Vibration test method for piezoelectric ceramic modulated all-fiber current transformer at the component level

Abstract

This invention discloses a component-level vibration testing method for a piezoelectric ceramic modulation type all-fiber current transformer, comprising: disassembling the modulation module from the all-fiber current transformer while maintaining the complete optical and electrical paths of the all-fiber current transformer; fixing the modulation module as a whole on a vibration table, applying vertical, horizontal, and axial vibrations sequentially to the modulation module without applying primary current to the all-fiber current transformer; and continuously monitoring the secondary output of the all-fiber current transformer using a fault recorder and recording any abnormal output currents. This invention effectively assesses the vibration resistance performance of the modulation module as a whole and its internal components, thereby providing targeted vibration suppression solutions.

Description

Technical Field

[0001] This invention relates to the field of electrical measurement, and more specifically, to a component-level vibration testing method for a piezoelectric ceramic modulation type all-fiber current transformer. Background Technology

[0002] DC current transformers are one of the key measuring devices in converter stations. Their main function is to measure DC current and transmit the measurement results to DC control and protection equipment. The reliability of DC current transformers is directly related to the safe and stable operation of the converter station. Currently, there are three types of DC current transformers used in converter stations: electronic optical current transformers with shunts as the core measuring element; zero-flux current transformers based on the principle of electromagnetic induction; and all-fiber optic current transformers based on the Faraday magneto-optic effect. In 2012, the State Grid Corporation of China first used all-fiber optic current transformers (FOCTs) in DC projects. In recent years, the number of FOCTs installed in new projects has been increasing year by year. As of December 2021, the State Grid Corporation of China's converter stations had installed more than 1,800 FOCTs, accounting for 39% of all types of DC current transformers.

[0003] However, FOCT field applications are prone to accidents. From December 2020 to January 2021, some converter station FOCTs experienced sudden changes in measurement current and differential protection activation due to conducted vibration interference in the field, leading to DC blockage or shutdown. Accident analysis revealed that the component causing FOCT vibration failure was the modulation module. FOCTs are divided into direct waveguide modulation type and piezoelectric (PZT) modulation type according to different modulation methods. The modulation module of the direct waveguide modulation type FOCT is located on the secondary side, while the modulation module of the PZT modulation type FOCT is located in the outdoor primary body, which operates in a harsher environment and is prone to vibration failure.

[0004] Because the current national standards do not assess the vibration characteristics of PZT-modulated FOCT modulation modules, the product's vibration resistance requirements do not match the field operating conditions, resulting in poor vibration resistance of PZT-modulated FOCTs and posing a potential threat to the safe and stable operation of DC systems. Summary of the Invention

[0005] To address the problem of sudden current changes in existing piezoelectric ceramic modulated fiber optic current transformers (FOCTs) under vibration conditions, this invention provides a component-level vibration testing method for FOCTs. This method deeply analyzes the underlying mechanisms by which external vibrations affect the modulation module and its internal components, leading to measurement failures in the FOCT. It effectively assesses the vibration resistance of the modulation module and its internal components, understands the vibration characteristics of the FOCT modulation module, and provides targeted vibration suppression solutions to improve product performance and ensure the safe and stable operation of DC measurement equipment within converter stations.

[0006] This invention provides a component-level vibration test method for a piezoelectric ceramic modulation type all-fiber current transformer, comprising: disassembling the modulation module from the all-fiber current transformer while maintaining the complete optical and electrical paths of the all-fiber current transformer; fixing the modulation module as a whole on a vibration table, applying vertical, horizontal, and axial vibrations sequentially to the modulation module without applying a primary current to the all-fiber current transformer; and continuously monitoring the secondary output of the all-fiber current transformer using a fault recorder and recording any abnormal output currents of the all-fiber current transformer.

[0007] Optionally, in order to determine the relationship between the vibration characteristics and vibration frequency of the all-fiber current transformer, frequency sweep tests of 8 minutes are carried out in the vertical direction, horizontal direction, and horizontal axis at frequencies of 10Hz to 150Hz and acceleration of 5g, and frequencies of 150Hz to 2000Hz and acceleration of 2g, respectively, to find the vibration sensitive frequency point of the entire modulation module.

[0008] Optionally, in order to determine the relationship between the vibration characteristics and vibration acceleration of the all-fiber current transformer, a 2-minute sweep frequency test is conducted near the sensitive frequency point by changing the acceleration in the vertical direction, horizontal transverse direction, and horizontal axial direction. Specifically, vibration tests are conducted near the sensitive frequency point of 10Hz to 150Hz at accelerations of 2g, 3g, and 4g, respectively, and vibration tests are conducted near the sensitive frequency point of 150Hz to 2000Hz at accelerations of 0.5g and 1g, respectively.

[0009] Optionally, in order to determine the influence of the depolarization fiber, polarization-inducing fiber, piezoelectric ceramic, and delay fiber inside the modulation module on the vibration characteristics of the all-fiber current transformer, the depolarization fiber, polarization-inducing fiber, piezoelectric ceramic, and delay fiber are removed from the modulation module and suspended, while the remaining part of the modulation module is fixed to the vibration table, thus maintaining the complete optical path and circuit of the all-fiber current transformer.

[0010] Optionally, vibration tests can be conducted near the sensitive frequency point of 10Hz to 150Hz with an acceleration of 5g, and near the sensitive frequency point of 150Hz to 2000Hz with an acceleration of 2g.

[0011] Optionally, the vibration test includes: applying vertical, horizontal, and axial vibrations to the remaining part of the modulation module without applying primary current to the all-fiber current transformer, continuously monitoring the secondary output of the all-fiber current transformer using a fault recorder, and recording the abnormal output current of the all-fiber current transformer.

[0012] Optionally, after the vibration test is completed, the depolarization fiber, polarization-inducing fiber, piezoelectric ceramic, and delay fiber are reset respectively. After the reset, the modulation module as a whole is subjected to the same vibration test to verify whether the abnormal output current of the all-fiber current transformer after the reset is consistent with the abnormal output current of each component before it is separated from the modulation module.

[0013] Therefore, to address the issue of sudden current changes in piezoelectric ceramic modulated fiber optic current transformers under vibration conditions, this invention proposes a vibration testing method at the modulation module component level for piezoelectric ceramic modulated fiber optic current transformers. By effectively assessing the vibration resistance performance of the modulation module as a whole and its internal components, targeted vibration suppression solutions are provided. This method fills the gap in current national standards regarding vibration testing of piezoelectric ceramic modulated fiber optic current transformers, promoting the technological development and further application of these transformers. It also provides strong support for strengthening quality supervision of grid-connected equipment, reducing equipment failure rates, and ensuring the safe operation of DC projects. Attached Figure Description

[0014] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0015] Figure 1 This is a schematic flowchart of a component-level vibration test method for a piezoelectric ceramic modulated all-fiber current transformer provided in an exemplary embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of the modulation module of a piezoelectric ceramic modulation type all-fiber current transformer element provided in an exemplary embodiment of the present invention. Detailed Implementation

[0017] Hereinafter, exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein.

[0018] It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0019] Figure 1A schematic flowchart of the component-level vibration testing method for piezoelectric ceramic modulated all-fiber current transformers provided by this invention is shown. Figure 1 As shown, the component-level vibration test method for a piezoelectric ceramic modulation type all-fiber current transformer includes: disassembling the modulation module from the all-fiber current transformer while maintaining the complete optical and electrical paths of the all-fiber current transformer; fixing the modulation module as a whole on a vibration table, applying vertical, horizontal, and axial vibrations sequentially to the modulation module without applying primary current to the all-fiber current transformer; and continuously monitoring the secondary output of the all-fiber current transformer using a fault recorder to record any abnormal output currents of the all-fiber current transformer.

[0020] In the embodiments of the present invention, for ease of description, "PZT" is used to represent piezoelectric ceramic and "FOCT" is used to represent modulated all-fiber current transformer.

[0021] The current national standard for DC current transformers, GB / T26271.1-2019, does not include vibration testing. The current national standards for electronic AC current transformers, GB / T20840.8-2007 and GB / T20840.6-2017, only include vibration tests for primary components during short-circuit current and vibration tests of the primary component mechanically coupled to the circuit breaker, assessing only vibrations caused by switching operations and short-circuit electrodynamics. Because the modulation module of the PZT modulation type FOCT is located in the lower part of the primary body (e.g., Figure 2 As shown in the figure, the vibration test in the above standard did not test the modulation module of PZT modulation type FOCT. The FOCT has a problem of insufficient vibration detection test standards and test methods, which leads to a mismatch between the product's vibration resistance technical requirements and the field operating conditions.

[0022] Therefore, the component-level vibration test method for PZT-modulated FOCT proposed in this invention was used to conduct a component-level vibration test on the modulation module of a PZT-modulated FOCT with a rated primary current of 3000A. The test specimen was placed horizontally without a primary current applied. The modulation module was fixed on a vibration table, and the vibration test was carried out according to the test plan in Table 1. Vertical vibration was applied to the entire modulation module in sequence, and the depolarization fiber, polarization-inducing fiber, piezoelectric ceramic, and delay fiber in the modulation module were removed from the modulation module and suspended. Vertical vibration was applied to the remaining part of the modulation module, and the secondary output of the optical CT was continuously monitored using a fault recorder.

[0023] Table 1 Vibration Test Scheme for PZT Modulation Type FOCT Modulation Module Component Level

[0024]

[0025]

[0026] (1) Experimental scheme 1:

[0027] The modulation module was fixed on a vibration table, and 8-minute frequency sweep tests were conducted at frequencies of 10Hz–150Hz and acceleration of 5g, and at frequencies of 150Hz–2000Hz and acceleration of 2g to identify the sensitive frequency points of the modulation module. Then, near these sensitive frequency points, the acceleration was varied, and 2-minute frequency sweep tests were conducted. Near the sensitive frequency point of 10Hz–150Hz, vibration tests were conducted at accelerations of 2g, 3g, and 4g, respectively. Near the sensitive frequency point of 150Hz–2000Hz, vibration tests were conducted at accelerations of 0.5g, 5g, and 2g, respectively.

[0028] Vibration tests were conducted at an acceleration of 1g, and the results are shown in Table 2.

[0029] Table 2. Overall vibration test results of the modulation module

[0030]

[0031] As shown in Table 2, ① when sweeping the frequency from 10Hz to 150Hz, the abnormal output current of the test sample is the largest at around 53Hz, and the maximum abnormal output current is -224A under 5g acceleration; when sweeping the frequency from 150Hz to 2000Hz, the abnormal output current of the test sample is the largest at around 1650Hz, and the maximum abnormal output current is -8535A under 2g acceleration; 53Hz and 1650Hz are the sensitive frequency points of the modulation module in the frequency ranges of 10Hz to 150Hz and 150Hz to 2000Hz, respectively; ② at the sensitive frequency points, the maximum value of the abnormal output current of the test sample increases with the increase of vibration acceleration.

[0032] (2) Test schemes 2, 3, 4, and 5:

[0033] To determine the effects of the depolarizing fiber, polarizing fiber, piezoelectric ceramic, and delay fiber on the abnormal output current of the FOCT, the depolarizing fiber, polarizing fiber, piezoelectric ceramic, and delay fiber were detached from the modulation module and suspended, while the remaining part of the modulation module was fixed to the vibration table, maintaining the complete optical and electrical path of the FOCT. Vibration tests were conducted at frequencies of 50Hz–60Hz and accelerations of 5g, and at frequencies of 1600Hz–1700Hz and accelerations of 2g. The test results are shown in Tables 3–6. After the vibration tests, the depolarizing fiber, polarizing fiber, piezoelectric ceramic, and delay fiber were reset. After reset, the modulation module as a whole underwent the same vibration test to verify whether the abnormal output current of the FOCT after reset was consistent with the abnormal output current before each component was detached from the modulation module.

[0034] Table 3 Results of vibration test on depolarization fiber disconnection from modulation module

[0035]

[0036] After the vibration test was completed, the depolarization fiber was reset. After the reset, the modulation module was subjected to the same vibration test. The abnormal output current of the test sample was the same as the abnormal output current before it was disconnected from the modulation module.

[0037] Table 4. Vibration test results of polarizing fiber disconnecting from modulation module

[0038]

[0039]

[0040] After the vibration test was completed, the polarizing fiber was reset. After the reset, the modulation module was subjected to the same vibration test. The abnormal output current of the test sample was the same as the abnormal output current before it was disconnected from the modulation module.

[0041] Table 5. Vibration test results of piezoelectric ceramics disconnecting from the modulation module

[0042]

[0043]

[0044] After the vibration test was completed, the piezoelectric ceramic was reset. After the reset, the modulation module was subjected to the same vibration test. The abnormal output current of the test sample was the same as the abnormal output current before it was disconnected from the modulation module.

[0045] Table 6 Results of vibration test on time-delay fiber disconnection from modulation module

[0046]

[0047] After the vibration test was completed, the delay fiber was reset. After the reset, the modulation module as a whole was subjected to the same vibration test. The abnormal output current of the test sample was significantly different from the abnormal output current before the delay fiber was disconnected.

[0048] Tables 3-6 show that: ① Vibration tests were conducted on the modulation module near 1650Hz. It was found that the delay fiber was most affected by vibration, accounting for 97.6% of the abnormal output current of the test sample, making it the key component causing abnormal output under vibration. The depolarization fiber, polarization-inducing fiber, and piezoelectric ceramics accounted for 1% to 6% of the abnormal output current of the test sample, and had a relatively small impact on the vibration resistance of the test sample under high-frequency vibration. ② After the delay fiber was reset, the abnormal output current of the test sample was significantly reduced compared to the abnormal output current before it was removed from the modulation module. This is because the process of removal and reset changed the installation method of the delay fiber in the modulation module. It is determined that the installation method of the delay fiber has a significant impact on its vibration resistance, and the performance of the product can be improved by changing the installation method of the delay fiber.

[0049] Therefore, the component-level vibration testing method for piezoelectric ceramic modulated all-fiber current transformers proposed in this invention provides an assessment of the modulation module of the piezoelectric ceramic modulated all-fiber current transformer and establishes a vibration assessment method that conforms to the actual operating conditions of converter stations. This overcomes the deficiency in the current national standard, where primary vibration testing only includes short-circuit electrodynamics and switching operations, and cannot assess the piezoelectric ceramic modulation module. This invention can determine the abnormal output current variation law of the modulation module at sensitive frequency points in the low-frequency range of 10Hz to 150Hz and the high-frequency range of 150Hz to 2000Hz under acceleration of 0.5g-5g, understand the relationship between the secondary output of the all-fiber current transformer and the vibration frequency and acceleration, and comprehensively clarify the vibration characteristics of the PZT modulation module. This invention can perform vibration fault analysis of all-fiber current transformers, reproduce and locate the fault location and cause, study the fault mechanism of each component in the modulation module affected by vibration, guide manufacturers to improve product design and installation manufacturing processes, and enhance the product's vibration resistance.

[0050] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the invention to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A component-level vibration testing method for a piezoelectric ceramic modulated all-fiber current transformer, characterized in that, include: The modulation module is disassembled from the all-fiber current transformer while maintaining the complete optical and electrical path of the all-fiber current transformer. The modulation module is fixed on the vibration table. No primary current is applied to the all-fiber current transformer. Vertical, horizontal, and horizontal axial vibrations are applied to the entire modulation module in sequence. In order to determine the influence of the internal components of the modulation module, namely the depolarization fiber, the polarization-inducing fiber, the piezoelectric ceramic, and the time-delay fiber, on the vibration characteristics of the all-fiber current transformer, the depolarization fiber, the polarization-inducing fiber, the piezoelectric ceramic, and the time-delay fiber are detached from the modulation module and suspended. The remaining part of the modulation module is fixed on the vibration table, so as to maintain the complete optical path and circuit of the all-fiber current transformer. A fault recorder was used to continuously monitor the secondary output of the all-fiber current transformer and record the abnormal output current of the all-fiber current transformer.

2. The method according to claim 1, characterized in that, To determine the relationship between the vibration characteristics and vibration frequency of the all-fiber current transformer, frequency sweep tests were conducted for 8 minutes each in the vertical direction, horizontal direction, and horizontal axis at frequencies of 10Hz to 150Hz and acceleration of 5g, and frequencies of 150Hz to 2000Hz and acceleration of 2g, to find the vibration-sensitive frequency point of the modulation module as a whole.

3. The method according to claim 2, characterized in that, To determine the relationship between the vibration characteristics and vibration acceleration of the all-fiber current transformer, a 2-minute sweep frequency test was conducted near the sensitive frequency point, changing the acceleration in the vertical direction, horizontal direction, and horizontal axis. Specifically, vibration tests were conducted near the sensitive frequency point of 10Hz to 150Hz at accelerations of 2g, 3g, and 4g, respectively, and near the sensitive frequency point of 150Hz to 2000Hz at accelerations of 0.5g and 1g, respectively.

4. The method according to claim 1, characterized in that, Vibration tests were conducted near the sensitive frequency range of 10Hz to 150Hz with an acceleration of 5g, and near the sensitive frequency range of 150Hz to 2000Hz with an acceleration of 2g.

5. The method according to claim 4, characterized in that, The vibration tests conducted included: applying vertical, horizontal, and axial vibrations to the remaining part of the modulation module without applying primary current to the all-fiber current transformer; continuously monitoring the secondary output of the all-fiber current transformer using a fault recorder; and recording the abnormal output current of the all-fiber current transformer.

6. The method according to claim 5, characterized in that, After the vibration test was completed, the depolarization fiber, polarization-inducing fiber, piezoelectric ceramic, and delay fiber were reset respectively. After the reset, the modulation module as a whole was subjected to the same vibration test to verify whether the abnormal output current of the all-fiber current transformer after the reset was consistent with the abnormal output current of each component before it was removed from the modulation module.

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