On improving the earthing quality in ship electric energy systems

This paper presents a contribution in improving the earthing system of ship electric grids, which affects the phenomena developed in highly unbalanced operating conditions like the single – and two-phase faults. Furthering previous work, an alternative to ungrounded earthing scheme is introduced, namely the grounding via a conditionally varying resistance. Within this framework, the mathematical expressions with respect to zero sequence impedance, of voltages and currents under study are yielded. Furthermore, as a means to easily evaluate the quality of earthing, appropriate indices are introduced. Thus, it is shown that the effect of the earthing scheme in fault conditions can be adjusted based upon certain design limits.