alarm rate of on-site monitoring is as follows:

[0087] (1) Test subjects:

[0088] FRA online monitoring sensor with shielded housing 11 (shielded housing 11 is CNC machined and has a black anodized and fine sandblasted surface);

[0089] (2) Experimental conditions and methods:

[0090] ① Shielding performance test: Simulate the electromagnetic environment at the root of the 10kV / 110kV bushing, and test the shielding effect of the sensor shielding shell 11 on high-frequency electric fields of 1kHz to 10MHz and low-frequency electric fields below 100Hz, as well as the suppression ratio of power frequency current (50Hz) and high-frequency signals of 1kHz to 10MHz.

[0091] ②Anti-interference test: Inject a 50pC partial discharge signal and superimpose a 25mA peak-to-peak interference current (interference frequency covers 50kHz, 500kHz, 1MHz~40MHz), and monitor the signal-to-noise ratio of the sensor output with an oscilloscope;

[0092] ③ Environmental and mechanical performance testing:

[0093] Environmental testing: Temperature cycling from -40℃ to 70℃, relative humidity from 0% to 95%, continuous operation for 72 hours, monitoring changes in transmission impedance;

[0094] Mechanical testing: Vibration from 10Hz to 500Hz (acceleration 50m / s²) 2 1000 cycles of IP65 protection testing to check the integrity of the housing and the contact of the wiring terminals;

[0095] Installation Test: Using a standardized 10kV / 110kV bushing root interface, the installation time for a single sensor was recorded; Variable 2: The high-frequency signal frequency was fixed at 50kHz, and the voltage was adjusted sequentially to 10V, 15V, and 20V.

[0096] (3) Experimental data and results:

[0097] ① Shielding performance:

[0098] Electric field shielding: 42dB high-frequency electric field shielding effect (125 times signal attenuation) from 1kHz to 10MHz, and 75dB low-frequency electric field shielding effect (3162 times signal attenuation) below 100Hz, which is twice as effective as traditional metal shells (high-frequency electric field shielding <20dB).

[0099] Signal suppression ratio: 55% suppression ratio for power frequency current (50Hz) (power frequency interference intensity is reduced by more than half), and 8% suppression ratio for useful signals at high frequencies of 1kHz to 10MHz (useful signal loss rate is controlled within 10%), avoiding the problem of "useful signal and interference attenuating at the same time" in traditional enclosures.

[0100] ② Anti-interference performance: In the full interference frequency range of 50kHz to 40MHz, the signal-to-noise ratio of the sensor to 50pC partial discharge signal is ≥2.1:1, and the narrowband interference suppression capability of 3MHz to 30MHz is 23dB, which is 17% higher than that of traditional sensors (signal-to-noise ratio <1.8:1).

[0101] ③ Environmental and mechanical properties:

[0102] Environmental testing: At -40℃~70℃ and 0%~95% humidity, the transmission impedance change rate is only ±4.2% (≤±10% requirement), with no performance drift;

[0103] Mechanical testing: After vibration and IP65 testing, the housing showed no deformation or corrosion, and the contact resistance of the wiring terminals changed by <0.01Ω;

[0104] Installation testing: The standardized interface reduces the installation time to 45 minutes per unit (compared to 2 hours per unit for traditional sensors), improving efficiency by 62.5%.

[0105] Compared with the prior art, traditional sensors have a transmission impedance change rate of over ±15% in high humidity (>80%) or low temperature (<-20℃) environments, and are prone to shell cracking after vibration. The FRA online monitoring sensor 1 provided in this application has significantly better environmental adaptability and mechanical stability than traditional products, and the installation efficiency is greatly improved.

[0106] The experiment shows that the FRA online monitoring sensor 1 provided in this application, through the optimized structure of the shielded housing 11 (grounding bolts 111, anti-corrosion treatment) and electromagnetic shielding design, achieves high anti-interference performance in complex power environments, while also possessing excellent temperature and humidity adaptability and mechanical reliability. The FRA online monitoring sensor 1 provided in this application meets the general technical specifications of the power industry and can be adapted to equipment of multiple voltage levels, such as 10kV distribution transformers and 110kV main transformers.

[0107] (iv) Experiments to solve the problem of "low processing and testing efficiency" and realize a fully automated testing system under all operating conditions:

[0108] (1) Specialized test hardware: Build a platform containing a 0.5MHz to 50MHz signal generator, a 2500A power frequency source, and a 100MHz oscilloscope, and design 6 types of specialized circuits to achieve performance quantification;

[0109] (2) Automated software: developed based on C++ MFC, including 14 types of basic wavelet denoising (CWTwy class) and FFT analysis (CDlgFFT class), supports automatic parameter setting, data acquisition, index calculation (such as linearity error), and report generation. The test time is reduced from 4 hours to 0.5 hours, and the error rate is reduced from 10% to 0.5%, solving the problem of inefficiency of manual testing. At the same time, it eliminates environmental interference during the test process and ensures the accuracy of performance evaluation.

[0110] The FRA online monitoring sensor 1 provided in this application, which is resistant to power frequency interference, includes a shielding housing 11, a toroidal core 12, and a balancing coil. The shielding housing 11 forms an accommodating cavity, and the balancing coil is wound on the toroidal core 12. The balancing coil and the toroidal core 12 together constitute the body, which is housed within the accommodating cavity. The dimensional error of the toroidal core 12 is controlled within a preset range. A grounding bolt 111 is provided at the bottom of the shielding housing 11. The grounding bolt 111 is adapted to the bushing root of the transformer to be monitored. The grounding bolt 111 is used to screw onto the bushing root of the transformer to be monitored. The grounding bolt 111 is connected to the grounding grid of the transformer to be monitored through a copper braided strap. By setting the shielding housing 11, the anti-interference capability is improved, and the winding status can be accurately monitored.

[0111] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0112] Finally, it should be noted that the above embodiments are merely examples for clearly illustrating the present invention and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. An online monitoring sensor for FRA (Flexible Radio Frequency) that resists power frequency interference, characterized in that: It includes a shielding shell, a toroidal iron core, and a balancing coil; the shielding shell is configured to form an accommodating cavity, the balancing coil is wound on the toroidal iron core, the balancing coil and the toroidal iron core together constitute the body, the body is housed in the accommodating cavity, and the dimensional error of the toroidal iron core is controlled within a preset range; The bottom end of the shielding shell is provided with a grounding bolt, which is adapted to the bushing root of the transformer to be monitored. The grounding bolt is used to screw into the bushing root of the transformer to be monitored, and the grounding bolt is connected to the grounding grid of the transformer to be monitored through a copper braided strip.

2. The FRA online monitoring sensor with anti-power frequency interference according to claim 1, characterized in that: The toroidal core is made of nanocrystalline alloy.

3. The FRA online monitoring sensor with anti-power frequency interference according to claim 2, characterized in that: The surface of the annular iron core is treated with resin curing.

4. The FRA online monitoring sensor with anti-power frequency interference according to claim 1, characterized in that: The shielding housing includes a metal outer shell and an anti-corrosion layer. The metal outer shell is arranged to form an accommodating cavity, and the anti-corrosion layer is disposed on the outer surface of the metal outer shell.

5. The FRA online monitoring sensor with anti-power frequency interference according to claim 4, characterized in that: The metal casing includes an aluminum alloy body and a stainless steel foil layer. The stainless steel foil layer is disposed on the inner surface of the aluminum alloy body, and the anti-corrosion layer is sprayed on the outer surface of the aluminum alloy body.

6. The FRA online monitoring sensor with anti-power frequency interference according to claim 4, characterized in that: The anti-corrosion layer includes an oxide layer, a fine sand layer, and an anti-ultraviolet coating. The oxide layer is formed by black oxidation treatment on the outer surface of the metal shell. Fine sand is sprayed onto the oxide layer to form the fine sand layer. The anti-ultraviolet coating is sprayed onto the fine sand layer.

7. The FRA online monitoring sensor with anti-power frequency interference according to claim 6, characterized in that: The thickness of the UV-resistant coating ranges from 5 to 8 μm.

8. The FRA online monitoring sensor with anti-power frequency interference according to claim 1, characterized in that: The gap between the balancing coil and the toroidal core is in the range of 0.1 to 0.2 mm.

9. The FRA online monitoring sensor with anti-power frequency interference according to claim 1, characterized in that: The balancing coil is encapsulated and fixed to the annular iron core using epoxy resin potting compound.

10. The FRA online monitoring sensor with anti-power frequency interference according to claim 1, characterized in that: The lead wires of the balancing coil are made of shielded cable.

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