SIGMA – Chroma On-line Monitoring Sub-system Dissolved Hydrogen, Chromatographic and Physical-chemical Tests
Gases dissolved in oil is recognized as one of the best indicators of the internal condition of transformers and reactors, and the analysis of the gas content of oil was largely propagated as a diagnostic tool for this equipment. This resulted in the development of a broad knowledge base and diverse techniques, to analyse the condition of the transformers.
Traditionally, the measurement of these gases is carried out by the extraction of a sample of oil for chromatographic analysis in a laboratory, reading the concentration of each gas separately with good accuracy. However, this process is generally carried out every few months, which leaves an interval, during which, the equipment is not monitored, allowing defects to evolve during this period to cause a serious transformer failure.
SIGMA Chroma Monitoring Sub-system is a software module that, together with the Treetech Gas Monitor GMP, can prevent this, it will store and analyse the data received from laboratory tests, with recognised techniques (for example: IEEE, IEC, Roger, Dornemburg, Duval, among others). The sub system will also carry out the on-line monitoring of hydrogen concentration in the oil. Hydrogen produced is considered a key gas for the detection of early problems in transformers. Whilst the individual measurement of hydrogen does not provide information about the exact type of defect, the detection of an increase in its concentration can indicate, immediately, the need for a chromatographic laboratory analysis.
The SIGMA Chroma provides the following information:
- The actual concentration of hydrogen in the oil, in ppm;
- The rate of change in the hydrogen concentration, in ppm/day;
- The results of chromatographic analyses carried out during the transformer’s life, stored in data banks. The analysis results are inserted manually into the system, by the user, or imported in a standard formatted file;
- Diagnoses obtained during the transformer’s life based on various analysis techniques, stored in data banks.
The SIGMA Chroma allows remote access to on-line measurements of hydrogen and to historical data, as well as, the results of chromatographic analysis and diagnostics obtained and stored in data banks. Remote access is carried out over the Intranet or Internet network, using a standard Internet browser. The system can also send alert messages by e-mail or text messaging to mobile phones (SMS) when the system diagnoses an abnormal condition, freeing operators from the need for permanent supervision of the system.
SIGMA Monitoring Systems and Sub-systems architecture
The SIGMA monitoring system is based on a Decentralized and Modular architecture, in which Intelligent Electronic Devices (IEDs) are used as sensors (data sources) interconnected to the SIGMA monitoring system over a communication network. Frequently these IEDs are pieces of equipment that are essentially used in transformers in protective, supervisory and control functions, supplying information to the monitoring system through one of their serial ports. This makes centralizing units at the body of the transformer unnecessary; this architecture eliminates the necessity for specific sensors, resulting in a significant reduction in the cost of the system. This is the case with SIGMA Ageing Sub-system, as shown in the diagram.
SIGMA monitoring software, obeying the same philosophy as the Treetech IEDs, is composed of independent and scalable modules called Sub-systems, allowing the user to build their own monitoring system, according to their needs. As such, the Treetech modular systems allow the monitoring of small-scale transformers, eliminating the financial barriers that previously limited the application of monitoring systems to large-scale equipment only.