Partial discharges (PDs) are an electrical phenomenon that occurs within a transformer whenever the voltage stress is
sufficient to produce ionization in voids or inclusions within a solid dielectric, at conductor/dielectric interfaces, or in
bubbles within liquid dielectrics such as oil; high-frequency transient current discharges will then appear repeatedly and
will progressively deteriorate the insulation, ultimately leading to breakdown. Fiber sensor has great potential on the
partial discharge detection in high-voltage equipment for its immunity to electromagnetic interference and it can take
direct measurement in the high voltage equipment. The energy released in PDs produces a number of effects, resulting in
flash, chemical and structural changes and electromagnetic emissions and so on. Acoustic PD detection is based on the
mechanical pressure wave emitted from the discharge and fluorescent fiber PD detection is based on the emitted light
produced by ionization, excitation and recombination processes during the discharge. Both of the two methods have the
shortage of weak anti-interference capacity in the physical environment, like thunder or other sound source. In order to
avoid the false report, an all-fiber combined PD detection system of the two methods is developed in this paper. In the
system the fluorescent fiber PD sensor is considered as a reference signal, three F-P based PD detection sensors are used
to both monitor the PD intensity and calculate the exact position of the discharge source. Considering the wave band of
the F-P cavity and the fluorescent probe are quite different, the reflection spectrum of the F-P cavity is in the infrared
region, however the fluorescent probe is about 600nm to 700nm, thus the F-P sensor and fluorescent fiber probe can be
connected in one fiber and the reflection light can be detected by two different detectors without mutual interference.
The all-fiber partial discharge monitoring system not only can detect the PDs but also can ensure the position of the PD
source and is of great anti-interference capacity in harsh environment.
Fiber Bragg gratings (FBGs) sensor has been widely used in all kinds of detection spaces. Nonlinear effects of the fiber Bragg gratings have been observed in high-temperature conditions, however, it occurred in low-temperature as well. In this paper, we take the low-temperature experiments in the low-temperature thermostat bath, temperature range from 10°C to -80°C, the Bragg wavelength shift with the temperature decreasing linearly at the very beginning and it shows linear characteristic range from room temperature to -45°C. However with the temperature goes down continuously, the nonlinear effects emerged, the turning point temperature of the nonlinear effect is at -45.3°C. Besides, the sensitivity of the FBGs decreased as well from 8.96pm/°C to 6.72pm/°C. Considering the physical characteristic of the silica fiber, which the thermo-optic coefficient and the thermal expansion coefficient of the fused silica is not constant if temperature goes down and it shows nonlinear features, therefore we conclude the nonlinear effect at low-temperature is attributed to the thermal expansion and the thermo-optic effect of the silica fiber. Thus, we predict that appropriate doping improvements in the silica fiber can modify the linear range of FBGs which can enhance the measure precision. In addition, we find that high sensitivity FBGs has a lower temperature turning point of the nonlinear effect. The invar packaged FBGs has a sensitivity of 24.3pm/°C at room temperature. It is higher than bare FBGs’ sensitivity which is about 8.96pm/°C at room temperature. The invar packaged FBGs’ temperature turning point is at about -54.5°C, which is lower than the bare FBGs’, -45.3°C, temperature turning point. This indicates that high sensitivity FBGs can also increase the linear temperature range. The experiment results and analysis show that we can either by increasing the sensitivity of FBGs or doping in the silica fiber to modify the linear range.
In recent years, Fiber Bragg Grating (FBG) sensors have been attracted a lot of interest, and widely and
increasingly researched in many important areas. In this work, we present the field of railway dynamic monitor
concerning the application of FBG sensors. We have built the principle and established the sensing system based on FBG
to monitor the situation of train and railway through the analysis of track strain during the train passage. We have
illustrated that FBG sensors set on the lateral and underside of the rail can detect the strain of rail and sensors on
different positions show distinct results. We have presented that the underside of the rail structure is the most suitable
position to monitor the strain in railway.