Research On All-digital Of Optical Current Sensing Technology

Optical current transformer (OCT) is a product of the times which meets thedevelopment needs of intelligent substation to current transformers. Comparing withthe traditional current transformer, OCT has better performance in the transientmeasurements, insulation and cost, etc. However, though OCT has been researchedfor several decades by domestic and foreign researchers, but large-scale applicationstill not yet achieved so far, as there are still many challenging problems to besolved before any practical applied. One key problem is that the optical fibertransmission system inside the OCT is influenced by the external vibrations.In this paper, firstly, from the measuring principle of OCT, OCT system areanalyzed in optical sensing signals using analog signal transmission vulnerable tothe specific reason for the vibration interference. It points out that the vibrationinterference is due to the vibration on the downside two-way optical fiber producedby dynamic loss caused by inconsistent. Improvement of the double optical pathmethod can improve the influence of vibration on uplink optical fiber, but notsuppressing the influence of vibration on the downside optical fiber.To solve this problem, a digital signal transmission optical sensing solutionswas propose by comparing the V/F converter and A/D converters digitize theadvantages and disadvantages of these two programs, the final choice of A/Dconversion solution. After using this program, the functional structure of theoriginal OCT signal processing was re-plan, and a fully digital OCT structure wasdesigned which can transform the optical sensor signal in the high-pressure side intodigital signal. And then, the digital signal will be transferred to the low-pressureside. The communication protocol between high-voltage side and low-voltage sidewas also ruled in this paper.A low-power data collection system in high-voltage side basing on theMSP430F149and AD7988-5was designed according to the requirement of all-digitalization structure. With the designed system, the optical sensing signal can besampled and sent to the signal processing system in the low-voltage side. At thesame time, a digital information processing system basing on TMS320F28335wasdesigned to receive the data from high-voltage side and demodulate the currentinformation. The signal from after digital information processing system will besent to the merging unit after a high order FIR filter.Finally, the test measured the power consumption of the high voltage of thecircuit is less than30mW, to meet the low power design requirements for energy laser module can reliably provide the required energy. By vibration tests to verifythe full digital OCT has a strong anti-vibration interference.