Avaliação didática de falta à terra em serviços auxiliares de corrente contínua em subestações de alta tensão

Abstract

Auxiliary services are categorized by the nature of the electrical current in which they operate, either alternating or direct current, or by the importance of the loads they supply, either normal or essential, respectively. This hierarchy exists because some of these loads can never be disconnected, otherwise the operation of the substation would become unfeasible. During the normal operation of a substation, electric current rectifiers are the primary feeders of the essential loads, however, when in an emergency state, where the supply of alternating current is interrupted, are installed in parallel to the system, banks of batteries, which can provide power to essential loads until the fault is resolved. The discharge of electrical current through contact of the conductor material with the ground is called a ground fault, and is a common occurrence in high voltage substations. In DC auxiliary services, this type of fault affects a vital part of the system. As a conclusion of this research, it was possible to model the electrical circuits with satisfactory results, in a didactic way, corresponding to the DC system for analysis of nominal currents and voltages. It was found that the characterization of ground faults in these circuits was determined by the increase in electrical currents and, consequently, the reduction in electrical voltage. Additionally, it was observed that faults near the DC system source present the worst fault scenarios, as this is the scenario in which the voltage is reduced more abruptly, due to the lower equivalent resistance in the system.