5. All Electric Ship

(1)

All Electric Propulsion System

(2)

HV voltage generation, conversion ,

transformation and distribution in ship

(3)

Marine Electrical System



 Maritime electric systems include power generation, distribution andMaritime electric systems include power generation, distribution and control, and consumption of electric power

control, and consumption of electric power on supply- service- andon supply- service- and fishing vessels as well as offshore installations.

fishing vessels as well as offshore installations. 

 Electric propulsion has increased especially for vessels with severalElectric propulsion has increased especially for vessels with several large

large

power consumers, for example cruise ships, floating

power consumers, for example cruise ships, floating production systems,production systems, supply- and service vessels.

supply- and service vessels. 

 Maritime electric systems are autonomous power systems. The primeMaritime electric systems are autonomous power systems. The prime movers, including diesel engines, gas- and steam turbines, are integral movers, including diesel engines, gas- and steam turbines, are integral parts of the systems.

parts of the systems. 

 The power consumers are large compared with the total capacity of theThe power consumers are large compared with the total capacity of the system, as for example thruster and propulsion

system, as for example thruster and propulsion systems for DPsystems for DP operated vessels, drilling systems, HVAC systems on board ship operated vessels, drilling systems, HVAC systems on board ship

(4)

Marine Electrical System



The overall power train efficiency with DEP is around 87-90%.

Use of permanent magnets in electric generators and motors as

well as general advances in semiconductor technology may

improve this figure to around 92-95% in the near future. Electrical

transmission will consist of three basic energy conversions:



From (rotating) mechanical energy into electrical energy: E-

From (rotating) mechanical energy into electrical energy:

E-generator

generator



From electrical energy into (rotating) mechanical

energy: E-motor



Some form of fixed or controlled electrical conversion in

between: power converter

(5)

Systematic overview of existing

types

E-generator E-generator



 _Mechanica_Mechanica_l_{l ==> Electrical:}_{==> Electrical: E-Generato}_E-Generato_rs_rs

  - DC Generators- DC Generators   _{- AC}_{- AC Generators}_Generators E-Motors E-Motors 

 _{Electrical ==> Mechanical: E-motors}_{Electrical ==> Mechanical: E-motors}



 - Driving motors- Driving motors



 - Synchronous Motor - Synchronous Motor



 - Positioning motors- Positioning motors

Power converters Power converters

Electrical ==> Electrical: power

Electrical ==> Electrical: power conversion or transformationconversion or transformation



 _{- Fixed}_{- Fixed transforme}_transforme_rs_rs



 - - Controlled convertersControlled converters



 _{- Static converters}_{- Static converters}



(6)

Structure of a combined power plant for

ships

(7)

Electric

Electric Propulsion

Propulsion

System

System (AES)

(AES)



 Electric propulsion of ships has been know for Electric propulsion of ships has been know for a long time to humana long time to human



 Dynamic changes in hDynamic changes in human discovery has givuman discovery has given en several up and several up and down indown in

history history



 Recent time havRecent time have seen a e seen a a lot of a lot of Passenger ships bePassenger ships being built with ing built with allall

electric system for

electric system for various advantage that over the conventional primevarious advantage that over the conventional prime movers

movers



 Early large passenger vessels employed the turboelectric system Early large passenger vessels employed the turboelectric system whichwhich

involves the use of variable speed, and therefore variable frequency, involves the use of variable speed, and therefore variable frequency, turbo-generator sets for the supply of electric power to the propulsion motors

generator sets for the supply of electric power to the propulsion motors directly coupled to the propeller shafts. Where,

directly coupled to the propeller shafts. Where, the generator/motor systemthe generator/motor system was acting as a speed reducing transmission sys

was acting as a speed reducing transmission system.tem.



 Electric power for auxiliary ship services required the use of separateElectric power for auxiliary ship services required the use of separate

constant

constant frequency frequency generator generator sets. sets. System System with with generating generating sets sets to to provideprovide power to both the propulsion system and ship ancillary s

power to both the propulsion system and ship ancillary services.ervices.



 However fixed voltage and frequency system are suitable to sHowever fixed voltage and frequency system are suitable to satisfy theatisfy the

requirements of the ship service loads. requirements of the ship service loads.

(8)

Marine Electrical System

(9)

Electric

Electric Propulsion

Propulsion

System

(AES)



 Other complication associatOther complication associated with ed with earlier systems is difficulties in earlier systems is difficulties in using multipleusing multiple

motor per shaft

motor per shaft when required propulsion power was beyond when required propulsion power was beyond the capacity of the capacity of aa single d.c. motor .

single d.c. motor .



 Developments in high power static converter equipment have – presented a veryDevelopments in high power static converter equipment have – presented a very

convenient means

convenient means of of providing variable speed providing variable speed a.c. and a.c. and d.c. d.c. drives at drives at the the largestlargest ratings likely to be required in a marine propulsion system.

ratings likely to be required in a marine propulsion system.



 The electric propulsion of ships requires electric motors to drive the propellers andThe electric propulsion of ships requires electric motors to drive the propellers and

generator sets to supply the electric power. It may seem rather illogical to use generator sets to supply the electric power. It may seem rather illogical to use

electric generators, switchgear and motors between the prime-movers (e.g. diesel electric generators, switchgear and motors between the prime-movers (e.g. diesel engines) and propeller when a gearbox or length of shaft could be all that is

engines) and propeller when a gearbox or length of shaft could be all that is required.

required.



 In the light of In the light of the above, hybrid of gas turbine or the above, hybrid of gas turbine or Diesel with electric couple withDiesel with electric couple with

dual

dual fuelling that fuelling that include include natural natural gas, gas, is is explorable option explorable option for for existing existing vessels, avessels, allll electric ship using natural gas is also a good option.

electric ship using natural gas is also a good option.



 Currently there is Currently there is interesting development for interesting development for new ship new ship need exploration onneed exploration on

technologie

technologies s to to improve integrated improve integrated full electric full electric propulsiopropulsion n with advanced with advanced power power management systems:

management systems:



 Improved converter and power electronics technologyImproved converter and power electronics technology 

(10)

Electric

Electric Propulsion

Propulsion

System

System (AES)

(AES)



 The AEThe AES gS give widespread ive widespread electrification of electrification of auxiliaries and auxiliaries and thethe

opportunity to use upgradeable and flexible layouts. It will include a low opportunity to use upgradeable and flexible layouts. It will include a low risk, cost effective and comprehensive Platform Management System risk, cost effective and comprehensive Platform Management System that has a standardized Human-Computer Interface supportable for its that has a standardized Human-Computer Interface supportable for its entire service life and the goal to be an Environmentally Sound Ship. entire service life and the goal to be an Environmentally Sound Ship. 

 The fit iThe fit into the goals nto the goals of the Eof the Environmentally Sound nvironmentally Sound Ship Ship where :where : freedom of operation in

freedom of operation in MARPOL special and restricted areas;MARPOL special and restricted areas;

unrestricted littoral operations; port independence; minimum onboard unrestricted littoral operations; port independence; minimum onboard storage of waste and reduced manpower whilst reducing cost of

storage of waste and reduced manpower whilst reducing cost of ownership and port reception costs.

ownership and port reception costs. 

 the also promise potential for replacing the current traditional systemsthe also promise potential for replacing the current traditional systems used in

used in steering gear, steering gear, fin stabilizers fin stabilizers with compact, with compact, power-densepower-dense actuators.

actuators. 

 They also offer potentials for possible use of electric valve actuatorsThey also offer potentials for possible use of electric valve actuators that

that will will simplify simplify system system architectures architectures systematic systematic integration integration of of upper upper deck to machinery.

(11)

Power generation



 A 2001 study concluded that fitting A 2001 study concluded that fitting a Navy cruiser with more energy-a Navy cruiser with more energy-efficient electrical equipment could reduce the ship’s fuel use by 10% to efficient electrical equipment could reduce the ship’s fuel use by 10% to 25%.

25%. 

 Ship fuel use could be reduced by shifting to advanced turbine designsShip fuel use could be reduced by shifting to advanced turbine designs such as an intercooled recuperated (ICR) turbine. Shifting to integrated such as an intercooled recuperated (ICR) turbine. Shifting to integrated electric-drive propulsion can reduce a ship’

electric-drive propulsion can reduce a ship’s fuel use by 10% to 25%.s fuel use by 10% to 25%. 

 There is There is Potential alternative Potential alternative hydrocarbon fuels hydrocarbon fuels Like biodiesel Like biodiesel andand liquid hydrocarbon fuels made from coal

liquid hydrocarbon fuels made from coal 

 Recent time has seen firms offering kite-assist systems to commercialRecent time has seen firms offering kite-assist systems to commercial ship operators.

ship operators. 

 Solar power might offer some potential for augmenting other forms of Solar power might offer some potential for augmenting other forms of shipboard power.

shipboard power. 

 Talking about the Talking about the question now the question now the electric propulsion electric propulsion , especially , especially withwith hybrid system offer the best answer to prob

(12)

Power generation



 Integrated electric-drive system derived from a commercially available system thatIntegrated electric-drive system derived from a commercially available system that

has been installed on ships such as

has been installed on ships such as cruise ships requires a technology that cruise ships requires a technology that is moreis more

torque-dense (i.e., more power-dense) .



 Candidates for a Candidates for a more torque-dense technology include a permanent magnet motor more torque-dense technology include a permanent magnet motor

(PMM) and a

(PMM) and a high-temperatuhigh-temperature superconducting (HTS) synchronous motor.re superconducting (HTS) synchronous motor.



 In addition, electric drive makes possible the In addition, electric drive makes possible the use of new propeller/sternuse of new propeller/stern

configurations, such as a podded propulsion ...

configurations, such as a podded propulsion ... that can reduce ship fthat can reduce ship fueluel

consumption further due to their improved hydrodynamic efficiency



 Podded drives offer greater propulsion efficiency and increased space within the Podded drives offer greater propulsion efficiency and increased space within the hullhull

by moving the propulsion motor outside the ships

by moving the propulsion motor outside the ships hull and placing it in a hull and placing it in a podpod

suspended underneath the hull.



 Podded drives are also Podded drives are also capable of azimuth improving ship capable of azimuth improving ship maneuverabilmaneuverability. Indeed,ity. Indeed,

podded drives have been widely adopted by the cruise

podded drives have been widely adopted by the cruise ship community for theseship community for these

reasons.



 The motors being manufactured now are as large as The motors being manufactured now are as large as 19.5 MW, and could provide19.5 MW, and could provide

the total propulsion power.

(13)

Azipod drive unit

(14)

Comparison of propulsion plants

efficiency

(15)

Weight of propulsion systems

(16)

Prime movers

Gas Turbines Gas Turbines 

 Gas turbine have been selected as the future prime mover primarilyGas turbine have been selected as the future prime mover primarily because of their high power to weight ratio.

because of their high power to weight ratio. 

 4. Weight sensitive ship designs favor gas turbines and projected light4. Weight sensitive ship designs favor gas turbines and projected light weight fuel cell power p

weight fuel cell power plants such as PEM.lants such as PEM. 

 They also provide significant reduction in the amount of routineThey also provide significant reduction in the amount of routine maintenance required when compared with diesel generators. maintenance required when compared with diesel generators. 

 The other significant factor is the low emissions.The other significant factor is the low emissions.

Diesel engine Diesel engine 

 Diesel engines offer fuel Diesel engines offer fuel costs savings of 50% if heavy fuels can becosts savings of 50% if heavy fuels can be used, and if emissions can be maintained at acceptable levels.

used, and if emissions can be maintained at acceptable levels. 

 Maintenance may include engine modifications such as dual fuelMaintenance may include engine modifications such as dual fuel

capability for in-port use, water injection, and timing retard, and exhaust capability for in-port use, water injection, and timing retard, and exhaust treatment such as selected catalytic reduction and

treatment such as selected catalytic reduction and oxidation catalysts.oxidation catalysts. 

 Heavy fuel use also requires careful selection of cylinder material andHeavy fuel use also requires careful selection of cylinder material and lube oil

(17)

Turbina



 A gas turbineA gas turbine, also called a, also called a combustion turbinecombustion turbine, is a rotary, is a rotary engineengine that extracts energy from a flow of

that extracts energy from a flow of hot gas produced by combustion of hot gas produced by combustion of gas or fuel oil in a stream of compressed air.

gas or fuel oil in a stream of compressed air. 

 It has an upstream air compressor It has an upstream air compressor radial or radial or axial flowaxial flow mechanicallymechanically coupled to a downstream

coupled to a downstream turbineturbine and a combustion chamber inand a combustion chamber in between.

between. 

 EnergyEnergy is released when compressed air is released when compressed air is mixed with fuelis mixed with fuel and ignitedand ignited in the

in the combustor combustor .. 

 The resulting gases are directed over the turbine's blades, spinning theThe resulting gases are directed over the turbine's blades, spinning the turbine, and, mechanically, powering the compressor.

turbine, and, mechanically, powering the compressor. 

 Finally, the gases are passed through aFinally, the gases are passed through a nozzlenozzle, generating additional, generating additional thrust by accelerating the hot e

thrust by accelerating the hot exhaust gases by expansion back toxhaust gases by expansion back to atmospheric pressure.

atmospheric pressure. 

 A steam turbineA steam turbine is a mechanical device that extractsis a mechanical device that extracts thermal energythermal energy from pressurized

(18)

Gas Turbine

(19)

Steam engine

(20)

COGAG



 Combined gas turbine and gasCombined gas turbine and gas

turbine (COGAG)

turbine (COGAG) is propulsionis propulsion system for ships using two

system for ships using two gas turbines

gas turbines connected to a singleconnected to a single propeller shaft

propeller shaft..



 AA gearboxgearbox andand clutchesclutches allow either allow either

of the turbines to drive the shaft or of the turbines to drive the shaft or both of them combined.

both of them combined.



 Using one or two gas turbines hasUsing one or two gas turbines has

the advantage of having two the advantage of having two different power settings.

different power settings.



 Since theSince the fuel efficiencyfuel efficiency of a gasof a gas

turbine is best near its maximum turbine is best near its maximum power level, a small gas turbine power level, a small gas turbine running at its full speed is more running at its full speed is more efficient compared to a twice as efficient compared to a twice as powerful turbine running at half powerful turbine running at half speed, allowing more economic speed, allowing more economic transit at cruise speeds.

(21)

Diesel engine

(22)

Prime movers

Electric drive Electric drive



 Electric drive transmissions have a higher specific fuel consumption, specificElectric drive transmissions have a higher specific fuel consumption, specific

weight and

weight and volume than volume than mechanical drive systems, but mechanical drive systems, but has advantages inhas advantages in arrangement which may compensate for these disadvantages.

arrangement which may compensate for these disadvantages.



 Advanced technology motors can be located very close to and on line with theAdvanced technology motors can be located very close to and on line with the

propulsors, at the extreme aft end of the ship, or in external pods. propulsors, at the extreme aft end of the ship, or in external pods.



 Electrical generator Electrical generator sets sets can can be be optimally optimally spaced spaced around the around the ship ship andand

electrically connected. In the longer term, combined with fuel cells, SFC, specific electrically connected. In the longer term, combined with fuel cells, SFC, specific weight and volume are comparable with gas turbine and diesel prime movers for weight and volume are comparable with gas turbine and diesel prime movers for direct drive systems.

direct drive systems. Zone Concept :

Zone Concept :



 The concept of dividing future classes of ship into zones to maximizeThe concept of dividing future classes of ship into zones to maximize

survivability also extends to the power system. survivability also extends to the power system.



 Each zone would be autonomous and include ventilation systems, coolingEach zone would be autonomous and include ventilation systems, cooling

systems, power distribution and other services which could be affected by systems, power distribution and other services which could be affected by damage to another part of the ship.

damage to another part of the ship.



 At least two supplies would be At least two supplies would be provided for all essential loads. Current classes,provided for all essential loads. Current classes,

using split generation and distribution, rely on the provision of normal and using split generation and distribution, rely on the provision of normal and alternative supplies via Automatic Change-Over Switches

(23)

Typical system with zoning

(24)

Fuel cell



 The fuel cell stack operates by utilizing electrochemical reactions betweenThe fuel cell stack operates by utilizing electrochemical reactions between an oxidant (air) and a fuel (hydrogen), with two electrodes separated by a an oxidant (air) and a fuel (hydrogen), with two electrodes separated by a membrane.

membrane. 

 The voltage of the fuel cell output can be controlled by a converter and it isThe voltage of the fuel cell output can be controlled by a converter and it is therefore able to connect to any point in the ship service or propulsion

therefore able to connect to any point in the ship service or propulsion distribution system.

distribution system. 

 The fuel cell stack is modularity give redundancy advantage. It also has theThe fuel cell stack is modularity give redundancy advantage. It also has the additional advantages of zero noxious emissions, and low thermal and

additional advantages of zero noxious emissions, and low thermal and acoustic signatures.

acoustic signatures. 

 In the short term the fuel cell system is required to use marine diesel fuel.In the short term the fuel cell system is required to use marine diesel fuel. Diesel fuel will require reforming within the fuel cell stack, or using an

Diesel fuel will require reforming within the fuel cell stack, or using an

external process, to produce a hydrogen rich gas which the fuel cell stack is external process, to produce a hydrogen rich gas which the fuel cell stack is capable of processing.

capable of processing. 

 The reformer will clearly add both size, weight and complexity to the fuel cellThe reformer will clearly add both size, weight and complexity to the fuel cell system. In the longer term technologies such as the Solid Oxide Fuel Cell system. In the longer term technologies such as the Solid Oxide Fuel Cell (SOFC) are contenders, which are more forgiving of impurities and can use (SOFC) are contenders, which are more forgiving of impurities and can use a fuel available world-wide, either methanol or gasoline.

(25)

Storage option



 The technologies being assessed for energy storage include areThe technologies being assessed for energy storage include are electro-chemical batteries (both conventional and advanced), electro-chemical batteries (both conventional and advanced), regenerative fuel cells (otherwise known as redox flow cells ) regenerative fuel cells (otherwise known as redox flow cells ) Superconducting Magnetic Energy Storage (SMES) and

Superconducting Magnetic Energy Storage (SMES) and Supercapacitors.

Supercapacitors. 

 Regenerative fuel cells store or release electrical energy by means of aRegenerative fuel cells store or release electrical energy by means of a reversible electrochemical reaction between two salt solutions (the

reversible electrochemical reaction between two salt solutions (the electrolytes). The reaction occurs within an electrochemical cell. electrolytes). The reaction occurs within an electrochemical cell. 

 The cell has two compartments, one for each electrolyte, physicallyThe cell has two compartments, one for each electrolyte, physically separated by an ion-exchange membrane.

separated by an ion-exchange membrane. 

 In contrast to most types of battery system, the In contrast to most types of battery system, the electrolytes flow into andelectrolytes flow into and out of the cells and are transformed electrochemically inside the cells. out of the cells and are transformed electrochemically inside the cells. The power is therefore determined by the size of the cell but the

The power is therefore determined by the size of the cell but the endurance is determined by the size of the two electrolyte tanks endurance is determined by the size of the two electrolyte tanks

(26)

Storage system

(27)

Prime movers



 All primemovers are potentially compliant with emerging emissionAll primemovers are potentially compliant with emerging emission

requirements, however, complexity for achieving compliance varies with requirements, however, complexity for achieving compliance varies with prime mover and fuel type.

prime mover and fuel type.



 Diesels require the most attention to Diesels require the most attention to emissions control followed at someemissions control followed at some

distance by gas turbines, where ultra low emissions levels have been distance by gas turbines, where ultra low emissions levels have been achieved for land-based systems.

achieved for land-based systems.



 Fuel cells emit the lowest levels of pollutants of all the primemoversFuel cells emit the lowest levels of pollutants of all the primemovers



 Heavier fuel cell systems and diesels represent larger machinery andHeavier fuel cell systems and diesels represent larger machinery and

structural weight. structural weight.



 Fuel cells can be used as a prime mover in an Integrated Full ElectricFuel cells can be used as a prime mover in an Integrated Full Electric

Propulsion (IFEP) system providing DC

Propulsion (IFEP) system providing DC electrical power output, and areelectrical power output, and are being developed as a replacement for diesel generators and gas turbine being developed as a replacement for diesel generators and gas turbine alternators.

(28)

Sail and solar power ship

(29)

Skysail

(30)

Propulsion motor



For efficient operation of propulsion motor there is a

requirement for a compact, power dense, rugged

electrical machine to be utilized for the propulsion

motor.



For the full benefits of electric propulsion to be

realized the machine should also be efficient,

particularly at part load,



In order to achieve suitable compact designs rare

earth permanent magnet materials may be required.



The machine topologies available for PMM are

deemed to be those based on radial, axial and

transverse flux designs.

(31)

PMM

(32)

Power for LNG ships



 These alternatives are more economical and offer greater overall efficiency withThese alternatives are more economical and offer greater overall efficiency with

an added advantage of providing greater flexibility and redundancy an added advantage of providing greater flexibility and redundancy



 Diesel plant also Diesel plant also raises are raises are inherited with problem of inherited with problem of vibration on membranevibration on membrane 

 LNG carrier it is necessary to understand the interaction between the structuralLNG carrier it is necessary to understand the interaction between the structural

resonance that is excited by the diesel engine and the separate resonance that resonance that is excited by the diesel engine and the separate resonance that is created within the membrane containment system interacting with LNG.

is created within the membrane containment system interacting with LNG.



 The traditional application of gas fired boilers for steam turbine propulsionThe traditional application of gas fired boilers for steam turbine propulsion

systems is no longer the only available option for LNG Carriers,” systems is no longer the only available option for LNG Carriers,”



 Direct drive, slow speed diesel plants, coupled with an on-board liquefactionDirect drive, slow speed diesel plants, coupled with an on-board liquefaction

plant to handle the cargo boil off, or 4 stroke medium speed diesel electric plant to handle the cargo boil off, or 4 stroke medium speed diesel electric propulsion or gas turbine with diesel electric drive appear to offer the greatest propulsion or gas turbine with diesel electric drive appear to offer the greatest operational efficiencies for the new designs of large LNG carriers.

(33)

Power generation for LNG ships



 Although slow or medium speed diesel engines have been selected for some of Although slow or medium speed diesel engines have been selected for some of

the recent LNG carriers with dual fuel installation option that uses both gas the recent LNG carriers with dual fuel installation option that uses both gas boil-off and ordinary bunkers.

off and ordinary bunkers.



 Variations of the dual fuel arrangements include:Variations of the dual fuel arrangements include:

-diesel engine or gas turbine driven generators with one propulsion shafting system -diesel engine or gas turbine driven generators with one propulsion shafting system

and a liquefaction plant; and a liquefaction plant;

-diesel engine or gas turbine driven generators with two propulsion shafting systems -diesel engine or gas turbine driven generators with two propulsion shafting systems

and a liquefaction plant; and a liquefaction plant;

-diesel engine or gas turbine driven generators with two azimuth thrusters and a -diesel engine or gas turbine driven generators with two azimuth thrusters and a

liquefaction plant. liquefaction plant.



 To date, slow speed diesel with re-liquefaction plant as well as a gasTo date, slow speed diesel with re-liquefaction plant as well as a gas

combustion unit, and medium speed dual fuel diesel with gas combustion units, combustion unit, and medium speed dual fuel diesel with gas combustion units, are the preferred options for the new large LNG carriers recently ordered in are the preferred options for the new large LNG carriers recently ordered in Korea.

Korea.



 It would appear that gas turbine with simple and combined cycles using heatIt would appear that gas turbine with simple and combined cycles using heat

recovery units to drive steam turbo alternators are another alternative being recovery units to drive steam turbo alternators are another alternative being explored. Industry is currently developing the fuel gas systems for these gas explored. Industry is currently developing the fuel gas systems for these gas turbine options.

(34)

Power generation for LNG ships



 A dual fuel diesel-electric system uses forced boil-off from the cargoA dual fuel diesel-electric system uses forced boil-off from the cargo tanks as the primary fuel and marine diesel oil as back-up fuel. The tanks as the primary fuel and marine diesel oil as back-up fuel. The arrangement can also be adapted to current LNG carrier designs. arrangement can also be adapted to current LNG carrier designs. 

 Shipbuilders and engine designers that are proponents of dual fuelShipbuilders and engine designers that are proponents of dual fuel systems point out that a gas-electric propulsion

systems point out that a gas-electric propulsion plant is more compactplant is more compact than the traditional steam turbine plant used for LNG carriers,

than the traditional steam turbine plant used for LNG carriers, increasing cargo capacity within the same dimensioned hull. increasing cargo capacity within the same dimensioned hull. 

 The IMO Gas Carrier Code requires two means of utilizing boil-off gasThe IMO Gas Carrier Code requires two means of utilizing boil-off gas on all LNG carriers. Conventional

on all LNG carriers. Conventional systems use the main boilers for systems use the main boilers for generating steam for propulsion. When this cannot be used, excess generating steam for propulsion. When this cannot be used, excess steam is redirected to the condensers. Similar arrangements are steam is redirected to the condensers. Similar arrangements are

required for the diesel propulsion systems. Current industry proposals required for the diesel propulsion systems. Current industry proposals for the alternative means of boil-off gas utilization are a liquefaction for the alternative means of boil-off gas utilization are a liquefaction plant or a gas combustion unit.

plant or a gas combustion unit. 

(35)

Power Distribution



As the demand for electrical are 3.3 kV or 6.6 kV but 11 kV is

used on some offshore platforms and specialist oil/gas

production ships e.g on some FPSO (floating production, storage

and offloading) vessels.



By generating electrical power at 6.6 kV instead of 440 V the

distribution and switching of power above about 6 MW becomes

more manageable.



As for electrical Power increases on ships (particularly

passenger ferries, cruise liners, and specialist offshore vessels

and platforms) the supply current rating becomes too high at 440

V.



To reduce the size of both steady state and fault current levels, it

is necessary to increase the system voltage at high power

ratings.

(36)

Component parts of an HV



 The component parts of an HV supply The component parts of an HV supply system are standard equipmentsystem are standard equipment with:

with:

HV diesel generator sets feeding an

HV diesel generator sets feeding an HV main switchboard.HV main switchboard. 

 Large power consumers such as thrusters, propulsion motors, air-Large power consumers such as thrusters, propulsion motors, air-conditioning (A/C) compressors and HV transformers are fed directly conditioning (A/C) compressors and HV transformers are fed directly from the HV switchboard.

from the HV switchboard. 

 An economical HV system must be simple to operate, reasonably pAn economical HV system must be simple to operate, reasonably pricedriced and require a minimum of maintenance over the life of the ship.

and require a minimum of maintenance over the life of the ship. 

 Experience shows that a 9 MW system at 6.6 kV would Experience shows that a 9 MW system at 6.6 kV would be about 20%be about 20% more expensive for installation costs.

more expensive for installation costs. 

 The principal parts of a The principal parts of a ships electrical system operated at HV would beships electrical system operated at HV would be the main generators, HV switchboard, FV cables, HV transformers and the main generators, HV switchboard, FV cables, HV transformers and HV motors.

HV motors. 

(37)

Ship HV Voltage system

(38)

HV Systems



 In the example shown the HV generators form a central power stationIn the example shown the HV generators form a central power station for all of the ship's

for all of the ship's electrical services.electrical services. 

 On a large passenger ship with electric propulsion, each generator mayOn a large passenger ship with electric propulsion, each generator may be rated at about 10 MW or more and producing 6.6 kV, 60 Hz be rated at about 10 MW or more and producing 6.6 kV, 60 Hz three-phase a.c. voltages.

phase a.c. voltages. 

 The principal consumers are the two The principal consumers are the two synchronous a.c. propulsionsynchronous a.c. propulsion electric motors (PEMs) which may each demand 12 MW or more in electric motors (PEMs) which may each demand 12 MW or more in thethe full away condition.

full away condition. 

 Each PEM has two stator windings supplied separately Each PEM has two stator windings supplied separately from the mainfrom the main HV switchboard via transformers and frequency converters.

HV switchboard via transformers and frequency converters. 

 In an emergency a PEM may therefore be In an emergency a PEM may therefore be operated as a half-motor withoperated as a half-motor with a reduced power output. A few large induction motors are supplied at a reduced power output. A few large induction motors are supplied at 6.6 kV from the main board with the circuit breaker acting as a 6.6 kV from the main board with the circuit breaker acting as a direct-on-line (DOL) starting switch.

(39)

Ship high voltage systems

These motors are: These motors are:

o Two forward thrusters and one aft thruster, and o Two forward thrusters and one aft thruster, and o Three air conditioning compressors

o Three air conditioning compressors 

 Other main feeders supply the 4Other main feeders supply the 440 V engine room sub-station (ER sub)40 V engine room sub-station (ER sub) switchboard via step-down transformers.

switchboard via step-down transformers. 

 An interconnector cable links the ER sub An interconnector cable links the ER sub to the emergency switchboard.to the emergency switchboard. 

 Other 440 V sub-stations (accommodation,galley etc.) around the ship areOther 440 V sub-stations (accommodation,galley etc.) around the ship are supplied from the ER sub.

supplied from the ER sub. 

 Some installations may feed the ships sub Some installations may feed the ships sub stations directly with HV andstations directly with HV and step-down to 440 V locally.

step-down to 440 V locally. 

 The PEM drives in this example are The PEM drives in this example are synchronous motors which require asynchronous motors which require a controlled low voltage excitation supply current to magnetise the rotor controlled low voltage excitation supply current to magnetise the rotor poles.

poles. 

 This supply is obtained from tThis supply is obtained from the HV switchboard via a step-downhe HV switchboard via a step-down transformer but an alternative arrangement would be to obtain the transformer but an alternative arrangement would be to obtain the excitation supply from the 440

(40)

Ship high voltage systems

(41)

High Voltages solid state

AC-DC-AC conversion

(42)

Solid State Switching Principle

•• _{The power systems engineers is interested in}_{The power systems engineers is interested in}_{high voltages primarily for}_{high voltages primarily for}

power transmission, and secondly for testing of his equipment used in power transmission, and secondly for testing of his equipment used in power transmission in laboratory

power transmission in laboratory

•• _{High voltage}_{High voltage can be}_{can be obtained locally}_{obtained locally} _{from power}_{from power}_{generating plant}_{generating plant}

through

through the the use use of of solid solid statestate

•• _{In many testing laboratories, the primary source of power is at low}_{In many testing laboratories, the primary source of power is at low}

voltage (400 V

voltage (400 V three phase or 230 three phase or 230 V single phase, V single phase, at 50 Hz). at 50 Hz). FromFrom which high voltage can be obtained

which high voltage can be obtained

•• _{On board ship the same technology can be used to use high voltage}_{On board ship the same technology can be used to use high voltage} •• _{Laboratory test are aimed to design the required high voltage}_{Laboratory test are aimed to design the required high voltage}



 Since insulation is usually being tested, the impedances involved areSince insulation is usually being tested, the impedances involved are extremely high (order of M ohm and the currents small (less than an extremely high (order of M ohm and the currents small (less than an ampere).

ampere). 

 High voltage testing does not usually require high power.High voltage testing does not usually require high power. 

 Thus special methods may be used which are not applicable whenThus special methods may be used which are not applicable when generating high voltage in high power applications.

(43)

Solid State Switching Principle



 In the field of electrical eng. & applied physics, high voltages are requiredIn the field of electrical eng. & applied physics, high voltages are required for

for several several applications applications As:As:

-a power supply (eg. hv dc) for the equipments such as electron microscope -a power supply (eg. hv dc) for the equipments such as electron microscope

and x-ray machine. and x-ray machine.

-Required for testing power apparatus – insulation testing. -Required for testing power apparatus – insulation testing.

-High impulse voltages are required for testing purposes to simulate over -High impulse voltages are required for testing purposes to simulate over

voltages due to lightning and switching. voltages due to lightning and switching. 

 Sometimes, high direct voltages are needed in insulation test on cablesSometimes, high direct voltages are needed in insulation test on cables

and capacitors. Impulse generator charging units also require high dc and capacitors. Impulse generator charging units also require high dc voltages of about 100-200kV.

voltages of about 100-200kV. 

 Normally for the generation of dc voltages of up to 100kV, electronicsNormally for the generation of dc voltages of up to 100kV, electronics

valve rectifiers are used and the output currents are about 100mA. The valve rectifiers are used and the output currents are about 100mA. The rectifier valves require special construction for cathode and filaments rectifier valves require special construction for cathode and filaments

since a high electrostatic field of several kV/cm exists between the anode since a high electrostatic field of several kV/cm exists between the anode and cathode in the non-conduction period.

and cathode in the non-conduction period. 

 The ac supply to the rectifier tubes maybe of power frequency or maybeThe ac supply to the rectifier tubes maybe of power frequency or maybe

of audo frequency from an oscillator. The latter is used when a ripple of of audo frequency from an oscillator. The latter is used when a ripple of very small magnitude is required without the use of costly filters to

very small magnitude is required without the use of costly filters to smoothen the ripple.

(44)

Half and Full Wave Rectifier



Rectifier circuits for producing high dc voltages from ac sources

maybe

a. a. Half-WaveHalf-Wave b. b. Full-WaveFull-Wave o

o

_{The rectifier can be an electron tube or a solid state devices.}

Nowadays, single electron tubes are available for peak inverse

voltages up to 250kV and semiconductor or solid state diodes up

to 250kV.

o

_{For higher voltages, several units are to be used in series. When a}

number of units are used in series, transient voltage distribution

along each unit becomes non-uniform and special care should be

taken to make the distribution uniform.

(45)

V out V out V

Vinin RRLL

Half Wave Rectifier Half Wave Rectifier

V V A AVVGG V V p p 0 0 T T

Mean Load Voltage or Average Value of half wave output Mean Load Voltage or Average Value of half wave output

(46)

R R _L_L ttoo tt11 tt22 ttoo tt11

+

--D D 11 D D 22 ttoo tt11 tt22 V Vpp V V_A_AV_VG_G

Full wave Rectifier Circuit Full wave Rectifier Circuit

Mean Load Voltage or Average Voltage Full-wave output Mean Load Voltage or Average Voltage Full-wave output

(47)

Voltage Multiplier Circuits



Both full-wave as well as half-wave circuits can

produce a maximum direct voltage corresponding to

the peak value of the alternating voltage.



When higher voltages are required voltage multiplier

circuits are used. The common circuits are the

voltage double circuit



Used for higher voltages.



Generate very high dc voltage from single supply

transformer by extending the simple voltage doubler

circuit.

(48)

Types of high voltages;



High d.c. voltages



High a.c. voltages of power frequency



High a.c. voltages of high frequency



High transient or impulse voltages of very short



duration - lightning overvoltages



Transient voltages of longer duration – switching



(49)



 The voltage doubler circuitThe voltage doubler circuit

makes use of the positive and

the negative half cycles to

charge two different capacitors.

These are then connected in

series aiding to obtain double

the direct voltage output. Figure

shows a voltage doubler circuit.



 In this case, the transformer willIn this case, the transformer will

be of small rating that for the

same direct voltage rating with

only simple rectification. Further

for the same direct voltage

output the peak inverse voltage

of the diodes will be halved.

Voltage doubler circuit Voltage doubler circuit

(50)

High Alternating Voltages



Required in laboratories and a.c. tests as well as for the



circuit of high d.c. and impulse voltage.



Test transformer are generally used.



Single transformer test units are made for high alternating voltages up

to about 200 kV.



However, for high voltages to reduce the cost (insulation cost

increases rapidly with voltage) and make transportation easier, a

cascade arrangement of several transformers is used.



For higher voltage requirement, series connection or cascading of the

several identical units of transformer is applied.

(51)

Cascade arrangement of transformers

(52)

1600 kV, 9.6

(53)



A typical cascade arrangement of transformers used to obtain up to

300 kV from three units each rated at 100 kV insulation. The low

voltage winding is connected to the primary of the first transformer,

and this is connected to the transformer tank which is earthed.



One end of the high voltage winding is also earthed through the

tank.



The high voltage end and a tapping near this end is taken out at the

top of the transformer through a bushing, and forms the primary of

the second transformer.



One end of this winding is connected to the tank of the second

transformer to maintain the tank at high voltage.



The secondary of this transformer too has one end connected to

the tank and at the other end the next cascaded transformer is fed.

Cascade arrangement of transformers

(54)



This cascade arrangement can be continued further if a still

higher voltage is required.



In the cascade arrangement shown, each

transformer needs only

to be insulated for 100 kV, and hence the transformer can be

relatively small. If a 300 kV transformer had to be used instead,

the size would be massive. High voltage transformers for testing

purposes are designed purposely to have a poor regulation.



This is to ensure that when the secondary of the transformer is

short circuited (as will commonly happen in flash-over tests of

insulation), the current would not increase to too high a value and

to reduce the cost. In practice, an additional series resistance

(commonly a water resistance) is also used in such cases to limit

the current and prevent possible damage to the transformer.

Cascade arrangement of transformers

(55)



 What is shown in the cascade transformer arrangement is the basic principleWhat is shown in the cascade transformer arrangement is the basic principle involved. The actual arrangement could be different for practical reasons. involved. The actual arrangement could be different for practical reasons. 

 In the cascade arrangement shown, each transformer needs only to be insulatedIn the cascade arrangement shown, each transformer needs only to be insulated for 100 kV, and hence the transformer can be relatively small. If a 300 kV

for 100 kV, and hence the transformer can be relatively small. If a 300 kV transformer had to be used instead, the size would be massive. High voltage transformer had to be used instead, the size would be massive. High voltage transformers for testing purposes are designed purposely to have a poor transformers for testing purposes are designed purposely to have a poor regulation.

regulation. 

 This is to ensure that when the secondary of the transformer is short circuitedThis is to ensure that when the secondary of the transformer is short circuited (as will commonly happen in flash-over tests of insulation), the current would not (as will commonly happen in flash-over tests of insulation), the current would not increase to too high a value and to reduce the cost. In practice, an additional increase to too high a value and to reduce the cost. In practice, an additional series resistance (commonly a water resistance) is also used in

series resistance (commonly a water resistance) is also used in such cases tosuch cases to limit the current and prevent possible damage to the transformer.

limit the current and prevent possible damage to the transformer. 

 What is shown in the cascade transformer arrangement is the basic principleWhat is shown in the cascade transformer arrangement is the basic principle involved. The actual arrangement could be different for practical reasons. involved. The actual arrangement could be different for practical reasons.

Cascade arrangement of transformers

(56)

High D.C. Voltages



Generation of high d.c. voltages is mainly

required in research work in the areas of pure

and applied physics.



Needed in insulation test.



Use rectifier circuit (diode) to convert a.c. to

d.c.



voltage. – vacuum rectifiers, semiconductor

diodes

(57)

Impulse High Voltage



Impulse voltages (IVs) are required in hv tests to simulate the

stresses due to external and internal overvoltages, and also for

fundamental investigations of the breakdown mechanisms.



Usually generated by discharging hv capacitors through switching

gaps onto a network of resistors and capacitors.



In hv technology, a single, unipolar voltage is termed an impulse

voltage.



Rectangular and wedge-shaped IVs are normally used for basic

experiments while for testing purposes, double exponential IVs are

used.



Standard test of impulse voltages can be represented as double

exponential wave, and its mathematical equation is defined as

follows;

V = Vo [exp(-αt) – exp(-βt)]

Where α and β are constants of microsecond values.

(58)

Controlled Rectification



The generated three power supply on a phase a.c. electrical ship

has a fixed voltage and frequency. This is generally at M0 V and

60 Hz but for high power demands it is likelv to be 6.6 kV and 60

Hz.



Speed control for a propulsion motor requires variable voltage for a

d.c. drive and variable frequency * voltage for an a.c. drive.



The set bus-bar a.c. voltage must be converted by controlled

rectification (a.c.--d.c.) ind/or controlled inversion (d. c. * a. c. )' to

match the propulsion motor type.



A basic rectifier uses semiconductor diodes which can only

conduct current in the direction of anode (A) to cathode (K) and

this is automatic when A is more positive than K.



The diode turns-off automatically when its current falls to zero.

Hence, in –a single-phase a.c. circuit a single diode will conduct

only on every other half-cycle and this is called half-wave

rectification.

(59)

-rectification.

rectification.

(60)

Controlled Rectification



 In this circuit an inductor coil (choke) smooth the d.c. load current evenIn this circuit an inductor coil (choke) smooth the d.c. load current even though the d.c. voltage is severely chopped by the thyristor switching though the d.c. voltage is severely chopped by the thyristor switching action.

action. 

 An alternative to the choke coil is to use a capacitor across the rectifier An alternative to the choke coil is to use a capacitor across the rectifier output which smooths the d.c. voltage. Full wave controlled rectification output which smooths the d.c. voltage. Full wave controlled rectification from a three-phase a.c. supply is achieved in a bridge Circuit with six from a three-phase a.c. supply is achieved in a bridge Circuit with six thyristors a shown

thyristors a shown 

 Other single-phase circuits using a biased arrangement with two diodesOther single-phase circuits using a biased arrangement with two diodes and a centre-tapped transformer will create full-wave rectification

and a centre-tapped transformer will create full-wave rectification

Similarly, four diodes in a bridge formation will also produce a full-wave Similarly, four diodes in a bridge formation will also produce a full-wave d.c. voltage output.

d.c. voltage output. 

 An equivalent three phase bridge requires six diodes for full-waveAn equivalent three phase bridge requires six diodes for full-wave

operation. A diode, having only two terminals, cannot control the size of operation. A diode, having only two terminals, cannot control the size of the d.c. output from the rectifier.

the d.c. output from the rectifier. 

 For controlled rectification For controlled rectification it is it is necessary necessary to use to use a set a set of three-terminalof three-terminal devices such as thyristors (for high currents) or tran

devices such as thyristors (for high currents) or transistors (for low -sistors (for low -medium currents).

(61)

Three-phase controlled rectifier bridge circuit.

(62)

Three-phase controlled rectifier bridge circuit.



 A basic a.c.-d.c. control circuit using a thyristor A basic a.c.-d.c. control circuit using a thyristor switch is shown in the nextswitch is shown in the next

slide. Compared with a diode, a thyristor has an

slide. Compared with a diode, a thyristor has an extra (control) terminalextra (control) terminal called the gate (G).

called the gate (G).



 The thyristor will only conduct when the anode is The thyristor will only conduct when the anode is positive with respect topositive with respect to

the cathode and a brief trigger voltage pulse is

the cathode and a brief trigger voltage pulse is applied between gate andapplied between gate and cathode (gate must be more positive than cathode).

cathode (gate must be more positive than cathode).



 Gate voltage pulses are provided by separate electronic circuit and Gate voltage pulses are provided by separate electronic circuit and thethe

pulse timing decides the switch-on point for the main (load)

pulse timing decides the switch-on point for the main (load) current. Thecurrent. The load current is therefore rectified to d.c. (

load current is therefore rectified to d.c. (by diode action) and controlled byby diode action) and controlled by delayed switching.

delayed switching.



 In this circuit an inductor coil (choke) In this circuit an inductor coil (choke) smooth the d.c. load current evensmooth the d.c. load current even

though the d.c. voltage is severely chopped by the

though the d.c. voltage is severely chopped by the thyristor switchingthyristor switching action.

action.



 An alternative to the choke coil is to use An alternative to the choke coil is to use a capacitor across the rectifier a capacitor across the rectifier

output which smooths the

output which smooths the d.c. voltage. Full wave controlled rectificationd.c. voltage. Full wave controlled rectification from a three-phase a.c. supply is achieved in

from a three-phase a.c. supply is achieved in a bridge Circuit with sixa bridge Circuit with six thyristors a shown