Research On The Error Based On Three - Phase Combined Transformer

With the development of electric technology, the demand for the three-phase three-element combined instrument transformers used in 6kV~35kV high voltage transmission system is increasing. The three-phase three-element combined instrument transformers with high accuracy, belonging to compulsory verification measurement equipment, has been the important driving force for the development of the modern electric power. Accurate verification on the error characteristics of the devices affects the fairness of the power supply, and is of great importance to ensure safe and stable operation of power grids and fair measurement for the power. At present, single phase method of verification for error measuring, which cannot truly reflect the error characteristics of the combined instrument transformers, is adopted in the delivery test of the equipment, thenet detection of the measuring mechanism and weekly inspection on the current transformers and voltage transformers. Three-phase method of verification is now at the research stage,with no verification procedures to depend on, and JJG313-2010 current transformersfor measuring and JJG314-2010 voltage transformers for measuring, are not systematically involved in the problem of calibration of the different three-phase combined instrument transformers. Moreover, JB/T10433-2004 three-phase voltage transformer,JB/T10432-2004 three-phase combined transformer and GB12701-2007 combined transformer only refer to the internal influence of combined transformerson each otherand do not havedetailed instructionson error detection circuit. Therefore it is necessary to put forward the feasible and effective three-phase method of verification.Firstly this paper theoretically and detailedly analyzes three methods of the testing three-phase combined instrument transformers: single phase method of verification,three-phase method of verification and indirect method, relying on a large number of experiments and much theory to analyze the disadvantages of the single-phase method of verification and indirect method. Based on the three-phase method of verification, it alsotheoretically analyzes the connection mode, magnetic field, electric field, harmonic and other error sources of the three-phase three-element combined instrument transformers,and provides the corresponding test results.The research results show that the single-phase verification method cannot truly reflect the real error characteristics of three-phase combined transformers, and the indirect method is difficult to detect the mutual influence. The Yyn connection mode of the voltageunit for the three-phase three-element combined instrument transformers have obvious influences on voltage error, while the YNyn connection mode can avoid this issue better.When loading the current and voltage in the same time, the mutual influence is obvious.When the voltage unit uses the three-phase three column iron cob, can avoid the influence of the third harmonic to the error. At last, conclude some suggests and methods to solve those discovered issues.