Adapting the FBG cavity sensor structure to monitor and diagnose PD and vibration sparking in large generator

The FBG cavity sensor was invented to measure and trend End Winding Vibrations (SEW) inside larger power generators. The sensor consists of a twin grating cavity which can be used to monitor vibration as well as temperature change by changing the center wavelength of the transmitting laser to track the movement of the interference fringes. This paper will discuss the adaptation of this FBG cavity structure to measure much higher frequency signals like those found in Partial Discharge (PD) events. Special package design is necessary to maintain the signal to noise ratio as the high frequency PD signal propagates along the conductor inside the stator slots to the end windings. The challenge would be the coupling of these signals to our PD sensors. They will be mounted at the same locations where SEW sensors would be installed for end winding vibration. We would select the windings with the highest induced voltage hence most susceptible to PD. By trending the vibration amplitude related to loading, we would be able to diagnose each winding structure has become loose. These sensing channels would be correlated with PD amplitudes as well as their signature; more work would be required to relate the signature to the degradation process of the insulation layer. By measuring time of arrival differences at both ends of the generator, we can estimate which slot is associated with the discharge event. The addition of the PD sensor to vibration and temperature capability makes TG Guard a comprehensive solution for safeguarding the generator; its diagnostic capability would also shorten maintenance time and reduced the required resources. Owner would know exactly what to do by integrating all the trending data.