An Analytical Evaluation of the Prospective ${\rm I}^{2}{\rm t}$ to Assess Short-Circuit Capabilities of Cables and Busways

At the occurrence of three-phase or single-phase faults, abnormal levels of thermal energy are developed during the time taken by protective devices to clear them. By conservatively assuming an adiabatic process, all of the thermal let-through energy I²t, also referred to as Joule Integral, is accumulated within the components involved in short circuits; therefore, the temperature of their conductive materials is elevated. The thermal energy is proportional to the square of the short-circuit current. Evaluating the prospective I²t is, therefore, crucial in order to assess the short-circuit capability of cables and busways to withstand the thermal stress without failing or triggering fires in neighboring materials. In this paper, in the general case of resistive-inductive circuits, methods to evaluate the Joule Integral and to perform the assessment will be provided. The differences for power frequencies of 50 and 60 Hz are also shown.