1

1 

目前工程中小电流接地选线检测元件大多按保护级选择，保护级互感器在所测电流远小于额定电流值时，综合误差难以满足要求，两级电流变换元件总误差是造成现场误判的主要原因。工程实际中使用的零序电流互感器线性测量范围超出了实际可能的接地电容电流。

To date, most engineering detecting element of medium and small current grounding line selection according to the protection level selection, protection level transformer in the test current is far less than the rated current value, the integrated error is difficult to meet the requirements, two levels of current transform element total error is the main cause of the misjudgment. The linear measuring range of the zero sequence current transformer used in the project is beyond the actual potential ground capacitance current. 

2

2 

零序电流互感器在小电流接地系统中应用，其一次电流值均很小，正常运行时其一次侧基本无电流，出现接地故障时其一次侧电流(故障电流)也很小，一般在10A以下。如系统接地故障电流大于10A时，按规定要求需装设消弧线圈进行补偿，带有消弧线圈补偿时接地故障电流更小，一般小于2～5A(最小可到0.2～0.5A)。在这样小的一次电流下常规零序电流互感器的变比和相角误差均很大，因此各互感器生产厂家对零序电流互感器均不能给出变比，也无误差保证指标。从零序电流互感器实际一、二次电流变化曲线(变比曲线)中可知：零序电流互感器电流变比值随一次电流值变化很大，而一次电流在小于1A时，已经不能再给出具体的二次电流输出值。

Zero sequence current transformer applied in the small current grounding system, the first time, current value is very small, when the normal operation of the basic no one side current, a ground fault in one of the primary side current (fault current) are also small, usually under 10 a. When the ground fault current is greater than 10 A, such as system requirements need to be installed in accordance with provisions compensate arc suppression coil, with arc suppression coil compensation when earthing fault current smaller, usually less than 2 ~ 5 A (minimum to 0.2 ~ 0.5 A). An electrical flow in such a small routine of zero sequence current transformer ratio and phase Angle error is very big, so the transformer manufacturers are given on the zero sequence current transformer are not better than, no error is guaranteed. From zero sequence current transformer actual curves of the primary and secondary current known (variable ratio curve) : the zero sequence current transformer electrorheological ratio change with a current value is large, and a current in less than 1 a, can no longer be given specific secondary current output value. 

3

3 

通过以上分析可知，测量环节的综合误差是目前各种小电流微机选线装置误判的主要原因，工程应用中尽量使参数配合适当，减小测量环节的综合误差，有效提高小电流接地选线系统的选线准确率。

Through the above analysis, the comprehensive error of measurement link is the misjudgment of the main causes of all sorts of small current microcomputer line selection device, make parameters in engineering application with appropriate, reduce the comprehensive error of measurement link, effectively improve the line selection of small current grounding line selection system accuracy. 

4

4 

工程中采取的有效措施包括： ①尽量选择准确度高的专用零序电流互感器，额定一次侧电流选择应保证：系统出现最大接地电容电流时处在零序电流互感器线性范围内(准确限值)，一次侧电流线性测量范围应向下延伸到0.2A左右，用以适应经消弧线圈接地的小电流接地系统。 ②零序滤序器应尽量使用变比较小的计量级(最好为S级)电流互感器组合而成，较小变比可使电容电流二次值较大，有利于检测装置电流变换器采集电流值，S级使电流互感器的测量精确线性范围更宽，有利于测量较小的电容电流。

Engineering effective measures include: (1) try to choose high accuracy for zero sequence current transformer, rated primary side current selection shall ensure that: the system appears most grounding capacitive current in zero sequence current transformer (limit) accurate linear scope, the primary side current linear measurement range should be down to about 0.2 A, in order to adapt to the small current grounding system arc suppression coil grounding. (2) zero sequence order filter should use as far as possible become smaller measuring level current transformer (best s-class), less variable than can make the capacitive current secondary value is bigger, is beneficial to collect current value detection device current converter, the s-class makes current transformer measurement precise linear range wide, is advantageous to the measurement of small capacitance current. 

5

5 

对小电流接地选线装置，零序电流互感器在小电流时的精度对装置有一定要求，为此建议：①如对互感器保护倍数有要求，且在低电流（0.5---5A）处要求不高的情况下，建议选取开口式互感器50/1A，在2%额定一次电流时误差必须在±10%以内。因为开口式互感器安装方便，在保护上也有一定的优势，而且剩磁上比闭口式互感器低得多。②如果对一次电流在小电流处精度要求很高的话，建议使用闭口式互感器，测量精度要达到0.5级，有必要时也可以提出0.5S级的误差要求。按制造规程规定：作为计量用的互感器可在150%额定一次电流的情况下仍能保证误差在一定范围内，对于小电流接地选线装置，可结合实际需要来确定变比，一般推荐为50/1A，精度可以提0.5或0.5S，负载1VA。

For small current grounding line selection device, the accuracy of zero sequence current transformer in the small current requirements to the device to a certain extent, therefore suggested: (1) such as multiples of transformer protection requirements, and in low current (0.5-5 a) under the condition of demand is not high, suggest select open type current transformer 50/1 a, while 2% rated primary current error must be within plus or minus 10%. Because of the convenient installation of open type transformer, there is also a certain advantage in protection, and the residual magnetism is much lower than the closed type transformer. (2) if the primary current in the small current accuracy requirement is very high, it is recommended to use silent type transformer, the accuracy of measurement to achieve 0.5, when necessary, also can request the error of 0.5 S level. : as stipulated in the manufacturing procedures for measurement of transformer can be in 150% of the rated primary current situation still can guarantee error within a certain range, for small current grounding line selection device, can be combined with the actual need to determine the strain ratio, generally recommended as a 50/1, the precision can be 0.5 or 0.5 S, load 1 va.