一种V/X接线牵引变压器短路电抗在线监测的方法

摘要

本发明公开了一种V/X接线牵引变压器短路电抗的在线监测方法。该方法在供电臂负馈线电流为0.9至0.95倍额定电流和0.95至1.0倍额定电流的两个时段，分别测试并记录变压器进线侧和馈线侧的电压矢量和电流矢量，采用推导的公式计算获得短路电抗的初步测试值，并重复测试和计算n(n不小于20)次，获得两组初步测试数据，针对每组数据，通过判断初步测试据的相对标准偏差剔除误差大的数，若去掉数据的量小于n/4，则剩余数据的平均值即为所测短路电抗的值。该方法测试简单、准确度高，监测所得的短路阻抗随时间变化的曲线可作为监测和判断绕组变形的依据。

主权项

1.一种V/X接线牵引变压器短路电抗在线监测的方法，其特征在于按照如下步骤进行测试：第一步：在α供电臂负馈线电流为0.9至0.95倍额定电流和0.95至1.0倍额定电流两个时段，分别以大于4000次/秒的采样频率记录变压器高压侧各相的电压和电流、α供电臂的正馈线和负馈线的电压和电流各10个工频周期的波形，据此，求得两个时段高压侧A、B两相之间的线电压向量A相电流向量正馈线电压向量正馈线电流向量负馈线电压向量负馈线电流向量通过下式计算拟从高压侧A、B端测试的短路电抗(x_kAB)的初步测试值，$x_{\mathrm{kAB}}=\left\{\right[\mathrm{Re}\left(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(2\right)}-{K{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}\right)\mathrm{Re}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}\right)-\mathrm{Im}\left(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(2\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}\right)\mathrm{Im}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}\right)$$-\mathrm{Re}\left(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(1\right)}-{K{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}\right)\mathrm{Re}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}\right)+\mathrm{Im}\left(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(1\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}\right)\mathrm{Im}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}\right)]\mathrm{Re}(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})$$-[\mathrm{Im}\left(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(2\right)}-{K{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}\right)\mathrm{Re}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}\right)+\mathrm{Re}\left(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(2\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}\right)\mathrm{Im}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}\right)-$$\mathrm{Im}\left(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(1\right)}-{K{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}\right)\mathrm{Re}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}\right)+\mathrm{Re}\left(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(1\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}\right)\mathrm{Im}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}\right)\left]\mathrm{Im}(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})\right\}/$$[\mathrm{Re}{(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})}^2+\mathrm{Im}{(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})}^2]+K\{\mathrm{Im}(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(1\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(2\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})$$\times \mathrm{Re}(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})-\mathrm{Re}(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(1\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(2\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})\mathrm{Im}(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})\}/$$[\mathrm{Re}{(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})}^2+\mathrm{Im}{(\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})}^2]+K\{\mathrm{Im}(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(1\right)}+K{{\stackrel{·}{U}}_{\mathrm{F\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(2\right)}+K{{\stackrel{·}{U}}_{\mathrm{F\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})$$\times \mathrm{Re}(\frac{{{\stackrel{·}{I}}_{\mathrm{F\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{F\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}})-\mathrm{Re}(\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(1\right)}+K{{\stackrel{·}{U}}_{\mathrm{F\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}}-\frac{{\stackrel{·}{U}}_{\mathrm{AB}}^{\left(2\right)}+K{{\stackrel{·}{U}}_{\mathrm{F\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}})\mathrm{Im}(\frac{{{\stackrel{·}{I}}_{\mathrm{F\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{F\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}})\}/$$[\mathrm{Re}{(\frac{{{\stackrel{·}{I}}_{\mathrm{F\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{F\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}})}^2+\mathrm{Im}{(\frac{{{\stackrel{·}{I}}_{\mathrm{F\alpha }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_A}^{\left(2\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{F\alpha }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_A}^{\left(1\right)}})}^2]$式中，K为比例系数，V/X接线牵引变压器出厂时给出，也可用仪器测得。第二步：在β供电臂负馈线电流为0.9至0.95倍额定电流和0.95至1.0倍额定电流两个时段，分别以大于4000次/秒的采样频率记录变压器高压侧各相的电压和电流、β供电臂的正馈线和负馈线的电压和电流各10个工频周期的波形，据此，求得两个时段高压侧C、B两相之间的线电压向量C相电流向量正馈线电压向量正馈线电流向量负馈线电压向量负馈线电流向量通过下式计算拟从高压侧C、B端测试的短路电抗(x_kCB)的初步测试值，$x_{\mathrm{kCB}}=\left\{\right[\mathrm{Re}\left(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(2\right)}-{K{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}\right)\mathrm{Re}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}\right)-\mathrm{Im}\left(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(2\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}\right)\mathrm{Im}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}\right)$$-\mathrm{Re}\left(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(1\right)}-{K{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}\right)\mathrm{Re}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}\right)+\mathrm{Im}\left(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(1\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}\right)\mathrm{Im}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}\right)]\mathrm{Re}(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})$$-[\mathrm{Im}\left(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(2\right)}-{K{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}\right)\mathrm{Re}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}\right)+\mathrm{Re}\left(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(2\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}\right)\mathrm{Im}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}\right)-$$\mathrm{Im}\left(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(1\right)}-{K{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}\right)\mathrm{Re}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}\right)+\mathrm{Re}\left(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(1\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}\right)\mathrm{Im}\left(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}\right)\left]\mathrm{Im}(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{C\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})\right\}/$$[\mathrm{Re}{(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})}^2+\mathrm{Im}{(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})}^2]+K\{\mathrm{Im}(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(1\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(2\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})$$\times \mathrm{Re}(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})-\mathrm{Re}(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(1\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(2\right)}-K{{\stackrel{·}{U}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})\mathrm{Im}(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})\}/$$[\mathrm{Re}{(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})}^2+\mathrm{Im}{(\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{T\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})}^2]+K\{\mathrm{Im}(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(1\right)}+K{{\stackrel{·}{U}}_{\mathrm{F\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(2\right)}+K{{\stackrel{·}{U}}_{\mathrm{F\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})$$\times \mathrm{Re}(\frac{{{\stackrel{·}{I}}_{\mathrm{F\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{F\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}})-\mathrm{Re}(\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(1\right)}+K{{\stackrel{·}{U}}_{\mathrm{F\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}}-\frac{{\stackrel{·}{U}}_{\mathrm{CB}}^{\left(2\right)}+K{{\stackrel{·}{U}}_{\mathrm{F\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}})\mathrm{Im}(\frac{{{\stackrel{·}{I}}_{\mathrm{F\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{F\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}})\}/$$[\mathrm{Re}{(\frac{{{\stackrel{·}{I}}_{\mathrm{F\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{F\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}})}^2+\mathrm{Im}{(\frac{{{\stackrel{·}{I}}_{\mathrm{F\beta }}}^{\left(2\right)}}{{{\stackrel{·}{I}}_C}^{\left(2\right)}}-\frac{{{\stackrel{·}{I}}_{\mathrm{F\beta }}}^{\left(1\right)}}{{{\stackrel{·}{I}}_C}^{\left(1\right)}})}^2]$式中，K的取值与第一步相同。第三步：重复第一、第二步共n次，n不小于20，得到两组初步测试数据，针对每组数据，分别根据其相对标准偏差剔除误差较大的数，即当相对标准偏差大于或等于0.2％时，去掉与平均值差距最大的数，按照这个方法不断去除误差最大的数，直至相对标准偏差小于0.2％为止，若去掉数据的量小于n/4，则剩余数据的平均值即为本次监测的短路阻抗值，否则，认为由于测试误差较大，放弃本次监测。