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.

The article describes an approach for simulating the fiber optic electric field sensor with a sensitive element operating on the Pockels effect arising in an optical waveguide recorded in a lithium niobate crystal. The sensor simulating was implemented in the NI LabVIEW programming environment and built using a mathematical apparatus based on the formalism of Jones matrices, which allowed to describe the polarization state of the light beam at the output of the sensor and to calculate the intensity of the interference signal at the photodetector input. Besides, additional modulation with a sawtooth signal and digital phase detection were used in the simulation. The sensor model described in the article can be easily modified and complicated, which makes it possible to use it for research and analysis of both parasitic effects and different optical sensor configurations.

One of the most important elements of the optical scheme of the fiber-optic current sensor is a quarter-wave plate, which converts two orthogonal linearly polarized modes into circularly polarized modes, which propagate further in the sensitive element of the sensor. To maintain the integrity of the system and ensure high-precision measurements, it is important that the plate is made of fiber, and its length is equal to a quarter of the beat length with an accuracy of a hundredth of a millimeter, which is technically very difficult to achieve. This article discusses a model of an electronically adjusted quarter-wave plate, which made it possible to check the operability of the fiber-optic current sensor circuit. The article also describes a method for manufacturing of quarter-wave plate, presents the results of temperature tests of plates of different lengths in the current sensor circuit, and estimates the effect of the quarter-wave plate temperature on the measurement error.

The paper describes the problem of fiber quarter-wave plate temperature dependency, its influence on the fiber optic current sensors (FOCS) output error, the method of this error compensation, and the results of this method implementation.