SIGMA – Efficiency On-line Monitoring Sub-system Cooling System Efficiency
Appropriate cooling of a transformer is fundamental for its safe operation to prevent the acceleration in the loss of useful insulation life, in the presence of high loading. Therefore, it is essential that the natural and forced cooling equipment, such as radiators, fans and oil pumps, should be in perfect working order, efficiently dissipating heat generated by internal losses. The total or partial failure (reduction in efficiency) of the cooling equipment can cause the activation of the transformer temperature protection or limit the transformer loading, making it totally or partially unavailable.
SIGMA Efficiency Monitoring Sub-system is a software module, which together with the Treetech Temperature Monitors TM1 and TM2, carries out monitoring of the cooling system efficiency, detecting reduced efficiency based on a comparison of measured temperatures with expected equipment temperatures. Should the measured temperature be well above the expected values, warnings are initiated, allowing measures to be taken, avoiding more serious problems, as well as actions to avoid or reduce over-heating, for example, switching on the forced cooling in advance (automatically or manually), redistributing the loading, etc. The expected temperatures are calculated as a function of the existing conditions of load currents, ambient temperatures and the thermal and electrical characteristics of the transformer as determined generally at the heat run test, such as temperature gradients, load and no-load losses, weights and oil volume.
SIGMA Efficiency permits remote access to on-line diagnostics and prognostics and to historical data, stored in data banks. Remote access is avaiable 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.