Abstract
A novel fiber-optic acoustic sensor using an erbium-doped fiber amplifier (EDFA)-based fiber ring laser and a balanced Sagnac interferometer for acoustic sensing of the partial discharge (PD) in power transformers is proposed and demonstrated. As a technical background, an experimental investigation on how the variations of the fiber birefringence affect the sensor performances was carried out, and the results are discussed. The operation principles are described, and the relevant formulas are derived. The analytical results show that an EDFA-based fiber ring laser operating in chaotic mode can provide a degree of polarization (DOP) tunable light beam for effectively suppressing polarization fading noises. The balanced Sagnac interferometer can eliminate command intensity noises and enhance the signal-to-noise ratio (SNR). Furthermore, it inherently operates at the quadrature point of the response curve without any active stabilizations. Several experiments are conducted for evaluating the performances of the sensor system, as well as for investigating the ability of the detection of high-frequency acoustic emission signals. The experimental results demonstrate that the DOP of the laser beam can be continuously tuned from 0.2% to 100%, and the power fluctuation in the whole DOP tuning range is less than 0.05 dBm. A high-frequency response up to 300 kHz is reached, and the high sensing sensitivity for detections of weak corona discharges, as well as partial discharges also is verified.
Highlights
Partial discharges are small electrical sparks that occur when voids exist within or on the surface of the high-voltage dielectric material inside power appliances, such as power transformers
As mentioned in the previous section, we propose a novel fiber optic acoustic sensor illustrated in Figure 4 for the partial discharge (PD) monitoring of power transformers
We presented a novel fiber-optic acoustic sensor using a balanced Sagnac sensor and an erbium-doped fiber amplifier (EDFA)-based fiber ring laser with the degree of polarization (DOP) tunable function
Summary
Partial discharges are small electrical sparks that occur when voids exist within or on the surface of the high-voltage dielectric material inside power appliances, such as power transformers. Like other types of fiber-optic interferometers, the fiber Sagnac interferometer sensor inevitably is subject to the effect of polarization fluctuations, which are known as polarization-induced signal fading or as polarization fading [20,21,22] This arises from the random changes of states of polarization (SOP) of two interference beams when propagating in long fiber with birefringence in the opposite direction [23]. It is obvious that the distribution state of SOP or the polarization fluctuation magnitude of the chaos beam is controllable This feature is useful for us to develop a unique chaotic laser source with a DOP tunable function for fiber-optic PD sensing.
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