套管型电磁式电流互感器及其应用

电流互感器(CT)是联接高压一次回路与控制保护回路的核心元件。笔者从CT的电磁转换原理探寻CT的结构尺寸及其内在规律,分析了CT误差产生的主要原因是漏磁通和励磁电流,而励磁电流又决定于CT的电气参数、铁心材质及结构尺寸。图解了CT制造时二次绕组均匀分布可将漏磁通降至最低,也只有绕组抽头各级都均匀绕制的CT,其复合误差试验的间接法与直接法才具有等价性。在满足CT使用要求的情况下,适当调整CT的电气参数,如多抽头CT的负载分级、无重合闸要求的暂态保护级CT工作方式由双循环变更为单循环等,可减小CT的误差、降低制造成本。最后,对内置式CT绝缘材料的选择、外置式CT的防潮性进行了说明,特别是对外置式CT现场组装时形成闭合回路的原因、闭合回路对误差的影响以及检测闭合回路存在的方法进行了详尽的解读。

Sleeve-type Electromagnetic Current Transformer and Its Application

Current transformer(CT) is a key component that links high voltage primary circuit and control protection circuit.This paper ascertains the structural dimension of CT on the basis of electromagnetic conversion principle.It is found that the leakage flux and exciting current are main sources to introduce the error of CT,and the exciting current depends on electrical parameters,core material and structural dimension of CT.It is demonstrated that uniformly distributed secondary windings of CT can minimize the leakage flux,and indirect test and direct test of composite error are equivalent only for the CT with uniform distribution of tapped windings.On the premise that performance requirements of CT are met,the error and manufacturing cost of CT can be reduced by appropriately changing CT’s electrical parameters,such as grading load of the CT with multi-tapped windings,and changing duty cycle of the CT with transient protection and without reclosing requirement from double-cycle to single-cycle.In addition,the selection of insulation materials for internal CT and the moisture resistance for external CT are described.Especially,the reason why closed circuit is formed in spot installation of external CT,the effect of the closed circuit on CT’s error,and the methods for detecting the closed circuits are discussed.