Design And Performance Research Of Wide-band Physically Compensated Fiber-optic Current Sensor

The power system has entered the era of smart grids.Real-time sensing of transient currents in power systems is of great significance to the studying system disturbances,faults,and control protection.Traditional electromagnetic current transformers have many problems due to their sensing characteristics,such as iron core saturation,narrow frequency band,and direct electrical connection with the power system,that make them unable to accurately measure high frequency transient currents.With the development of optic current sensor,the most important one is the research on fiber-optic current sensor.However,the research on fiber-optic current sensor has mainly focused on the accuracy of power frequency and low-frequency currents measurement.The main focus is on the error elimination methods and stability of the corresponding optical systems and optical devices,and there are little researches on the measurement of high-frequency current waveforms and transient current waveforms.Therefore,research on fiber-optic current sensor with wide band and temperature adaptability can deeply obtain more abundant transient current waveforms information including lightning current,and provide data support for power system protection and lightning arrester design.Aiming at the difficulty that the fiber-optic current sensor can not take into account both wideband measurement and wide temperature range adaptability,this paper proposes a straight-through optical path structure for fiber-optic current sensors by coupling a Faraday rotator at the geometrical midpoint of the double-wound sensing fiber.The Jones matrix theory is used to establish a theoretical model of the sensing characteristics to study the environmental sensitivity reflected by the normalized output light intensity under various birefringence conditions;the linear range of its work and theoretical analysis errors are studied.The finite element model of the improved structure is established by using COMSOL finite element simulation software,and the mechanism of improving the temperature adaptability was analyzed by coupling the magnetic field and the light field.Based on the principle of the designed fiber-optic current sensor,the sensor performance test platforms including the equivalent current response test platform and the impulse lightning current test platform are designed,which lay a solid foundation for realizing the measurement of large-value transient current in the wide frequency domain.The sensor linearity has a good response and linear relationship under the 0-2000 A power frequency current,and the goodness of fit of the fitted curve is 0.999 9(the traditional basic structure is 0.997 5).Through testing the frequency and temperature characteristics of the sensor,the results show that the sensor has good frequency response characteristics,the amplitude error of the 10 Hz-10 k Hz frequency response test does not exceed 2.3%,and the phase shift is less than 2°.Through experimental research,the response characteristics of the sensor under typical non-sinusoidal equivalent current excitation,including short-circuit transient current,harmonic current,triangular waveform current,typical demagnetization current,etc.,are all similar to each other over 0.962 5.Through the lightning current impulse response experiment,the standard 8/20?s transient lightning current waveform with a magnitude of 3.0 k A in the laboratory is measured: the amplitude error is less than 2.1%;the waveform similarity is:0.997 1,which proves that the equivalent frequency band is at least it can cover 54.7k Hz;the temperature characteristic experiment shows that the improved structure of fiber-optic current sensor can improve the temperature adaptability,and the output voltage error within the range of-20??60? is less than 4.3%(the traditional basic structure is 29%).Therefore,the improved structure of the fiber-optic current sensor proposed in this paper has a wide measurement frequency band and excellent temperature adaptability,which can meet the measurement requirements of typical transient current waveform parameters of power system and have engineering application value.