Purpose/Aim
Distributed detection and localization of cable partial discharge (PD) is a difficult problem in engineering. Conventional methods cannot sense the PDs toward the full length of cables. The existing distributed optical fiber sensing scheme based on Rayleigh backscattering intensity detection cannot describe PDs quantitatively. Based on the principle of coherent optical time-domain reflectometer (COTDR), this work realized the quantitative detection and localization of cable PDs, and obtained the time-frequency features of PD caused acoustic waveforms.
Experimental/Modeling methods
A series of partial discharge tests were carried out on a 30 m long 35 kV three-phase cable. The built-in optical fiber in the filling layer was connected with an external 2 km long single-mode optical fiber to simulate the full length of the cable. In the COTDR system, the Rayleigh backscattering light of the sensing fiber interferes with the local oscillator light and is measured by the photodetector. The return time of the scattering light corresponds to the position where PD occurs along the cable. The phase variation in the sensing fiber can be demodulated quantitatively from the intensity variation of the interference light, and then the time-frequency information of the PD acoustic signal is obtained.
Results/discussion
The cable PD acoustic signals caused by scratch fault were located and restored on the length of 2 km. The relationship between the time-frequency characteristic of acoustic signals and the level of PDs was obtained.
Conclusions
This work provided a new scheme for detection and localization of cable PDs, which brought new possibility for on-site monitoring. Moreover, the detection results are an important basis for pattern recognition of cable partial discharge defects.
 

distributed optical fiber sensing,COTDR,cable insulation defect,dual frequency pulse