Quasi-Distributed Optical Fiber Transducer for Simultaneous Temperature and Vibration Sensing in High-Power Generators

In this paper, a new multiparametric optical fiber transducer is presented for simultaneous temperature and vibration sensing in hydroelectric high-power generators. The optical transducer holds three multiplexed fiber Bragg gratings (FBGs) as the sensing elements. In the transducer, each FBG can simultaneously measure temperature and vibration independent of the other FBGs. With a temperature characterization, it is possible to determine the thermal stability (1.5 °C) over the test duration and the thermal sensitivity of the packaged FBGs 10 pm/°C. Moreover, the vibration characterization tests rely on an impact hammer and a shaker. With the impact hammer test, the transducer package natural frequency of 565 Hz is determined. The shaker performed a frequency sweep over 5 Hz to 1 kHz, and the transducer mean vibration sensitivity is found to be 7.2 pm/g. Subsequently, the power plant installation is performed using six transducers. They are installed into six different windings slots to sense stator bars of a 370-MVA hydroelectric generator. With this instrumentation, 23 h of simultaneous vibration and temperature sensing is carried out. All the FBGs used to monitor vibration were able to monitor the frequency of mechanical vibration (2 Hz) and electromagnetic vibration (120 Hz) of the generator. During the power plant test, the machine was turned OFF due to a failure and all the FBGs were able to measure the temperature as well as vibration changes caused by the machine shutdown.