Applied Sound Frequency Monitoring in the Transformer Oil Using Fiber Optic Sagnac Interferometer

The fiber optic Sagnac interferometer is well established as a sensor for detection of physical perturbations such as acoustic and vibration. In this paper acoustic signals generated in the cylindrical cavity submerged in transformer oil were measured by the fiber optic sensor array in one Sagnac loop. Two different external sound frequencies, f1 and f 2, were applied to the sensor array simultaneously by using piezoelectric with frequency range from 5 kHz to 90 kHz. Based on the experimental results, fiber optic sensor detected harmonic series of applied sound frequency such as f(1), f(2), 2f(i), 2f(2), vertical bar f1- f 2 vertical bar, vertical bar f1+ f 2 vertical bar. Suggested fiber optic sensor array can be applied to monitor physical quantities such as internal sound pressure and vibration due to partial discharge in the real electric transformer system.