Broadband Transfer Characteristics of DC Electronic Current Transformers

The frequent operation of the switching devices inside the converter valve (mainly composed of thyristors) and other equipment in the converter station of ultra-high voltage direct current (UHVDC) transmission system generates a large number of high harmonics and high-frequency interference, which is the main source of error of the DC electronic current transformers (ECT). In order to better understand the transfer characteristics of DC ECT, this paper considers the effects of temperature and frequency on the shunt and low-pass filter at the same time, and combines the field test at different temperatures with different current frequencies, the results are compared and fitted to obtain the broadband model of the transformer taking into account the temperature. Based on this model, the mechanism and degree of influence of different equipment parameters on the broadband transfer characteristics of the transformer are further analyzed by setting different analog circuit parameters and digital sampling frequencies. The results show that different temperatures, shunt radius, shunt residual inductance, low-pass filter cut-off frequency, sampling frequency of the combined unit affect the broadband transfer characteristics of the transformer, and when a certain threshold is reached, the accuracy of the transformer does not meet the current standard requirements, which should be taken into account during the analysis process, and the results have a reference value for the parameter selection of the transformer.