Operation-State Monitoring and Energization-Status Identification for Underground Power Cables by Magnetic Field Sensing

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Abstract
In this paper, a novel nondestructive method based on magnetic field sensing is proposed for underground power cable operation-state monitoring and energization-status identification. The magnetic field distribution of the cable is studied using finite element method (FEM) for the power cable operating in different states, i.e., current-energized state (the cable is energized and carries load current) and voltage-energized state (the cable is energized but carries no load current). This innovative method can reconstruct all the source parameters of the cable based on a set of measured magnetic field values. Stochastic optimization technique is applied to realize the reconstruction based on the measured magnetic field. The technology is developed with an artificial immune system algorithm that is able to find out the global optimum with high probability even if very little knowledge about objective function is provided. Application of this method is demonstrated on an 11 kV cable with metallic outer sheath. The results highly match with the actual source parameters of the cable. For application in practice, possible limitations introduced by the nonidealistic of magnetoresistive sensor on magnetic field measurement are discussed and corresponding solutions are suggested. An experimental setup is constructed and the test results are used for the demonstration of this method. This paper shows that the proposed method is able to monitor the operation states of an underground power cable with high accuracy. Engineers can also correctly identify the energization status of the target cable during onsite maintenance. This method is adaptable to other kinds of power cables simply by updating the geometrical and material parameters of the cable in the FEM computation. Moreover, this is an entirely passive method and does not need any active signal injection into the cable.

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