Onboard DC grid

The onboard DC grid has been proposed, as a replacement for the present AC power distribution system for ships with electric propulsion.

This concept represents a new way of distributing energy for low-voltage installations on ships. It can be used for any electrical ship application up to 20 megawatts and operates at a nominal voltage of 1000V DC. The onboard DC grid is simply an extension of the multiple DC links that already exist in all propulsion and thruster drives, which usually account for more than 80 percent of the electrical power consumption on electric propulsion vessels.

Benefits

In addition to boosting efficiency by up to 20 percent, other benefits include space and weight savings of up to 30 percent and flexible placement of electrical equipment.^[1] This allows for significantly more cargo space and a more functional vessel layout where the electrical system is designed around the vessel functions and not vice-versa.

The efficiency improvement is mainly achieved from the system no longer being locked at a specific frequency (usually 60Hz on ships), even though a 60Hz power source can also be connected to the grid. This new freedom of being able to control each power source totally independently opens up numerous ways of optimizing fuel consumption.

The reduced weight and footprint of the installed electrical equipment will vary depending on the ship type and application. One comparison using the Onboard DC Grid instead of the traditional AC system for a PSV,{{subst:|reason=what is PSV? No jargon!|date=October 2011}} reduced the weight of the electrical system components from 115,520 kilograms (254,700 lb) to 85,360 kilograms (188,200 lb).

Fuel savings

The biggest potential for fuel savings lies in the ease with which energy storage devices, such as batteries or super capacitors, can be added to the system. Energy storage will help the engines level out load variations from the thrusters and other large loads.

Operational optimization

Onboard DC Grid allows for new ways of thinking regarding operational optimization. The system is flexible and can combine different energy sources such as engines, turbines, and fuel cells. This means that there is the potential to implement an energy management system that takes into account varying fuel prices and the availability of different fuels.

Challenges

Because the main AC switchboard with its AC circuit breakers and protection relays is omitted from the new design, a new protection philosophy that fulfills class requirements is needed for selectivity and equipment protection. ABB has proposed a solution for protecting the onboard DC grid using a combination of fuses and controlled turn-off semiconductor power devices. Because all energy-producing components have controllable switching devices, the fault current can be blocked much faster than is possible with traditional circuit breakers with associated protection relays.

References

1. ^ "Onboard DC Grid - A significant step forward in electric propulsion increasing vessel efficiency up to 20%" (PDF). ABB. http://www05.abb.com/global/scot/scot293.nsf/veritydisplay/9aef0fff204391adc12578ab001a3dd6/$file/abb%20onboard%20dc%20grid_flyer_2011.pdf. Retrieved 2011 October 16. 

External links

• "Theme site www.dc-grid.com". http://www.dc-grid.com. Retrieved 2011 October 16. 
• "Discussion group on LinkedIn". http://www.linkedin.com/groups?home=&gid=3919853. (registration required)