Background. Backup transformers are stored at power plants and grid companies to replace those that have failed. Transformers are on stand-by for 12–15 years or more. During storage, degradation of transformer nodes occurs despite the lack of connection, since water dissolved in oil affects the package plates, oxidizes the contacts of the on-load tap changing, low voltage (LV) terminals, etc. Due to current shortage of transformers, particular attention to the choice of informative methods for monitoring their condition is reasonable. The practical relevance of this study is the fact of disability of emergency failure of a new transformer after long-term storage.
Materials and methods. To analyze changes of transformer parameters after long-term storage, the following methods have been used: dependence of Rh(U), tgd(U); dependence of breakdown voltage in oil Upr(N); vibration phenomena on the turns of coils; transformer housing vibration tests.
Results. A study of the parameters of backup transformers has been conducted. The authors have studied the influence of temperature (–10 and +20 °C) and aging products of solid insulation on furan compounds during long-term storage on the parameters of the insulation system. Deterioration of the insulation due to degradation of transformer oil and paper insulation due to excess moisture content in the oil has been detected. The most informative method to analyze the condition of backup transformers has been determined; it is oil analysis for moisture content.
Conclusions. The authors have been established that for periodic monitoring during long-term storage it is sufficient to monitor the oil for moisture content. Other methods should be used only when preparing the transformer for voltage supply, since they are uninformative and quite expensive.