Research on Error Characteristic and Error Influence Quantity of Instrument Current Transformer by Using Different Verification Methods

Based on the designed error verification platform of three-phase combined transformer, the error characteristic of current transformer (CT) unit in three-phase instrument combined transformer is measured. The error influence quantities are also given by a comparison and analysis with single-phase and three-phase verification methods, which including the influences induced by the three phases of the instrument combined transformer simultaneously up-current and both PT and CT are excited at the same time. The results show that the size of the secondary load has a certain influence on its error characteristics, and CT shows different error characteristics under rated load and lower limit load. The three phases of CT unit up-current at the same time only has little influence on its error characteristics. However, if PT unit is in excitation state at the same time, the error of CT at the test points with small current (<20% rated current) increases greatly; especially the phase angle error is even out of tolerance.