A robust framework for cable rating and temperature monitoring

This paper introduces a robust framework for the temperature monitoring of power cables based on real-time current measurement only, or current measurement in conjunction with cable surface or sheath temperature measurement. The method is based on modeling the temperature response of a cable by summing an appropriate number of exponential functions. These functions are related to a thermal ladder circuit for installations that can be analyzed in such terms, or are mathematically fitted to numerically simulated results for those that cannot. The robustness of the method stems from the fact that exponential functions can be easily rendered into an inherently stable real-time formulation depending on the temperatures calculated at the previous increment and final conditions. The hypothetical final conditions are established at each time interval by simple steady-state calculations based on the present temperatures. This allows entry into territory that is forbidden for normal superposition methods, namely, a thermally unstable environment. Despite erroneous initial conditions, the algorithm will converge and it has the added merit of being extremely light, computationally speaking. The method provides an alternative method for transient cable rating, is inherently suited for real-time implementation, and provides a framework that can accommodate a changing thermal environment caused by, for example, such a phenomenon as moisture migration.