Study On Fiber-Optic Voltage Transformers Based On Invar Capacitor Divider

Power systems are significant to national economy, and voltage transformers becomethe important equipment of power systems to obtain potential signal used in protectingand metering. Along with the development towards high voltage and capacity,conventional electromagnetic voltage transformer exhibited some inherent disadvantagesfor its sensing mechanism;Such as: big size, high cost, complicated insulation structureand potential exploding dangers and so on. Optic voltage transformers overcomeshortcomings of waveform distortion induced by saturation and lower measuringaccuracy caused by pressure drop of conventional voltage transformer;having manydistinguished advantages, such as: compacted structure, no dangers of burning andexploding, enlarged measuring bandwidth, wide dynamic range, strong anti-jamming, nohigh voltage caused by secondary side open, easy to interface with computer, digitaloutput, fitted with power systems demand for automatization and digitalization and etc.;Which became researching emphases of scholars in all of the world gradually. On thebasis of achievements in existence, In this paper, a new type of fiber-optic voltagetransformers is proposed based on invar capacitor divider. Only change intrinsic standoffratio of capacitor voltage divider is needed while voltage transformers are applied to varygrades, but not the structure of transducers. In this way, measurement requests could beeasily satisfied. These conveniences insure large-scale production and remarkablyadvanced measuring accuracy.At first, present status of the research work of optic voltage transformers isobjectively commented;Then, main problems existed in Pockels electro-optic effectbased OVT and capacitor voltage divider based OVT, and problems on voltagetransformers with conventional technique and light transmitted by fiber are allsummarized. Based on these, a new structure of optic-electric voltage transformers isbrought forward. Furthermore, fiber-optic voltage transformers based on intermodeinterference principle of elliptical core dual-mode fibers and converse piezoelectric effectof quartz crystals are theoretically discussed. White light interferometer based onmultimode laser and DC phase tracking system is theoretically analyzed, mathematicalmodel of zero phase tracking errors is built;and then specific compensation method ofzero phase tracking errors is given.Secondly, capacitor voltage divider based on invar is deeply researched, andintegrated system model is built;Mathematical model of capacitor voltage divider underthe high voltage insulation condition is derived;Calculation formula for radius size ofcolumnar capacitors is drawn also. To seek factors influence the accuracy of transformersmeasurement, mathematical model of capacitor voltage divider between temperature,non-coaxial degree, radius of capacitors and electrostatic field force is built and thefunction law affected system response by these factors is received. Finite element analysisis used to analyze electric field of capacitor voltage divider, in this way, isoline curve andkey potential distribution numerical value of capacitor are gained also.Then, digital interface of voltage transformers is designed. According to criterionIEC60044-7, process layer communication modules of optic-electric voltage transformersis designed, function of every part is analyzed in detail. Furthermore, hardware circuit andsimulation results of process layer communication system are given.Finally, the overall optical path of the sensor system is designed and numericalanalyzed. Specific numerical value of optimum voltage applied on the quartz crystal, fiberwinding turns and sensing fiber length are all given. Experiments are carried out fordilatability of quartz crystals, columnar capacitors and its parameters under differentvoltages. Then studies on experiment techniques are carried out, coupling methodsbetween laser diode and single-mode fibers with polarization maintenance, fiber windingmethods and weld methods between the single-mode and dual-mode fibers are all broughtforwards;Parameters of experimental device are ascertained.