The development of a current and temperature monitoring optical device intended to be used in high-voltage environments, particularly transmission lines, is presented. The system is intended to offer not only measurement reliability, but to be also practical and light weighted. Fiber Bragg gratings (FBGs) are employed in the measurement of both physical parameters: the current will be acquired using a hybrid sensor head setup—an FBG fixed on a magnetostrictive rod—while a single-point temperature information is provided by a dedicated grating. An inexpensive and outdoor-suitable demodulation method, such as the fixed filter technique, should be used in order to improve the instrumentation robustness, avoiding expensive and complex auxiliary electronics. The preliminary results for laboratory tests are also discussed. 1. Introduction Unfailing measurements in power systems are obligatory in various situations, such as in substations, in oil industry, and in power transmission [1, 2]. Particularly, parameters of transmission lines such as temperature and conductor current should be monitored, providing important data for ampacity assessment [2]. Though, usual instrument transformers in electric power facilities present significant size, besides being heavy. Numerous optical current sensing devices that make use of the Faraday effect have been discussed, since optical systems frequently offer a wider dynamic range, lighter weight, improved safety, and electromagnetic interference immunity [3], due to the intrinsic insulating aspects of optical fibers. Nevertheless, some drawbacks can be mentioned; the Faraday Effect, besides requiring complex compensation techniques, also demands expensive auxiliary electronics, maintenance, and specially designed optical fibers to become reliable. So far, optical fiber sensors (OFSs) have been highly employed in environments where the use of electrical sensors is not reliable or may create unsafe circumstances. What makes this possible is the use of fiber Bragg gratings—intrinsic optical fiber sensors which are, frequently, wavelength demodulated, requiring the use of a piece of equipment called optical spectrum analyzer (OSA) [4]. Despite its reliability, the wavelength demodulation procedure implies the use of high-cost equipments to attend the high spectral resolution monitoring requirements, a rather restrictive aspect for outdoor monitoring. Quite a few designs of hybrid optical current sensors have been presented; some of which explore the magnetostrictive actuation of a ferromagnetic rod over a fiber Bragg grating,
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