IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 48, NO. 5, SEPTEMBER/OCTOBER 2012 1731 An Examination of Mutual Influences Between High-Voltage Shore-Connected Ships and Port Earthing Systems During Phase-to-Ground Faults Giorgio Sulligoi, Member, IEEE, Daniele Bosich, Aldo da Rin, and Fabio Tosato Abstract—High-voltage shore connection (HVSC) is a technical solution to supply ships at berth in an economic way while re- ducing air pollution in city ports. When multiple megawatt-HVSC installations are to be exercised, electric power has to be delivered to the port from a primary high-voltage (HV) line at voltages higher than 100 kV. In this case, large earth fault currents can arise on the HV side, flowing through the port earthing system and the bonded ship hulls. Due to these faults, possible dangerous voltage gradients in sea water around the bonded ship hulls may occur. This phenomenon is pointed out and investigated in this paper to identify possible safety issues in some given scenarios. Index Terms—Dangerous voltage gradient, earth fault current, high-voltage line, high-voltage shore connection, port earthing system. I. I NTRODUCTION A. Context M ANY TYPES of recently built ships require electrical power in excess of 10 MW to keep certain services run- ning during berthing. High-voltage shore connections (HVSCs) are a solution to provide ships with this amount of power without operating shipboard prime movers and generators un- der such conditions [1]–[4]. Several city ports throughout the world have already implemented or are interested in shore connections, which are an effective way of eliminating the quote of air pollution caused from ship bunker fuel combustion. Moreover, power supply can become cost effective as, aside from eliminating environmental externalities, in some cases, it ensures revenues to port authorities and contextual savings to ship owners. The increasing interest in HVSC and the need for standardization of electrical requirements (in terms of system description, equipment, integration, management, personnel Manuscript received October 10, 2011; revised February 3, 2012; accepted March 6, 2012. Date of publication July 19, 2012; date of current version September 14, 2012. Paper 2011-PCIC-540.R1, presented at the 2011 IEEE Electric Ship Technologies Symposium, Alexandria, VA, April 10–13, and approved for publication in the IEEE TRANSACTIONS ON I NDUSTRY AP- PLICATIONS by the Petroleum and Chemical Industry Committee of the IEEE Industry Applications Society. G. Sulligoi and F. Tosato are with the University of Trieste, 34127 Trieste, Italy (e-mail: gsulligoi@units.it; tosato@units.it). D. Bosich and A. da Rin are with the University of Padua, 35122 Padua, Italy (e-mail: dbosich@units.it, aldodar_1968@libero.it). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TIA.2012.2209621 safety, etc.) have brought the development of a new joint IEC- ISO-IEEE standard on HVSC systems [5], which applies to shore connections in the voltage range above 1000 V a.c. and up to and including 15 kV a.c. To the benefit of the reader, a brief nomenclature for voltage levels is introduced, which will be utilized throughout this paper. Therefore, in the following, the terms low voltage (LV), medium voltage (MV), and high voltage (HV) will be referred, according to the European harmonized standard CENELEC HD 637 S1, to the following: LV: above 50 V a.c. up to and including 1000 V a.c. (category 1); MV: above 1000 V a.c. up to and including 30000 V (category 2); HV: above 30 000 V a.c. (category 3). B. Port Facilities of ElectricPower Systems All-electric cruise liners, commercial ships with loading/ unloading electrical auxiliaries, or even some types of naval vessels can require, at the pier, electrical power on the order of 1–20 MW per single ship. Such requirements, in addition to the power for conventional dock services, can easily result in the installation of many tens of megawatts within a single port area. Such an amount of power must be supplied from an HV network with a voltage exceeding 100 kV (the effective voltage will be case dependent on local standards; for instance, in Italy, it is usually 132 or 220 kV) through a primary substation [4]. Differently from MV, HV networks exceeding 100 kV are normally operated as solidly grounded distribution systems, and under the most critical condition (case of a phase-to-ground fault on the primary HV network), fault current levels can reach several kiloamperes (in Italy, for example, up to some tens of kiloamperes [6]). It is well known that, in general, the earth fault current may split, and only a part of it flows through the ground resistance to the remote earth (with the rest of it returning directly, even in galvanic way, to the local neutral through sky wires, cables shields, utility poles grounds, etc.). Therefore, in this work, a value of 10 kA will be assumed to be the reference current flowing through the port grounding (which includes, as an “appendix,” the ship hull) to the remote earth. With the phenomenon being linear, a lower (or higher) current will simply lead to proportional decrease (or increase) of the 0093-9994/$31.00 © 2012 IEEE