The Design And Implementation On Signal Processing System Of All Fiber Optical Current Transformer

All fiber optical current transformer converts electric current to optical phase based on Faraday effect and gets electric signal from optical phase through photovaltaic conversion, which transforms the detection of electric current to the detection of electric signal.All fiber optical current transformer is mainly composed of optica fiber sensing and signal processing system. The design quality of signal processing system directly affects measuring accuracy and long-term stability of the system.As an interface between optical fiber sensing and signal processing system, phase modulator is regarded the main object for signal processing system. Around the phase modulator, the paper proposed a kind of scheme on modulation, demodulation and closed-loop from the perspective of signal processing on the basis of previous research achievements. The system controls the phase modulator with return-to-zero square wave with equal duty ratio, implements the analog coherent demodulation with a sine wave acted as the local oscillator signals, and fulfills closed-loop measurement by digital circuit generating step wave. The proposed scheme offers advantages such as high precision, high sensitivity and extending dynamic measurment range.The signal processing system design of all fiber optical current transformer is divided into three parts including hardware, logic and software design. Hardware design analyzes the selection of key components and key points of circuit design, logic design is responsible for the process of closed-loop feedback, digital filter and communication interface, and software design gives out two types of upper computer interface, Matlab GUI and C#GUI respectively. In order to verify the feasibility and effectiveness of the proposed scheme, an engineering prototype is designed and a system validation platform is built according to IEC60044-8standard. The experimental results show that the engineering prototype meets0.2level of IEC60044-8standard when rated current is1000A at room temperature.