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Monday, 6 January 2020

High Voltage System - Reason for having High Voltage System On board ships



As we already know about the voltages used onboard a ship. It is usually a 3phase, 60Hz, 440 Volts supply being generated and distributed onboard ship.

  1. Higher power requirement on board ship is the foremost reason for the evolution of HV in ships.
  2. Higher power requirement has been necessitated by development of larger vessel required for containers transport particularly reefers containers and cruise vessels.
  3. Gas carriers needing extensive cargo cooling electric propulsion.
  4. For a ship with large electrical power demand, it is necessary to utilize the benefits of a high voltage installation.


The design benefits relate to the simple ohms laws relationship that current (for a given power) is reduced as the voltage is increased. Working at high voltage onboard ship significantly reduces the relative overall size and weight of electrical power equipment.



When Heavy loads are connected to the Low voltage system the magnitude of current flow becomes too large resulting in overheating due to high iron and copper losses.

P = V * I * COS(Φ)

Copper losses = I^2 * R (KW)

Already High Voltage levels of 3.3 KV, 6.6 KV and 11 KV are regularly employed ashore for regional power distribution and industrial motor drives.

For example, a motor (let us assume a bow thruster), maybe a smaller size if it designed to operate on 6600 Volts. For the same power, the motor would be of a smaller size if is designed for 6600 Volts when compared to 440 Volts.

Thus these are the major reasons why recent ships have shifted towards the high voltage systems. The main disadvantage Highlighted by the owner, when working in an HV installation, is the very necessary adherence to stringent safety procedures.

Advantages:

  1. For a given power, higher Voltage means Lower current, resulting in:
  2. Reduction in size of generators, motors, cables, etc.
  3. Saving of space and weight.
  4. Ease of Installation.
  5. Reduction in cost of Installation.
  6. Lower losses- more efficient utilization of generated power.
  7. 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 strictly adherence to stringent safety procedures.





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