中低压电力电缆金属屏蔽接续状态带电测试技术

Live test technology for metal shielding of medium andlow voltage power cables in continuous state

现有中低压电力电缆线路金属屏蔽连接不良时需要线路停役,测试周期长且效率低,针对该问题,提出电缆金属屏蔽接地引线带电测试金属屏蔽电阻的方法。利用异频耦合测试电缆金属屏蔽感应电压和电流,运用电磁感应及欧姆定律构建方程计算电缆金属屏蔽回路或支路电阻,并通过电阻大小判断金属屏蔽连接状态。经实验室模拟测试发现,在不改变原有接地状态时,测试所得电缆金属屏蔽电阻参数与实际一致。单回路电缆线路受地网影响无法检测判别10Ω电阻以下的电缆金属屏蔽连接状态,而双回路及以上电缆线路检测不易受地网影响,可通过回路电阻、支路电阻与理论值比较,或支路电阻相互比较判断电缆金属屏蔽的连接状态。检测技术经工程应用表明,采用异频法带电检测金属屏蔽电阻,进而判断中低压电缆金属屏蔽连接状态的方法具有可行性。

The defects of poor metal shielding connection of medium and low voltage cable lines are tested for a long time,which requires the lines are out of service.A method to measure the resistance of cable metal shield circuit by using different frequency coupling is presented.Combined with electromagnetic induction law and Ohm′s law,the circuit resistance or branch resistance is calculated by constructed simultaneous equations,which is used for judging the connection state of metal shielding.Through laboratory simulation test,it is found that the test cable metal shielding resistance parameters are consistent with the actual values when the original grounding state is not changed.The connection state of cable metal shielding with resistance below 10Ωcan not be detected and judged for single-circuit cable lines.While double-circuit and above cable lines are not easy to be affected by the grounding grid,and the connection state of cable metal shielding can be judged by comparing the circuit resistance and branch resistance with theoretical value,or by comparing the branch resistance with each other.The detection technology is verified by the engineering application,which is effective and feasible to judge the metal shielding connection state for medium and low voltage cables.