偏心及返回导体对特高压用计量CT误差影响分析

为明确电能计量装置自身误差受电磁场影响程度,对特高压用计量电流互感器(CT)开展一次绕组偏心及返回导体对误差影响的定量分析。首先根据磁路平衡原理建立在圆柱坐标内CT误差数学模型,推导出不同位置的外加磁场点对CT误差影响计算公式,并结合实例得到有限元与解析解结果一致,证明推导公式的正确性;然后在二维电场中对1 000 k V工程中典型CT尺寸及一次电流进行磁场分布仿真,定量的得到对于特高压用计量CT,一次绕组偏心大于1/8的CT半径后会铁心内部会产生局部饱和,导致误差产生突变进而导致超差可能;此外,仿真结果指出外部返回导体距离CT中心应大于3倍CT半径后,返回导体引起的磁场对CT误差的干扰才能被忽略;最后搭建实际特高压误差测试平台对一次绕组偏心开展试验,测试数据与仿真结果趋势一致。

Analysis of error of measurement current transformers in the UHV under primary winding eccentricity and return conductor influence

In order to make clear the influence of the error of electric energy metering device with electromagnetic interference,a quantitative analysis of error with the primary winding eccentricity and the return conductor on CTs had been developed on the measurement CTs in UHV project.Firstly,the error mathematical model of CTs had been established in cylindrical coordinates by the principle of magnetic circuit balance in order to find the error change of CTs with applied magnetic field at different positions.Secondly,a simulation of two-dimensional electric field had been done with typical size and primary current of measurement CTs in 1 000 kV engineering.It can be found by this simulation that the local saturation will occur when the primary winding offset distance from the center of CTs greater than 1/8 radius,and the error changes greatly which leads to the possibility of excess error limit.In addition,the simulation results indicate that the interference of the magnetic field caused by the return conductor to CTs error can be ignored when the return conductor distance to the CT center greater than 3 times of CTs' radius.Finally,a test loop had been built to obtain the error data with deviation of primary winding of CTs.The experimental data is consistent with the simulation results on the problem of primary winding deviation.