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0Faraday fiber-optic sensor for measuring ultrahigh currents
Y.V. Pizhiyalkovskiy1'2', N.I. Starostin1, S.K. Morshnev1, A.I. Sazonov1
1-Kotelnikov Institute ofRadio Engineering and Electronics (Fryazino Branch) of the Russian Academy of Sciences, Vvedensky Sq. 1, Fryazino, Moscow region, 141190 Russia 2- ERSO Transformer Solutions LLC, 21, Elektrozavodskaya Street, Moscow, 107023
An optical method of electric current sensing employing the Faraday effect has become widely popular in the high energy industry due to its accuracy, safety, and ease of implementation. Contemporary optical current sensors are typically based on a fiber reflective interferometer that uses a spun highly birefringent optical fiber (spun fiber) as the sensing element [1]. The range of currents that can be measured by such a sensor is naturally constrained by the maximum value of the Faraday phase shift n/2, which corresponds to a current of Imax ~ 500 kA. However, in applications such as measuring the plasma current in thermonuclear reactors, the current can exceed this limit and reach a value of several mega-amperes [2]. To address this issue, the differential method of current measurement using a typical fiber-optic sensor scheme can be used [3]. The method is based on using two sequentially spliced spun fibers with different megneto-optical sensitivities and covering the current conductor in opposite directions (Fig. 1). The residual phase shift that light accumulates after passing through the fibers will be considerably less than the phase shift induced in a single-fiber sensing element. The integral sensitivity of the sensor is thus reduced, thereby resulting in an increase in the upper limit of the measured current.
The most practical way to obtain the appropriate spun fibers is to draw them with different birefringence or spin pitch. However, a change in the parameters at the fibers splice causes mode coupling. As a result, the secondary waves arising there contribute to the interference signal, thus making the sensor's output characteristic nonlinear [4]. In this study, we propose a new signal processing for the correct current value recovering, adapted for differential measuring method. The new approach compensates for this effect, making the response of a sensor with a differential sensing element linear.
In the experiment, we demonstrated the ability to measure currents up to 50 MA with high linearity. For this, spun fibers with a spin pitch of 3 mm and birefringence beatlengths of 7.1 mm and 10.7 mm at a wavelength of ^=1.55 ^m were used.
The work was carried out within the framework of the state task of the Kotelnikov Institute of Radio Engineering and Electronics of the Russian Academy of Sciences.
[1] K. Bohnert, et al, Optical fiber sensors for the electric power industry, Optics and Lasers in Engineering 43.3-5 (2005): 511-526.
[2] M. Wuilpart, et al, Polarimetric optical fibre sensing for plasma current measurement in thermonuclear fusion reactors, 2020 22nd International Conference on Transparent Optical Networks (ICTON). IEEE, 2020.
[3] Patent RF RU2792207C1 (PCT WO2023158334A1), Volokonno-opticheskij chuvstvutelnij element datchika elektricheskogo toka i magnitnogo polja [Fiber-optical sensing element of an electric current and magnetic field sensor], S.K. Morshnev, Y.V. Przhiyalkovsky, N.I. Starostin, M.Y. Yanin, Declared 15.02.2022. Published 20.03.2023. (In Russian).
[4] Y.V. Przhiyalkovskiy, et al, Fiber-Optic Sensor for MA Current Measuring, Journal of Lightwave Technology, vol. 42, no. 9, pp. 34233429 (2024).
* yankus.p@gmail.com
45° Splice pM fiber delay line
Fig. 1. Optical circuit.
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Spun fiber 2
Photodetcctor
