Research On Single-turn High Current Generator Combining AC And DC Based On Capacitance Dc-blocking

Ac and dc hybrid power grid operation make the interactions between ac and dcsystems becomes more and more obvious. When dc power network runs in a unipolarearth loop, CT in the ac grid will produce a dc bias. Dc bias will exacerbate CT core’smagnetization, thus influence on the performance of the CT measurement and protection.At present, there are two main method to simulate hybrid ac or dc current system.One is using dc current circuit and ac current circuit respectively through currenttransformer at the same time, but this method is only applied to the cross-core currenttransformer while the actual operation of the current transformer is generally a conductiverod which is installed. Another method is to use an arbitrary current generator to generatea power frequency ac current wih dc current, though this signals can be directly connectedto current transformer with a conducting rod, current magnitude is limited.This paper study a kind of cross-core ac and dc synthesis big current generator basedon capacitive to realize single turn insulation, by means of capacitance blockingtechnology and non-polarity capacitance’s current characteristics that the dc source circuitand ac source circuit flows the common branch of ac and dc superimposed current,meanwhile ac current source and dc current source are independent with each other, so asto produce synthetic ac and dc current; At the same time, in order to ensure the workingreliability and safety of the system, this paper design a monitoring and analysis system soas to real-time monitor the working status of the whole system and automatically completecorresponding protection action through the analysis of the monitoring data of each link.In order to verify the performance of the designed system,according to the projectdesign requirements of system, this paper conduct confirmatory test for this system. Testcontent includes: capacitance group shunt and fault tests; capacitance temperature rise test;ac and dc circuits interaction experiment; large current ac and dc synthesis test.Experimental results show that the designed system meets the design requirements,realizes single turn ac5000A and dc50A current synthesis and smooth control, andprovides ideal apparatus for related experimental study of current transformer dc bias.