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Emergency power supply & Shaft Alternators for ships machinery operation

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 .

The emergency generator must be rated to provide power for the driving motors of the emergency bilge pump, fire pumps, steering gear, watertight doors and possibly fire fighting equipment. Emergency lighting for occupied areas, navigation lights, communications systems and alarm systems must also be supplied. Where electrical control devices are used in the operation of main machinery, these too may require a supply from the emergency generator.

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A switchboard in the emergency generator room supplies these various loads . It is not usual for an emergency generator to require paralleling, so no equipment is provided for this purpose. Automatic start up of the emergency generator at a low voltage value is usual on modern installations.

alternating-current-distribution-system

Fig: A.C. distribution system


Emergency Generator Operation

To ensure reliable operation in the event of an emergency, the emergency generator/alternator set, if fitted, is to be run up (on load if possible) weekly. Prior to this test, oil, water and fuel levels must be checked. Where possible, the prime mover is to be started by a simulated power failure. These tests and their results are to be recorded in the Engine Room Log Book. Tests should include:- Where a load test requires the emergency switchboard to be blacked out, this should be carried out at least once every 3 months. This will involve blackout of the ESB by manually disconnecting it from the MSB and observing the auto start and paralleling sequence.

“Black-out Tests” must be subject to a risk assessment and critical operations checklist to ensure all electronic equipment connected to the ESB is properly shut down prior to the blackout, and that any other risks have been assessed. The test should be carried out alongside or at anchor.

Once running, the generator load should be increased to the maximum practical load for at least 15 minutes and all electrical load, relevant temperature and pressure readings records.

All maintenance carried out on emergency generator sets is to be in accordance with the manufacturer’s instructions. Suitable frost precautions must be taken with water cooled engines. On air-cooled engines the air path is to be maintained unrestricted with venting arrangements clear of obstruction and free to operate.

Any faults or defects in the emergency generator/alternator, its prime mover and associated equipment, must be rectified and immediately reported to the appropriate management office. Where the above requirement cannot be complied with the shore advice must be consulted and a suitable alternative procedure developed.

Shaft Alternators for ships operation

Some vessels may be fitted with shaft alternators from which the vessel’s main electrical supply can be generated. Officers must understand that the stopping of the prime mover engine (hence the shaft) upon which the alternator is operating, could result in the complete loss of power from all main engines and some auxiliaries.

In bad weather conditions it is advisable to change over the power generation from the shaft generator to the diesels or other source to avoid the fluctuations of prime mover shaft revolutions causing a blackout. In vessels fitted with shaft alternators, all Officers should be aware that the action of changing from shaft alternator power to diesel alternator power (or vice-versa) can occasionally result in total loss of power.

The OOW should ensure, as far as practical, that the vessel is clear of other traffic and is down-wind, down-tide of other navigational hazards when the change of power source is made. The Engine Room will expect suitable notice for the changeover, which is to be effected in good time (at least 30 minutes) before manoeuvring is requested.

The sudden loss of power whilst the vessel is steaming full ahead may lead to consequential problems like Main engine (Diesel) cylinder liner and cover cracks etc due to cooling water disruptions.

The Officers should familiarise themselves with the configuration of the shaft generator on their vessel as there are several different types available which may or may not be paralleled with the ship’s diesel generators. The Reefer sockets may also be powered by shaft alternators in some cases.

In some engine room configurations, the shaft alternators are designed to operate berth to berth and even during the port stay. The Chief Engineer is to ensure that his staff are instructed clearly about the recommended operating procedures on each vessel.


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.....





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