Hv Genration - Transpformation - Converson & Distribution

D1MC Semester 1 / Energy Conservation Management ( ECM06) / May 2007 /

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To Be A World Class Maritime Academy


SHIPBOARD POWER GENERATION CONVERSION AND DISTRIBUTION

SYSTEM


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General Power Systems

• Majority of merchant ships have a 3-phase 3 wire, 440 V insulated neutral earth power systems

• This power system falls in the category of LV and meets the power demands of medium capacity motors up to 200 kW


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contd

• 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]


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Losses in Electrical Systems

• Copper Losses in electrical cables and machine windings

• Hysteresis Loss in magnetic cores

• Eddy current loss in conductors and cores

• All these losses are current dependent and rise to very high levels in LV machines for large power ratings


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Benefits of H V Power Systems

• Ships with large electrical loads now operate at high voltage of 3.3-6.6 kV

• Such high voltage reduces the magnitude of current and thus lowers iron/copper/eddy current losses and also results in a cooler motor operation

• Low current flow reduces conductors size and hence lowers cost of electrical equipment

• Power transmission more efficient with low loss


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contd

• A 6 MW motor load at 440 V and 0.8 pf will require SB fault level to be of 90 kA and cable full load current of 3300 A

• Same power system at 6.6 kV, needs SB fault level of only 9 kA and cable full load current of 220 A


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contd

• Flexibility of power system layout– Prime Mover-Generator units can be located at

convenient location away from the propellers – Propulsion motor can be located at the astern

below the water surface – This results in shorter shaft and reduced vibration


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contd

• Load Diversity– A set of prime movers can meet the demand of

propulsion as well as ships electrical load– Prime movers can be operated at economical

speed at all times – Propulsion load can be regulated to meet

emergency electrical load without adversely affecting the ships passage time


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contd

• Ease of Control– With advancement in power electronics fine speed

regulation of ac motors has become common practice


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Typical Marine HV Systems

• 3.3 kV

• 6.6 kV

• 11 kV

• By generating electrical power at 6.6 kV instead of 440 V, distribution and switching power about 6 MW becomes easy


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Principal Components of HV System

• Main Generators

• HV Switch Board

• HV Cables

• HV Transformers

• HV Motors (2-12 MW)


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Typical HV Equipment Rating

• Main SB = 6.6 –11 kV, Bus Cap =1250A

• Cargo SB = 6.6 kV, Bus Cap =1250 A

• Ballast Pp Motor = 6.6 kV, 330 – 2000 kW

• HD Copm = 6.6 kV, 770 kW, 3560 rpm

• Bow Thrusters = 6.6 kV, 3 MW,

• Transformer = 3400 kVA, 6600/450 V

• Reefer Transformer = 6600/450 V,


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Typical HV Power System


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HV/LV Power Supply system


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Propulsion Plant Layout


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HV Propulsion Power System


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Concept of Electrical Propulsion


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Typical Azipod Prime Mover


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Azipod Drive Unit


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Typical EL Propulsion


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Twin Shaft EL Propulsion


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Earth Connections

• Distribution systems of these high voltage usually have their neutral points earthed to the ship’s hull through a resistor

• The resistor in neutral line limits earth faults currents and protects equipment


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Types of Neutral Connections

• Insulated Neutral System

• Earthed Neutral System

• Resistance earth Neutral System


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Insulated Neutral to Earth

• This system is totally insulated from the ship’s hull• This system maintains continuity of power supply to

the equipment even in the event of single phasing fault.

• This ensure power supply to critical equipment• The power supply to the equipment can disrupt only

if two single phase faults occur simultaneously in two lines which is then equivalent to short circuiting faults

• But such fault occur very rare


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Insulated Earth Neutral

Gen

Earth

Load


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Insulated Earth 3-Phase

Earth

LoadGen

Single Earth Fault no effect


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Insulated Earth 3-Phase

Earth

LoadGen

Double Earth short Circuit


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Neutral Earthed System

• Earthed Neutral is done in 3-phase system for supply voltage of 3.3-6.6 kV and above

• If a solidly earthed system is used for such high voltage then magnitude of earthed current will be extremely high which can damage the equipment

• The earth current is limited by connecting a resistor in series between earth and neutral point

• The earth current due to single phasing is limited not to exceed rated current at maximum load


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Neutral Earth 1-Phase

Gen

Earth

Load

Fault


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Neutral Earth 3-Phase

Earth

LoadGen

Fault in Line


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Switch Boards

• Switchboard is the main electrical power control center of the ship

• All generators deliver their electrical power to the main switch board.

• Main switch board supplies power to section boards, motor starters, lighting boards and other distribution lines

• Main switch board is connected to emergency switch board/ generator/battery back up


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Types of Switch Boards

• Open front Type– All essential switch gears are exposed in front of

the panel. Used for dc power system

• Dead Front Type– All switch gears and live parts are concealed

behind the front sheet panel– Only the operating handle and instruments appear

on the front. Mandatory for ac power system


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Contd

• Dead front SB is made accessible by providing hinged doors in the front panel

• Some times too many equipment crowd the SB which make maintenance difficult

• Indication Lamp is provided in the switchboard to show that the shore supply is available for connection to bus bar


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FPSO Electrical system Layout


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Shuttle Tanker Electrical System Layout


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Shuttle Tanker Electrical Line Diagram


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Drill Ship Electrical System Layout

Hv Genration - Transpformation - Converson & Distribution

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