Real-time transformer oil monitoring using planar frequency-based sensor

Abstract

Efficient power transfer is highly dependent on the quality of oil which plays a major role in transformer units used for energy distribution. In this work, a meta-surface inspired Complimentary Split Ring Resonator (CSRR) structure designed to work at 2.94 GHz, with an engineered slit between its active waveguide and CSRR ground plane is used. A miniaturised pipeline is made to pass through the slit, which carries the sample of transformer oil derived from the actively used transformer. The degraded oil samples are characterised for their dielectric properties (dielectric constant varying from 2.77 to 2.823), viscosity (25.11–27.9 cP), turbidity (1.314–4.709 cm−1), density (819–831 mg/ml) and structural changes, which confirms the structural modifications, as a function of the age of the sample and the ambient effects. Degraded oil samples show the formation of alkenes, alkynes and aromatic compounds from simple hydrocarbons as a result of extended usage. The changes in their frequency responses of the sensor are correlated to the changes in the oil samples at their physical and chemical level. A shift in frequency from about 135.5 to 470.5 MHz for samples with degradation time from 24 h to 504 h is obtained. The proposed technique is non-destructive, since there is no physical contact between the analyte molecules and the sensor itself; thereby maintaining the sensor parameters intact, even if the sensor is used for extended duration of time. A miniaturised, reusable, frequency-based sensor is hence demonstrated to detect the quality of transformer oil, in the real-time setup, for industrial applications.