Considerations on on-site evaluation of transformer oil quality

Transformer oil quality is generally evaluated by taking oil samples for detailed analyses in the laboratory. This approach, although convenient and widely used, presents a significant drawback regarding the representativeness of the samples, primarily related to the nonhomogeneous nature of the oil (particulate content) and the cleanliness of the sampling bottles. It also suffers from the nonnegligible influence of the time between the sampling and the actual evaluation of the oil samples, as well as the difficulty of detecting time variations in the parameters evaluated. This paper presents a new approach to the onsite evaluation of transformer oil quality which eliminates the use of sampling bottles. The efforts so far in this current development have concentrated on particle counts, particle collection and identification. It can be easily extended to include other parameters useful for evaluating the oil quality: tan/spl delta/; dielectric strength; water content; etc.