An all-fiber current transformer with self-diagnosis of optical path status and self-diagnosis method

Abstract

The present invention relates to an all-fiber current transformer with self-diagnosis of optical path status and a self-diagnosis method. Before welding, the all-fiber current transformer with self-diagnosis of optical path status is used to diagnose and record the average value of polarization intensity of multiple cycles, which is stored in a register as the polarization intensity before welding; after welding, the all-fiber current transformer with self-diagnosis of optical path status is used to diagnose and record the polarization intensity of multiple cycles, which is compared with the polarization intensity before welding to obtain the deviation; if the deviation does not exceed the first threshold, the optical path state is normal, if the deviation exceeds the first threshold and does not exceed the second threshold, the current coefficient of the all-fiber current transformer is adjusted according to the polarization intensity after welding, if it exceeds the second threshold, an alarm signal is output and the fuse is re-broken. The present invention solves the problem that the existing all-fiber current transformer cannot diagnose the polarization characteristics of the optical path through the system, and meets the new requirements of the smart grid for improving the reliability and stability of the current measurement device.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber current transformers, and in particular to an all-optical fiber current transformer with self-diagnosis of optical path status and a self-diagnosis method. Background Art

[0002] With the development of power systems towards high voltage and high current, the construction of a new generation of smart substations has put forward new requirements for the integration and intelligence of primary equipment such as current transformers. The all-fiber current transformer based on optical sensing technology is a passive electronic current transformer that uses an all-fiber optical path to achieve closed-loop detection of current signals. It has the advantages of large dynamic range, wide measurement bandwidth, good anti-electromagnetic interference performance, small size, light weight, easy integration with high-voltage equipment, and the ability to measure DC signals. It has been promoted and applied in many major projects in recent years. Domestic UHV DC transmission projects will enter a period of intensive construction, with an average of 2 projects started each year. It is estimated that the total market demand for all-fiber current transformers will be around 1.6 billion yuan in the next five years, and the market prospects are great.

[0003] However, most of the all-fiber current transformers currently in operation are imported products, with long procurement cycles, high prices, and service responses that cannot meet the needs of current projects. The research on domestic all-fiber current transformers started late, and some core components rely on imports, but the overall performance is on par with imported products, and some performance indicators are internationally leading and advanced. With the continuous maturity of technology, the focus of domestic research has also shifted from the short-term test performance of all-fiber current transformers to long-term operation reliability research, and from the external technical indicators of the transformer to the research of internal key state parameters.

[0004] Domestic all-fiber current transformers use a single optical path structure based on a lithium niobate optical waveguide phase modulator. Signal sending and transmission are completed in the same polarization-maintaining optical fiber. Although the single optical path structure has advantages in terms of earthquake resistance and temperature stability, it is inconvenient in terms of optical path detection. Since a closed optical path is formed after the optical path is fused, there is no external measurement point, and the performance of the optical path cannot be detected by some test equipment. Once the equipment fails, the fault can only be detected by cutting off the optical path, which increases the on-site operation and maintenance costs and risks, and limits the promotion and application of all-fiber current transformers. At the same time, after the optical path is closed, the overall fusion quality of the polarization-maintaining optical fiber cannot be detected, and there are potential risks. The above unreliable problems need to be solved urgently.

[0005] At the same time, with the development of technology and the emergence of new demands on the user side, new requirements have been put forward for such products in terms of improving reliability and stability, and improving functional diversity. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides an all-optical fiber current transformer with self-diagnosis of optical path status and a self-diagnosis method, which can perform real-time monitoring and diagnosis of the optical path status of the all-optical fiber current transformer during on-site fiber fusion and long-term operation, solving the problem that the existing all-optical fiber current transformer cannot diagnose the polarization characteristics of the optical path through the system, and meeting the new requirements of the smart grid for improving the reliability and stability of current measurement devices.

[0007] To achieve the above object, the present invention provides an all-fiber current transformer with self-diagnosis of optical path status, comprising: an all-fiber sensing ring, a polarization-maintaining transmission optical fiber and a collection module;

[0008] The acquisition module includes a transmitting unit, a collecting unit and a diagnostic unit; the transmitting unit outputs an optical signal, which is output to the all-fiber sensing ring through a polarization-maintaining transmission optical fiber and returned, and is detected by the collecting unit and converted into an electrical signal for output; the diagnostic unit calculates the polarization intensity based on the electrical signal, compares the deviation between the polarization intensity after fusion and the polarization intensity before fusion, and if the deviation does not exceed a first threshold, the optical path state is normal; if the deviation exceeds the first threshold but does not exceed a second threshold, the current coefficient of the all-fiber current transformer is adjusted according to the polarization intensity after fusion; if it exceeds the second threshold, an alarm signal is output and the fuse is re-broken.

[0009] Further, the diagnosis unit includes a cumulative averaging section, a maximum value generating section, a switching section, a calculating section, and a comparing section;

[0010] The cumulative averaging section accumulates and averages the electrical signal of each effective sampling period to obtain the flat area mean value v 0 The maximum value generating unit obtains the highest voltage value v of the electrical signal of each cycle 2 The calculation unit obtains the stored no-light voltage value v 1 And calculate:

[0011]

[0012] The switching unit performs mode switching. If it is the pre-fusion mode, the base value storage unit works to average the polarization intensity of each period and stores it in the register as the polarization intensity before fusion, and the comparison unit does not work. If it is the post-fusion mode, the base value storage unit does not perform the average calculation, and the comparison unit compares the deviation between the polarization intensity of each period and the polarization intensity before fusion stored in the base value storage unit with the first threshold and the second threshold, and outputs the diagnosis result.

[0013] Furthermore, adjusting the current coefficient of the all-optical current transformer according to the polarization intensity after fusion includes: accumulating the deviation of the polarization intensity of each cycle from the polarization intensity before fusion and taking the average, calculating the proportion of the polarization intensity exceeding the polarization intensity before fusion, and adjusting the current coefficient according to the proportion.

[0014] Furthermore, the acquisition module sets a normally closed indicator light, which lights up if the second threshold is exceeded.

[0015] Furthermore, the acquisition module further includes a differential demodulation unit, a feedback control unit, an integral filter unit and a digital output unit; the differential adjustment unit adjusts the flat area mean value v 0 Perform differential demodulation to obtain the open-loop current increment value ΔI, integrate and filter ΔI to obtain the current measurement value I, which is output by the digital output unit; the feedback control unit performs digital-to-analog conversion on ΔI, outputs a feedback signal to the modulator, and performs closed-loop control on the optical path.

[0016] Furthermore, the transmitting unit includes a light source, a coupler, a polarizer, a modulator and a polarization-maintaining fiber delay ring; the light emitted by the light source becomes linearly polarized light after passing through the coupler and the polarizer; the pigtail of the polarizer and the pigtail of the modulator are fused at 45°, and the linearly polarized light is decomposed into two beams of orthogonal linear polarized light at the 45° fusion point and injected into the modulator pigtail, and transmitted along the X-axis and Y-axis of the polarization-maintaining fiber respectively.

[0017] Furthermore, the all-fiber sensing ring includes a sensing fiber, a quarter wave plate and a reflector;

[0018] The linearly polarized light transmitted along the X-axis and Y-axis respectively becomes left-handed and right-handed circularly polarized light after passing through the quarter-wave plate, and propagates into the sensing optical fiber;

[0019] The current transmitted in the current-carrying conductor generates a magnetic field, which produces a Faraday magneto-optical effect in the sensing optical fiber, causing the phase difference of the two circularly polarized light beams to change and be transmitted at different speeds. After being reflected at the reflector, the polarization modes of the two circularly polarized light beams are interchanged, passing through the sensing optical fiber again, and experiencing the Faraday effect again to double the phase difference generated by the two light beams. After passing through the 1 / 4 wave plate again, it is restored to linearly polarized light, interference occurs at the polarizer, and the phase difference signal is carried into the acquisition unit through the polarization-maintaining transmission optical fiber and converted into an electrical signal.

[0020] Furthermore, the acquisition unit includes a detector, an amplifier circuit and an analog-to-digital conversion circuit; the detector converts the detection acquisition into an electrical signal, the amplifier circuit performs amplification and filtering, and the analog-to-digital conversion circuit converts it into a digital signal and sends it to the diagnosis unit.

[0021] Another aspect of the present invention provides a method for performing optical path state self-diagnosis using the all-optical fiber current transformer for optical path state self-diagnosis, comprising:

[0022] Before splicing, an all-fiber current transformer with self-diagnosis of optical path status is used for diagnosis and the average value of polarization intensity of multiple cycles is recorded and stored in a register as the polarization intensity before splicing;

[0023] After splicing, an all-fiber current transformer with self-diagnosis of optical path status is used to diagnose and record the polarization intensity of multiple cycles, which is compared with the polarization intensity before splicing to obtain the deviation;

[0024] The deviation of the polarization intensity of each cycle from the polarization intensity before welding is compared with the first threshold and the second threshold. If the deviation does not exceed the first threshold, the optical path state is normal. If the deviation exceeds the first threshold but does not exceed the second threshold, the current coefficient of the all-optical current transformer is adjusted according to the polarization intensity after welding. If it exceeds the second threshold, an alarm signal is output and the fuse is re-broken.

[0025] Further,

[0026] Among them, v 0 The average value of the flat area is obtained by accumulating and averaging the electrical signals in the effective sampling interval of each cycle; v 2 is the highest voltage value of the electrical signal in each cycle; v 1 is the stored no-light voltage value.

[0027] The above technical solution of the present invention has the following beneficial technical effects:

[0028] (1) In view of the defects of the existing technical solutions, the present invention extracts the comb wave peak level from the high-frequency signal of the detector, combines the open-loop error signal and the detector no-light voltage value, and gives a polarization intensity state quantity that can describe the change of the polarization characteristics of the optical path. According to the polarization intensity comparison analysis, the system can judge the quality of the polarization-maintaining optical fiber axial fusion splicing by itself. At the same time, the online monitoring of the polarization intensity can also analyze the operation and service life of the polarization-maintaining optical path of the all-optical current transformer, thereby improving the reliability and convenience of product operation and maintenance.

[0029] (2) The present invention realizes the analysis and rapid diagnosis of the optical path status of the all-optical current transformer during on-site fiber fusion and long-term operation, thereby ensuring the construction quality and long-term operation reliability of the all-optical current transformer and providing reliable data support for product performance optimization and fault analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the composition of the all-optical current transformer;

[0031] Figure 2 It is the detector output waveform when a square wave modulation signal is applied;

[0032] Figure 3 is a schematic diagram of each component of polarization intensity;

[0033] Figure 4 This is the light path self-diagnosis flow chart;

[0034] Figure 5 Schematic diagram of calculating polarization intensity for FPGA. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0036] The all-fiber current transformer with self-diagnosis of optical path status includes an all-fiber sensor ring 1, a polarization-maintaining optical fiber 2 and a collection module 3. Figure 1 .

[0037] The optical fiber sensing ring 1 is composed of a polarization-maintaining optical fiber pigtail, a quarter-wave plate, a circular-maintaining optical fiber, and an optical fiber reflector to realize the conversion of current signals to optical phase differences. The optical fiber sensing ring 1 and the polarization-maintaining optical fiber 2 form the primary optical path of the all-optical current transformer, which is the sensing part and transmits polarized light signals with high fidelity.

[0038] The acquisition module 3 consists of two parts: an optical device and a signal processing unit, which realize current signal detection, digital output and self-diagnosis of the optical path state. The optical device mainly provides the physical basis of all-fiber sensing. The optical device includes an SLD light source, a coupler, a polarizer, a modulator and a polarization-maintaining optical fiber delay ring that provide optical signals. It is fused into an optical path transmission and modulation system based on a linear reflective structure to realize the transmission of a large primary current. A broadband high-speed PIN-FET photodetector is selected to ensure high-fidelity photoelectric signal conversion during the primary current transmission process; the signal processing unit uses a 100-megahertz high-speed A / D acquisition chip to more quickly capture the changes in the high-frequency signal of the detector output signal. The FPGA with stronger performance and more resources is selected to shorten the self-diagnosis processing time of the optical path state. The amplifier circuit, analog-to-digital conversion circuit (AD), FPGA, and digital-to-analog conversion circuit are electrically connected. On the one hand, the signal processing unit completes the photoelectric conversion, analog-to-digital conversion, digital differential demodulation, resampled digital output, etc. of the optical information returned by the all-fiber primary sensing component, and on the other hand, it completes the extraction, analysis, algorithm diagnosis, etc. of the high-frequency feature quantity of the comb wave.

[0039] In engineering applications, the acquisition module 3 is installed in the electronic unit. Each electronic unit is equipped with two sets of power modules to power the device. The electronic unit is placed in the panel cabinet of the converter station control room to improve the anti-interference ability of the secondary components.

[0040] The optical path working process is as follows:

[0041] The light emitted by the light source becomes linearly polarized light after passing through the coupler and polarizer. The pigtail of the polarizer and the pigtail of the phase modulator are fused at 45 degrees, and the linearly polarized light is injected into the modulator pigtail at 45 degrees, decomposing into two mutually orthogonal linearly polarized lights that are transmitted along the X-axis and Y-axis of the polarization-maintaining fiber respectively. After passing through the 1 / 4 wave plate, these two orthogonal linearly polarized lights are respectively converted into left-handed and right-handed circularly polarized lights, and propagate into the sensing fiber. The modulator performs phase modulation on the linear polarized light passing through. The linear polarized light polarized from the polarizer is decomposed into two mutually perpendicular linear polarized light beams after passing through the 45° fusion point. They are transmitted along the X-axis and Y-axis of the polarization-maintaining optical fiber respectively. They are modulated once when passing through the modulator, enter the delay ring and the optical fiber sensor ring, and are reflected by the reflector at the end of the sensor ring and then exchanged with the polarization axis for transmission (the linear polarized light input along the X-axis is transmitted along the Y-axis when returning; the linear polarized light input along the Y-axis is transmitted along the X-axis when returning) and returns along the original optical path. They are modulated again when passing through the modulator. The two linear polarized light beams are modulated twice by the modulator during the round trip process, and the total phase difference is equal to the sum of the two modulation phases. The modulation signal sent by the digital-to-analog conversion is the digital signal sent by the FPGA, which is converted into an analog signal by the digital-to-analog conversion module and applied to the modulator to modulate the optical path. The current transmitted in the current-carrying conductor generates a magnetic field, which produces the Faraday magneto-optical effect in the sensing optical fiber, causing the phase difference of the two circularly polarized light beams to change and transmit at different speeds. After reflection at the reflector, the polarization modes of the two circularly polarized light beams are interchanged (i.e., left-handed light becomes right-handed light, and right-handed light becomes left-handed light) and pass through the sensing optical fiber again, and experience the Faraday effect again to double the phase difference generated by the two beams of light. After the two beams of light pass through the 1 / 4 wave plate again, they are restored to linearly polarized light. The two beams of light interfere at the polarizer, and the light carrying the phase difference signal enters the optical receiving component and is converted into an electrical signal. The interfered light reaches the photodetector through the optical fiber coupler, converting the optical signal into an electrical signal and entering the subsequent detection circuit for processing.

[0042] The detector output signal is a cosine function of the phase difference. Since the slope of the cosine function is zero at zero phase, it is not sensitive to small phase differences and cannot distinguish the sign of the phase difference. At the same time, the demodulation algorithm is complex. The existing technical solution uses square wave modulation technology to make the phase difference information produce ±π / 2 offset, which improves the sensitivity of the system and simplifies the difficulty of information demodulation. At the same time, the feedback signal is generated according to the differential value of the open-loop signal, and the modulator is used to perform closed-loop control of the optical path, thereby improving the measurement accuracy and dynamic measurement range. The detector output waveform after applying square wave modulation is as follows: Figure 2 shown.

[0043] After applying the square wave bias signal, when the current of the current-carrying conductor is not 0, the Faraday phase difference is φ F , feedback phase difference φ R , the detector output voltage v and the Faraday phase difference φ F Then there is the following relationship:

[0044]

[0045] P 0 is the power of the linear polarized light before the interference, k is the photoelectric conversion coefficient of the detector, and under closed-loop feedback:

[0046]

[0047] Differential demodulation obtains the open-loop error signal Δv:

[0048]

[0049] Then the open-loop current increment ΔI is:

[0050] ΔI=KΔv

[0051] K is the current coefficient, and the output current measurement value I is obtained by integrating and filtering ΔI:

[0052] I=∑ΔI=K∑Δv

[0053] Based on the FPGA function, the present invention adds an optical path diagnosis unit, that is, extracts the high-frequency peak of the detector output signal and calculates the amplitude, and gives the parameter "polarization intensity" that can describe the polarization characteristics of the optical path. Figure 3 shown.

[0054] where v 2 is the maximum value of the detector signal in a single sampling period; v 0 is the average value of the flat area signal of a single sampling period of the detector; v 1 It is the detector's no-light voltage value (the detector's output signal intensity when there is no light signal input).

[0055] The calculation formula is as follows:

[0056]

[0057] The polarization intensity completes data extraction and analysis calculation in the FPGA, and gives a parameter value in each sampling period. On the one hand, the polarization intensity can be analyzed and self-diagnosed in the FPGA, and an alarm is given when the system fails. On the other hand, it can be sent to the background online monitoring platform for real-time display through digital signal transmission, providing data support for the operation experience summary and fault analysis of the all-optical current transformer.

[0058] In one embodiment, the diagnosis unit includes a cumulative averaging section, a maximum value generating section, a switching section, a calculating section, and a comparing section;

[0059] The cumulative average part accumulates and averages the electrical signals of the effective sampling interval of each cycle to obtain the mean value v of the flat area.0 The maximum value generating unit obtains the highest voltage value v of the electrical signal of each cycle 2 ; The calculation unit obtains the stored no-light voltage value v 1 And calculate:

[0060]

[0061] The switching unit switches the modes before and after welding, thereby switching the comparison unit and the base value storage unit.

[0062] If it is the pre-fusion mode, the base value storage unit works to take the average of the polarization intensity of each period and stores it in the register as the polarization intensity before fusion, and the comparison unit does not work; if it is the post-fusion mode, the base value storage unit does not perform the average calculation, and the comparison unit compares the deviation between the polarization intensity of each period and the polarization intensity before fusion stored in the base value storage unit with the first threshold and the second threshold, and outputs the diagnostic result.

[0063] In one embodiment, adjusting the current coefficient of the all-optical current transformer according to the polarization intensity after welding includes: accumulating the deviation of the polarization intensity of each cycle from the polarization intensity before welding and taking the average value, calculating the proportion of the polarization intensity exceeding the polarization intensity before welding, and adjusting the current coefficient according to the proportion. For example, the first threshold is ±0.2%, the second threshold is ±1.0%, the maximum value of the polarization intensity is 1, and it can only reach 1 under ideal conditions; the polarization intensity before welding is 0.9032, and after welding, it becomes 0.9011, the change range is about -0.23%, exceeding the first threshold and less than the second threshold, the optical path diagnosis unit multiplies -0.23% by a proportional factor, and corrects the current coefficient. The polarization intensity after correction should not deviate from 0.9032 by more than the first threshold. Assuming that the polarization intensity after correction is 0.9030, the system accuracy meets the 0.2 level accuracy requirement. With the long-term operation of the product (the optical path is constantly aging, or corroded, squeezed, etc.), the polarization intensity will slowly decrease, and the polarization intensity can be monitored in real time. According to the change curve, the normal operation life of the optical path can be predicted.

[0064] Since the comb wave peak is a high-frequency signal and does not contain primary current information, the square wave modulation type all-fiber current transformer currently uses filters out (does not collect) the comb wave characteristic data. Under the control of the modulation signal trigger, the FPGA first extracts the maximum level value from the trigger sampling moment to the beginning of the effective sampling interval, then accumulates and averages the sampling values ​​of the effective sampling interval, and calculates the polarization intensity in the next sampling cycle. The schematic diagram is shown in the figure. Figure 5 .

[0065] Flowchart of the self-diagnosis technology solution for all-fiber current transformer Figure 4: The FPGA-based diagnosis process for optical path welding before and after is as follows:

[0066] 1) Before optical path splicing, an all-fiber current transformer with self-diagnosis of optical path status is used for diagnosis and the average polarization intensity of multiple cycles is recorded and stored in a register as the polarization intensity before splicing.

[0067] 2) After the optical path is welded, an all-fiber current transformer with self-diagnosis of the optical path status is used to diagnose and record the polarization intensity of multiple cycles, which is compared with the polarization intensity before welding to obtain the deviation;

[0068] 3) If the deviation value does not exceed the first threshold, it indicates that the optical path is fused normally; if the deviation exceeds the first threshold but does not exceed the second threshold, the current coefficient of the all-fiber current transformer is adjusted according to the polarization intensity after fusion. If the deviation value exceeds the second threshold, it indicates that the optical path is fused abnormally, and the panel indicator "PWR" of the circuit control device is always on. Repeat the fiber fusion until the panel indicator "PWR" is off, indicating that the polarization-maintaining fiber axial fusion quality is normal and the optical path can operate normally.

[0069] The technical solution of the present invention is fully implemented in FPGA. The detector output signal is converted into a digital quantity by AD and then enters FPGA. The sampling of the detector signal by FPGA is controlled by the rising and falling edges of the square wave modulation signal level. Each modulation cycle contains a high-frequency peak and a subsequent flat area level.

[0070] The trend of polarization intensity can be used to determine the long-term working condition of the optical path, such as whether fiber extrusion causes polarization characteristics changes, predict the accuracy changes caused by optical path characteristics, and perform product maintenance in advance.

[0071] In summary, the present invention relates to an all-fiber current transformer with self-diagnosis of optical path status and a self-diagnosis method. Before welding, the all-fiber current transformer with self-diagnosis of optical path status is used for diagnosis and the average value of polarization intensity of multiple cycles is recorded, which is stored in a register as the polarization intensity before welding; after welding, the all-fiber current transformer with self-diagnosis of optical path status is used for diagnosis and the polarization intensity of multiple cycles is recorded, which is compared with the polarization intensity before welding to obtain the deviation; if the deviation does not exceed the first threshold, the optical path state is normal, if the deviation exceeds the first threshold and does not exceed the second threshold, the current coefficient of the all-fiber current transformer is adjusted according to the polarization intensity after welding, if it exceeds the second threshold, an alarm signal is output and the fuse is re-broken. The present invention solves the problem that the existing all-fiber current transformer cannot diagnose the polarization characteristics of the optical path through the system, and meets the new requirements of the smart grid for improving the reliability and stability of the current measurement device.

[0072] It should be understood that the above specific embodiments of the present invention are only used to illustrate or explain the principles of the present invention, and do not constitute a limitation of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included in the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundaries of the appended claims, or the equivalent forms of such scope and boundaries.

Claims

1. An all-fiber current transformer with self-diagnosis of optical path status, characterized in that: It comprises: an all-fiber sensing ring (1), a polarization-maintaining transmission optical fiber (2) and a collection module (3); The collection module (3) comprises a transmitting unit, a collection unit and a diagnostic unit; the transmitting unit outputs an optical signal, which is output to the all-fiber sensor ring (1) via a polarization-maintaining transmission optical fiber (2) and returned to the optical fiber sensor ring (1), and is detected by the collection unit and converted into an electrical signal for output; the diagnostic unit calculates the polarization intensity based on the electrical signal, compares the deviation between the polarization intensity after fusion and the polarization intensity before fusion, and if the deviation does not exceed a first threshold, the optical path state is normal; if the deviation exceeds the first threshold but does not exceed a second threshold, the current coefficient of the all-fiber current transformer is adjusted according to the polarization intensity after fusion; if the deviation exceeds the second threshold, an alarm signal is output and the fuse is re-broken; in, ； v0 is the flat area mean obtained by accumulating and averaging the electrical signals in the effective sampling interval of each cycle; v2 is the highest voltage value of the electrical signal in each cycle; and v1 is the stored no-light voltage value.

2. The all-fiber current transformer with optical path status self-diagnosis according to claim 1, characterized in that: The diagnostic unit includes a cumulative averaging unit, a maximum value generating unit, a switching unit, a calculating unit and a comparing unit; the cumulative averaging unit accumulates and averages the electrical signal of each effective sampling period to obtain a flat area mean value v0; the maximum value generating unit obtains the highest voltage value v2 of the electrical signal of each period; the calculating unit obtains the stored no-light voltage value v1 and calculates the polarization intensity; The switching unit switches the mode before and after welding, and realizes the switching of the comparison unit and the base value storage unit. If it is the pre-welding mode, the base value storage unit works to average the polarization intensity of each period, and stores it in the register as the polarization intensity before welding, and the comparison unit does not work; if it is the post-welding mode, the base value storage unit does not perform the average calculation, and the comparison unit compares the deviation of the polarization intensity of each period and the polarization intensity before welding stored in the base value storage unit with the first threshold and the second threshold, and outputs the diagnosis result.

3. The all-fiber current transformer with optical path status self-diagnosis according to claim 2, characterized in that ,Adjusting the current coefficient of the all-optical current transformer according to the polarization intensity after welding includes: accumulating the deviation of the polarization intensity of each cycle from the polarization intensity before welding and taking the average, calculating the proportion of the polarization intensity exceeding the polarization intensity before welding, and adjusting the current coefficient according to the proportion.

4. The all-fiber current transformer with optical path status self-diagnosis according to claim 2, characterized in that ,The acquisition module sets a normally closed indicator light, and lights the indicator light if the second threshold is exceeded.

5. The all-fiber current transformer with optical path status self-diagnosis according to claim 1 or 2, characterized in that: The acquisition module also includes a differential demodulation unit, a feedback control unit, an integral filtering unit and a digital output unit; the differential demodulation unit performs differential demodulation on the flat area mean value v0 to obtain an open-loop current increment value ∆I, performs integral filtering on ∆I to obtain a current measurement value I which is output by the digital output unit; The feedback control unit performs digital-to-analog conversion on ∆I, outputs a feedback signal to the modulator, and performs closed-loop control on the optical path.

6. The all-fiber current transformer with optical path status self-diagnosis according to claim 1 or 2, characterized in that: The transmitting unit includes a light source, a coupler, a polarizer, a modulator and a polarization-maintaining fiber delay ring; the light emitted by the light source becomes linearly polarized light after passing through the coupler and the polarizer; the pigtail of the polarizer and the pigtail of the modulator are fused at 45 degrees, and the linearly polarized light is decomposed into two orthogonal linearly polarized lights at the 45-degree fusion point and injected into the modulator pigtail, and transmitted along the X-axis and Y-axis of the polarization-maintaining fiber respectively.

7. The all-fiber current transformer with optical path status self-diagnosis according to claim 6, characterized in that The all-fiber sensing ring (1) includes a sensing fiber, a quarter wave plate and a reflector; the linearly polarized light transmitted along the X-axis and the Y-axis respectively becomes left-handed and right-handed circularly polarized light after passing through the quarter wave plate, and enters the sensing fiber for propagation; The current transmitted in the current-carrying conductor generates a magnetic field, which produces a Faraday magneto-optical effect in the sensing optical fiber, causing the phase difference between the two circularly polarized light beams to change and be transmitted at different speeds. After being reflected at the reflector, the polarization modes of the two circularly polarized light beams are interchanged, passing through the sensing optical fiber again, and experiencing the Faraday effect again to double the phase difference between the two light beams. After passing through the 1 / 4 wave plate again, it is restored to linearly polarized light, and interference occurs at the polarizer. The phase difference signal is carried through the polarization-maintaining transmission optical fiber (2) and enters the acquisition unit to be converted into an electrical signal.

8. The all-fiber current transformer with optical path status self-diagnosis according to claim 7, characterized in that The acquisition unit includes a detector, an amplifier circuit and an analog-to-digital conversion circuit; the detector converts the detection acquisition into an electrical signal, the amplifier circuit performs amplification and filtering, and the analog-to-digital conversion circuit converts it into a digital signal and sends it to the diagnosis unit.

9. A method for performing optical path state self-diagnosis using the all-optical fiber current transformer for optical path state self-diagnosis according to any one of claims 1 to 8, characterized in that: include: Before splicing, an all-fiber current transformer with self-diagnosis of optical path status is used for diagnosis and the average value of polarization intensity of multiple cycles is recorded and stored in a register as the polarization intensity before splicing; After splicing, an all-fiber current transformer with self-diagnosis of optical path status is used to diagnose and record the polarization intensity of multiple cycles, which is compared with the polarization intensity before splicing to obtain the deviation; The deviation of the polarization intensity of each cycle from the polarization intensity before welding is compared with the first threshold and the second threshold. If the deviation does not exceed the first threshold, the optical path state is normal. If the deviation exceeds the first threshold but does not exceed the second threshold, the current coefficient of the all-optical current transformer is adjusted according to the polarization intensity after welding. If it exceeds the second threshold, an alarm signal is output and the fuse is re-broken.

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