A semi-annual or annual inspection is best suited for sampling and analyzing of insulating oil. This allows for accurate tracking of changes to the oil and helps track latent faults. The silica gel is checked and replaced if necessary. A triennial or quinquennial inspection allows for a complete inspection of the unit. This inspection includes testing the windings, inspection of the bushings, and allows for inspection of the components and accessories that are only accessible when the transformer is shut down.
Power quality is rather difficult to evaluate.
However, we can perceive the parameters which degrade the quality of the sinewave. Typically more than ten short-circuits in the life of a transformer of a 0.5 to 5 MVA size. Frequencies of Inspections and Detection Tests Inspections and tests allow for evaluation of the transformer's components and condition by a non-destructive and non invasive method. Tests on the insulating oil allow for evaluation of the chemical properties, as well as any by-products and contaminants. By contaminants, we mean all foreign products of insulating oil.