Modelling seabed buried cables for electromagnetic transient analysis

This study proposes the expressions for return impedances and admittances for the transient modelling of subsea cables buried below the seabed. Unlike buried cables or overhead lines where only one of the external media shows losses, for a subsea cable buried in the seabed both media are lossy. The expressions are derived from quasi-transverse electromagnetic (quasi-TEM) approximation of a full-wave modelling. A comparison of a full-wave-based results and the ones using a quasi-TEM approximation indicates wideband validity of the proposed expressions. Two test cases are considered: a single-core armoured cable and a three-core (i.e. pipe-type) configuration. An evaluation of the characteristic admittance and the propagation function in the frequency domain is carried out to assess the impact of the change in the external media when compared with a cable floating in the sea. A transient model for the subsea cable is derived in frequency domain and time-responses are obtained using the numerical Laplace transform. The results indicated some differences in the transient waveform obtained when compared with the responses for a cable floating in the sea.