Faculty Publications
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Item Effects of transformer-oil temperature on amplitude and peak frequency of partial discharge acoustic signals(Institute of Electrical and Electronics Engineers Inc., 2018) Shanker, T.B.; Nagamani, H.N.; Antony, D.; Punekar, G.S.The behavior of partial discharge (PD) acoustic emission (AE) signals in the transformer oil for a temperature range of 30-75 °C is studied via laboratory experiments. The AE signals are analyzed using the fast Fourier transform (FFT) to obtain the peak frequency and the AE amplitude. A peculiar behavior of reduction in the peak frequency and the AE amplitude observed above 65 °C is reported. An attempt is made to explain the reduction in the AE amplitude after a certain temperature by correlating it with the properties of the transformer oil such as the viscosity and the breakdown voltage. This AE signal analysis is perhaps an important advancement in the PD diagnosis and the PD spectrum analysis at different temperatures in the transformer oil. © 1986-2012 IEEE.Item An Investigation on the Influence of Thermal Damage on the Physical, Mechanical and Acoustic Behavior of Indian Gondwana Shale(Springer, 2020) Srinivasan, V.; Tripathy, A.; Gupta, T.; Singh, T.N.In the present study, the effect of thermal treatment on the physical, mechanical and fracturing behavior of Gondwana shale samples from India was investigated. Acoustic Emission signals were used to identify the changes brought in by temperature variations on the crack damage zones and failure attributes in shale. The results suggested that mechanical parameters such as uniaxial compressive strength, tensile strength (?t), elastic modulus, mode-I fracture toughness (KIC), cohesion, and brittleness index (B1) exhibited a strong negative correlation with thermal damage (Dt). But, the internal angle of friction and brittleness index (B2) showed a reasonable positive relation with thermal treatment. The deformation of the shale was dominated by its clay mineral enrichment, the characteristics of which changed with heating. The intensity of fracturing as observed from acoustic signals was chiefly controlled by the orientation of bedding planes and the degree of thermal treatment. The initiation and propagation of macro-crack were found to be greatly influenced by the degree of thermal damage. Under compression, thermally damaged samples showed similar deformation pattern, while under Brazilian tensile load, the deformation path became inconsistent with increasing temperatures. It was observed that thermal damage in tested shale decreased the layer compaction, which eased the fracturing intensity, thereby reducing the overall strength of the samples. The present investigation concludes that even a slight change of the thermal conditions can substantially alter shale fracturing behavior and failure attributes posing serious safety concerns of deep geo-engineering structures. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.