Low Loss Concept (LLC)

LLC is an energy efficient and highly redundant power distribution system for electric propulsion applications.

The Low Loss Concept (LLC) is a power distribution system comprising higher efficiency, lower weight and volume, and a high system redundancy. The basic motive for the design is to reduce and eliminate the need for supply (pulse) transformers to the frequency converters, especially those supplying electric propulsion.

LLC is available for both Low Voltage and Medium Voltage applications. It covers all power applications between 5MW and 45MW in both the Low Voltage and Medium Voltage versions. It is effective also in vessels with operating profiles that require variable speeds, such as OSVs.

The LLC power distribution system has been patented internationally by the Wärtsilä Group.


    The LLC concept has proven advantageous in several aspects

    • The transformerless configuration of the LLC system results in a higher system efficiency of 2% – 3%. This in turn implies a 10% lower fundamental current supplied from the switchboard to the frequency converter.
    • The lower electric losses in the system will result in improved fuel economy and a reduced need for auxiliary machinery systems.
    • The introduction of the LLC transformer in the electric distribution system reduces the overall short circuit current level by 15% to 20%. This allows for a system design comprising Low Voltage (LV) components, and subsequently significant weight and volume reductions compared to traditional systems that include transformers. For certain applications, the weight reduction may be 35% to 40% compared to competing designs.
    • The Total Harmonic Distortion (THD) of the voltage in a LLC system is slightly better than in a traditional 12 pulse system, and is always designed to be less than 5%.
    • The dual supply to the frequency converters, and the four galvanic separated switchboards, increase the total system availability significantly. The converter supplying the propellers will continue to operate should a switchboard failure occur.
    Technical data

    The LLC solution is based on a common 30 degrees phase shifting transformer, which provides the power supply to the 12 pulse rectifying bridge, thus cancelling harmonic currents caused by the frequency converters.

    Example Schema SLD LLC
    Example SLD LLC

    Related references

    Press releases


    10 August 2010
    • Twentyfour7. article

    Low Loss Concept

    LLC is an effective way of avoiding the use of heavy and space-consuming transformers in the power distribution...

    E&A acquisition

    With the acquisition of L-3 Marine Systems International (MSI) Wärtsilä broadens its offering within the area of Electrical & Automation. We now have extensive experience in supplying automation, navigation, communication, electrical distribution, electrical power & propulsion, dynamic positioning, sonar and underwater communications, entertainment, safety and security technologies, for a wide variety of vessel types. These products and systems are well regarded in the cruise & ferry, commercial cargo, offshore and oil & gas markets as well as with navies around the world.

    The products of Wärtsilä SAM Electronics, Wärtsilä Valmarine, Wärtsilä Lyngsø Marine, Wärtsilä Dynamic Positioning & Control Systems, Wärtsilä JOVYATLAS EUROATLAS, Wärtsilä Elac Nautik, Wärtsilä FUNA and Wärtsilä APSS, are well known and respected throughout the industry. With our resources in Norway we can now proudly claim that this makes Wärtsilä the marine industry’s leading E&A provider. We can now provide our customers with the latest technologies and greater opportunities for meeting their present and future needs.

    Read more about our acquisitions


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