An electromagnetic instrument transformer is a common device used to measure large current values in high-voltage electrical networks; it has been in use for more than a century. However, the optical current transformer, a promising technology also known as a fiber optic current sensor (FOCS), offers increased safety and ease of operation, as well as the absence of errors caused by the magnetic circuit of legacy transformers. Although the FOCS scheme is well known and has been actively developed for over a quarter century, it has certain disadvantages that limit its use. This paper describes the authors’ efforts to solve these problems in order to make FOCS technology competitive and widely adopted. We upgraded the FOCS optical circuit, expanded the frequency band of the captured current signal, and reduced the solution’s cost. We designed new signal processing algorithms to compensate for errors caused by internal factors in the measurement circuit, as well as those caused by environmental influences. We developed an FOCS computer model based on the Jones matrix formalism to enhance the experimental debugging. It allowed us to define the requirements for elements of the optical circuit and its production accuracy.

Optical fiber sensors are of particular interest for applications in the high-voltage environments of the electric power industry due to their characteristic properties including dielectric nature, immunity to electro-magnetic interference, and small size and weight. We have studied current sensor that employs the Faraday effect in the spun fiber and signal processing based on the additional harmonic modulation of the self-consistent polarization interferometer. We replaced the traditional PZT transducer with the LiNbO3 waveguide electro-optical modulator that allowed to increase significantly the modulation frequency and to reduce the length of the fiber delay line. Original error compensation methods allowed us to achieve the accuracy of ±0.2% in amplitude in the temperature range of about 50 °C.

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