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History of Shore Power Supply by Ships
We all know that many ships when in port use shore to ship power to carry out maintenance work. However, in the past, during wars and environmental catastrophes, large ships were proposed to provide electrical power to small cities or remote areas that were affected. There are several such instances where ships were responsible for supplying electrical power from ship to shore. For example, a US war ship was proposed to supply power to the city of New Orleans after it was hit by the hurricane Katrina.
During World War II, a few US war ships were specifically assigned to supply power to the shore. All these massive ships had turbine generators, which were driven by steam from the oil fired boilers. The turbine generators moved the electric propulsion motors to generate power. All these ships were also equipped with long cables and transformers so that they could deliver power to long distanced places at higher voltages.
A ship named Wiseman powered the city of Manila during World War II and also the port of Mason during the Korean War. It delivered 5,806,000 kwh, a generation capability greater than 1.4 Mw. Also, a ship named Sturgis equipped with a nuclear power plant provided power to the Panama Canal Zone from 1968 to 1975 with a generation capacity of 10 Mw.
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Ship to Shore Power - Still Viable?
Presently there are only a handful of ships that are used to supply power to the shore, probably due to the fact that there are hardly any areas remaining that are not easily accessible at the time of emergencies. But the same phenomena and strategy are used to deliver power to ships from shore or transferring power from one ship to another.
For example, submarine USS- Key West once received power from a war ship anchored off Monaco. This helped to shut down the nuclear reactor of the submarine for some time, giving a bit of relief to the labor intensive submarine. Thus electrical power can be transferred from ship to shore, shore to ship, and from one ship to another.
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Power Producing Capability of Ships - Some Facts
How much power can a ship provide or need?
The amount of power a ship can produce and requires depends on the size of the ship and also on the unit of measure. However for ship to shore or shore to ship power supply the unit for measuring power is quite interesting. The unit of measuring power is nothing but a single shore power cable. This means that the ship's power generation capability is determined after looking at the number of shore power cables attached to it. Also, the ship is considered a load, and it is assumed that it can deliver as much power as it can draw.
The cables are rated to 400A at 450V; 3 phase, i.e. 0.312 MW as unity power factor. A submarine or a war ship connects up to 8 cables, yielding a total of 2.5 MW.
The amount of power a navy ship can deliver to the shore ranges from 2.5 to 21 MW, excluding the power required to power the ship and its power plant.
The problem and the solution within
It is widely believed that a ship can deliver much more power than it usually does. Most of the power generated is used and wasted in the propulsion system of the ship. In the greatest number of ships the steam produced from the oil fired boilers is directly sent to the propulsion turbines which are directly coupled to the propeller shaft. A considerable amount of steam is wasted in the process as propulsion doesn’t consume all the steam produced.
To prevent the wastage of steam, many steam plants fired by oil or by a nuclear reactor use an arrangement in which though the turbines are directly attached to the shaft, the steam can be diverted upstream where it is used to drive a large turbine generator. The used steam and the condensate again goes back to condensate system from where it can be reused, thus forming a loop.
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In the Future, the All-electric Ship
The future is definitely for the “all-electric" ships. A considerable amount of research time and money is being spent to prevent the undesirable loss of steam and to use that energy in other important activities on the ship. For example, in future the US navy is concentrating on using just “all electric" ships to provide it with more power supply for it combat activities. A future destroyer, DD(X) is an “all electric" ship with Rolls-Royce MT-30 gas turbine generators, producing a total of 78MW of electrical power.