Frequency controlled electric motors

Many of the auxiliary systems on board are in continuous operation, like seawater and freshwater pumps, fans, compressors, etc. Normally these are designed for full speed operation and high air and sea water temperature. This equipment is hence over dimensioned for the operational pattern of the fleet as the need for full capacity is in the range of 25% to 45% of the operating time, and can be higher for selected vessel types.

Traditional electrical motors cannot vary their motor load based on the actual demand and, therefore, the motor runs on a too high load most of the time. Frequency converted motors will regulate the frequency in order to adapt the motor load to the actual need at all times. Then, the total energy consumed by all the electrical motors on board can be reduced significantly. This technology can be applied to all electrical motors on board, but normally will be applied to motors over a certain size.

Applicability and assumptions

It is assumed that motors with frequency converters can be installed for all electrical motors on board for all ships in each included segment and that there are no limitations on type and size of such motors, independent of vessel age.

A frequency converter will enable the electrical motors on most equipment on board to run on part loads instead of on/off as is the case today.

Cost of implementation

Estimated extra cost for installing frequency controlled electrical motors compared to traditional motors are set to $100 to $200 (USD) per kW installed auxiliary engine power on board. It is assumed that the installation cost will decrease over time to half by 2030 due to the increased demand, more modern technology and more producers of ship equipment.

For operational costs it is estimated an extra cost of $3,000 (USD) per year for maintenance of the more sophisticated equipment compared to when standard equipment is used.

Reduction potential

The reduction potential is estimated at 2% to 10% of the total fuel consumption for auxiliary engines.

The effect is assumed not to increase over time as this is fairly standard equipment which has been available for shore applications for many years.

Other References

1. Air pollution and energy efficiency / IMO energy efficiency appraisal tool
2. ABB / Using Variable Frequency Drives (VFD) to save energy and reduce emissions in newbuilds and existing ships