Multichannel optical-fibre heterodyne interferometer for ultrasound detection of partial discharges in power transformers

Abstract

A multichannel interferometric system is proposed for the ultrasonic detection of partial discharges using intrinsic optical fibre sensors that may be immersed in oil. It is based on a heterodyne scheme which drives at least four sensor heads in order to localize the source of the acoustic emissions. Proper design of the sensing head improves its sensitivity through magnification and reaches a compact encapsulated probe able to be installed within power transformers. The optoelectronic implementation and the experimental tests are presented to optimize the resolution (4 channels—4 mrad). In addition, the results of ultrasound measurements at 150 kHz with an optical fibre sensor immersed in water in an acoustic test bench are shown, in which a resolution better than 10 Pa was obtained. Finally, the set-up for three-phase power transformers is demonstrated and characterized to detect and locate the source of acoustic emissions.

Variable configuration fiber optic laser doppler vibrometer system

“…3 Figure 4 shows the basic scheme proposed for the heterodyne FLDV signal recovery. The DAQ and signal processing implement an I/Q phase demodulation instead of a frequency demodulation [2]. It is completely digital and is implemented in LabVIEW.…”

“…Although the common path sensor has been used for many applications [7 9], to our knowledge there are no reports in the literature of multiple channel common path fiber vibrometers, possibly due to problems associated with processing the data. Possible approaches for signal recovery include (a) phase generated carrier (PGC) [10], (b) channelled spectrum analysis [11], and (c) PGC with the fringe counter for every ± 2π phase change [2,12]. In the work reported here, the PGC with the fringe counter approach was used.…”

“…The amplitude of the vibration was set to obtain the particular condition when J 0 = J 1 . This calibration point corresponds to a modulation index m = 2.4 and can be used in(2) in order to find the magnitude of the target displacement. The carrier signal was observed with the spectrum analyzer for a stationary target (without vibration), when it is vibrating at 20 kHz with an amplitude corresponding to the calibration point where J 0 = J 1 are shown in Figs.…”

Instrumentation System for Location of Partial Discharges Using Acoustic Detection With Piezoelectric Transducers and Optical Fiber Sensors

“…This is feasible because of the internal installation of the OF sensor. In the case that the region is too large to be monitored by one OF sensor, more OF sensors could be included [25]. Fig.…”

Optical fiber sensor of partial discharges in High Voltage DC experiments

“…Currently acoustic techniques using OF sensors are being developed [6][7][8][9]. There are some studies in this field but not many demonstrations with real PD signals.…”