Analysis Of The Influence Of DC Bias On Current Transformer

Energy interconnection technology such as HVDC technology is an important technical guarantee for large scale access and long-distance transportation of clean energy.HVDC technology has many advantages such as long distance,large capacity and so on.With the rapid development of high voltage technology,more and more problems come with it.At present,the AC power supply in the existence of the DC component problem becomes increasingly prominent.Electromagnetic current transformer is a very important power equipment in the power system.It is directly related to the reliable operation of the relay protection of the power system and the accuracy of the energy measurement.And the DC bias effect will have a serious impact on the current transformer,so the study and analysis of DC bias on the current transformer effect is ten minutes important significance.Firstly,the influence of DC bias on the current transformer is analyzed in detail by the equivalent model of DC bias and the equivalent model of current transformer T.For the protection of current transformers,its role is to the system of abnormal state or fault status information transmitted to the relay protection device,it must focus on its transient saturation characteristics.The influence of DC bias and remanence on the initial saturation time of current transformer is analyzed by theoretical analysis of the relationship between excitation current and flux of current transformer after fault.Secondly,the influence of DC bias on the current transformer for protection is further verified by simulation experiment.Through the simulation of the basic magnetization curve of the current transformer,the simulation model of the current transformer is used to study the transient saturation characteristic of the Simulink simulation component in MATLAB.The study shows that the forward DC bias will accelerate the current transformer saturation,while the reverse DC bias delay current transformer saturation,and with the DC component of the join,the excitation current waveform distortion,even harmonic,especially Second harmonic increase significantly.Thirdly,differential protection is the main protection of the transformer,and the most common differential protection brake principle is based on the second harmonic brake.Through the simulation analysis of DC bias,the current transformer saturation second harmonic content increases,it is easy to lead to relay protection devicerefusing,affecting the power system security.Finally,for the metering current transformer,its role is to the normal operation of the system current transmission to the measurement equipment,it should focus on its steady-state transmission characteristics.The error of current transformer is deduced by theoretical analysis,and then the magnetic permeability of core is measured according to the relationship between core permeability and core inductance.The influence of DC bias on the current transformer is analyzed by AC and DC hybrid experimental methods.The experimental results show that with the increasing of the DC component,the core permeability decreases,the current transformer error increases,the angle difference and the ratio difference are obviously increased.