直流电流互感器(direct-current current transformers,DCCT)是高压直流输电系统中的重要测量设备。为保证其准确可靠,DCCT投运前和停电维护时需现场校准。对于电子式DCCT现场抗干扰及数字化同步两大关键问题,该文提出电子式DCCT的校准方法并设计一套校准系统,主要包括直流电流源、作为标准器的磁调制式直流电流比较仪(DC current comparator,DCC)和具有光纤数字同步的电子式DCCT校验仪。重点对标准器和校验仪进行了现场抗干扰分析,对于标准器现场使用时可能遇到的母线偏心和邻近通流导体干扰情况进行仿真分析,优化磁屏蔽结构,研制了DCC样机,经中国计量科学研究院校准,该DCC不确定度为5×10-6,在此基础上进行了母线偏心和邻近导体影响测试,验证了优化的屏蔽结构能够有效抵御现场干扰;为检验校准系统,采用0.2级DCCT进行了校准测试,结果表明校准系统不确定度优于5×10-4。
The direct-Current current transformer (DCCT) is one of the important measurement equipment in high-voltage direct current transmission systems. 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. For the electronic DCCT, field anti-interference and digital synchronization are two key problems. This paper proposed a calibration method of dc electronic current transformers, and designed a set of the calibration system, mainly including a dc current source, a magnetic modulation DC current comparator (DCC) as the current standard, and an electronic DCCT calibrator with fiber-optic digital synchronization. And then anti-interference analysis was carried out for the standard and calibrator. The simulation analysis of the standard was done for the cases of bus eccentric and neighboring conductor which may be encountered when using in fields. On this basis, the magnetic shielding of the standard was optimized designed and a prototype DCC was developed. The uncertainty of this prototype was calibrated as 5×10-6by National Institute of Metrology, China. On this basis, impact tests of bus eccentric and neighboring conductors was done. These tests verified the optimization of the shielding structure, and the structure can effectively resist interferences. In order to inspect the calibration system comprehensively, the field calibration simulation experiment was done using the DCCT whose accuracy is at the level of 0. 2 as the transformer being calibrated. The experimental results show that the uncertainty of the calibration system is better than 5×10-4. © 2016 Chin. Soc. for Elec. Eng.
Proceedings of the CSEE
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