Page 43: of Marine News Magazine (July 2020)

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WORKBOAT ENGINES

VARIABLE SPEED GENERATOR SETS OFFER

ADVANTAGES FOR COMMERCIAL SHIPS

Østensjø Rederi

By Joerg Habermaas and Jochen Thurner,

Application Engineering, Commercial Marine & Offshore, MTU 'XHWRHFRQRPLFQHFHVVLW\FRPPHUFLDOVKLSRSHUDWRUVKDYHEHFRPHLQFUHDVLQJO\IRFXVHGRQÀQGLQJFRVW

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GHGLFDWHGWRÀQGLQJZD\VWRGHOLYHUWKHULJKWWHFKQRORJLHVWKDWZLOOPHHWDQRSHUDWRU·VVSHFLÀFUHTXLUHPHQWV n recent years, interest in variable speed units as a driver shifted gears. To optimize fuel consumption, the driver always of certain commercial vessels has gained interest. Vari- intends to use a low engine speed (highest possible gear), as a

Iable speed technology allows the speed of an engine to slower running engine saves fuel for the same load.

be regulated and adjusted according to the electrical load that To achieve these bene?ts, the frequency typically is adjusted is connected, which makes it more economical to run. in two steps via converters. First from AC (alternating current)

Compared to traditional, constant speed units, variable to DC (direct current) and in a second step back to AC via an units can offer several advantages, such as up to 15% reduc- inverter. The single line diagram in Figure 3 shows one example.

tion in fuel consumption, up to 20% increase in time between Using the example of a wind-platform supply ship that has overhauls, lower noise emissions and increased power density recently been in operation with a variable speed unit, we can with less installation space. give a glimpse of the advantages.

Variable speed units are particularly useful in operating On a typical platform supply ship, four units with a capac- modes with a high percentage of low loads – such as when an ity of approximately 2,100 kW each are used to power the offshore supply vessel (OSV) is in a standby phase. vessel. An arrangement of the units with their electrical com- ponents is shown in Figure 3.

Fuel efficiency

The high performance that this arrangement can offer is nec-

Common constant speed gensets are designed to optimize essary due to redundancy requirements and comes in handy in fuel consumption at high loads above 75%. The speci?c fuel cases of bad weather – but is not needed for a majority of a ship’s consumption depends on load in relation to engine speed. To operation time. Having this arrangement in place during typi- clarify, the functionality is comparable to a car with manually cal use for diesel engines results in high proportions of low load 43 www.marinelink.com MN