Tuesday, March 2, 2010

Onshore Power Supply for Ships—reducing ship engine emissions

Excerpt from U.S. Coast Guard “Proceedings of the Marine Safety & Security Council” magazine by Mr. Thane Gilman, P.E., U.S. Coast Guard Systems Engineering Division.

Onshore power supply (OPS) provides ships with a source of electrical power as an alternative to the ship’s service electrical power system. This can lessen engine emissions in the port area since the ship no longer has main or auxiliary engines operating.

On the other hand, there are difficulties associated with high voltage, varying frequencies, and infrastructure costs that must be addressed in order to justify an onshore power supply installation.

System Requirements
A typical OPS system requires many components. At the very least, significant infrastructure is required for the cable handling system, switchgear, protective boxes, transformers, and power cables. Additionally, this equipment must not interfere with vessel cargo operations, cranes, or passenger transit, so proper location of the ship/shore interface is critical. The onshore power one-line electrical diagram shows a typical onshore power supply system.

The design of many modern vessels with high-voltage electrical distribution systems, such as those of 6,600 volts or 11,000 volts, enables more power to be transferred with less cable area than traditional 450V electrical systems. However, most of the vessels comprising the world’s fleets are 440V to 480V systems. The in-port power requirements for different types of vessels can vary substantially.

The most notable benefit is reducing engine emissions in the port area. Once the infrastructure is set up, ships that make relatively frequent calls to particular ports can transition to onshore power supply as a matter of routine.

A secondary benefit of a secured plant is that maintenance and repairs can be facilitated on equipment that is not in operation. Also, the interval for receiving engine bunker fuel may be increased slightly as less ship fuel is used, and the relative cost of the energy provided by the shore facility may be favorable compared to the operating cost of ship engine/generator combinations.

Cost. The cost of infrastructure, including electrical equipment such as transformers, switchgear, power cables, cable handling equipment, and associated support structures on the piers, is significant. Obviously, as the distance from the shore utility to the ships on the piers increases, the cost multiplies. Similarly, the cost increases as the number of onshore power supply locations increases.

Compatibility. The ship and shore frequencies must match within limits for OPS to even be considered. It generally requires a frequency converter for a 50-Hertz supply (shore) to work with 60-Hertz loads (ship), or vice versa. Frequency converters at the power levels required are an expensive addition to an already significant infrastructure.

Safety and quality of power. Standards must be agreed upon between ship operators and shore personnel as to safety procedures at a particular installation. Additionally, the minimum quality of electrical power required needs to be defined by the ship, such that safe disconnection of shore power can be initiated if the power quality deteriorates to a level where ship equipment may be damaged.

Standardization. Efforts to formally develop an international standard for OPS installations have been underway within the International Organization for Standardization since 2006.

For more information:
Full article and “Environmental Protection” edition of USCG Proceedings is available at http://www.uscg.mil/proceedings/Winter2008-09/.

Subscribe online at http://www.uscg.mil/proceedings/subscribe.asp.

Direct requests for print copies of this edition to: HQS-DG-NMCProceedings@uscg.mil.