Low and High Voltage Supply Onboard Ship

http://boatrepairpensacola.com/wp-content/uploads/2015/01/wiring.jpgGenerally electrical power generated at power station is at low voltages (generation voltage will be
around 11 to 33kV) depending on the power output rating of the generator and transmitted to the load centers by stepping up the generating power through step-up transformer. The voltages used on board  a ship is usually a 3phase, 60Hz, 440 Volts supply being generated and board  a ship is usually a 3phase, 60Hz, 440 Volts supply being generated and distributed  on board. As the ship size increases, there is a need to install more powerful engines and other machineries.This increase in size of machineries and other equipment demands more electrical power and thus it is required to use higher voltages on board a ship.Any Voltage used on board a ship if less than 1kV(1000 V) then it is called as LV (Low Voltage) system and any voltage above 1kV is termed as High voltage.
High voltage supply onboard ship
1. High voltage systems are more extensive with complex networks and connections,
2. Isolated equipment MUST BE earthed down
3. Access to high voltage areas should be strictly limited and controlled
4. Isolation procedures are more involved
5. Switching strategies should be formulated and recorded
6. Specific high voltage test probes and instruments must be used
7. Diagnostic insulation resistance testing is necessary
8. High voltage systems are usually earthed neutral and use current limiting resistors
9. Special high voltage circuit breakers have to be installed

Reasons for Using High Voltage Systems On board Ships
– Higher power requirements on board vessels is the foremost reason for the evolution of HV in ships.
– Higher power requirements have been necessitated by development of larger vessels required  for container transport particularly reefer containers
– Gas carriers needing extensive cargo cooling Electrical Propulsion.
–  For ships with a large electrical power demand it is necessary to utilise the benefits of a high voltage (HV) installation.
–  As per ohms law relationship that current (for a given power) is reduced as the voltage is incresed.
–  Working at high voltage significantly reduces the relative overall size and weight of electrical power   equipment.
As per Ohms law
Power = Voltage x Current
When large loads are connected to the LV system the magnitude of current flow becomes too large
resulting in overheating due to high iron and copper losses.
P = VI Cos
Copper loss =I² R [kW]
Advantages:
For a given power, Higher voltage means Lower current, resulting in:
– Reduction in size of generators, motors, cables etc.
– Saving of Space and weight
– Ease of Installation
– Reduction in cost of Installation
– Lower losses – more efficient utilization of generated power
– Reduction in short circuit levels in the system which decides the design and application of the
electrical equipment used in the power system.
Disadvantages:
1. Higher Insulation Requirements for cables and equipment used in the system.
2. Higher risk factor and the necessity for strict adherence to stringent safety procedures.

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