整流器中点对绝缘监测的影响及其解决措施

在IT系统内,整流器二极管导通电压变化、直流侧线路对地绝缘电阻不对称下降,将造成整流器中点对地电压不平衡,直流电流经过大地流入交流系统中性点,从而造成基于直流注入法的绝缘监测装置(IMD)误报警或漏报警。通过分析,可将中点对地电压等效为一个作用于原系统直流阻抗网络的戴维南模型,进而推导出整流器中点对IMD的影响机理。同时,提出改变注入信号方向的思路,分别记录正反向两次注入信号时所监测的绝缘电阻值,对记录结果进行处理,可以得到真实绝缘电阻值。最后通过实验验证了理论分析的正确性。

Effects of neutral-point of rectifier on Insulation monitoring and its solution

In IT system, It will cause the neutral-point voltage of rectifier unbalance when conduction voltage of diode changes or the DC side line-to-ground insulation resistance decline asymmetrily,then DC current will flows into the neutral point of the AC system through the earth, which makes IMD that based on DC injection false or missing alarming. Through analysis, the neutral-point voltage to ground of rectifier can be equivalent to a Thevenin model ,Which can act on the DC impedance network of the original system,then derive the mechanism of neutral-point voltage on IMD,meanwhile,the idea of change injection signal direction are present,record the insulation resistance value in forward and reverse way,the real insulation value can be calculated after processing the record.Finally,experiment results validate the proposed scheme.