一种附加阻抗法在测量配电网电容电流中的应用

Application of an Additional Impedance Method in Measuring Capacitance Current of Power Grid

针对中性点不接地方式的系统,提出了一种在配电网电容电流实时测量应用中的方法—附加并联阻抗法,即在系统的任意一相投入附加阻抗。在保持中性点位移电压的幅值低于最大允许值(低于相电压15%)的同时,对两次简单的电阻值和附加电感量进行变动。从而测量出不同的中性点位移电压的幅值。为了精确地得到系统绝缘电阻和对地分布电容,可用相应的附加电感、电阻和测得的中性点位移电压的幅值进行求解。最后对配电网的对地电容电流进行计算。并且给出了基于PSCAD软件对6 kV配电网中性点不接地系统的仿真计算结果。从而验证了本方法的可行性,并且具有很高的测量精确度。因为对中性点电压与其他量之间的相位关系可以不予考虑,所以,具有测量范围广和测量简单、能够应用于电网绝缘参数的测量,以及附加阻抗对系统的正常运行影响小的优点。

For the system with neutral ungrounded mode,an additional parallel impedance method is proposed in the application of capacitive current real-time measurement in power grid,in which the additional impedance is put into any phase of the system.While keeping the magnitude of the displacement voltage at the neutral point below the maximum allowable value(below 15%of the phase voltage),two simple resistances and additional inductances are changed.The amplitude of displacement voltage at different neutral points is measured.In order to accurately obtain the system insulation resistance and the distributed capacitance to the ground,the corresponding additional inductance,resistance and the measured neutral point displacement voltage amplitude can be used to solve the problem.Finally,the ground capacitive current of distribution network is calculated.The simulation results of 6 kV distribution network neutral grounding system based on PSCAD software are given.The feasibility of this method is verified,and the measurement accuracy is very high.Because the phase relationship between neutral point voltage and other variables can not be considered,it has the advantages of wide measurement range and simple measurement,and it can be applied to the measurement of insulation parameters of power grid.The additional impedance has little impact on the normal operation of the system.