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

Abstract

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 10 Ω can 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.

Keywords

• medium and low voltage cables
• metal shielding
• loop resistance
• live test
• different frequency coupling
• connection status