This is one of the greatest discoveries of all time where electrical energy – the easiest way to transfer power over great distances, is obtained from mechanical energy which in turn is derived from:
- A basic form of fossil fuel namely diesel, petrol and kerosene;
- Conventional means namely gas, steam, and water turbines;
- Non-conventional means namely wind, wave and tidal energies; and of course
- Futuristic means such as nuclear, solar or biomass energy, to name a few!
To be specific, the electrical generators on board a ship (also called alternators when they generate alternating current) may be driven by a diesel engine, a steam or gas turbine, or the main propulsion engine itself (as is the case on most ships today).
These ‘prime movers’ use some form of fuel (and consequently heat energy) that is converted into mechanical energy.
The type of prime mover is determined by the design of the ship and by economic factors involved. The generator’s armature, magnetic field, and associated circuits change this mechanical energy into electrical energy.
Electrical installation of Ship Generator
Wires and cables deliver this power to the electrical loads. The motor, one of the loads connected to a generator, is designed to convert electrical energy back into mechanical energy to do work. Since generators form the heart of the electrical system’s design, their correct rating is the key to a safe, workable and economical system.
Choosing Ship’s Generator
When choosing a marine generator, cognisance must be given to hie nature of the load.
They may be connected to systems that are classified as single-phase, two-wire insulated, three-phase, three-wire insulated and three-phase, four-wire, earthed neutral or minor variants of these.
The generator is often susceptible to large system load swings, loads causing distortion, the connection of motors and the connection of large heater elements for air conditioning systems.
In addition to satisfying the apparent system load requirements, consideration must be given to the special requirements of any large loads, unusual operational requirements, spare capacity requirements and the required system operating philosophy.
International Maritime Regulations (e.g. SOLAS) require at least two generators for a ship’s main electrical power system.
As already mentioned, the generators are normally driven by dedicated diesel engines but this can be expensive, taking up additional space that could be used for other purposes.
For ships engaged on long sea voyages, it will be economical to drive the generators from the main propulsion plant.
International Maritime Regulations also require at least one electrical generator to be independent of the speed and rotation of the main propellers and associated shafting.
Accordingly at least one generator must have its own prime mover.
If a minimum of two generators are installed, one of which is driven from the propeller shaft, failure of one of the generators could make the ship non-compliant with the International Regulations.
For this reason many owners opt to provide three generators.
One is used for the normal sea load (e.g. the shaft generator), leaving two available to meet any unusually high loads or to provide security while manoeuvring.
Alternately, the third is retained, as a standby set, able to provide power should one set fail in service or requires specific maintenance work.
In some applications such as a generator supplying a large SCR (Silicon Controlled Rectifier) type load, the generator rating may be increased well beyond its full-load value, in order to account for harmonic heating and the inductive requirements of the SCR devices.
The output from each of these generators is fed to the main switchboard and then distributed to the various auxiliary services comprising the electrical load.