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.