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Research and application of all-fiber optic current transformer based on optical reciprocity loop
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Abstract
Aiming to the problems of traditional active electromagnetic transformer such as easy magnetic saturation, poor stability and anti-interference ability, and limited installation, etc., this paper designs the optical fiber current transformer to measure current by rotation angle based on Faraday magneto-optic effect; HB Spun optical fiber is used as sensing element without saturation and can be used for high current measurement. The designed transformer uses the optical reciprocity loop to eliminate the interference of temperature and optical fiber defect on the measurement of optical rotation angle, and uses reflector to enlarge the optical rotation angle to four times, which can realize accurate measurement of small current; Sensing element uses flexible fiber ring with shape variability characteristic, which helps for measurement of current in complex space. The paper compares flexible fiber ring with different loops to standard current transformer, the results show that optical reciprocity loop can eliminate the interference of temperature on the current measurement and the accuracy of all-fiber current transformer is 0.5 in the range of -5 ℃~70 ℃, which can realize the accurate measurement of small current. -
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References
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Overview
Overview: With the smart grid development and the increase of voltage level, demand for high current and high voltage measurement is increasing gradually, and the weakness of bulky insulation structure, easy magnetic saturation, low anti-interference ability and low precision of electromagnetic transformer are gradually exposed. The optical fiber current transformer designed in this paper has the advantages of high accuracy, simple insulation structure and strong ability of anti-interference, so it can meet the needs of smart grid development and the increase of voltage level. This transformer utilizes the principle of optical reciprocity to eliminate the influence of temperature and external disturbance on current measurement, so it realizes the high precision measurement. In order to verify the measurement characteristics of the optical reciprocal loop, the optical fiber sensing rings wound in different circles are placed in the temperature control box, and the measured value of the sensing rings and the standard current value are compared in the full temperature range. The results show that the sensing rings has the advantage of high precision and good temperature-reducing characteristics. Finally, the measured values of the different circles of optical fiber rings are compared with the standard current values in the full range. It is found that the more the circles of optical fiber sensing rings, the higher the measurement accuracy of optical fiber sensing rings. The Central Yellow River Diversion Project and Xiaolangdi Yellow River Diversion Project is an important project in the construction of Dashui Network in the "Twelfth Five-Year Plan" of Shanxi Province. The water supply range is wide. In order to ensure the reliable operation of the power system in the project, stator selective protection grounding system of hydropower station power station is gradually being promoted, and zero-sequence current as an important criterion for the device requires accurate measurements. The detection of the zero sequence current of the motor unit requires transformers with large measuring range, high precision of the small current measurement. In this paper, the optical fiber sensing ring of the transformer designed is a flexible structure, which can be directly wound on the spot according to the shape of the measured conductor, thereby avoiding the work of disassembling the measured conductor. Because the optical transformer designed has a large range, high precision in full range, and can be wound on the spot, it can be applied to the stator selective protection grounding system of hydropower station power station, which broadens the field of use of optical transformers.
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Figure 1.
Faraday magneto-optic effect
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Figure 2.
Closed-loop optical path diagram of passive all-fiber current transformer
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Figure 3.
Principle diagram of zero sequence direction of generator stator
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Figure 4.
Diagram of bus routing in the yellow river diversion site
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Figure 5.
Temperature characteristics of flexible fiber rings with (a) 8, (b) 16, (c) 30, (d) 60 circles
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Figure 6.
The schematic diagram of all-fiber current transformer
