Impact of Harmonic Current on Residual Current Devices Performance in a Steel Making Plant

Unfortunately, it is impossible to root out faults within an electrical power system regardless its complexity. Nevertheless, it is possible to minimize the detrimental implications generated by faults by setting up an accurate protection system. Nowadays, due to the widespread usage of non-linear devices, figuring out the more suitable protection device for this kind of load has become a challenge for electrical engineers across the world, especially concerning low-voltage systems. Most commonly, residual current devices (RCD) are used to protect low-voltage devices. Nonetheless, the behavior of RCDs might be affected by non-linear loads because of harmonic components. Consequently, a false trip command might be sent out, resulting in the disconnection of important loads, significant costs, and, most importantly, jeopardizing the lives of people. The purpose of this paper is to evaluate the performance of RCDs at high frequencies caused by harmonic components. Firstly, it is evaluated a real situation that has taken place in a steel-making plant in Brazil. Secondly, an IEC Type B protection relay is set up aimed to protect non-linear loads. Thirdly, is made a comparison, in terms of performance, between an IEC Type A and IED type B relay. Finally, it is proved that the IEC Type B relay is a suitable protection device for non-linear loads.