换流站直流电流互感器现场测试的关键技术

Key Technology on Field Tests for DC Current Transformer of Converter Station

高压直流输电的控制保护系统需要依靠直流电流互感器(DCCT)提供相应电气量的测量信号,故DCCT对高压直流输电控制保护系统的稳定准确运行具有决定性作用。然而受制于合理试验方法、精密实验设备以及相关标准规程的缺乏,针对DCCT的现场测试工作尚无法在较大范围内充分开展。为此针对DCCT现场测试中直流分量精确提取、DCCT的数字输出接口、DCCT无同步信号接入下的数据同步以及测试系统不确定度等关键技术问题开展了研究,提出了一种直流电流互感器现场同步测试方法。通过前置AD采集单元采集DCCT输出信号,结合含有直流分量的小波系数来精确提取直流分量,采用FPGA实现DCCT的数字接口,基于绝对延时时间实现数据同步,分析了测试系统不确定度来源并给出了评定方法。研制出了1套直流电流互感器现场测试系统,结合±500k V永富直流工程,在国内首次开展了从低电流至额定电流等不同电流输入情况下换流站全站数字量输出型DCCT的现场同步测试,结果表明该测试系统整体不确定度优于5×10-4。

DC current transformer(DCCT)provides measurement signals for an HVDC control and protection system,which plays an important role in the accurate and stable operation of the control and protection system.However,field tests of DCCT have never been carried out due to the deficiency of feasible test methods,sophisticated equipment and relative standard.Consequently,we studied the key technologies for DCCT field tests,such as the accurate extraction of DC components,the digital output interface of DCCT,the data synchronization of DCCT without synchronous signal access and the uncertainty of test system.Meanwhile,we analyzed and estimated the source of the uncertainty with the DCCT output signal acquired by the A/D acquisition unit,which is decomposed by the wavelet to obtain the direct current.Moreover,the FPGA was applied for the digital interface of the DCCT on the basis of the synchronization of the absolute time delay.In order to complete the field tests of DCCT,a set of DC transformer test system was developed for the±500 k V Yongfu HVDC system.At last,the first field tests in China with multiple values of DC,from 10%rated current to100%rated current,were carried out for all the DCCT with digital output in the converter station.The results reveal that the uncertainty of the developed test system is less than 5×10-4.