As explained in section 2.0, the system as it was initially deployed in Eletrosul used a viewing software to remotely access the data. This viewing software had to be installed in each user’s remote computer.

This solution, while functionally perfect, was inconvenient in some aspects, such as limiting access to the system to previously prepared computers, the waste of computer engineer time to install the viewing software for the users and also to download the necessary updates.

To avoid these inconveniences, and in line with the most modern cloud-computing trends, in which the applications are executed only in remote servers, using as local interface only the internet browser, the Sigma monitoring interface has been updated to use the so called Web 2.0 technologies.

Thus, there is no longer need to install specific software on users’ computers; the users now use only their internet browser. Therefore, any upgrades to the system are restricted to the monitoring servers, and do not affect the user computers. The access to the system is possible from any computer in the Eletrosul Intranet, as long as the user has a user ID and a password.

System access security can be preserved through the cryptographed connection protocol HTTPS, in addition to the login and password to access the system.

In order to reduce the cost and facilitate the installation of monitoring systems, the feasibility of using wireless communications between sensors on the transformer and the substation control room has been verified by a pilot in Santo Ângelo substation, at the time the system was installed in a transformer bank, using the Wi-fi standard.  Gas sensors which were already in place were integrated as well as new bushing capacitance and tangent delta monitors.  Data are directly transmitted to a router connected to the corporate network and acquired by the Sigma 4 software.

The application performance proved entirely satisfactory, demonstrating the feasibility of this technology with great potential to reduce costs and installation time.

The open and modular architecture of the monitoring system has also allowed the inclusion of a new engineering item for loading simuation. The simulation is possible in two ways:

• Based on current load conditions at ambient temperature, with the user inserting the new hypothetical loading value;
• Based on hypothetical load evolution curves and ambient temperature in 24 hours.

In both modes the user can see the consequences of hypothetical situations in terms of temperatures reached and loss of life related, and can compare the maximum temperature that would be achieved with the temperature of bubble formation due to moisture, also calculated by the monitoring software. In all simulations, the user can modify the cooling command mode (automatic or manual) and the enabling temperatures, as well as the cooling hysteresis.

The evolution of the Sigma monitoring systems has provided them with a capability to exchange data with other Eletrosul systems, such as the SAGE supervising system.

This connectivity is possible through different methods, selected according to the need and convenience of the application. Examples of possibilities are SQL databases or, in other standards, OPC, web services, open communication protocols (eg Modbus, DNP 3.0, TCP / IP), among others.

The use of automated online monitoring of transformers and reactors has several features that may be beneficial for the maintenance of that kind of equipment, such as reducing risk of catastrophic failure, controlling and extending service life, migrating from preventive to predictive maintenance, with the consequent increase in the availability of the equipment and reduction of the costs due to lack of equipment availablity, among others.

However, the monitoring system is presented as a useful tool not only for maintenance engineering but also for the operation and planning, due to loading simulation and prediction of future temperature as a function of current load, associated with equipment status diagnoses, which provide an indication of the risk to use overloaded equipment, for example.

Another example of the usefulness of the monitoring system could be observed when a 245 kV bushing failed in the Santo Ângelo substation. In this case, the evolution of the bushing defect was extremely fast, leaving no time to remove it from operation before failure, unlike what is normally expected for defects in bushings [6]. However, the presence of the monitoring system with the storage of measurements in databases allowed further analysis of the occurrence, leading to conclusions that would be impossible without the monitoring system – like the fact that the defect evolved very quickly.

Therefore, the monitoring system allowed the technicians to deepen their knowledge about the evolution of this type of defect and to improve the system itself and the procedures when this kind of defect takes place.

This paper has presented the history of installation, expansion, customization and operation of the Sigma monitoring systems in Eletrobras Eletrosul, as well as the evolution of this system over time, including the architectures used to install sensors on the equipment, data output architectures, communication media and user interfaces.

The results obtained were presented as well as the benefits gained with the developments and improvements of the system over time, mostly allowed by Sigma’s open, decentralized and modular architecture.

Considering the importance of transformers and reactors in the Eletrosul park for the SIN, the installation of the online monitoring system for that equipment, as well as the possibility of the system evolution and of its uses over time is of great significance to increase the electric power system reliability and the supply continuity, in addition to contributing to cost reductions that help to reduce rates.

1. Amom, Jorge, Alves, Marcos, Vita, André, Kastrup Filho, Oscar, Ribeiro, Adolfo, et. al., “Sistema de Diagnósticos para o Monitoramento de Subestações de Alta Tensão e o Gerenciamento das Atividades de Manutenção: Integração e Aplicações”, X ERLAC – Encontro Regional Latinoamericano do CIGRÉ, Puerto Iguazu, Argentina, 2003.
2. Alves, Marcos, “Sistema de Monitoração On-Line de Transformadores de Potência”, Revista Eletricidade Moderna, Maio/2004.
3. Alves, Marcos, “Field Experience with On-Line Monitoring of Two 150MVA 230kV Transformers with On-Load Tap Changers”, Cigre SC A3 International Technical Colloquium, September/2007.
4. Vasconcellos, M. Alves, “Especificação de Sistemas de Monitoração On-line para Transformadores de Potência Baseados em uma Arquitetura Descentralizada”, V Workspot, Brasil, Abril 2008.
5. Lavieri Jr., Arthur, Hering, Ricardo, “Novos Conceitos em Sistemas de Energia de Alta Confiabilidade”, Encarte Especial Siemens Energia, http:// mediaibox.siemens.com.br/upfiles/232.pdf, Janeiro/2001.
6. Melo, Marcos A. C., Alves, Marcos, “Experiência com Monitoração On-Line de Capacitância e Tangente Delta de Buchas Condensivas”, XIX SNPTEE – Seminário Nacional de Produção e Transmissão de Energia Elétrica. Rio de Janeiro, Brasil, 2007.