Novel Fiber Optic Current Transformer With New Phase Modulation Method

Abstract

Based on the transverse electro-optic effect of lithium niobate crystal, combined with polarizers and Faraday rotator, this paper presents a collinear closed-loop fiber optic current transformer with spatial non-reciprocity modulation method, and the feasibility of the scheme is verified by both the theoretical and experimental evidences. The detection scheme avoids the limitation of the transition time of the sensing fiber coil on the phase modulation frequency, improves the sensitivity and stability of the system, and reduces the volume and cost of fiber optic current transformer. The sawtooth wave modulation scheme is adopted to realize phase bias modulation and feedback modulation through phase shift of sawtooth wave to achieve closed-loop detection effect, which enhances the signal to noise ratio and simplifies demodulation mode. The experimental results show that the current ratio errors measured at room temperature range from 1% to 120% of rated current meet the requirements of national standard GB/T 20840.8-2007 and reach the accuracy level of 0.2S. The temperature stability of the current transformer is also tested, and the ratio error measured at the rated current does not exceed ±0.2% in the range of -30 °C to 50 °C.

Keywords

Fiber optic current transformer / spatial phase modulation / closed-loop detection / current ratio error / temperature stability

References

[1] Lee B. Review of the present status of optical fiber sensors. Optical Fiber Technology: Materials, Devices and Systems, 2003, 9(2): 57-79.

[2] Bohnert K, Gabus P, Kostovic J, Brandle H. Optical fiber sensors for the electric power industry. Optics and Lasers in Engineering, 2005, 43(3/4/5): 511-526.

[3] X. K. Song, P. L. Yan, Z. H. Xiao, D. W. Liu, and Y. B. Liu, “Comment on the technology and application of fiber optic current transformer,” Power System Protection and Control, 2016, 44(8): 149–154.

[4] Wang X X, Zhang C X, Zhang C Y, Wu Z J. A new all digital closed-loop fiber optic current transformer. Automation of Electric Power Systems, 2006, 30(16): 77-80.

[5] Culshaw B. The optical fibre Sagnac interferometer: an overview of its principles and applications. Measurement Science & Technology, 2005, 17(1): R1.

[6] Ghosh A, Gupta P B D, Mandal A K. Development of a fiber-optic current sensor with range-changing facility using shunt configuration. IEEE Sensors Journal, 2013, 13(4): 1347-1354.

[7] Qi Y F, Feng Q, Zhang J, Zhang X, Wang M J, Tian D S, . Design of fiber-optic current transformer based on passive phase modulator. Acta Optica Sinica, 2019, 39(4): 0406004.

[8] Liu Y, Xia J S, Zhang Y. Problem of linear birefringence effect in optical current transducer and its countermeasure. Journal of Transducer Technology, 2000, 19(3): 11-14.

[9] Sun S, Wang Z P, Wang Y K. Effect of delayline length on the all-fiber optic current transformer. Optics & Optoelectronic Technology, 2013, 11(2): 48-51.

[10] Ortiz V H, Flores J L, García-Torales G. A review on optical current transducers for power system metering. Proceedings of SPIE, 2007

[11] Wang X, Wang X X, Yu J, Zhang Y, Wang T T, Ma F. Eigen frequency tracking measurement of fiber optic gyroscope based on sawtooth wave modulation. Chinese Journal of Lasers, 2017, 44(12): 153-158.

[12] Xiao Z H, Cheng S, Zhang G Q, Guo Z Z, Yan P L, Yu W B. Research on sensitivity characteristic of fiber optic current transformer. Electric Power Automation Equipment, 2017, 37(1): 212-216.

[13] Zhong Y C, Zhou J, Chen S H. Study on measuring the direction of current based on the Faraday magneto-optic effect. Optical Technique, 2016, 42(1): 78-80.

[14] Li X Y, Hao J H, Yang H R, Yang J W, Zhou H, We Y T, . Research and development of sagnac ringlike optic current sensor. Opto-Electronic Engineering, 2011, 38(7): 1-6.

[15] Li K W, Wang Z B, Zhang R, Wang G L, Wang Y L. LiNbO₃ transverse electro-optical modulation characteristics for light pass along optical axis. Optics and Precision Engineering, 2015, 23(05): 1227-1232.

[16] Liu X S, Xiao W B, Wu H M, Xiao Y S, Huang L Z. Design of integrated testing system for optical fiber current transformer based on labview. Computer Measurement & Control, 2017, 25(7): 35-42.

[17] Hu T T, Ma X C, Zhang C Y. Calibration of the accuracy for all fiber-optical current transducer. High Voltage Apparatus, 2012, 48(5): 80-83.