Projeto e implementação de um sistema de detecção de faltas à terra em serviços auxiliares em corrente contínua

Abstract

The auxiliary DC power system is the most critical component of a protection, control and monitoring system. Any failure of the DC power system may render system protection devices unable to detect faults, secctionalizers and breakers unable to trip, etc. The auxialiary DC power system consist of battery array, battery charger, distribution system, switches, protective devices and monitoring equipment. Most of the auxiliary DC power systems are ungrounded. The primary intent of ungrounded systems is to keep system operating after first ground fault. This allow maintenance staff to find and correct the fault before a second ground fault occur on another bus. Detecting the presence of a ground fault is simple and several methods can be used such as indicator lights, voltmeters, voltage and current sensitive relays, etc. In high impedance ground faults current sensitive relays must be able to detect small current values in presence o high load current. Most of the methods for ground fault detection are nonselective that is, the faulted bus is detected but the fault could be anywhere in the network. Common methods of localization are fault isolation by network switching and circuit tracing using a signal injector and a portable sensor/detector. Network switching is the simplest method but the search process eliminate the continuity of the service. Circuit tracing using a superimposed signal is the preferred method for locating a fault since the continuity of the service is maintained. In both methods the search may be very difficult, time consuming and require well trained personel that are familiar whith the entire power system network. Detecting and locating a ground fault is still a challenge. The aim of this thesis is develop a intelligent system to detect and locate ground faults in auxiliary DC power systems. The proposed system is based on circuit tracing method and utilizes a superimposed signal and electromagnetic sensor deployed on the power system. These sensors are resonant filters magnetically coupled to the poles of auxiliary DC power system and they are reponsible to determine the circuit under fault.