Selected Electrical Question And Answer for MEO Class 2 (6)

(a)                State what are the main considerations when designing a ship’s main electrical power supply system, with respect to the type of services supplied, and state the minimum number of generators that may be utilised.                                                            (5m)                            

(b)               What are the considerations under which minimum number of generators may be designed for? Discuss if the generators should be design for equal load sharing, or if not the design considerations you would deem essential. List the main loads you would include in your design appraisal.                                                   (5m)

Answer :-

(a)                Main consideration for electrical circuit design with respect to type of sources supplied:

1)      electrical load is divided into essential and non essential sources for safety of personnel and safe navigation. Essential services are necessary for loads which required to handle in emergency situation.

2)      In case of fire in ER or blackout, essential services will receive power from emergency sources.

3)      The distribution system provide power to essential services which are duplicated from separate section of switchboard.

4)      Lighting in machinery spaces:

1)      2 sets to prevent darkness.

2)      Switches of double pole type.

3)      Emergency lighting.

5)      Undesired restarting after trip due to low voltage except for essential services e.g. steering gear.

6)      Remote stop of vent fan and pumps delivery oil to boilers and main engine.

7)      Electrical power to starting fire pump not passing thru engine room.

8)      Heating and cooking equipment is controlled by multiple switch mounted reset to equipment.

9)      Fire detection system from main and emergency sources.

(b)               Number of rating of generator sets:

1)      power rating of generators determined by power demand of the electrical load.

2)      The designer estimates the number and power rating of the requird generator by assessing power demand at sea, port and all other situations.

3)      With one generator out of services:

1)      the remaining set or sets must ensure power to essential services.

2)      the remaining set or sets must have reserve power to permit starting of largest motor without excessive voltage dip.

4)   For UMS ship:

1)      where one generator supplies power, stand by generator should start automatically in case of power failure.

2)      Where 2 generators operate in parallel, any loss of one generator, the remaining set should be able to supply power.