基于两端宽频零序电压幅值比的三芯电缆绝缘老化评估方法

Insulation Aging Evaluation Method of Three-core Cable Based on the Amplitude Ratio of Wide-band Zero Sequence Voltage at Head and Tail Ends

工频条件下三芯电缆绝缘监测信号微弱,难以判断电缆绝缘老化水平,为实现三芯电缆的绝缘在线监测,提出基于首末端宽频零序电压幅值比的三芯电缆绝缘评估方法。该方法通过首末端零序电压幅值比计算电缆绝缘层的相对介电常数,以规避各相线芯、金属屏蔽层和护套之间的耦合影响。首先建立三芯电缆零序网络的分布式频变参数模型,推导首末端零序电压幅值比与相对介电常数的数学联系,并根据宽频量测数据,利用最小二乘法求解相对介电常数。PSCAD仿真结果表明所推导的表达式能正确反映电缆首末端零序电压幅值比随频率的变化关系,相对介电常数求解结果验证了所述方法的正确性和有效性。

The insulation monitoring signal of the three-core cable is weak under power frequency condition,and it is difficult to judge the insulation aging level of the cable.In order to realize online insulation monitoring of the three-core cable,this paper proposes a method for insulation evaluation of the three-core cable based on the amplitude ratio of wide-band zero sequence voltage at the head and end which calculates the relative dielectric constant of the cable insulation layer through the amplitude ratio of zero sequence voltage at the head and end to avoid coupling effect between each phase core,the metal shielding layer and the sheath.Firstly,the paper establishes a distributed frequency dependent parameter model of three-core cable zero sequence network and derives the mathematical relationship between the amplitude ratio of zero sequence voltage at the head and the end and the relative dielectric constant.According to the wide-band measurement data,it uses the least square method to calculate the relative dielectric constant.The PSCAD/EMTDC simulation results show that the derived expression can correctly reflect the relationship between zero sequence voltage amplitude ratio at the head and end of the cable and the frequency,and the solution results of the relative dielectric constant verify the correctness and effectiveness of the proposed method.