The safe and stable operation of the DC electric power transmission depends to a large extent on the protection and monitoring systems operating in all corners of the converter station. 

And all kinds of high-voltage transformers and sensors provide a solid guarantee for the protection system and converter station equipment in the accurate measurement under transient conditions. Usually there are two kinds of DC current transformers used in converter stations: zero-flux DC current transformer and photoelectric current transformer. According to the advantages and disadvantages of the two DC transformers in insulation and accuracy grade, the transformers with different characteristics are arranged on the key nodes of the converter station. Zero-flux DC current transformer is used to measure the DC current value of neutral line, DC field neutral line and NBGS switch in valve hall. The photoelectric current transformer is mainly used to measure the current value of the inner pole line of Valve Hall, the Pole Line of DC field and the high voltage side circuit of DC filter.