Abstract
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.
Highlights
The widely adopted method to measure electric current at higher voltages is with an instrument transformer, a transducer converting primary current into proportional secondary current signals using two inductively coupled wire coils on a magnetic core
The devices that implement this approach are known as fiber optic current sensors (FOCS)
The fiber delay line in the optical circuit of the FOCS must provide such a delay between two orthogonally polarized modes that when light is propagated from the modulator to the mirror and back, the phase of the modulating voltage changes sign to the opposite
Summary
The widely adopted method to measure electric current at higher voltages is with an instrument transformer, a transducer converting primary current into proportional secondary current signals using two inductively coupled wire coils on a magnetic core. Major changes in the primary current signal during transients in the controlled network (starting currents, faults, etc.) cause saturation of the magnetic circuit, leading to a lack of information transmission about the primary current during the first periods of the emergency transient This information is important for successful localization and elimination of the accident; the error of measuring current transformers reaches 90%. The devices that implement this approach are known as fiber optic current sensors (FOCS). This type of measurement devices has been a niche solution for over a quarter of a century. This paper describes the authors’ efforts to solve these problems and make FOCS technology competitive and preferable
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