Test tool for electric field distribution test verification

Abstract

Different from a single-point detector which can only measure one position, the test tool for electric field distribution test verification provided by the utility model has the advantages that the area array photoelectric detector is integrated with a plurality of photoelectric detectors and a plurality of output channels, so that multi-point simultaneous measurement can be carried out on an electric field in insulating oil; the electric field intensity of the insulating oil can be better represented through the electric field intensity of each detection point, the measurement result is more accurate and reliable, and meanwhile, the whole process of generation, movement and convergence of interface charges can be observed; besides, the photoelectric detectors have the same linear responsivity, and test verification is performed through the shockproof optical platform, so that mutual electromagnetic coupling is avoided, noise interference is also considered, and good test precision is ensured while the test efficiency is improved.

Description

Technical Field

[0001] This application relates to the technical field of electric field measurement in oil, and particularly to a test tooling for electric field distribution test and verification. Background Art

[0002] Current research on electric fields mostly uses simulation calculation methods. However, since simulation results often lack relevant experimental verification, their reliability is not high. At the same time, the traditional method of using sensors for measurement also has the problem that the measured electric field is affected by the sensor. With the rapid development of laser and computer technologies, non-contact electric field measurement methods have gradually become an important research means. Among them, the electric field measurement method based on the Kerr effect has unique advantages, can directly measure the electric field distribution under high voltage, and has the characteristics of high reliability and easy calculation. Foreign scholars first proposed the Kerr photo - electric field measurement method in the early 1980s. Subsequently, scholars proposed the electric field modulation technology on this basis and further developed the Kerr effect method based on the alternating current (AC) electric field modulation technology. This method greatly improves the sensitivity of electric field measurement and has thus been widely applied.

[0003] The oil electric field measurement device based on the Kerr effect using a single - point photodetector adopts a coaxial optical path structure, introduces AC modulation technology to improve the measurement sensitivity; optimizes the electrode form to improve the measurement accuracy, meeting the needs of oil electric field measurement under the oil - paper structure; constructs two independent polarization angles by rotating the analyzer to meet the needs of two - dimensional electric field measurement; adopts a split - type two - dimensional stepping movement mechanism to meet the needs of distributed electric field measurement; optimizes the selection of AC modulation frequency and uses a lock - in amplifier with a high sampling rate to meet the needs of real - time measurement of transient electric fields. This device realizes the on - line real - time measurement of the non - contact electric field in transformer oil under DC voltage, AC - DC composite voltage, and polarity - reversed voltage. However, since the CCD used in the conventional Kerr photo - electric effect method can only receive a single signal, only the field strength at a single point between the plates can be obtained under continuous voltage application, and the simultaneous measurement of the electric field in oil cannot be achieved. Moreover, the measurement results are easily affected by the stability of the test tooling and noise interference, resulting in relatively low accuracy of the measurement results. Summary of the Utility Model

[0004] The purpose of this application aims to solve at least one of the above - mentioned technical defects, especially the technical defect that the CCD used in the conventional Kerr photo - electric effect method in the prior art can only receive a single signal, only the field strength at a single point between the plates can be obtained under continuous voltage application, the simultaneous measurement of the electric field in oil cannot be achieved, and the measurement results are easily affected by the stability of the test tooling and noise interference, resulting in relatively low accuracy of the measurement results.

[0005] The present application provides a test tooling for electric field distribution test and verification. The test tooling includes a motor control system, an optical path system, a test cavity, a surface array photodetector, and an oscilloscope disposed on a shock-proof optical platform;

[0006] The motor control system, the test cavity, the surface array photodetector, and the oscilloscope are arranged in sequence from left to right. The surface array photodetector integrates a plurality of photodetectors and a plurality of output channels, and each photodetector has the same linear responsivity. Each output channel on the surface array photodetector is connected to the input end of the oscilloscope;

[0007] The optical path system includes a He-Ne laser, a spatial filter, a plano-convex lens, a polarizer, and a quarter-wave plate arranged in sequence from left to right between the motor control system and the test cavity, quartz window plates symmetrically embedded on both left and right sides of the test cavity, and an analyzer arranged between the test cavity and the surface array photodetector. An optical path for light intensity measurement is formed among the He-Ne laser, the spatial filter, the plano-convex lens, the polarizer, the quarter-wave plate, the test cavity, the analyzer, and the surface array photodetector;

[0008] Wherein, the motor control system is used to drive the He-Ne laser to move;

[0009] The surface array photodetector is used to convert the light intensity signal into a voltage signal and then input it to the oscilloscope;

[0010] The oscilloscope is used to measure the electric field strength in insulating oil with the collected test data.

[0011] Optionally, a plurality of photodetectors are all arranged in the center of the circuit board of the surface array photodetector. A plurality of output channels are symmetrically distributed on the left and right sides of the circuit board. A corresponding amplifier circuit is provided between each photodetector and each output channel;

[0012] Wherein, each amplifier circuit respectively converts the light intensity signal detected by the corresponding photodetector into a voltage signal and outputs it through the corresponding output channel.

[0013] Optionally, the circuit board is encapsulated with an all-aluminum shell.

[0014] Optionally, the amplifier circuit uses a feedback capacitor to reduce noise.

[0015] Optionally, the operational amplifier in the amplifier circuit is an LMP7721 operational amplifier.

[0016] Optionally, the size of the feedback capacitor in the amplifier circuit satisfies the requirement that the signal frequency corresponding to a 3 dB drop in the DC gain of the operational amplifier is not greater than the maximum cut-off frequency.

[0017] Optionally, the photodetector is a photodiode operating in the photovoltaic mode.

[0018] Optionally, the photodiode is an S1133 photodiode.

[0019] Optionally, when the He-Ne laser emits visible red light with a wavelength of 632.8 nm, the visible red light is expanded into a uniform light spot with a diameter of 21 mm through the spatial filter and the plano-convex lens.

[0020] Optionally, the number of photodetectors and output channels integrated in the area array photodetector is eight each.

[0021] It can be seen from the above technical solutions that the embodiments of the present application have the following advantages:

[0022] An experimental tooling for testing and verifying electric field distribution provided by the present application. The experimental tooling includes a motor control system, an optical path system, a test cavity, a surface array photodetector, and an oscilloscope arranged on a shock-proof optical platform. Among them, the motor control system, the test cavity, the surface array photodetector, and the oscilloscope are arranged in sequence from left to right. The surface array photodetector integrates multiple photodetectors and multiple output channels, and each photodetector has the same linear response. Each output channel on the surface array photodetector is connected to the input end of the oscilloscope. The optical path system includes a He-Ne laser, a spatial filter, a plano-convex lens, a polarizer, and a quarter-wave plate arranged in sequence from left to right between the motor control system and the test cavity, quartz window plates symmetrically embedded on both left and right sides of the test cavity, and an analyzer arranged between the test cavity and the surface array photodetector. During the test process of the present application, the motor control system can move the He-Ne laser. After placing the specimen and insulating oil processed according to the national standard in the test cavity, an AC modulation voltage and a DC voltage are applied to the test cavity. The laser emitted by the He-Ne laser is expanded into a uniform light spot by the spatial filter and the plano-convex lens. After passing through the polarizer, the quarter-wave plate, the left quartz window plate, the test cavity, the right quartz window plate, and the analyzer, the light spot is perpendicularly incident on the surface array photodetector. The surface array photodetector converts the light intensity signals of multiple detection points in the uniform light spot into voltage signals and inputs them to the oscilloscope. The electric field intensity in the insulating oil is measured through the test data collected by the oscilloscope. Different from a single-point detector that can only measure one position, the present application proposes a surface array photodetector integrating multiple output channels. In this way, not only can the electric field in the insulating oil be measured at multiple points simultaneously, and the electric field intensity of the insulating oil can be better characterized through the electric field intensities of each detection point, and the measurement result is more accurate and reliable. At the same time, the entire process of the generation, movement, and convergence of interfacial charges can also be observed. In addition, each photodetector in the present application has the same linear response, and the test and verification are carried out through a shock-proof optical platform, thus avoiding electromagnetic coupling between each other and taking into account noise interference, ensuring good test accuracy while improving the test efficiency. Description of the Drawings

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a schematic structural diagram of an experimental tooling for testing and verifying electric field distribution provided by an embodiment of the present application;

[0025] Figure 2 Schematic diagram of the principle of the Kerr effect method based on AC modulation provided by an embodiment of the present application;

[0026] Figure 3 PCB circuit board design diagram of the circuit board of the area array photodetector provided by an embodiment of the present application;

[0027] Figure 4 Schematic diagram of the packaging structure of the area array photodetector provided by an embodiment of the present application;

[0028] Figure 5 Schematic diagram of the principle of the amplifier circuit provided by an embodiment of the present application;

[0029] Figure 6 Schematic diagram of the structure of the feedback capacitor noise reduction model provided by an embodiment of the present application;

[0030] Figure 7 Schematic diagram of the structure of the voltage shunt negative feedback circuit provided by an embodiment of the present application;

[0031] Figure 8 Schematic diagram of the equivalent circuit of the photodiode provided by an embodiment of the present application;

[0032] Figure 9 Schematic diagram of the circuit structure of the amplifier circuit provided by an embodiment of the present application. Detailed implementation manners

[0033] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0034] In one embodiment, as Figure 1 shown, Figure 1 Schematic diagram of the structure of a test tool for electric field distribution test and verification provided by an embodiment of the present application; The present application provides a test tool for electric field distribution test and verification. The test tool includes a motor control system, an optical path system, a test cavity, an area array photodetector, and an oscilloscope arranged on a shock-proof optical platform.

[0035] The motor control system, the test cavity, the area array photodetector, and the oscilloscope are arranged in sequence from left to right. The area array photodetector integrates a plurality of photodetectors and a plurality of output channels, and each photodetector has the same linear response degree. Each output channel on the area array photodetector is connected to the input end of the oscilloscope.

[0036] The optical path system includes a He-Ne laser, a spatial filter, a plano-convex lens, a polarizer, and a quarter-wave plate that are sequentially arranged from left to right between the motor control system and the test cavity, quartz window plates symmetrically embedded on the left and right sides of the test cavity, and an analyzer arranged between the test cavity and the area array photodetector.

[0037] It should be noted that the improvement of this application lies in the structure of the system. The following descriptions of methods in the examples are only to prove that the system can achieve effects in applications. These effects in the system are realized depending on the hardware structure. Based on different objects and in different operation processes, the method steps and detection effects may vary or may not vary, which are not limited herein.

[0038] In specific implementation, the He-Ne laser is driven to move by the motor control system. After placing the specimen and insulating oil treated according to the national standard in the test cavity, an AC modulation voltage and a DC voltage are applied to the test cavity. The laser emitted by the He-Ne laser is expanded into a uniform light spot by the spatial filter and the plano-convex lens. After passing through the polarizer, the quarter-wave plate, the left quartz window plate, the test cavity, the right quartz window plate, and the analyzer, the light is incident perpendicularly into the area array photodetector, and the area array photodetector converts the light intensity signals of multiple detection points in the uniform light spot into voltage signals and inputs them to the oscilloscope. The electric field strength in the insulating oil is measured through the test data collected by the oscilloscope.

[0039] It should be noted that controlling and driving an object to move through a motor system is a prior art. The specific motor model and control method can be selected according to actual needs. In this embodiment, the optical path system is quickly adjusted through the motor system, and no improvement is made to the motor system and the control method, which are not limited herein.

[0040] In this embodiment, when measuring the electric field strength in the insulating oil, a test tooling including a motor control system, an optical path system, a test cavity, an area array photodetector, and an oscilloscope can be set up. This test tooling can be set on an anti-vibration optical platform, so as to minimize the influence of the external environment during the experiment and effectively improve the measurement accuracy.

[0041] Schematically, as Figure 1As shown in the figure, the optical path system of the present application may include a He-Ne laser, a spatial filter, a plano-convex lens, a polarizer, a quarter-wave plate, a quartz window plate, and an analyzer; the He-Ne laser, the spatial filter, the plano-convex lens, the polarizer, and the quarter-wave plate may be sequentially arranged from left to right between the motor control system and the test cavity. The quartz window plate may be symmetrically embedded on the left and right sides of the test cavity, and the analyzer may be arranged between the test cavity and the area array photodetector, thus forming an optoelectronic detection route from the He-Ne laser to the oscilloscope. The spatial filter and the plano-convex lens in this optoelectronic detection route can expand the laser emitted by the He-Ne laser, thereby realizing the simultaneous measurement of the electric fields at multiple points.

[0042] Furthermore, in order to improve the detection accuracy of the electric field strength and cooperate with the enlarged light spot detected by the spatial filter and the plano-convex lens, the area array photodetector of the present application may be integrated with multiple photodetectors and multiple output channels, and each photodetector has the same linear response. Each output channel on the area array photodetector is connected to the input end of the oscilloscope. This can not only realize the simultaneous measurement of the electric fields at multiple detection points in the oil, making the measurement results accurate and reliable and having sufficient persuasiveness, but also observe the entire process of the generation, movement, and convergence of the interfacial charges. In addition, setting each photodetector to have the same linear response can effectively avoid electromagnetic coupling between them and also take into account the noise interference, ensuring good test accuracy while improving the test efficiency.

[0043] It can be understood that when setting the number of channels of the area array photodetector in the present application, the number of output channels can be set based on this tooling according to the specific usage situation. Theoretically, it can be set to 8, 16, 32, etc. As long as there is no crosstalk between them through reasonable layout and wiring, it can become a test tooling.

[0044] After the test tooling of the present application is configured, the specimen and the insulating oil can be processed according to the national standard and then placed in the test cavity, and the optical path can be adjusted so that the light spot can be normally incident on the area array photodetector after passing through the optical path system. Then, the present application can adjust the optical path such as the area array photodetector and the analyzer according to the feedback of the oscilloscope reading. When the reading is about 1V, it is considered that the adjustment is completed. Then, an AC modulation voltage and a DC voltage are applied to the platform, and data can be collected by the oscilloscope at the back end. Finally, a fast Fourier transform is performed on the test data, and finally the electric field strength value in the oil can be obtained.

[0045] In a specific embodiment, since this application improves the existing test tooling corresponding to the Kerr optoelectronic effect method and uses the improved test tooling to measure the electric field strength in insulating oil. Therefore, the process of calculating the electric field strength value in the oil through the voltage signal fed back by a single photodetector is the same as the existing calculation process, which is as follows:

[0046] The Kerr effect method utilizes the optical anisotropy presented by certain liquid media under the action of an electric field. By measuring the change in the light intensity of a linearly polarized laser beam passing through the liquid media, the phase differences θ of two components parallel and perpendicular to the electric field direction are obtained respectively. This phase difference is proportional to the Kerr constant of the liquid media, the length of the electric field region, and the square of the electric field strength, as shown below:

[0047]

[0048] In the formula, B is the Kerr constant of the medium, E is the electric field strength, and L is the length of the electric field region.

[0049] The advantage of this method is that it can directly utilize the electro-optical properties of the substance to be measured without the need to introduce other media. Using a laser as the measurement medium, non-contact on-line real-time measurement can be achieved, so it is widely used in research in the field of liquid medium space electric field measurement.

[0050] For liquid media with a low Kerr constant, the measurement sensitivity will be affected. To improve the sensitivity, the Kerr effect method based on AC modulation can be adopted. The schematic diagram of the principle of this method is as Figure 2 shown Figure 2 In the figure, taking the single optical path polarization interference structure as an example to illustrate the principle of the AC modulation method: The laser beam (632.8 nm) emitted by a He-Ne laser is set as a linearly polarized light by a polarizer, and then becomes a circularly polarized light after passing through a quarter-wave plate and is incident on the Kerr effect test cavity. Under the action of the Kerr effect, the passing beam generates an additional phase difference containing electric field information and becomes an elliptically polarized light, and finally forms the interference of polarized light after being detected by an analyzer. In addition to applying the DC electric field to be measured on the test object, an AC modulation electric field also needs to be applied. The phase difference generated by the combined action of the two is:

[0051]

[0052] The optical intensity signal is converted into a voltage signal by a photodetector and input into an oscilloscope and a lock-in amplifier to further separate the composite signal to obtain the DC component I dc of the optical intensity, the fundamental frequency component I 1ω and the harmonic component I 2ω . The DC electric field E dc and the AC electric field E a can be calculated by the following formulas.

[0053]

[0054] In the above embodiments, the test tooling includes a motor control system, an optical path system, a test cavity, a surface array photodetector, and an oscilloscope arranged on a shock-proof optical platform. Among them, the motor control system, the test cavity, the surface array photodetector, and the oscilloscope are arranged in sequence from left to right. The surface array photodetector integrates a plurality of photodetectors and a plurality of output channels, and each photodetector has the same linear response. Each output channel on the surface array photodetector is connected to the input end of the oscilloscope. The optical path system includes a He-Ne laser, a spatial filter, a plano-convex lens, a polarizer, and a quarter-wave plate arranged in sequence from left to right between the motor control system and the test cavity, quartz window plates symmetrically embedded on both left and right sides of the test cavity, and an analyzer arranged between the test cavity and the surface array photodetector. During the test of this application, the motor control system can control the movement of the He-Ne laser. After placing the specimen and insulating oil treated according to the national standard in the test cavity, an AC modulation voltage and a DC voltage are applied to the test cavity. The laser emitted by the He-Ne laser is expanded into a uniform light spot by the spatial filter and the plano-convex lens. After passing through the polarizer, the quarter-wave plate, the left quartz window plate, the test cavity, the right quartz window plate, and the analyzer, the light is perpendicularly incident on the surface array photodetector. The surface array photodetector converts the light intensity signals of multiple detection points in the uniform light spot into voltage signals and inputs them to the oscilloscope. The electric field strength in the insulating oil is measured through the test data collected by the oscilloscope. Different from a single-point detector that can only measure one position, this application proposes a surface array photodetector integrating multiple output channels. In this way, not only can the electric field in the insulating oil be measured at multiple points simultaneously, and the average value of the electric field strength at each detection point can better characterize the electric field strength of the insulating oil, but also the measurement results are more accurate and reliable. At the same time, the entire process of the generation, movement, and convergence of interface charges can be observed. In addition, each photodetector in this application has the same linear response, and the test is verified through a shock-proof optical platform, thereby avoiding electromagnetic coupling between each other and taking into account noise interference, ensuring good test accuracy while improving the test efficiency.

[0055] In one embodiment, as Figure 3 shown, Figure 3 This is the PCB circuit board design diagram of the circuit board of the surface array photodetector provided by the embodiment of this application; Figure 3 Among them, a plurality of photodetectors are all arranged in the center of the circuit board of the surface array photodetector, and a plurality of output channels are symmetrically distributed on the left and right sides of the circuit board. Corresponding amplifier circuits are provided between each photodetector and each output channel.

[0056] Among them, each amplifier circuit converts the optical intensity signal detected by the corresponding photodetector into a voltage signal and outputs it through the corresponding output channel.

[0057] In this embodiment, the area array photodetector can have multiple photodetectors and multiple output channels. For example, Figure 3 the area array photodetector in [reference] has eight output channels. Eight photodetectors are closely arranged in a rectangular shape in the middle of the circuit board. The power interface is above. There are four output channels on each side of the left and right of the circuit board. The output channels on the left and right sides are symmetrically arranged. An amplifier circuit is between each output channel and the corresponding photodetector, which is used to amplify the electrical signal detected by the photodetector and send it to the oscilloscope through the corresponding output channel. In this way, the corresponding voltage waveform can be output through the oscilloscope, and the corresponding electric field strength can be calculated.

[0058] In one embodiment, as Figure 4 shown, Figure 4 is a schematic diagram of the packaging structure of the area array photodetector provided by the embodiment of the present application; Figure 4 in [reference], the circuit board is encapsulated with an all-aluminum shell, which can not only play a protective role, but also dissipate heat faster.

[0059] In one embodiment, the amplifier circuit uses a feedback capacitor to reduce noise. This method not only has a relatively simple structural design, but also does not introduce additional noise, thereby effectively reducing the high-frequency noise gain of the operational amplifier circuit.

[0060] Specifically, the role of the amplifier circuit in the present application is to convert the photocurrent signal into a voltage signal. The circuit is an I / V conversion circuit. The circuit schematic diagram is as Figure 5 shown, Figure 5 is the schematic diagram of the amplifier circuit provided by the embodiment of the present application; Figure 5 in [reference], R1 is the feedback resistor, and its size is proportional to the output voltage. The formula is as follows, where is the input photocurrent:

[0061]

[0062] Figure 5 in [reference], the non-inverting input terminal resistor R2 is used as a balancing resistor. The size of the balancing resistor is determined according to the parallel value of the resistor connected to the inverting input terminal and the feedback resistor. The on-resistance of the photodiode is generally several hundred ohms, and the feedback resistor is 50 kΩ; the output terminal resistor R3 is used to increase the current load, play a role in stabilizing the output voltage, and can also resist noise interference. The size of the resistor is generally obtained by the maximum output voltage of the operational amplifier / the maximum allowable passing current. A resistor R4 is connected in parallel across the photodiode to reduce the equivalent resistance of the diode, raise the conduction current threshold, and avoid the outflow of dark current.

[0063] Furthermore, since the noise of the amplifier circuit mainly consists of three parts: the feedback resistor of the amplifier circuit, the input noise current, and the noise voltage. The noise caused by the feedback resistor and current noise of the amplifier circuit is relatively easy to analyze. However, the input noise voltage of the amplifier circuit will generate a high-frequency gain, and its magnitude is related to the feedback resistor in the amplifier circuit and the capacitance of the photodetector. Moreover, due to the parasitic capacitance around the feedback resistor itself and the 1 / f response characteristic of the input noise voltage, the total output noise of the amplifier circuit becomes more complex.

[0064] Schematically, as Figure 6 shown, Figure 6 is a schematic structural diagram of the feedback capacitance noise reduction model provided by an embodiment of the present application; Figure 6 In the equivalent model of, i p represents a current source, and C i represents the sum of the capacitance CD of the photodetector itself, the input capacitance C id of the operational amplifier, and C icm , that is, C i = C D + C id + C icm . The noise voltage of the operational amplifier is applied to the capacitance C i , and a corresponding noise current will be output, and the noise current will pass through the feedback resistor R f . According to the above analysis of the noise, in the state of high gain of the amplifier circuit, the stray capacitance will automatically bypass the feedback resistor, and the noise gain will be controlled at 1 + (C i / C s ). With the addition of the feedback capacitance, the peak value of the noise gain is reduced to 1 + (C i / (C s + C f ). In the case where the bandwidth required by the experiment is not high, from the perspective of minimizing additional circuit components as much as possible, the method of using feedback capacitance to reduce noise is the simplest, and no additional noise will be introduced, thereby effectively reducing the high-frequency noise gain of the operational amplifier circuit.

[0065] In one embodiment, the operational amplifier in the amplifier circuit is an LMP7721 operational amplifier.

[0066] In this embodiment, the amplifier circuit may include an operational amplifier, and the operational amplifier can be selected according to its performance, etc. For example, the present application can select the LMP7721 operational amplifier as the amplifier in the amplifier circuit.

[0067] It can be understood that an operational amplifier is an integrated circuit containing many transistors. Generally, the function of an amplifier is to amplify the input voltage and then output it. The ratio of the output voltage to the input voltage is called the voltage gain. An ideal operational amplifier has characteristics such as infinite input impedance, almost zero output resistance, and infinite open-loop gain. Among them, taking the voltage shunt negative feedback circuit as an example for the inverting proportional operation circuit, the circuit structure diagram is as Figure 7 shown, Figure 7 which is the schematic diagram of the voltage shunt negative feedback circuit provided by the embodiment of the present application; since the gain of the operational amplifier is generally much greater than 10 5 , so the circuit is under the condition of deep negative feedback. According to virtual short and virtual open, the relationship between the output and input voltages can be obtained:

[0068]

[0069] The present application can determine the performance of different operational amplifiers according to the above formula and select the operational amplifier with the best performance for optoelectronic detection.

[0070] In one embodiment, the size of the feedback capacitor in the amplifier circuit satisfies the requirement that the signal frequency corresponding to the 3dB decrease in the DC gain of the operational amplifier is not greater than the maximum cut-off frequency.

[0071] In this embodiment, to determine the size of the feedback capacitor in the amplifier circuit, the requirements of the actual test frequency need to be considered, that is, the requirement that the signal frequency corresponding to the 3dB decrease in the DC gain of the operational amplifier is less than the maximum cut-off frequency. The specific formula is as follows:

[0072]

[0073] In the formula, represents the feedback resistor, represents the feedback capacitor, GBP represents the gain-bandwidth product of the operational amplifier, represents the junction capacitance, represents the stray capacitance between the positive and negative input terminals of the operational amplifier.

[0074] The present application considers parameters such as the gain-bandwidth product of the operational amplifier selected for the test fixture and its own junction capacitance, and determines that the parameters of the feedback capacitor satisfy the condition, so that it can not only meet the requirements of the test frequency but also reduce the high-frequency noise gain of the operational amplifier circuit.

[0075] In one embodiment, the photodetector is a photodiode operating in the photovoltaic mode.

[0076] In one embodiment, the photodiode is an S1133 photodiode.

[0077] In the above embodiments, when selecting a photodetector, an S1133 photodiode operating in the photovoltaic mode can be selected. The photodiode can convert an optical signal into an electrical signal to achieve the detection of a physical state. Its working principle is as follows: When light irradiates on a semiconductor material, electron-hole pairs will be released, thereby generating a current; photons transfer energy to the irradiated semiconductor atoms, causing electron carriers and holes to be excited to the conduction state. After transitioning to the conduction state, not all carriers participate in the formation of the current. The photocurrent is mainly formed by the carriers released inside the depletion region of the semiconductor junction, relying on the acceleration effect of the depletion region electric field. The potential difference of the PN junction is formed by the atoms in the depletion layer, increasing the conduction energy of the carriers and reducing the recombination probability at the same time. The carriers generated by thermal motion diffuse through the PN junction to form a net charge layer, and the net charge is balanced by the electric field formed by the PN junction and the diffusion motion, finally forming the built-in electric field of the PN junction. The carriers released outside the depletion layer diffuse inside the semiconductor until they reach the depletion layer or are finally recombined. The carriers reaching the depletion region move to both sides of the diode under the acceleration of the electric field and become conduction current.

[0078] The photodiode in this application can be equivalent to an electronic component, and its analog circuit is as Figure 8 shown, Figure 8 which is a schematic diagram of the equivalent circuit of the photodiode provided by the embodiment of this application; Figure 8 In it, the output signal of the photodiode can be a voltage or current signal, and using the current signal as the output signal can exhibit better linear and bandwidth characteristics. The photocurrent generated by the photodiode is proportional to the incident power, and the current is converted into a voltage by the backend amplifier circuit. The photodiode has two working modes, namely the photoconductive mode (biased) and the photovoltaic mode (unbiased). If the photodiode operates in the photoconductive mode, due to the increased loss region of the photodiode, the junction capacitance is reduced, and introducing a reverse bias voltage can greatly improve its response speed and linearity, but there are also some problems, such as correspondingly increasing its dark current and noise, and the dark current will increase with the increase of temperature. If the photodiode operates in the photovoltaic mode, that is, without reverse bias, no additional noise and dark current will be added, and in this working mode, the output magnitude of the photocurrent is almost independent of temperature. Therefore, the test tooling of this application selects a photodiode operating in the photovoltaic mode, and the model of the photodiode can be selected as S1133, so as to better detect the electric field strength.

[0079] Furthermore, when the amplifier circuit of this application uses the feedback capacitance noise reduction method to reduce noise and uses the LMP7721 operational amplifier and the S1133 photodiode in the photovoltaic mode, an amplifier circuit as Figure 9 shown can be constructed, and the parameter settings in this amplifier circuit can be as shown in Table 1 below:

[0080]

[0081] Table 1 Parameters of the Amplification Circuit of the Test Tooling

[0082] Based on the above analysis, the present application conducts a simulation analysis on the Figure 9 amplification circuit shown in the figure. The input photocurrent is set to 0.01 A, the feedback resistor is 50 kΩ, the feedback capacitor is 220 pF, the ideal output voltage is 500 mV, and an AC sweep analysis is performed with the bandwidth set to 1 Hz - 10 MHz. After simulation, an output voltage of 500 mV is obtained, which is the same as the expected value. The effective frequency of the voltage output by the amplification circuit is cut off at 14.14 kHz, and the effective bandwidth is significantly limited.

[0083] In one embodiment, when the He-Ne laser emits visible red light with a wavelength of 632.8 nm, the visible red light is expanded into a uniform light spot with a diameter of 21 mm through the spatial filter and the plano-convex lens.

[0084] In this embodiment, the entire system mainly consists of four parts: a laser source system, an optical path system, a test cavity, and a planar array photodetector. Among them, the optical path system mainly consists of a He-Ne laser, a spatial filter, a plano-convex lens, a polarizer, a quarter-wave plate, a quartz window plate, a analyzer, etc. The laser source system refers to the motor control system that controls the movement of the laser. The He-Ne laser can emit visible red light with a wavelength of 632.8 nm. The laser is expanded into a uniform light spot with a diameter of 21 mm through the spatial filter and the plano-convex lens, and then the light spot passes through optical devices, the test cavity, etc. Finally, multiple photodetectors in the planar array photodetector respectively receive the optical signals of each detection point in the light spot, and after being amplified by the amplification circuit and converted into voltage signals, they are output, so as to calculate the electric field strength of each detection point.

[0085] In one embodiment, the number of photodetectors and output channels integrated in the planar array photodetector is eight each, so that the optical signals of eight detection points in the light spot can be detected simultaneously, thereby effectively improving the detection accuracy and detection efficiency.

[0086] Finally, it should also be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, such that a process, method, article or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the element.

[0087] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The embodiments can be combined as needed, and the same or similar parts can be referred to each other.

[0088] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A test fixture for electric field distribution test verification, characterized in that: The test fixture includes a motor control system, an optical path system, a test cavity, a surface array photoelectric detector and an oscilloscope arranged on a shockproof optical platform; The motor control system, the test cavity, the area array photodetector and the oscilloscope are arranged in sequence from left to right, the area array photodetector integrates a plurality of photodetectors and a plurality of output channels, and each photodetector has the same linear responsivity, and each output channel on the area array photodetector is connected to the input end of the oscilloscope; The optical path system includes a He-Ne laser, a spatial filter, a plano-convex lens, a polarizer and a quarter-wave plate which are sequentially arranged from left to right between the motor control system and the test cavity, quartz windows symmetrically embedded on the left and right sides of the test cavity, and an analyzer arranged between the test cavity and the surface array photodetector, wherein an optical path for light intensity measurement is formed between the He-Ne laser, the spatial filter, the plano-convex lens, the polarizer and the quarter-wave plate, the test cavity, the analyzer and the surface array photodetector; Wherein, the motor control system is used to drive the He-Ne laser to move; The surface array photoelectric detector is used to convert the light intensity signal into a voltage signal and then input it into the oscilloscope; The oscilloscope is used to measure the electric field strength in the insulating oil using the collected test data.

2. The test fixture for electric field distribution test and verification according to claim 1, characterized in that: A plurality of photodetectors are arranged in the center of the circuit board of the planar array photodetector, a plurality of output channels are symmetrically distributed on the left and right sides of the circuit board, and a corresponding amplification circuit is arranged between each photodetector and each output channel; Each amplifier circuit converts the light intensity signal detected by the corresponding photodetector into a voltage signal and outputs it through the corresponding output channel.

3. The test fixture for electric field distribution test and verification according to claim 2, characterized in that: The circuit board is packaged in a full aluminum shell.

4. The test fixture for electric field distribution test and verification according to claim 2, characterized in that: The amplifier circuit uses a feedback capacitor to reduce noise.

5. The test fixture for electric field distribution test and verification according to claim 4, characterized in that: The operational amplifier in the amplifying circuit is an LMP7721 operational amplifier.

6. The test fixture for electric field distribution test and verification according to claim 5, characterized in that: The size of the feedback capacitor in the amplifier circuit satisfies the requirement that the signal frequency corresponding to a 3dB drop in the DC gain of the operational amplifier is not greater than the maximum cut-off frequency.

7. A test fixture for electric field distribution test verification according to any one of claims 1 to 6, characterized in that: The photodetector is a photodiode operating in a photovoltaic mode.

8. The test fixture for electric field distribution test and verification according to claim 7, characterized in that: The photodiode is a S1133 photodiode.

9. The test fixture for electric field distribution test and verification according to claim 1, characterized in that: When the He-Ne laser emits visible red light with a wavelength of 632.8 nm, the visible red light is expanded into a uniform light spot with a diameter of 21 mm through the spatial filter and the plano-convex lens.

10. The test fixture for electric field distribution test and verification according to claim 1, characterized in that: The number of photoelectric detectors and output channels integrated in the planar array photoelectric detector is both eight.

Images