Fabio Tosato

Reducing voltage sags through fault current limitation

Short circuit current limitation in distribution utilities can be an effective way to improve power quality, since the expected voltage sag amplitude during faults can be dramatically reduced. A simple series LC circuit tuned at the net frequency, with the capacitor shunted by a metal oxide varistor (MOV), proves to be a well suited limiter to reach the goal. In the paper, the properties of such a circuit are analyzed and its operation is investigated through computer simulation. The relevant pro and con aspects are outlined and discussed.

Shore-to-Ship Power

This contribution starts with a review of the state of the art of existing high-voltage shore connection (HVSC) systems in terms of principles, rules, publications, technologies, and relevant installations. Then, tutorial sections present the main technical aspects of HVSC systems as ship-to-shore interface, shore equipment (transformers, converters, etc.), onboard devices (cubicles, shore switchboard, etc.), operating sequences, and feasibility aspects, for both commercial and military applications. Finally, some technical challenges are presented, concerning intentional/unintentional bonding, interactions between HVSC bonding and cathodic protection systems, bonding opportunity, and electrical safety aspects related to bonding issues in case of large earth fault currents in port facilities.

Limiting hull touch voltages in large power shore connection systems during phase-to-ground faults: A solution proposal

High Voltage Shore Connection (HVSC) is a technical solution to supply ships at berth in an economic way while reducing air pollution in city ports. The increased power demand of modern cruise ships may reach several tens of MVA, requiring a primary port voltage supply at voltage >100 kV. When a phase-to-ground fault arises on the HV side, safety problems due to increasing ship hull touch voltage may arise. A possible solution is proposed in this paper, based on an HV/HV y-Δ-y transformer with secondary resistance grounded neutral in the distribution power supply utility substation, with the aim to reduce phase-to-ground fault current at port.

High voltage ship-to-shore connection for electric power supply support in landing operations: An analysis

The increasingly presence of HVSC connection onboard ships opens the path for innovative applications, such as ship-to-shore connection. Indeed, it is possible to supply power to land during emergency (mainly to deployed camps/bases), thanks to the electric power generation capabilities of modern all electric ships. However, the use of the same system to provide both the HVSC and ship-to-shore connection functions require a careful assessment of the equipment to be installed both onboard and on land. To achieve that, ship-to-shore connection requires a shore side mobile substation, containing all the necessary equipment for the land power distribution, and a ship side substation, either implemented in shipboard power system or installable at need. To successfully implement such a system, an appropriate design of protection systems is required, assuring proper protection to equipment and people. Moreover, the capability of the ship-to-shore connection to supply an existing land power system implies a high rate of adaptability, and a careful assessment of the land power systems grounding and protections. The development of such technology will be relevant for military applications, but civilian application is possible and foreseen in future (dual-use technology). In this paper, an analysis of possible ship-to-shore connection configurations is made, together with considerations about protection of both the connection equipment and the supplied land power systems.

Mitigation of voltage sag effects on sensitive plants: an exemplary case study

Abstract Process-interruptions and related costs often force industrial customers to adopt proper solutions to mitigate the voltage sags effects. A trivial solution would be to feed the whole plant through UPS devices, but in many cases this would be technically or economically not practical. Partial solutions given by proper changes in the plant or desensitising critical equipment often become the most viable way. This paper deals with an exemplary case study given by Elettra, the synchrotron light source facility of Trieste (Italy). After a description of the facility, the paper illustrates a methodology, based on field measurements and experimental tests, aiming to individuate proper local actions that will drastically reduce the effects of voltage sags on the considered plant. The methodology described with reference to this particular case study has general validity and may be regarded as an approach ‘guideline’ to the problem.

Studies on asymmetrical short circuit currents in shipboard medium voltage direct current distribution systems fed by AC generators

DC distribution is a promising technology for addressing incoming issues in AC conventional distribution. In marine power systems, given the high power requirements of electric propelled vessels, Medium Voltage DC (MVDC) distribution is on study. Among all the relevant issues of DC distribution, short circuit currents definition and interruption is the most problematic now. Rail-to-rail faults are commonly studied, and models and methods to address their calculation are present in literature. Conversely, rail-to-ground faults are more complex to assess. Indeed, their fault loop include also AC generation systems, so their grounding configuration must be considered. Moreover, rail-to-ground faults produce currents that can be non-symmetrical and non-sinusoidal on AC side, depending on DC side grounding configuration, rendering unsuitable common system models and methods to assess fault currents. In this paper, a study on fault currents in a shipboard power system with different DC side grounding configurations has been done, highlighting when the resulting currents are symmetrical or not. Considerations about practical applicability of proposed configurations has been also done, pointing out pros and cons and defining the most recommendable practices.