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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, and , 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 , , , , , . 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.

In this paper, sound pressure sensitivity of the fiber optic acoustic sensor according to sensor direction and mandrel material were investigated experimentally. Three different directions were selected as stand, lay, and hole. Hollow cylinder type mandrel dimension is 30 mm in outer diameter, 45 mm in length, and 2 mm in thickness, and about 50 m optical fibers were wounded on the surface of the mandrel. Non-directional sound speaker was used as a sound source. Sagnac interferometer and single mode fiber, a laser with 1,550 nm in wavelength, coupler were used. Based on the experimental results, lay direction`s sensitivity is the highest in the frequency range of 2 kHz~4 kHz. `PTFE+carbon` material is more sensitive than PTFE in the frequency range of 5 kHz~20 kHz. Sound pressure detection sensitivity depends on the mandrel direction and material under certain frequency.

To substitute TLS in the hybrid system which is combined with Sagnac interferometer and fiber bragg grating (FBG) it is necessary to investigate how the laser source (TLS and CW) and sensor material variate the response of fiber optic sensor. Two different hollow cylinder type mandrel materials are proposed which are PTFE and PTFE+carbon and 18 m optical fiber is wounded at the mandrel surface. CW laser source experiments had been done in the oil tank which is filled with transformer oil in the 1 kHz~20 kHz frequency range. Also Sagnac interferometer fiber optic sensor is combined with FBG called hybrid system and TLS used as a light source. Based on the experimental results PTFE sensor showed more higher magnitude of detection signal rather than carbon sensor and this result is agreement with the McMahon`s theoretical results. Phase variation is inversely proportional to the elastic modulus of the mandrel material. In PTFE fiber sensor, tunable laser source showed more higher performance rather than CW case. Therefore, TLS fiber optic sensor can be applied to the hybrid system which is combined with Sagnac and FBG.

In this paper physical quantities were measured using by the fiber optic sensor when a pendulum ball collides to the fixed ball on the wall. Both steel ball dimensions are 1 inch in diameter. The fiber optic Sagnac interferometer was used to detect the impact time. It is made a 1mm penetrated hole and optical fiber in the Sagnac loop passed through the hole. A ball was welded on the steel plate wall as a fixed ball. When the another ball collides to the fixed ball the fiber optic sensor detects the impact force in between them. Based on the experimental result impact time was measured about 0.14ms at the angle of 30 degree. This fiber optic sensor technique can be expanded to the moving bodies.

In this paper it is shown that a fundamental technology of hybrid system combining Sagnac interferometer and FBG. Fiber optic sensor array, i.e. two sensors in the Sagnac loop was suggested. Fiber optic sensor array was fabricated in the transformer oil and external sound applied to the sensor directly using by piezoelectric. Tunable laser source was used as a light source. Applied sound frequency range is from 5kHz to 90kHz. From this experiment it is confirmed that fiber optic sensor using Sagnac interferometer in the transformer oil can detect applied sound frequency. In real electric transformer system suggested fiber optic sensor array can be applied to monitoring physical quantities such as internal temperature, sound pressure and vibration due to partial discharge.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

For condition monitoring of large scale electrical power transformers, a fiber-optic multi-stress sensor system was constructed by combining fiber-optic acoustic sensors and fiber Bragg grating temperature sensors in a fiber-optic Sagnac interferometer. To separate the grating signals from the interferometer output, an attenuator was placed at an asymmetrical position in the Sagnac loop. By balancing the counter propagating light intensities with the attenuator, the background noises could be suppressed to obtain grating signals with enough signal-to-noise ratio. With the preliminary experiments, the temperature and the vibration information at multiple locations could be measured simultaneously with single optical circuit and signal processing unit.

Fiber Bragg grating (FBG) sensors are employed in a fiber-optic Sagnac interferometer sensor to measure multi-stress information of electric power systems. By using the hybrid sensor configuration, it was possible to measure the temperature and the vibration signal in an insulating transformer oil bath at the same time. A novel fiber-optic Sagnac interferometer design and a signal processing technique were used to separate the FBG sensor signals from the interference signal. The preliminary experimental results are presented to show the feasibility of the sensor system.

It is interesting to measure the impact force when the moving pendulum ball collides to the fixed body. In this paper physical quantities were measured using by fiber optic sensor when a pendulum ball collides to the fixed ball on the wall. Both steel ball dimensions are 1 inch in diameter. The fiber optic Sagnac interferometer is well established as a sensor for acoustic and vibration. It is made a 1mm penetrated hole and optical fiber in the Saganac loop passed through the hole. The ball was welded on the wall as a fixed ball. When the external force applied to the fixed ball the optical fiber in the Sagnac loop detects the impact force. The output signal is proportional to the output voltage in the oscilloscope. Based on the result suggested fiber optic sensor can measure the impact intensity and this technique can be expanded to the moving bodies.

In this paper, an optical fiber sensor (OF sensor) utilizing the principal of the Sagnac interferometer was proposed to detect the discharge acoustic signals which generated from a needle‐sphere electrode system in insulating oil. The performance of the OF sensor was checked by a sinusoidal calibration signal generated by a PZT actuator at 198 kHz. The detected discharge signals consisted of the acoustic signal and electrical noise. The noise signal could be removed by a digital low‐pass filter. It was demonstrated that the OF sensor in this research had a possibility to detect the discharge acoustic signals in the power apparatus.