Temperature Monitoring For Stator Bar In Large Generator Based On Fiber Bragg Grating

The temperature of stator bar affects insulation life of large generators. Monitoring the temperature is a key to safety, reliable operation of large generators. So temperature measurement for stator bar is significant. The technology of temperature monitoring with Fiber Bragg Grating (FBG) for stator bar online is studied in this paper.In this paper, stator bar must be impregnated into epoxy resin by vacuum pressure, so impact of the epoxy resin curing on FBG sensing performance is studied when bare grating implanted into bar. Epoxy resin and FBG in a special mold were cured together at 80℃and the process was monitored. It was found that the center wavelength of the FBG drift 3.32nm to shortwave because of the shrinkage of epoxy resin during curing. Center wavelength of FBG would be constant after curing is finished. The temperature sensitivity of FBG is increased due to epoxy resin, and temperature sensitivity is 5.8 times and 2.67 times of the bare FBG at 20℃~80℃and 80℃~120℃respectively. The post-curing FBG has better temperature measurement repeatability, quick response. Hard curing can protect FBG well and reduce stress to it.The need for FBG package was argued in the paper. FBG packaged mental tube was tested and the result shows that FBG has good temperature measurement stability. Two packaging to FBG were proposed using epoxy glass and small copper tube. Two types of FBG embedded in row insulation placed or on the copper wire were discussed. The copper section loss was calculated due to the temperature test wire in the paper. The result shows that the copper section lost is more 6 times as the sectional tolerance of a bar.Temperature measurement system with FBG is designed, which can achieve 72 points'temperature test at the same time. Measurement accuracy is±0.5℃and temperature measurement resolution of 0.1℃. An information management interface was developed by Visual Basic 6.0 software, which can show temperature and its changing curve, alarm over limitation, and look up historical data and so on in order to provide basic maintenance for generator.