High Accuracy Ratio Of Transformer Design, Construction And Validation

In the field of the modern electrical measurement, the proportional transformer as the arm of precise bridge is more and more important and more attention is paid in metrology. In the application, two important transformer bridges are concerned------resistance bridge and capacitance bridge. It is the key technology for Transformer Bridge to provide the precision ratio adopting inductive coupling windings. Compared to traditional resistance voltage divider and capacitance voltage divider, there are some advantages which are of high precision、high input impedance、low out impedance and stability and so on. Nevertheless, because of the magnetic error and the capacitive error, devices providing inductive coupling ratio make that the disseminating ratio and the ratio of winding turns don’t equal precisely. To get the disseminating bridge matching the precise of impedance standard, the structure of traceable bridge must be considered carefully, and then actual ratio should be got by calibrating the transformer.1) Based on the system errors of the proportional transformer are analyzed, the structure of two-stage which is independent designed can reduce the magnetic error; the triaxial guards which are researched in more detail can reduce the error of parasitic admittance.2) Based on the application of the two-stage and triaxial guards, the structure and design process of the proportional transformer are introduced in detail, including the design of a isolation proportional transformer and any other auxiliary transformer which would be used in an improved straddling method. The winding groups of the two-stage transformer are discussed, the taps are done carefully. The methods---the bootstrap method and the straddling method---are analyzed, and the system errors in calibration are discussed.3) After an improved straddling method is adopted, using an easy method of it calibrates the proportional transformer under test, and then gets the uncertainties of the ratio10:1, one gets1.1x10-8for the in-phase and5.5x10-8for the quadrature.4) After completing the calibration, some problems in the experiment are summarized, and suggestions put forward for solution, it laid a good foundation for the future research work.