Wärtsilä Low Loss Concept (LLC) Power Distribution System

The Wärtsilä Low Loss Concept (LLC) is a power distribution system for electric propulsion that offers higher efficiency, lower weight and volume, and high redundancy. It reduces or eliminates the need for supply (pulse) transformers to the frequency converters supplying electric propulsion. The system is internationally patented by Wärtsilä.

LLC is available for Low Voltage and Medium Voltage applications, covering power ranges between 5 MW and 45 MW. It is also effective on vessels with variable-speed operating profiles, such as OSVs.

How it works

LLC is based on a common 30-degree phase-shifting transformer that supplies the 12-pulse rectifying bridge, cancelling harmonic currents caused by the frequency converters. Frequency converters have dual supply and the system uses four galvanically separated switchboards.

Key benefits

• Transformerless configuration gives 2–3% higher system efficiency and 10% lower fundamental current from switchboard to frequency converter
• Lower electrical losses improve fuel economy and reduce the need for auxiliary machinery
• Overall short-circuit current level reduced by 15–20%, enabling use of LV components and significant weight and volume savings; for certain applications weight reduction may be 35–40% compared to competing designs
• Voltage THD slightly better than a traditional 12-pulse system, always designed below 5%
• High availability: the converter supplying the propellers continues to operate if a switchboard fails

References

Installed on vessels such as the PSV Viking Lady (four Wärtsilä 32DF dual-fuel engines with LLC), RRS Discovery and the PSV Viking Prince.