Contribuições na Aplicação da Análise da Assinatura Elétrica para Detecção de Falhas em Geradores Síncronos.

Geradores síncronos são elementos fundamentais dos sistemas elétricos de potência. Desta forma, o monitoramento contínuo destas máquinas, incluindo a detecção precoce de falhas, torna-se imperativo para garantir a confiabilidade do fornecimento de energia, a estabilidade do sistema e a redução de prejuízos causados por paradas não-programadas. No contexto de manutenção preditiva de máquinas rotativas, tem se destacado a utilização da análise da assinatura elétrica (ESA - Eletrical Signature Analysis), que consiste basicamente na análise dos sinais elétricos da máquina sob monitoramento no domínio da frequência. Este trabalho apresenta contribuições na aplicação de ESA para a manutenção preditiva de geradores síncronos, considerando-se aspectos práticos. O trabalho abrange as particularidades da aplicação de ESA para geradores síncronos com rotor de polos salientes e polos lisos. As principais contribuições deste trabalho são a proposição de uma metodologia para distinção de falhas rotóricas de origem elétrica e de origem mecânica nas componentes espectrais e a aplicação de ESA a geradores interligados no sistema elétrico de potência. As hipóteses levantadas são abordadas através de análise teórica, resultados experimentais em laboratórios de modelo reduzido e análise de sinais de grandes geradores em operação em usinas

Integrating Smart Grid Devices into the Traditional Protection of Distribution Networks

Smart grids are a reality in distribution systems. They have assisted in the operation, control, and most of all, the protection of urban networks, significantly solving the contingencies of these networks. This paper treats the initial stage of implementing smart grid switching devices in distribution networks. In this stage, smart grid technologies need to operate with the traditional protection elements (such as fuses, reclosers, and sectionalizers). This fact can create trouble in the protection schemes because there are two distinctive philosophies. In some companies, especially those without substantial capital, these two protection philosophies can run together for many years. The most popular intelligent electronic devices (IEDs) available in the market are studied to verify their features and the possibility to incorporate techniques to allow the two philosophies to work together. After that, the proposed approach shows how the existing IEDs can interact with the traditional devices. Special functions can also be incorporated to inform the control center of an operational problem, increasing the observability of the network. With the proposed approach, the IEDs are transformed into intelligent agents. Practical examples using real distribution systems are presented and discussed, proving the efficacy of the proposed methodology

Comparison among Methods for Induction Motor Low-Intrusive Efficiency Evaluation Including a New AGT Approach with a Modified Stator Resistance

Induction motors consume a great portion of the generated electrical energy. Moreover, most of them work at underloaded conditions, so they have low efficiencies and waste a lot of energy. Because of this, the efficiency estimation of in-service induction motors is a matter of great importance. This efficiency estimation is usually performed through indirect methods, which do not require invasive measurements of torque or speed. One of these methods is the modified Air-Gap Torque (AGT) method, which only requires voltage and current data, the stator resistance value, and the mechanical losses. This paper approaches the computation of a modified stator resistance including the mechanical losses effect to be applied in the AGT method for torque and efficiency estimation of induction motors. Some improvements are proposed in the computation of this resistance by using a direct method, as well as the possibility to estimate this parameter directly from the nameplate data of the induction motor. The proposed methodology only relies on line voltages, currents, and nameplate data and is not intrusive. The proposed methodology is analyzed through simulation and validated through experimental results with three-phase induction motors. Also, a comparison of methods for in-service induction motors efficiency estimation is presented for the tested motors

A Study of Fault Diagnosis Based on Electrical Signature Analysis for Synchronous Generators Predictive Maintenance in Bulk Electric Systems

The condition of synchronous generators (SGs) is a matter of great attention, because they can be seen as equipment and also as fundamental elements of power systems. Thus, there is a growing interest in new technologies to improve SG protection and maintenance schemes. In this context, electrical signature analysis (ESA) is a non-invasive technique that has been increasingly applied to the predictive maintenance of rotating electrical machines. However, in general, the works applying ESA to SGs are focused on isolated machines. Thus, this paper presents a study on the condition monitoring of SGs in bulk electric systems by using ESA. The main contribution of this work is the practical results of ESA for fault detection in in-service SGs interconnected to a power system. Two types of faults were detected in an SG at a Brazilian hydroelectric power plant by using ESA, including stator electrical unbalance and mechanical misalignment. This paper also addresses peculiarities in the ESA of wound rotor SGs, including recommendations for signal analysis, how to discriminate rotor faults on fault patterns, and the particularities of two-pole SGs