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Wärtsilä Low Loss Concept (LLC)

A proven energy efficient and highly redundant power distribution system for electric propulsion applications.

The system is available for both Low Voltage and Medium Voltage applications. It features a transformerless design, and its benefits include high redundancy, high efficiency and superb system availability.

The Low Loss Concept 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.

Previous developments have been within the fields of electric propulsion, hybrid concepts and fuel economy. The Low Loss Concept (LLC) is a new alternative to power distribution systems, comprising higher efficiency, lower weight and volume, and a high system redundancy. It represents a fresh approach in supplying power to the frequency drives for electric propulsion.

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.

Detailed description

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.

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.