Noise analysis and SNR optimization design of fiber optical current transformers

Optical Fiber Current Transformer (FOCT) is susceptible to various types of noise, which leads to a decrease in its measurement accuracy, especially when the primary current is small. Improving its signal-to-noise ratio is one of the key technologies of FOCT. This article comprehensively analyzes FOCT's optical signal noise, signal detection noise and noise sources introduced by the external environment, and gives the calculation method of FOCT SNR. The influence of different noise sources on the signal-to-noise ratio is simulated through theory, and the FOCT signal-to-noise ratio optimization design plan is proposed. It is pointed out that the receiver optical power can be increased, increasing the number of sensitive optical fibers of the sensor head and selecting the appropriate closed-loop feedback phase modulation bias operating point method can effectively improve the signal-to-noise ratio and has been verified by experiments. Based on this design FOCT prototype, rated current of 600 A when meet GB / T 20840.8-2007 predetermined 0.2S level requirements, and the SNR is 30.2dB at 1% rated current, the ratio error is less than 0.61%, the phase error is less than 12.39'.

I. Introduction

The fiber optic current transformer (Fiber Optical the Transformer Current: FOCT) is based on the principle of Faraday magneto-optic effect with the advantages including: anti-electromagnetic interference, large measurement dynamic range and bandwidth, able to measure DC, facilitating the high voltage applications, easy to integrate into high voltage equipment [1]–[4], which meets the construction needs of the new generation of smart substations.