How is Power Generated and Supplied on a Ship?
A ship is like a floating
city with all the privileges enjoyed by any normal land city. Just like a
conventional city, the ship also requires all the basic amenities to sustain
life on board; the chief among them is power or electricity. In this article we
will learn as to how power is generated and supplied on board a ship.
Power generation On board
Shipboard power is
generated using a prime mover and an alternator working together. For this an
alternating current generator is used on board. The generator works on the
principle that when a magnetic field around a conductor varies, a current is
induced in the conductor.
The generator consists
of a stationary set of conductors wound in coils on an iron core. This is known
as the stator. A rotating magnet called the rotor turns inside this stator
producing magnetic field. This field cuts across the conductor, generating an
induced EMF or electro-magnetic force as the mechanical input causes the rotor
to turn.
The magnetic field is
generated by induction (in a brushless alternator) and by a rotor winding
energized by DC current through slip rings and brushes. Few points to be noted
about power on board are :
§
AC, 3 phase power is preferred over
DC as it gives more power for the same size.
§
3 phases is preferred over single
phase as it draws more power and in the event of failure of one phase, other 2
can still work.
Power Distribution on board
The Power Distributed
on board a ship needs to be supplied efficiently throughout the ship. For this
the power distribution system of the ship is used.
A shipboard
distribution system consists of different component for distribution and safe
operation of the system. They are:
§
Ship Generator consisting of prime
mover and alternator
Main switch board which is a metal enclosure taking power from the diesel
generator and supplying it to different machinery.
§
Bus Bars which acts as a carrier and
allow transfer of load from one point to another. Circuit breakers which act as
a switch and in unsafe condition can be tripped to avoid breakdown and
accidents. Fuses as safety device for machinery.
§
Transformers to step up or step down
the voltage. When supply is to be given to the lighting system a step down
transformer is used in the distribution system.
§
In a power distribution system, the
voltage at which the system works is usually 440v.
§
There are some large installations
where the voltage is as high as 6600v.
§
Power is supplied through circuit
breakers to large auxiliary machinery at high voltage.
§
For smaller supply fuse and miniature
circuit breakers are used.
§
The distribution system is three
wires and can be neutrally insulated or earthed.
§
Insulated system is more preferred as
compare to earthed system because during an earth fault essential machinery
such as steering gear can be lost.
Emergency Power
In case of the failure
of the main power generation system on the ship, an emergency power system or a
standby system is also present. The emergency power supply ensures that the
essential machinery and system continues to operate the ship.
Emergency power can be
supplied by batteries or an emergency generator or even both systems can be
used.
Rating of the
emergency power supply should be made in such a way that it provides supply to the
essential systems of the ship such as
a)
Steering gear system
b)
Emergency bilge and fire p/p
c)
Watertight doors.
d)
Fire fighting system.
e)
Ships navigation lights and emergency lights.
f)
Communication and alarm system.
Emergency generator is
normally located outside the machinery space of the ship. This is done mainly
to avoid those emergency situations wherein access to the engine room is not
possible. A switch board in the emergency generator room supplies power to
different essential machinery.
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