Study On The Optical Electric Current Transformer Based On The Optically Powered PCB-Rogowski Probe

The current transformer is an important device for electronic components protecting and current measuring in the electric power equipment, whose measurement precision and working stability directly affect the normal operation of power equipment. With the development of electric technology, the specifications and required functions of the current transformer are getting higher standard in domestic. The traditional electromagnetic current transformer are unable to meet the requirement of intelligent,miniaturization which advocated by modern science and technology, so the development of a new type of current transformer had great significance today.In this paper, the optical fiber transmission optically powered type current transformer and their system are studied, the structure of light powered PCB- Rogowski coil probe optical electric current transformer is designed which to conducting the experiments of parameters. The study including the following aspects:(1) The optical current transformer based on the optical fiber transmission and light powered supplement are put forward and implemented. The input and output of measuring probe are in light mode which equivalent for "all-optical" type. The light sensor probe and the signal transmission circuit that has anti-electromagnetic characteristics are developed.The sensing probe of PCB- Rogowski coil has no connecting to the measured circuit,which can be achieved for the measurement of isolating high pressure loop. The power consumption of designed optical current transformer probe is less than 50 μW. It makes a possible solution to supply the probe for LD power in long-distance situation, and solves the key problem of the low power consumption of CMOS switch circuit and the power supply stability of optical powered probe.(2) The PWM-PPM modulation and transmission circuit are put forward and conducted. The output of voltage frequency converter probe is modulated by PWM-PPM,then drives LD and transmit signal via optical fiber for transmission. The PPM signal drives LD and signal transmission in optical fiber could ensure the micro-power consumption and broad band of the measured circuit, and also improve the accuracy ofmeasurement and anti-interference of signal.(3) The signal transmission and processing system of optical fiber photoelectric transformer are designed. The designed signal processing system is using FPGA technology for data reduction and DSP technology for data processing at the lower voltage side of the system which to ensure the stability of transmission system; On the high side of voltage amplification circuit, filter circuit and V/F conversion circuit are designed and the simulation analysis to the signal processing system is conducted. The simulation result shows that the designed signal processing system has high measurement precision.(4) The simulation tests to the various parameters of photoelectric current transformer are executed, and error sources are analyzed. The measured signal de-noised by lifting wavelet transform algorithm, the improvement of double threshold function is studied; the improved adaptive algorithm of de-noising method is put forward. Compared with the traditional wavelet denoising method, the parameters such as SNR, reconstruction mean square error and denoising time are improved.