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Ships Power Generation Equipment & Distribution System

The complete electrical plant on board ship is made up of power generation equipment, a distribution system and the many power utilising devices. Electricity is used for the motor drive of many auxiliaries and also for deck machinery, lighting, ventilation and air conditioning equipment.

A constant supply of electricity is essential for safe ship and machinery operation, and therefore standby or additional capacity is necessary together with emergency supply equipment. Emergency equipment may take the form of an automatically starting emergency alternator or storage batteries may be used.

ships machinery spaces
container ships machinery info
The complete range of electrical equipment will include generators, switch gear for control and distribution, motors and their associated starting equipment and emergency supply arrangements.

Alternating or direct current

Alternating current has now all but replaced direct current as the standard supply for all marine installations. The use of alternating current has a number of important advantages: for example, reduced first cost, less weight, less space required and a reduction in maintenance requirements. Direct current does, however, offer advantages in motor control using, for example, the Ward-Leonard system which provides a wide range of speed.


Machine rating

Motors and generators, both d.c. and a.c., are rated as Continuous Maximum Rated (CMR) machines. This means they can accept a considerable momentary overload and perhaps even a moderate overload for a longer duration.

Temperature affects the performance of all electrical equipment and also the useful life of the insulation and thus the equipment itself. The total temperature of an operating machine is a result of the ambient air temperature and the heating effect of current in the windings, Temperature rise is measured above this total temperature. Adequate ventilation of electrical equipment is therefore essential. Classification Societies have set requirements for the various classes of insulation. The usual classes for marine installations are E, B and F where particular insulation materials are specified and increasing temperature rises allowed in the order stated.

Enclosures

Depending upon the location, a motor or generator will have one of a number of possible types of enclosure. 'Drip-proof is most common and provides protection from falling liquids or liquids being drawn in by ventilating air. A 'watertight enclosure' provides protection for immersion under a low head of water for up to one hour.

'Weatherproof, 'hose proof and 'deck watertight' provide immersion protection for only one minute. 'Totally enclosed' can also be used or an arrangement providing ducted ventilation from outside the machinery space. A 'flameproof enclosure is capable of withstanding an explosion of some particular flammable gas that may occur within it. It must also stop the transfer of flame, i.e. contain any fire or explosion.


High efficiency electric motors

Electric motors are not 100% energy efficient but generally have energy efficiency that could be anything from 75% to 95%. Thus choice of energy efficient electric motors for a ship will make energy saving over the long term. These days, there are standards for energy rating of electric motor and efforts are made to make these motors more energy efficient. Figure 9.10 shows an example of rating practiced by Europe.
electrical motors energy efficient rating


Figure – Example of energy efficiency rating of electric motors

In choice of electric motors for ship, the idea of energy efficiency needs to be taken into account early and during the shipbuilding stage. For existing ships, when an electric motor needs to be replaced due to maintenance requirement, procurement of an energy efficient electric motor should be considered.





Related Info:

  1. A.C. motors for ships machinery
    2. Supplying alternating current to a coil which is free to rotate in a magnetic field will not produce a motor effect since the current is constantly changing direction. Use is therefore made in an induction or squirrel cage motor of a rotating magnetic field produced by three separately phased windings in the stator. ...

  2. Use of A.C. generators
    3. A coil of wire rotating in a magnetic field produces a current. The current can be brought out to two slip rings which are insulated from the shaft. Carbon bushes rest on these rings as they rotate and collect the current for use in an external circuit. Current collected in this way will be alternating, that is, changing in direction and rising and falling in value. To increase the current produced, additional sets of poles may be introduced....

  3. D.C. motors for ships machinery
    4. When a current is supplied to a single coil of wire in a magnetic field a force is created which rotates the coil. This is a similar situation to the generation of current by a coil moving in a magnetic field. In fact generators and motors are almost interchangeable, depending upon which two of magnetic field, current and motion are provided.....

  4. Use of D.C. generators
    5. A current is produced when a single coil of wire is rotated in a magnetic field. When the current is collected using a ring which is split into two halves (a commutator), a direct or single direction current is produced. The current produced may be increased by the use of many turns of wire and additional magnetic fields....

  5. Emergency power supply for ships machinery operation
    6. In the event of a main generating system failure an emergency supply of electricity is required for essential services. This can be supplied by batteries, but most merchant ships have an emergency generator. The unit is diesel driven and located outside of the machinery space .

  6. Maintenance requirement for ships electrical equipment
    7. With all types of electrical equipment cleanliness is essential for good operation. Electrical connections must be sound and any signs of sparking should be investigated. Parts subject to wear must be examined and replaced when necessary. ...

  7. Choice of batteries for ships machinery spaces - Lead acid and alkaline batteries
    8. The battery is a convenient means of storing electricity. It is used on many ships as an instantly available emergency supply. It may also be used on a regular basis to provide a low-voltage d.c. supply to certain equipment.....

  8. Ships battery maintenance guidance
    9. The electrolyte level should be maintained just above the top of the plates. Any liquid loss due to evaporation or chemical action should be replaced with distilled water. Only in an emergency should other water be used. It is not usual to add electrolyte to batteries.....

  9. Operating characteristics of battery for ships machinery spaces
    10. Having been 'discharged' by delivering electrical power a battery must then be 'charged' by receiving electrical power. To charge the battery an amount of electrical power must be provided in the order of the capacity.....

  10. Insulation resistance measurement
    11. Good insulation resistance is essential to the correct operation of electrical equipment. A means must be available therefore to measure insulation resistance. Readings taken regularly will give an indication as to when and where corrective action, maintenance, servicing, etc., is required....

  11. Use of navigational light circuits
    12. The supply to the navigation lights circuit must be maintained under all circumstances and special provisions are therefore made. To avoid any possibility of accidental open circuits the distribution board for the navigation lights supplies no other circuit.....

  12. Ward—Leonard speed control system
    13. As a very flexible, reliable means of motor speed control the Ward-Leonard system is unmatched.The system is made up of a driving motor which runs at almost constant speed and powers a d.c. generator .....

  13. Danger of electric shock to human body
    14. The resistance of the human body is quite high only when the skin is dry. The danger of electric shock is therefore much greater for persons working in a hot, humid atmosphere since this leads to wetness from body perspiration.....




Marine machineries - Useful tags

Marine diesel engines ||Steam generating plant ||Air conditioning system ||Compressed air ||Marine batteries ||Cargo refrigeration ||Centrifugal pump ||Various coolers ||Emergency power supply ||Exhaust gas heat exchangers ||Feed system ||Feed extraction pump || Flow measurement || Four stroke engines || Fuel injector || Fuel oil system || Fuel oil treatment ||Gearboxes || Governor || Marine incinerator || Lub oil filters || MAN B&W engine || Marine condensers || Oily water separator || Overspeed protection devices || Piston & piston rings || Crankshaft deflection || Marine pumps || Various refrigerants || Sewage treatment plant || Propellers || Power Plants || Starting air system || Steam turbines || Steering gear || Sulzer engine || Turbine gearing || Turbochargers || Two stroke engines || UMS operations || Drydocking & major repairs || Critical machinery || Deck machineries & cargo gears || Control and instrumentation ||Fire protection ||Engine room safety ||





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