The GMM-FBG Current Transformer And Its Application Technology

To build smart grid, online fault current detection of electric transport devises and high precision fault diagnoses are sticking points in keeping the electric equipments operating effectively. On considering the limitation of the traditional electromagnetic current transformer and photo-electric current transformer in fault current detection, we design a ferromagnetic circuit included fault current detection system using giant magnetostrictive material (GMM) and fiber Bragg grating (FBG).Based on the large flexible coefficient of GMM, the reliability of FBG and the similarity of the temperature properties between Monel alloy and GMM, we construct a Monel-GMM-FBG current transformer by jointing Monel alloy stick and GMM stick and then transversely putting tow FBGs with the same central wavelength of one fiber on the center of the sticks. We invest the system by putting it into the temperature control box. The result shows that Monel alloy can compensate the surrounding temperature effect on the FBG wave length enlargement.Firstly, a magnetic circuit system within magnetism-guided loop is constructed based on Monel-GMM-FBG sensor after analyzing the influence of fault current in one phase of the three-phase circuit on Monel-GMM-FBG sensors of the other phases by numerical analysis. And then sensors with magnetism-guided loop in different phases are proved independent of each other by theory analysis and experiment when the current changes abruptly. So the fault current in three-core wires can be detected.This paper gives a power frequency mutual-inductance device with magnetism-guided loop based on Monel-GMM-FBG sensing, presents a scheme of demodulating FBG alternating strain signal by a distributed-feedback (DFB) laser and detects individual frequency current under bias magnetic field. The full- scale accuracy and current-detecting sensitivity are proved to be much higher than side-band demodulation based on wavelength-division multiplexing. This designed device is featured for its simple structure, stability, precise measurement, and can be used for practical current detection for power system.