CN107831408A - A kind of universal design of ultra high-frequency partial discharge sensor, optimization and method of testing - Google Patents

Abstract

The invention relates to a general design, optimization and testing method of a UHF partial discharge sensor. The steps are: 1) Determine the design bandwidth of the sensor; 2) Determine the structure of the sensor that can realize the bandwidth; 3) Conduct a simulation and comparative analysis of the processing material parameters of the sensor; 4) Design the impedance transformer and determine the parameters of the impedance transformer; 5 ) Determine the final values of all relevant parameters of the sensor to obtain the overall sensor model; 6) Carry out simulation verification on the overall sensor model; 7) Select the key parameters of the physical model of the sensor and use instruments and equipment for parameter testing; 8) Use the discharge model to Performance testing of the physical model of the sensor; final testing of the physical model of the sensor; 10) The final sensor is completed based on the optimization and improvement experience summarized from the simulation and test results in the above steps. The invention is a more scientific, reasonable and universal optimization design method to standardize and solve problems in practical application.

Description

A general design, optimization and testing method for UHF partial discharge sensors

technical field

The invention relates to the field of partial discharge detection, in particular to a general design, optimization and testing method of a UHF partial discharge sensor.

Background technique

The safe and reliable operation of power equipment is the fundamental guarantee for the stability of the entire power system. However, due to various factors such as manufacturing, transportation, on-site assembly, operation and maintenance, some insulation defects that threaten insulation performance inevitably exist in transformers, circuit breakers, switch cabinets, power cables and other power transmission and transformation equipment. Insulation defects that lead to insulation failures in power equipment often produce partial discharges in the early stages. Partial discharge in power equipment is an electrical discharge phenomenon in the insulating medium, which is mainly caused by weak parts with local defects in the insulation of the equipment. A very uneven electric field distribution will be generated at the defect, resulting in a decrease in insulation strength. Under the action of power frequency alternating electric field, when the local electric field strength reaches the intrinsic breakdown field strength of the medium, the medium will break down locally and form partial discharge. This kind of discharge occurs in a part of the medium and partially bridges the insulation between conductors. Usually, it does not immediately cause insulation penetration breakdown, but it can cause local damage to the dielectric, especially organic dielectrics such as epoxy materials. At the same time, the electrical corrosion of partial discharge can further expand the scope of insulation defects, and eventually lead to the penetration of insulation damage.

Partial discharge is an important parameter to reflect the insulation performance. It is not only the precursor and manifestation of the insulation degradation of power equipment, but also the cause of further insulation degradation. If partial discharge exists for a long time, the electrical insulation performance of power equipment will be reduced, and under certain conditions, flashover along the surface may even develop into a violent burning arc, which will eventually lead to insulation failure. Once an accident occurs in the power equipment, it will usually lead to a power outage, which will definitely cause serious economic losses and social impact. The use of appropriate methods to detect partial discharge inside power equipment is an effective means to judge the long-term reliability of equipment insulation, and can detect early potential dangers in time to prevent accidents. Partial discharge is used to study the cause and severity of internal insulation faults of power equipment, and it can also evaluate and predict the insulation state and life of the equipment.

Among the many partial discharge detection methods, the ultra high frequency method (ultra high frequency, UHF) has been widely used due to its advantages of high sensitivity and easy on-line monitoring. The principle is: the dielectric strength and breakdown field strength of insulating parts in power equipment are relatively high, and when a short-term local breakdown occurs in a small dielectric range, a nanosecond pulse current will be generated. This kind of pulse has a very short rise time, can excite electromagnetic waves with UHF band range (300MHz-3GHz) or even higher frequency components, and gradually spread from the discharge source. The principle of the UHF method is to use a UHF sensor to receive the UHF signal excited and propagated by the partial discharge steep pulse to obtain the relevant information of the partial discharge. In the ultra-high frequency method, the partial discharge ultra-high frequency sensor (also called a coupler) is the core component of the entire partial discharge detection system, which requires an ultra-wide operating frequency range, which plays a significant role in the detection frequency band, sensitivity and accuracy of the detection system. It plays a vital role, and its performance determines the ability of the entire system to detect partial discharge. In the actual sensor design, it is necessary to consider the influence of the sensor performance parameters, the impedance matching with the transmission line in the ultra-wide frequency band, the size of the sensor, and the installation method.

The research on the UHF method has been carried out for many years, but no normative standard has been issued so far, because there are still some problems to be solved in practical application. There are several important issues in the optimization of UHF sensors: the design of unified specifications, the influence of sensor parameter changes on performance, and the realization of ultra-wide detection frequency band and impedance matching of built-in sensors. The sensors used in different systems vary greatly, and many researchers have not designed the working bandwidth, input impedance, signal transmission and other links of the sensor according to a clear requirement and parameter. UHF sensor is the core of the detection system, and its standard design and reasonable parameter requirements become the premise and important guarantee for the realization of sensor calibration. Aiming at the problem of partial discharge in GIS, CIGRE set up a special working group 15/33.03.05 to conduct relevant investigation and research, and found that the sensitivity of the UHF method is affected by parameters such as sensor performance. At present, ultra-wideband antennas are generally used as sensors to meet the requirements of ultra-wideband detection range (300MHz-3GHz). Although a lot of research work has been carried out around UHF sensors, there are still few studies on the design of the sensor body and the influence of different parameters on the performance, and this work will provide the necessary theoretical basis for sensor design. On the other hand, the actual partial discharge detection requires the sensor to have an ultra-wideband detection range, which is easy to achieve for an external sensor with a relatively low size requirement, but how can the built-in sensor be installed in a limited installation space? To achieve this standard also needs to be fully considered in the sensor design. At the same time, in the early days, people only expected to obtain the signal generated by the discharge from the sensor, but they often did not care about whether the real frequency band of the signal received by the sensor matched the detection system, and whether the signal was attenuated and distorted after being transmitted by the detection system. Eliminates interference while filtering out useful information in many signals. From the perspective of professional antenna design, because the input impedance of the 50Ω coaxial line often used in practical applications is far from that of the ultra-wideband antenna, it is necessary to design a corresponding impedance matching link to achieve a good signal transmission effect, and this part is in the literature There are few introductions and researches.

Based on the above analysis, the design and optimization of the UHF sensor is the key to the reasonable use of the UHF method for partial discharge detection, and the actual engineering application puts forward higher requirements for the UHF method. There are obvious deficiencies in the design and optimization of the system, and a more scientific, reasonable and general optimization design method is needed to standardize and solve problems in practical applications.

Contents of the invention

The purpose of the present invention is to provide a scientific, reasonable and complete universal design, optimization and testing method for partial discharge UHF sensors.

For realizing above-mentioned purpose of the invention, the technical scheme that the present invention takes is:

A general design, optimization and testing method of a UHF partial discharge sensor of the present invention comprises a model design optimization stage and an object test optimization stage, and the method steps are:

Model design optimization stage:

1) Determine the sensor design bandwidth in combination with the characteristics of the measured signal, the frequency range of the expected detection signal, the type of actual detection equipment, and the environmental conditions of the sensor installation.

2) According to the design bandwidth determined in 1), determine the sensor structure that can realize the bandwidth; Parameters of body type, size, structure.

3) For the processing material parameters of the sensor, take different values for simulation and comparative analysis, check the influence on the performance of the sensor, and optimize and determine its value. The processing material parameters of the sensor include plate thickness, dielectric constant, softness and hardness, etc.

4) According to the impedance characteristics of the sensor obtained by the simulation calculation in 3), and the wave impedance of the feeder used, design the impedance converter and determine the parameters of the impedance converter.

5) Refer to the parameter calculation results in 3) above, combined with other factors such as the actual microwave sheet specifications, price, and the design of the impedance transformer, determine the final values of all relevant parameters of the sensor, and obtain the overall model of the sensor. The relevant parameters of the sensor include: Antenna size , structure, processing material thickness, dielectric constant, impedance transformer structure, size, material thickness, dielectric constant, surface copper clad form and other parameters.

6) Carry out simulation verification on the overall sensor model; if the requirements are not met, start from step 5) by optimizing and adjusting the overall sensor model; if the requirements are met, make the physical model of the sensor, and the model design optimization stage is completed.

Physical test optimization stage:

7) Use instruments and equipment to conduct parameter tests on the key parameters of the physical model of the sensor, and compare them with the design values to verify whether the sensor meets the design goals; if the design requirements are met, record the test results, summarize the points that can be optimized and improved, and carry out sensor testing. Optimize, improve and verify, further improve the sensor parameters, and prepare for the next stage of testing; if the design requirements are not met, return to step 2), continue to optimize and adjust the parameters of the sensor and the overall model; the key parameters include: S11 parameters /SWR, input impedance, frequency bandwidth, pattern, gain, lobe width, etc.

8) Utilize the discharge model to perform a performance test on the physical model of the sensor. By comparing and analyzing the signal receiving situation under different working conditions, check the sensor's ability to receive and record the real discharge signal. The working conditions include: detection distance, angle; if If the performance requirements are met, record the test results, summarize the points that can be optimized and improved, optimize and verify the sensor, further improve the sensor performance, and prepare for the next stage of testing; if the performance design requirements are not met, return to step 2) and continue Optimize and adjust the parameters of the sensor and the overall model.

9) Install in the actual application environment (such as GIS, transformer, switchgear, etc.) to conduct the final test on the physical model of the sensor, and check the signal receiving ability and working condition of the sensor under real working conditions. If the application requirements are met, record the test results, summarize the points that can be optimized and improved, optimize and verify the sensor, and further improve the practicability of the sensor; if the application requirements are not met, return to step 2) and re-optimize and adjust the parameters of the sensor and the overall model.

10) Synthesize the optimization and improvement experience summarized from the simulation and test results in the above steps to complete the final sensor.

Further, the sensor structure described in step 2) of the method of the present invention can be designed according to the antenna structure: according to the previously determined design bandwidth, determine the type of antenna that can realize the bandwidth, and determine the sensor body according to the design principle and formula of the antenna. Basic parameters.

The technical solution process adopted by the present invention is shown in Fig. 1 .

The beneficial effects produced by the present invention by adopting the above-mentioned technical scheme are:

The present invention proposes a general design, optimization and testing method for UHF partial discharge sensors. Starting from the requirements of partial discharge detection, taking into account the requirements of relevant theory and actual partial discharge detection, the standardized design and testing of UHF sensors Leverage provides a complete solution. The invention provides a guarantee for the reasonable use of the ultra-high frequency method for partial discharge detection, meets the higher requirements of the actual engineering application for the ultra-high frequency method, and makes up for the current design and optimization of the partial discharge ultra-high frequency sensor. Insufficient, it solves the problems in the design and practical application of the UHF sensor.

The advantages are summarized as:

1) The present invention proposes parameter requirements based on actual application requirements, and makes it possible to verify the sensor and compare the performance of sensors designed by different manufacturers through standardized design and unified and reasonable parameter requirements.

2) Taking into account the impact of sensor parameter changes on performance, the sensor performance is optimized to the greatest extent in the design stage, the optimal model of the sensor is obtained, and the necessary theoretical basis for sensor design is provided.

3) Taking into account the ultra-wide detection frequency band of the sensor and the impedance matching with the coaxial transmission line, so that the designed sensor can most truly reflect the characteristics of the partial discharge signal and achieve a good signal transmission effect. It is developed based on UHF signals The power equipment insulation fault diagnosis provides a solid foundation.

4) While taking into account the performance of the sensor, other factors such as the installation of the sensor and the purchase of materials are fully considered, which is more in line with the actual detection requirements.

5) Three test stages are proposed for the sensor, including parameter test, performance test and practical application test, so that the designed sensor not only meets the parameters and performance requirements at the beginning of the design, but also meets the actual detection and application requirements of partial discharge signals, so that Get field applications faster.

6) Starting from the test results, each test link considers the problem of further optimization and improvement of the sensor, so that the test results form a closed-loop feedback to the final sensor design, and the process is more scientific and reasonable.

The general design, optimization and testing method of a UHF partial discharge sensor proposed by the present invention is suitable for the design and development of a variety of UHF sensors for power equipment detection, such as gas insulated switchgear (gasinsulated switchgear, GIS), Power transformers, switch cabinets, cables, etc. It is also applicable to different installation forms, such as built-in and external UHF transducers.

Description of drawings

Fig. 1 is a design flow chart of the UHF sensor of the present invention;

2 is a simulation model diagram of a planar equiangular helical antenna according to an embodiment of the present invention;

3 is a basic structural diagram of the planar equiangular helical antenna described in the embodiment of the present invention;

Fig. 4 is a planar equiangular helical antenna under different wrapping angles according to an embodiment of the present invention;

Fig. 5 is a simulation result diagram of the parameters of the antenna S11 when the wrap angle according to the embodiment of the present invention takes different values;

Fig. 6 is the simulation result figure of antenna input impedance (real part) when the included angle of the embodiment of the present invention takes different values;

Fig. 7 is a simulation result diagram of the maximum gain of the antenna when the wrapping angle according to the embodiment of the present invention takes different values;

FIG. 8 is a schematic diagram of impedance matching according to an embodiment of the present invention;

Fig. 9 is the principle of the gradient line impedance converter described in the embodiment of the present invention;

Fig. 10 is the simulation result figure (S11) described in the embodiment of the present invention;

FIG. 11 is a simulation result diagram (direction diagram, f=1.75GHz) of the embodiment of the present invention;

Fig. 12 is a test result diagram of an antenna with an original length impedance converter described in an embodiment of the present invention;

Fig. 13 is a test result diagram of the antenna configured with a horizontal impedance converter according to the embodiment of the present invention;

Fig. 14 is a time-domain comparison diagram of the receiving comparison results of actual partial discharge signals according to the embodiment of the present invention;

Fig. 15 is a comparison diagram in the frequency domain of the receiving comparison results of actual partial discharge signals according to the embodiment of the present invention;

Fig. 16 is a result diagram of pulse phase distribution of the floating potential discharge experiment described in the embodiment of the present invention;

Fig. 17 is a graph showing the sensor signal and pulse current results of the suspension potential discharge experiment described in the embodiment of the present invention;

Fig. 18 is a graph showing the experimental results of the metal spike discharge described in the embodiment of the present invention;

Fig. 19 is a test result diagram of the lateral change of the sensor position according to the embodiment of the present invention;

Fig. 20 is a test result diagram of the longitudinal change of the sensor position according to the embodiment of the present invention;

FIG. 21 is a time-domain waveform diagram of a received signal according to an embodiment of the present invention;

Fig. 22 is a frequency-domain waveform diagram of a received signal according to an embodiment of the present invention.

Detailed ways

In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the invention will be clearly and completely described below in conjunction with the drawings and specific embodiments. Apparently, the accompanying drawings in the following description are an embodiment of the present invention, and those of ordinary skill in the art can also obtain other accompanying drawings according to these drawings without any creative work.

Embodiment: Take the design process of the built-in UHF sensor of GIS equipment as an example to illustrate:

1. Model design optimization stage

1. Bandwidth determination

Partial discharge signals in GIS are usually within the ultra-wideband detection range. Considering the compact structure of GIS equipment and the limited internal installation space, the designed sensor bandwidth of this embodiment is 700MHz~~3GHz.

2. Determine the basic parameters of the sensor body

The planar equiangular helical antenna has the characteristics of detection frequency bandwidth, pattern, impedance and polarization basically unchanged in the whole frequency band, so it has been widely used in partial discharge detection. Therefore, this embodiment adopts a planar equiangular helical antenna as the body of the UHF sensor for design.

An arm of a planar equiangular helical antenna consists of two equiangular helixes, any of which satisfies the following equation:

In the formula: r is the distance from any point on the helix to the origin; r0 is the distance from the starting point to the origin of the helix, that is, the inner diameter; is the angle of rotation of the helix; a is the growth rate of the helix, which has the following relationship with the wrap angle α:

In the formula, α is the angle between the tangent line at a point on the helix and the vector radius (as shown in Figure 3). when When changing, the wrap angle α remains unchanged, so it is called an equiangular helix. Two helical lines with a difference of δ angle form an antenna arm, and when one arm is rotated by 180°, the second arm is formed, thus forming a planar equiangular helical antenna together.

The planar equiangular helical antenna is a frequency-invariant antenna, and its basic parameters such as the inner and outer diameter directly determine the working bandwidth. According to the approximate formula:

In the formula: R is the outer diameter of the antenna; r0 is the inner diameter; λmax is the upper limit wavelength of the bandwidth; λmin is the lower limit wavelength of the bandwidth. Combined with the size requirements of the actual built-in sensor, this embodiment designs a self-complementary arm structure planar equiangular helical antenna with a bandwidth of 700MHz-3GHz, and the corresponding inner and outer radii are 2 and 109mm, respectively.

3. Determine the parameters of the processing material of the sensor body

For planar equiangular helical antennas, the parameters of the dielectric substrate and the size of the wrap angle will inevitably have a certain impact on the performance of the antenna. Therefore, this embodiment adopts the Ansoft HFSS software based on the finite element method to model and simulate the planar equiangular helical antenna, as shown in FIG. 3 . Unnormalized lumped port excitations are used in the simulations. The boundary condition simulates open free space with a radiation boundary greater than 1/4 wavelength away from the radiation source. The solution type is mode-driven solution, and the center frequency is set to a linear frequency sweep of 1.75GHz.

Taking the wrap angle α of the two arms of the antenna as an example, when the wrap angles of the helix are 84°, 81°, 77.5°, 70° and 65.58° respectively, the tightness of the helix and the width of the antenna arm will change accordingly ,As shown in Figure 4. Figure 5 shows the simulation results of the antenna performance parameters when the wrap angle takes different values.

It can be seen from Figure 5 that as the wrap angle decreases, the S parameter shifts to the right before 1.25GHz, making the lower limit of the low frequency band rise; ° and 65.58 ° are more obvious. Figure 6 shows that the amplitude of the real part of the input impedance of the sensor increases significantly in the range below 1.5GHz during the wrap angle reduction process, and the oscillation intensifies, but after falling to 65.58°, the amplitude falls back to some extent. In the range greater than 1.5GHz, the real part of the impedance tends to be consistent. Figure 7 shows that in the low frequency band lower than 1.25GHz, with the increase of the wrap angle, the maximum gain basically shows a downward trend; there is no obvious change in the middle frequency band; there is no obvious rule in the high frequency band above 2.5GHz, and the peak gain is Highest. It can be seen that the wrap angle has a great influence on the impedance. Increasing the wrap angle can obviously reduce the amplitude of the impedance in the low frequency band and weaken the oscillation of the impedance, but it will weaken the gain in the low frequency band.

In principle, the selection of the wrap angle should make the S11 amplitude as low as possible in the working frequency band and the gain as large as possible to ensure the sensor bandwidth; on the other hand, the real part of the impedance should be as close as possible to the characteristic impedance of the transmission line.

4. Design of Impedance Transformer

When the transmission line is connected to the load, if the wave impedance at both ends does not match, signal reflection will occur, so that part of the signal energy returns to the signal source and cannot be transmitted to the next-level unit, causing interference to the real signal, and at the same time it will form a resident on the transmission line. Wave. It can be seen from the previous results that the input impedance of the planar equiangular helical antenna fluctuates around 135Ω in the range of 800MHz to 3GHz. The actual common coaxial transmission line impedance is generally 50Ω. Therefore, within the required frequency range, it is necessary to add an impedance matching link to complete the impedance matching between the planar equiangular helical antenna and the transmission line, realize the impedance consistency transformation from the transmission line to the load, maximize the efficiency of the transmission line, and reduce the reflection caused by reflected waves. signal distortion. The basic principle of impedance matching is shown in Figure 8.

Theoretical and simulation results show that in a certain frequency band, the input impedance of the planar equiangular helical antenna has certain characteristics, that is, the real part of the impedance is about 135Ω, and the imaginary part is basically zero, similar to a pure resistive load. In view of this situation, a ladder impedance converter can be used to achieve the matching on the required bandwidth, that is, N equal-length transmission line segments are used between the load and the transmission line to form a converter, and the input impedance Z0 of the transmission line is gradually transformed to that of the load. Enter the impedance value Z _L . The more the step number N of the converter is, the smaller the step change of impedance between each section is, and the less the reflection caused by the step change of impedance is. When N is infinite, these transmission line segments approximately become a continuous gradient line, as shown in Figure 9.

For the impedance converter of this structure, the longer the gradient line length is, the lower the reflection coefficient amplitude will be. However, the internal space of GIS is limited, and the installation of too long impedance transformer will bring great difficulties. Based on the above analysis, this embodiment designs two forms of exponential asymptote microstrip line impedance transformers. One is the original length impedance transformer with a length of 210mm and a single-sided grounding structure; the other is an impedance transformer optimized for horizontal placement for easy installation, with a length of 101mm and a double-sided symmetrical structure.

5. Determine the overall model of the sensor

Considering that the input impedance of the coaxial line connected to the sensor is 50Ω, the closer the impedance of the coupler is to the input impedance of the coaxial line, the easier it is to achieve impedance matching. At the same time, the lower the S11, the lower the return loss; the higher the gain, the more sensitive the effect of receiving signals. In addition, the specifications of the antenna microwave plate manufacturer's products must be considered. Therefore, it is necessary to comprehensively consider various factors to determine the appropriate value of each parameter. Finally, the sensor parameters determined in this embodiment are shown in Table 1.

Table 1 Finalized sensor parameters

6. Simulation verification and physical production of the overall sensor model

See Figure 10 for the S11 simulation results obtained after the sensor takes the values of the parameters in the above table. Obviously, the sensor S11 before and after optimization within the design frequency band can be kept below -10dB, which meets the design requirements. However, compared with the structure of the original length, the lower limit of the bandwidth is significantly increased after the transverse optimization, and the overall upward shift of the S11 curve reduces the performance of the sensor. In other words, this optimization method essentially trades off the performance of the sensor for the convenience of installation space and installation operation at the expense of low-frequency characteristics and return loss.

Figure 11 shows the simulation results of the direction pattern (f = 1.75GHz). The figure shows that the sensor has the maximum gain on the central axis; the width of the main lobe is about 90°, which conforms to the characteristics of the non-frequency-variable antenna and can receive partial discharge signals from different directions around it.

In summary, the overall model of the sensor meets the design requirements. Therefore, a physical model is made to prepare for the next stage of testing.

2. Physical test optimization stage

7. Parametric testing

According to the value of the previous parameters, the plate is selected to make the real object, and the S11 parameter is selected as the parameter test object, and the test is carried out in the microwave anechoic room. The results are shown in Figure 12 and Figure 13.

In Figure 12, the test curve shows that the lower limit of the actual bandwidth of less than -10dB reaches 567MHz, and the upper limit exceeds 3GHz, which fully meets the design goals and partial discharge test requirements, and achieves a relatively ideal reception effect. As for Figure 13, because of the horizontal Z-type impedance converter, the acceptance effect on low-frequency signals is reduced, the lower limit of the bandwidth is raised to 832MHz, and the upper limit reaches about 3GHz, and the overall position of the S11 curve is relatively high, which has reached the requirement of -10dB critical. This further confirms that the transversely optimized impedance transformer is obtained by sacrificing sensor performance for structural optimization. In addition, the test results are in good agreement with the previous simulation results, which also verifies the correctness and effectiveness of the simulation.

Error analysis and optimization improvement experience summary: Comparing Figures 10 and 11 with Figures 12 and 13, it is found that although the test results and simulation curves are in good agreement, there are still some local deviations. The reasons can be attributed to the following points.

1) During the assembly and welding process of the antenna and the impedance transformer, it is impossible to completely guarantee that the welding point is completely smooth and completely consistent with the width of the high-impedance end of the microstrip line. This will form electromagnetic wave reflection, and then make the high-frequency S11 rise compared with the simulation calculation results.

2) The outermost arc curve of the equiangular helix is actually replaced by the connection of several straight line segments. This will inevitably have a certain impact on the low-frequency characteristics of the sensor.

3) There may be slight deviations between the parameters of the microwave plates used in the production and the values in the simulation.

4) Formulas (1) and (2) are empirical formulas, not strict and accurate calculation formulas, which is also one of the reasons for the deviation between the final production object and the design target.

8. Performance testing

In order to further verify the practicability of the sensor, this embodiment uses the above sensor to conduct an experimental test for receiving the actual partial discharge signal.

1) Experimental circuit

In order to simulate the partial discharge signal in the actual GIS, the partial discharge model sample is used to simulate the metal spike defect and the floating potential defect for experiment. The sensor is placed at a distance of 0.5m from the test object, and is connected to a digital oscilloscope TEK DPO7354C through a double-shielded coaxial transmission line, with a bandwidth of 3.5GHz and a maximum sampling rate of 40GS/s. At the same time, lead the signal of the low-voltage arm of the voltage divider to the oscilloscope to observe the applied voltage; connect a 50W non-inductive sampling resistor in series in the circuit of the test product to observe the discharge pulse current.

2) Comparison experiment of sensors connected to different impedance converters

Place two sensors equipped with different impedance transformers at the same time, and keep an equal distance from the test object. The receiving comparison results of the actual partial discharge signal (in this case, the floating potential discharge) are shown in Figures 14 and 15. In a complete cycle in the time domain, it can be clearly seen that the positive and negative signal amplitudes of the sensor connected to the original long impedance converter are higher than the signal amplitudes of the sensor connected to the horizontal optimized impedance converter. Spectrum analysis of the single discharge signal is shown in Figure 15, and it is found that the two sensor signals are significantly different in the low frequency band around 0.5GHz. In this frequency band, the original length sensor has higher signal amplitude due to smaller return loss. This also confirms the previous conclusion from the perspective of the frequency domain, that is, the horizontal impedance transformer optimizes the structure and volume at the expense of bandwidth, gain and other indicators, resulting in a decrease in signal amplitude.

3) Experimental test of floating potential discharge

Two adjacent but not in contact metal nuts fixed on insulating studs are used to simulate floating potential defects, and the experimental results are shown in Figures 16 and 17.

Figure 16 shows that this kind of defect mainly occurs on the rising edge of the positive and negative half cycle of the power frequency voltage, and has a significant phase distribution feature. In Figure 17, the time when the two sensors receive the signal pulse is consistent with the rising time of the current signal, indicating that the UHF signal and the pulse current received by the sensor can reflect the occurrence of partial discharge at the same time, and it can still be seen that the connection source The sensor signal amplitude is higher for long impedance transformers.

4) Experimental test of metal spike discharge and sensor characteristics

The experimental results obtained by simulating the metal spike defect are shown in Figure 18. The received signal of the sensor and the peak value of the pulse current still maintain a good consistency, and the positive and negative polarity signal amplitude of the horizontally optimized sensor is still lower than that of the original long sensor. In addition, it can also be seen that this defect has a phase distribution characteristic that is clearly different from the levitation potential. The discharge mainly occurs near the peak value of the positive and negative half cycle of the power frequency voltage, and the amplitude of the discharge signal of the positive half cycle of the power frequency voltage is high, the discharge pulse current is sparse, and the ultra-high frequency signal corresponds to it; while the discharge signal of the negative half cycle of the power frequency voltage The amplitude is small, the discharge pulse current is very dense, and the UHF signal is weak at this time.

5) Sensor position change test

In order to test the change of the received signal of the sensor with the increase of the distance to verify the practical performance of the sensor, the distance between the sensor and the discharge test object is changed respectively in the lateral (x direction) and longitudinal (y direction) distances, and the change of the peak value Vpp of the signal is analyzed. 20 signal acquisitions were performed at each position, and the test results are shown in Figures 19 and 20.

It can be seen that when the test distance increases in both directions, the average value of the peak-to-peak value of the signal is basically maintained within a certain range, and there is no great fluctuation. Similar to the previous results, the amplitude of the original long sensor is always higher than that of the transverse optimized sensor. It can be seen that the change of the sensor position does not have a significant impact on the received signal, and the sensor's receiving performance is good.

9. Practical application test

After the previous tests, the sensor was finally installed in an actual 252kV GIS cavity, and a spike defect was set in the cavity to replace the model sample in the aforementioned test circuit for the test. Figures 21 and 22 show the time domain and frequency domain waveforms of the received signal.

The time domain waveform shows that the output signal of the sensor can accurately reflect the occurrence of partial discharge. It can also identify the electromagnetic wave mode composition of the partial discharge signal in GIS, such as each TE mode and TM mode. It can be seen that the designed built-in UHF sensor can receive PD signals very well in the actual detection environment, has good performance, and meets the practical requirements, and can be used in the online detection of PD in GIS in the future. monitor.

10. Optimization improvement and verification

Based on the optimization and improvement experience in the previous process, the connection and fixing method of the designed sensor, the installation and sealing in the GIS cavity have been improved and optimized, and the practical improvement plan has been verified by comparing and testing the improved sensor. feasibility. Finally, the entire process of sensor design, optimization and testing is completed.

In the embodiment of the present invention, a built-in UHF sensor with ultra-wide frequency band is designed to meet the requirements of partial discharge detection, and a series of detailed tests are carried out.

The parameter test shows that the S11 parameter has reached the expected design goal and achieved a relatively ideal reception effect. The performance test shows that the signal amplitude of the sensor connected to the original long impedance transformer is relatively high; although the structure and volume of the sensor connected to the horizontal optimized impedance transformer are optimized, the performance is affected, resulting in a low amplitude of the received signal; The UHF signal received by the sensor can correctly reflect the occurrence of partial discharge and the discharge characteristics of different defects, and is less affected by position changes, and the sensor has good receiving performance.

The receiving test inside the GIS cavity shows that the sensor can receive the partial discharge signal well in the actual detection environment, the signal recognition is high, and the bandwidth and size of the sensor meet the practical requirements, which can be used in the future The GIS station is monitored online, and the rationality of the technical solution of the present invention is further verified.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: and the present invention A technical solution similar to the technical solution described in the foregoing embodiments, or an equivalent replacement of some of its technical features, etc., does not make the essence of the corresponding technical solution deviate from the technical idea and protection scope of the technical solution of the embodiment of the present invention.

Claims (6)

1. a general design, optimization and testing method of UHF partial discharge sensor, is characterized in that: the method comprises model design optimization stage and object test optimization stage, method step is: Model design optimization stage 1) Determine the sensor design bandwidth based on the characteristics of the measured signal, the frequency range of the expected detection signal, the actual type of detection equipment, and the environmental conditions of the sensor installation; 2) According to the design bandwidth determined in step 1), determine the sensor structure that can realize the bandwidth; and determine the basic parameters of the sensor body according to the principle of the sensor structure and related formulas; 3) For the processing material parameters of the sensor, take different values for simulation and comparative analysis, test the influence on the performance of the sensor, and optimize and determine its value; 4) According to the sensor impedance characteristics obtained by the simulation calculation in step 3), and the wave impedance of the feeder used, design the impedance converter and determine the parameters of the impedance converter; 5) Refer to the parameter calculation results in the previous step 3), combine the actual microwave plate specifications, prices and other factors, and the design of the impedance transformer to determine the final values of all relevant parameters of the sensor, and obtain the overall model of the sensor; 6) Carry out simulation verification on the overall sensor model; if the requirements are not met, re-optimize and adjust the overall sensor model from step 5); if the requirements are met, make a physical model of the sensor, and the model design optimization stage is completed; physical test optimization stage 7) Use instruments and equipment to test the key parameters of the physical model of the sensor, and compare them with the design values to verify whether the sensor meets the design goals; if the design requirements are met, record the test results, summarize the points that can be optimized and improved, and carry out sensor Optimize, improve and verify, further improve the sensor parameters, and prepare for the next stage of testing; if the design requirements are not met, return to step 2), continue to optimize and adjust the parameters of the sensor and the overall model; the key parameters include: S11 parameters /SWR, input impedance, frequency bandwidth, pattern, gain, lobe width; 8) Use the discharge model to test the performance of the physical model of the sensor, and test the sensor’s ability to receive and record real discharge signals by comparing and analyzing the signal reception under different working conditions. The working conditions include: detection distance, angle; if If the performance requirements are met, record the test results, summarize the points that can be optimized and improved, optimize and verify the sensor, further improve the sensor performance, and prepare for the next stage of testing; if the performance design requirements are not met, return to step 2) and continue Optimize and adjust the parameters of the sensor and the overall model; 9) Install the final test on the physical model of the sensor in the actual application environment (such as GIS, transformer, switch cabinet, etc.) to verify the signal receiving ability and working condition of the sensor under real working conditions; if the application requirements are met, record the test results , summarize the points that can be optimized and improved, optimize and verify the sensor, and further improve the practicability of the sensor; if the application requirements are not met, return to step 2), and re-optimize and adjust the parameters of the sensor and the overall model; 10) Combine the optimization and improvement experience summarized from the simulation and test results in the above steps to complete the final sensor. 2. The general design, optimization and testing method of a UHF partial discharge sensor according to claim 1, characterized in that: the structure of the sensor in the above step 2) can be designed according to the antenna structure: according to the previous steps 1) Determine the design bandwidth, determine the type of antenna that can achieve this bandwidth, and determine the basic parameters of the sensor body according to the principle and formula of the antenna. 3. A general design, optimization and testing method for a UHF partial discharge sensor according to claim 1 or 2, characterized in that: Step 2) The basic parameters of the sensor body refer to the determination of the sensor body type, size, The parameters of the structure. 4. A general design, optimization and testing method for a UHF partial discharge sensor according to claim 1 or 2, characterized in that: Step 3) The processing material parameters of the sensor include plate thickness, dielectric constant, hardness degree. 5. A general design, optimization and testing method for a UHF partial discharge sensor according to claim 1 or 2, characterized in that: Step 5) The relevant parameters of the sensor include: antenna size, structure, and thickness of processed materials , Dielectric constant, impedance transformer structure, size, material thickness, dielectric constant, surface copper clad form. 6. A general design, optimization and testing method for UHF partial discharge sensors according to claim 1 or 2, characterized in that: Step 7) The key parameters include: S11 parameters/SWR, input Impedance, bandwidth, pattern, gain, lobe width.