Oil-level measurement in power transformer using optical sensor

This paper describes the use of intensity based fiber optic sensor for continuous level measurement of transformer oil in power transformer. Cladding removed portions of a multimode fiber act as sensor which works on evanescent wave interaction principle. The sensing principle is based on intensity of light which is disturbed by the change in proximity of air or oil to the sensor. The phenomena of refraction, total internal reflection are taken into account for experimentation and verifications. The intensity of light is detected and analyzed by using light dependent resistor (LDR) and LabView respectively at the detecting end which provides the corresponding reading for the level of transformer oil in which the optical fiber is immersed. Besides the magnetically coupled float operated conventional level indicator this sensor has many advantages which includes electromagnetic interference resistance, low temperature influence, intrinsically safety, low cost and simple design. A reference fiber is introduced in parallel with the sensing fiber to eliminate the intensity variation of source light and temperature variation of the transformer oil. The optical sensor used is well suited for real time monitoring of transformer oil in power transformer.