Partial Discharge Sensing of Fiber Composed Submarine Cable based on $\varphi$ -OTDR

The partial discharge generated by operation voltage applied on insulation defects is one of the main reasons leading to the failure of HV submarine cables. However, the pulsed current method which is widely adopted by partial discharge cable on the land is unable to obtain high frequency pulsed signal due to attenuation of the long submarine cable. In this paper, a heterodyne interferometric phase-sensitive optical time reflectiont
$\varphi$
-OTDR) based method is proposed to detect the partial discharge acoustic disturbance on the composed fiber in the submarine cable. The methodology consists of the signal sampling of the balanced photodetector, orthogonal IQ demodulation, phase threshold expansion, and unwinding. The proposed methodology is verified by the partial discharge experiment by a preset insulation defect in a 110
$\mathbf{kV}$
single-core submarine cable. The results show that the partial discharge can be distinguished by the phase fission. Besides, the location error is within 10 meters.