Equivalent Thermal Conductivity of Metallic-Wire for On-Line Monitoring of Power Cables

Abstract

The usage of advanced cable thermal model enhanced by adequate on-line monitoring technologies is one of emerging requirements in smart grid implementation to overcome the conservativeness in the cable rating and permitting correct operation in all circumstances. The current commercially available on-line thermal analysis systems employ the traditional IEC-based method, which is far less accurate than the more robust finite-element method, especially in presence of complex cable configurations and surrounding media. This paper presents an innovative theoretical and computational procedure, which overcomes a major obstacle in using the finite-element method for on-line monitoring of power cables. The procedure is based on replacing the metallic-wire layer in the cable, which requires extensive modeling and significant processing time, by an equivalent thermal conductivity, which is theoretically derived and verified in this paper. This equivalent formula can be incorporated in the finite-element model and, therefore, avoid allocating significant number of finite-element mesh elements associated with the metallic-wire. This is particularly important when many operating scenarios have to be analyzed by the on-line monitoring system in the real time frame. The proposed model provides precise modeling and timely efficient calculation of cable ampacity on the actual occurring conditions of ambient, soil and environment as captured in real-life by the installed sensors. Practical applications to actual cable systems is presented which have shown substantial reduction in the computational time.