Direct current connections

As with many vessels, the thrusters and propulsion accounts for a huge percentage of the total power needed by the 93m, 5,000 tonne Dina Star, and of course these run on a DC current that usually has to be converted over from AC.

ABB’s Onboard DC Grid owes much of its efficiency to the fact the system isn’t locked at the usual ship’s 60Hz frequency, even though a 60Hz power source can be fed back to it. So, the freedom to independently control each power consumer opens up lots of routes to get the best out of the fuel consumption.

However, the main challenge with DC distribution has been to achieve complete selectivity and equipment protection equivalent to AC distribution. AC currents are by nature far simpler to break because of their wave configuration crosses zero every half cycle. DC circuit breakers do exists to but these are usually more complex, more expensive and bulky than their AC counterparts, so a lot of attention has been paid in protecting the equipment and making sure safe operation is maintained in case of failure.

By Stevie Knight