Experimental Validation of the Adiabatic Assumption of Short-Circuit Tests on Bare Conductors

According to various international standards, many high-voltage devices must withstand short-circuit tests. Due to the enormous power and current requirements, they have to be tested in very specialized and expensive power laboratories, which are scarce and not affordable for the vast majority of electrical product manufacturers. It is proposed to break the time limit of about one second imposed by the standards by using a lower current to heat for a longer time, requiring more affordable equipment and thus reducing the cost for testing. This work analyzes the limits of the adiabatic assumption in short-circuit tests in order to quantify how the duration of these tests can be extended to reduce the power required and the current applied, while obtaining almost the same results, i.e., the same temperature at the end of the heating phase of the tests. For this purpose, bare cylindrical conductors are analyzed and the temperature dependence of the properties of the conductor material is considered. Experimental and simulation results presented in this paper suggest that by applying this approach, short-circuit tests intended for product design, verification and quality control can be performed in much less demanding and affordable laboratory facilities.

I. Introduction

Power systems are experiencing a steady growth worldwide, thus leading to an increase in short-circuit levels [1], [2], [3]. Short-circuits are among the most common fault modes in electrical networks, and are complex electromagnetic transient phenomena that have received much attention in the scientific field [4]. Short-circuits are considered damaging fault modes, because they can cause severe thermal and mechanical stress on the components involved [5], [6], thus increasing the risk of power system failure [7]. Because of their damaging effects, electrical protections must clear short-circuit faults as quickly as possible. However, electrical protection devices take some time to clear short-circuits, tend to generate particularly high temperatures [8] and have the potential to produce powerful faults [9], so electrical protections play a critical role in ensuring that short-circuit currents do not cause irreversible damage to the electrical equipment involved.