Ultrasonic detection coherence of fiber Bragg grating for partial discharge in transformers

As a traditional approach of partial discharge (PD) in power transformers, ultrasonic detection with piezoelectric transducers (PZT) has drawbacks of low sensitivity and low detection efficiency. In order to overcome these disadvantages, an ultrasonic detection system based on fiber Bragg grating (FBG) is developed for PD in power transformers. Take the advantage of good insulation ability and immunity to electromagnetic interference, the optical sensor can be put into the transformers and detect the weak PD signal directly. In this paper, ultrasonic detection theory of FBG was analyzed, and PD detection experiments in transformer oil were carried out to test the performance of this FBG ultrasonic detection system. Furthermore, in order to demonstrate the coherence and distributed measuring ability, PD detection experiments based on multi-point FBG string with different center wavelength were conducted. Study results show the performance of FBG ultrasonic detection system is better than traditional PZT sensor, and satisfactory detection coherence of FBG with different center wavelength is proved. Moreover, distributed ultrasonic measuring of PD in power transformers can be realized by multi-point FBG string with application of wavelength-division and time-division multiplexing technology.