Partial discharge (PD) is the indicator of the insulation defect in cables. However

the pulse current method

which is widely adopted in land cables

cannot obtain PD signals of high-voltage direct current (HVDC) submarine cables due to attenuation and installation position. To detect the PD of the HVDC submarine cable

a PD vibration diagnosis methodology using the embedded fibre based on the heterodyne interferometric phase-sensitive optical time-domain reflectometry (φ-OTDR) and Hilbert demodulation is proposed. The proposed method is verified by a PD experiment with preset defects in 220 kV submarine cables under DC voltage. The results show that the PD can be detected by fibre using the proposed method. Among the three types of PD generated in preset defects in 220 kV submarine cables under DC voltage

the inception voltage of corona discharge

internal airgap discharge and surface discharge is 18

14 and 14 kV

respectively. The peak value of the phase difference in corona discharge is the smallest

and the peak value of the phase difference in surface discharge is close to that in internal airgap discharge. A recommended parameter configuration is provided through statistical analysis

where a modulation frequency of 10 kHz and a pulse width of 100 ns achieve a 10% detection probability at 2.25 km fibre length and 10 m spatial resolution.