New approach of maintenance of power transformers and main accessories: off-line test vs. on-line monitoring systems

摘要

When a utility is thinking about the task of define the strategy to follow in the maintenance of its Power Transformers (PT), one of the most important decision is to define the diagnosis techniques to implement, it's necessary to decide between off-line tests or online monitoring systems. The paper will show different strategies follow in Spain at different utilities. The first contribution will explain the point of view of Iberdrola Distribucion Electrica (IBD). The paper will explain the way follow at IBD from conventional diagnosis techniques of PTs (Time Based Maintenance) to modern on-line monitoring systems and showing how both are complete compatible, and how all the strategy is based on "management of information". The second contribution will give the point of view of Red Electrica de Espana (REE), the Spanish TSO. REE has decided not to install on-line monitoring systems as a standard in the grid transformer fleet. The maintenance is based mainly on off-line techniques and dissolved gas and oil quality analysis. However, two different kinds of on-line monitoring systems have been developed for special applications. The third contribution come from Iberdrola Power Generation (IPG) and will describe its strategy and experiences of Power Transformers Predictive Maintenance and Condition Assessment, mainly of Generator Step - Up Transformers (GSU) to different generation technologies where, as another important issue in order to avoid unscheduled outage and transformer incidents, describes the importance of a close chase of all transformer life cycle steps: definition, acceptance operation and maintenance. Regarding Maintenance Management strategy and as a result of the nature of its main activity, it is established in a different scenario, where there are human resources in most the power stations and scheduled outages allows periodical visual checks, oil samples and deeper predictive maintenance and condition assessments evaluations through electrical testing. However, On-Line Monitoring is also consider as the near future way for maintenance and human resources optimization, but in this scenario, at least in the first place, test to select might be more oriented to incipient fault detection than transformer condition assessment. The last contribution will show the view of Endesa Distribucion Electrica (EDE). The paper explains EDE's experiences using off-line maintenance techniques and on-line monitoring techniques. On one hand, off-line are a well known group of traditional techniques based in many years of experience, which good results are contrasted. On the other hand, on line monitoring techniques put in practice in EDE are in testing period, in order to check its effectiveness. One important thing is to show up that both techniques have its contribution in PT's maintenance.