Wärtsilä Low Loss Concept, for Diesel Electric Propulsion
As the popularity of diesel electric propulsion increases, attention is being focused on ways of improving the system which is often criticized for being bulky and heavy. A traditional DE ship propulsion system consists of two or more propulsion units. Each unit comprises of a generating set (engine and generator) plus a drive system with its own propulsion transformer, frequency converter for speed control and propeller system. The transformers are heavy and take up considerable space. The number of propulsion units used in a medium sized vessel ranges from at least four up to as many as seven.
In an attempt to solve some of these negative features, Wärtsilä has produced a Low Loss Concept (LLC) for DE installations that offers improved performance at lower cost. This is achieved by avoiding the use of heavy and space consuming transformers in the DE power distribution systems. It has the additional benefit of improved levels of redundancy. In the LLC system, the propulsion transformers are eliminated and replaced by one or two Low Loss Concept transformers in a central location. Each transformer becomes part of the switchboard unit and controls several propulsion units.
Wärtsilä LLC is available for low voltage (690V) and medium voltage (6600V) applications, covering power requirements of 5-70 MW. Low-voltage systems have already been installed on some 65 vessels, and medium voltage installations are in development.
As the genset power is applied directly to the speed controlling frequency converters, eliminating the propulsion transformers increases the system efficiency by two to four per cent and decreases the current supplied from the switchboard to the frequency converter by ten per cent. The resulting efficiency can deliver significant fuel savings in the region of between $40,000 and $135,000 depending on the vessel size/type and operational profile.
The basic LLC concept of two propulsion units served by one LLC transformer can be used with low-voltage power distribution for installed power levels up to 14 MW. For higher powers there is LLC Quattro using four LLC transformers connected in a ring extending the propulsion power range up to 20MW.
In traditional designs of medium voltage (6600 V) systems, propulsive powers of between 30 to 40 MW can be realized. Using the LLC design, enables the use of medium voltage systems in large vessels and offshore platform applications to increase up to 70 MW of installed power,"
The first complete LLC system was delivered in2004 and installed on the MV Normand Skipper, a platform supply vessel (PSV). By the end of 2010, some 70 ships featuring low- voltage versions of the Wärtsilä LLC have been delivered. Pilot sales of Quattro LLC began last year and medium- voltage versions of the LLC solution are being marketed for use in vessel and drilling platform applications
Comparison of the tradional and LLC systems for DE propulsion
Caption: Diagram showing difference between traditional DE arrangement
and the Wärtsilä LLC arrangement with the propulsion transformers
eliminated and replaced by one LLC transformer in a central location.
[image credit: Wärtsilä Corp.]