Study On Influence Of DC Bias On Current Transformers And Its Compensation Measures

Current transformer is an important transmission device in power systems. Theexistence of DC bias will have serious effect on the metering and measurementaccuracy of measuring current transformers, and will bring severe impact to the fairsex of power market. Therefore, it has important practical significance to analyzethe influence of DC bias on the transfer characteristics of current transformers andresearch the compensation method for DC bias.In this paper, the experimental scheme that research the influence of DC bias onthe error characteristics of current transformers is designed on the premise of theanalysis to the steady-state equivalent of measuring current transformers and theDC bias current circuit. In order to analyze the error variation of currenttransformers under DC bias, an error measurement method based on the algorithmfor three-parameter least squares fit to sine wave is put forward. Meanwhile, thetest scheme that study the excitation characteristics of current transformers underDC bias is designed on the basis of the test method of excitation characteristics ofprotective current transformers, and the influence of DC bias on the coremagnetization curve of transformers and the exciting current is also studied indetail.In order to restrain or compensate the influence of DC bias on errors of currenttransformers, this paper puts forward to a digital compensation algorithm for allkinds of problems caused by DC bias based on the experimental analysis listedbefore. Moreover, the compensation algorithm is verified in the simulationenvironment. The simulation results prove that the compensation algorithm canrealize the compensation to the error of measuring current transformers no matterwhether the DC bias exists, and the compensation effect is more ideal. Thisprovides an important reference value for the solution of various problems causedby DC bias and the improvement of measurement accuracy of current transformers.Finally, the research results and conclusions of this paper are summarized, and theprospect for future work is put forward.