Existing methods for cable insulation condition identification using signals such as partial discharges and DC leakage currents in cables are constrained by the weakness of the measurement signals

which makes it difficult to be effectively applied in practice. This paper proposes a novel method to identify the insulation condition of transmission cables in offshore wind farm online based on the correlation between the amplification factor of the harmonic currents (i.e.

the ratio of the amplitude of the harmonic currents at both ends of the cable) and the cable insulation condition. It has been found that within the nominal cross-section and length of offshore wind farm transmission cable and the possible grid strength at the grid connection point

the current amplification factors corresponding to some harmonics below the 25th order are highly sensitive to cable insulation parameters. Given this perspective

the correlation function between the harmonic current amplification factor and the insulation parameter of the cable is constructed

then a set of overdetermined equations is established based on the harmonic measurement data at different moments

and finally

the insulation parameter is solved by using the Levenberg-Marquardt algorithm. Compared with the existing methods

the proposed method only uses harmonic measurements

which is easy to obtain

and practical cases verify the effectiveness of the method.