Application Research Of Interferometry Measurement Technique In Optical Current Transformer

With the development of digital grid, the optical current transformer (OCT) is widely applied. Including the operating principle of OCT based on magneto-optical rotation is reflecting current information of grid by measuring light intensity. On the basis of the research of existing transformer, we lead interference measure which is an established technique into the operating principle of transformer and change the existing measure method of light intensity into measuring the visibility of interference fringe. And then achieve the aim of measuring the current of grid.In this paper, the OCT designed of which applied sensing principle is Faraday magneto-optical rotation effect, sensing way is straight optical path type and sensing material is that used in the"sensing heads of ZF-7 type dense flint magneto-optic glass"is based on interferometry. The sensing principle of transformer sensing heads and operating principle of detecting element is deduced theoretically and then the operating principle of the OCT is explained.By using"Ansoft emulation software", the external magnetic field of circular live wire is emulated. The site and length of magneto-optical material are defined via internal response degree of magneto-optical material and the size of effective magnetic field, the length of magneto-optical material is 50mm and the site is 10mm away from wire. According the test requirements, the type and parameter of apparatus correlated with experience are defined and experimental system of transformer is built. Meanwhile, output interference design is processed by using digital image processing technology in order to collect and apply data. Metrical function of transformer is estimated on the basis of theoretical deduce and test data. The result concluded from the fitting data which obtained by using least square method is consistent with the theory. According to the residual error and retested result, plane of polarization angle of initial system is set asπ/4 . And the element of leading inaccuracy into system measuring is analyzed.Combined with the test criterion of electronic current transformer, detecting system applied in the interferometry transformer is built. The performance of transformer system is tested. When the rated current is 1000A, the accuracy of this system is better than 1%.