Online Monitoring and Lifetime Estimations of Materials for Electrical Insulation

High voltage equipment has irreplaceable position in power generation, distribution and delivery. As high reliability is demanded, there is strong effort to keep continuous energy supply without any interruption caused by unplanned outages. Therefore monitoring systems and devices are involved to follow and describe the state of operated machinery and alert if unexpected situation occur. In case of electrical machines and transformers especially, the key part to monitor is the insulation subsystem of the machine. Various diagnostic parameters are to be monitored, e.g. loading, temperature, gas analysis, partial discharges activity, bushings condition, etc. The more parameters is obtained, the more precise may be the further actions. Of course for the most precise description of insulating system state it is necessary to include all available information. However the more parameters are monitored, the harder is to make a simple overview and future development prognosis and the more complex the matter gets. A simple, however widely applicable methodology of evaluation of these diagnostic parameters must be applied to perform simple description of operated object. The paper deals with the most important aspects of monitoring. The choice of diagnostic parameters and accessible points to measure is discussed. Further setting the criteria values and evaluation of diagnostic parameters with regards to material lifetime expectancy is described. As measured parameters are obtained, a simple methodology for evaluation with strong explanatory power is proposed. The field experience with such monitoring systems brings another trouble, which is false alarm alerts and the reliability of monitoring system itself, which is further discussed in the paper.