Research On The Anti-interference And Uncertainty Of The Field Calibration For HVDC Current Transformer

Recent years, the technology of high voltage direct current transmission is in rapid development home and abroad. Direct-Current current transformer?DCCT? is an important measurement equipment in high-voltage direct current transmission system. In order to ensure its accurate and reliable, field calibration is needed before the DCCT putting into operation and at the time of outage maintenance. However, there are few relevant calibration technologies at home and abroad.Based on the analysis of DCCT field calibration technology and current standards at home and abroad, this paper has proposed a set of high-voltage site calibration system, mainly including dc current source, magnetic modulation dc current comparator?DCC? as current standard, and electronic DCCT calibrator with fiber-optic digital synchronous. And then analyze the factors affecting the uncertainty of the calibration system, puts forward the specific methods and measures to solve the problem.From the principle of DCC, we have got the conclusions that the harmonic in Dc current source have no impacts on the dc measurement of DCC, at the same time the DCC can be used to monitor the harmonic component. A harmonic test system has been designed using the method of dc-harmonic double circuit superposition. The harmonic response characteristic result of DCC tested by this system is the same as the result of theoretical analysis.To improve the electromagnetic environment in field calibration, a method of bus ring in the shape of a butterfly has been put forward. And it can effectively reduce the electromagnetic interference which is produced by the field wiring.The simulation analysis of the standard has been done for the cases of bus eccentric and neighboring conductor which may be encountered when using in field. On this basis, the magnetic shielding of the standard has been optimized designed and a prototype DCC has been developed. The uncertainty of this prototype is calibrated as 5×10-6 by national institute of metrology, China. On this basis, impact tests of bus eccentric and neighboring conductor have been done. These tests have verified the optimization of the shielding structure can effectively resist interferences.Anti-interference analysis of the DCCT calibrator has been carried out. It has demonstrated that the structure of current directly input and the technology of fiber synchronization can effectively resist the interferences caused by the uncertain of dc source, the field electromagnetic environment, and the changes of environmental temperature.In order to inspect the calibration system comprehensively, the field calibration simulation experiment has been done using the DCCT whose accuracy is level 0.2 as the transformer being calibrated. The experimental results show that the uncertainty of calibration system is better than 5×10^-4.