The DC field equipment of most converter stations are imported, the degree of localization is lower than the average level of the industry, and most of the key technologies are in the hands of foreign enterprises. 

This basic situation directly leads to equipment if abnormal, or even forced outage, often resulting in high maintenance and replacement costs. DC power transmission is the point-to-point transmission, more importantly, as an important channel of power transmission equipment, once the fault outage, China’s south and east China will appear unprecedented power gap. Therefore, it is necessary to carry out on-site measurement and measurement of DC transformer before the peak of power supply in summer. In the field test of DC transformer, the relative error between the output value of the secondary conversion of DC transformer and the standard value, the short-time stability of the error and the periodic stability of the error are mainly investigated, and when the current rises, the current drops the same current value error value difference and so on important content.