Study Of The Influence Of DC Bais On Measuring Current Transformer

Current transformer(CT) is an important transmission device in power systems. The existence of DC bias will have serious effect on the measurement accuracy of current transformers and will bring severe impact to the fair sex of power market. With the continuous expansion of grid and the increase of the total electricity load, the problem about instrument metering deviations caused by CT DC bias will have incalculable economic loss and social effects. It has important practical significance to study with CT DC bias.This paper carried out related work on this problem. Firstly, built the CT excitation features of the core model based on JA theory, foreshadowing for further theoretical research; secondly, established the DC bias equivalent model and CT formula for counting the mass change of the DC bias error, through theoretical calculations of different core materials, at different voltage levels CT in the basic circumstances and under different DC interference CT error characteristic mass change, the measurement with normal CT and after DC interference error in the DC interference are analyzed in comparison.Finally, through to the 110kV?220kV, two kinds of different voltage grade, different materials, light load and full load cases of CT for different conditions of the DC bias error test, validated the correctness of theoretical analysis, the results showed that: Non-linear increase in magnetic flux density and the secondary load increases will lead the original CT error curve move to the negative direction, angle curve move to the positive direction; CT with initial low permeability and high saturation flux density materia in the absence DC bias is better, but under a DC component associated with CT core easily saturation flux density; Along with the rising of the straight flow, the error of the CT also will increase. For variable ratio is smaller, the DC component of a rated power flow, the greater the CT, the worse under dc bias magnetic interference; For the same CT the same dc interference cases, access to the current is smaller, the greater the impact on, the closer into the current rating is relatively smaller.