<title>AC current sensing with fiber Bragg grating</title>

Abstract

ABSTRACT In order to overcome the problems existed in current transducer, A method was proposed to realize large current measurement in high voltage application, which based on the combination of traditional CT and FBG by making use of the high resolution and the perfect electrical isolation strength of FBG. The principles of current transducer and FBG dynamic demodulation were introduced. The dynamic performance of the system was verified with experiments. After signal processing, the repeatability of the system is no more than ±4% without any means of compensation. And the linearity of the system sensitivity is of R 2 0.9958 .A new and effective method for large voltage measurement in high voltage field was proposed in this paper. Keywords: FBG dynamic demodulation, alternative current sensing, current transducer 1. INTRODUCTION Photo current transducers (CT), which are based on Faraday effect, have been studied extensively and have been applied in power distribution industry for more than ten years. Faraday effect is the ideal transduction mechanism for current measurement theoretically. The Faraday rota tion is linearly related to the current. And the fiber used in the system has the isolation strength up to 500,000 thousand volts. But its applications was restricted by induced linear birefringence and also with the temperature and wavelength sensitivities of th e Verdet constant and the vulnerability of the scale factor to vibration have thus far limited the application of this technique. The measurement is realized by convertin g the output voltage of a traditional current transducer into phase variation by fiber interferometer or piezoelectricity (PZT) material. Determining the measure current, the signal from the interferometer is interfered easily by vibr ations acting on the fiber. In order to overcome these problems, one solution is to convert the output of CT into photo signal by a high-power light-emitting diode. The other is to convert the output current amplitude into frequency by a related circuit. The output of the circuit drives a photodiode. These solutions improved vibration interference a lot. The disadvantage of the solutions is that the linearity of converters is not ideal and the converters need power in the high line potentials side. In order to improve large current measurement at high potentials, making use of the high resolution of CT and the high voltage strength of fiber, a new method for large current measurement is proposed by combining traditional CT with fiber Bragg grating (FBG).