Research On The Optical Measurement Method Of Very Fast Transient Overvoltage

Under the vigorously promotion of the construction of Ultra-High Voltage(UHV) grid, the voltage grade of Gas Insulated Substation (GIS), which is widelyadopted in China, is increasingly high. The secondary equipment near GIS is harmedby Very Fast Transient Overvoltage (VFTO), which is triggered by GIS disconnectoroperation. This phenomenon threats to the safe operation of the whole power system.In recent years, as the secondary equipment installation position is getting close toGIS, this problem becomes more prominent. To sum up, it is urgent to develop aVFTO online measuring device in power system, with the features of widefrequency band, fast response, high sensitivity and strong anti-interferencecapability. Aiming at the situations above, this paper, based on Pockels effect,proposed an optical voltage measuring method to measure the VFTO signal withhigh frequency characteristics, and develop online measuring device.Firstly, this paper explained VFTO phenomenon in the view of electronicmovement and flux, and theoretical derivation was given. The proposed method wasapplied to explain the VFTO and VFTC phenomenon on the252kV GIS, which wasconsistent with the test data. The feasibility of this interpretation method wasverified. According to the test data, the basic frequency characteristics of the VFTOwas determined.According to the basic characteristics of VFTO, the optical measurement partof the measuring system was designed. Optical voltage sensor head material waschose. By comparing the merits of the transverse electro-optic modulation andlongitudinal electro-optic modulation, the an electro-optic modulation method wasselected. Optical voltage sensor head structure was designed. Besides, photoelectricdetector circuit model was discussed and its performance parameters were given.According to the basic characteristics of VFTO, VFTO optical measurementsignal detection system was designed. With the help of Advanced Design System2008, impedance matching problem in high frequency circuit design wasanalyzed. Single light signal detection and double light path signal detectionmethods were proposed. By simulation and experiment measurement, theadvantages and disadvantages of the two methods were compared. The finalselection was double light path signal detection method.Finally, a testing platform and test prototype were built. Experiment schemeand measuring method was designed to evaluate the prototype. In this paper,acquisition system was evaluated by using high frequency optical signals instead ofthe optical signal modulated by VFTO. The author developed a high frequency source and tested its performance. The display interface was made by using theLabView program. Besides, a complete set of VFTO online measuring system wasset. The measuring results showed that, when impedance matching was prepared, thesystem frequency range was0Hz~10MHz, which met the requirements ofmeasurement.