DC magnetic bias may change the error of current transformer (CT). Through establishing mathematical model, the change of excitation current of CT before and after getting DC interference is analysed, thus the error characteristics of CT under DC magnetic bias is studied. From theoretical derivation, it is found that under DC interference, the error may increase. Based on features of traditional CT error measurement system, the strategy suitable for CT error measurement under DC interference is proposed, and the error measurement is conducted by using this strategy. The test data indicate that when interference current reaches 1% of the primary current of CT, the accuracy of CT will decrease 1~2 grades. This phenomenon is consistent with the theoretical derivation, thus the correctness of the theoretical analysis is proved.%直流偏磁会引起电流互感器( CT)误差的改变。通过建立数学模型,分析CT受到直流干扰前后的励磁电流变化,研究直流偏磁下CT误差特性。理论推导发现直流干扰下,CT 的误差会增加。基于传统CT误差测量系统的特点,提出适合直流干扰下测量CT误差的方案,并使用该方案对CT进行直流干扰下的误差测量。试验数据表明,当干扰直流量占CT一次额定电流的1%时,会使CT的准确度下降1~2个等级。该现象与理论推演一致,理论分析的正确性得以论证。
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