bahan kuliah minggu 13 (electric propulsion)
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Electric Propulsion
ELECTRIC PROPULSION IS SELECTED IN MANY SHIPSWHICH USED TO HAVE MECHANICAL PROPULSION!
Typical DE vessels have been icebreakers, seismic explorationvessels, shuttle tankers, cable ships, pipe layers, cruise liners
Pentti Häkkinen /Electric propulsion and systemsWärtsilä New Professionals 3.-7.11.2008
Higher freedom in location of main generator units Diesel engine load can be kept in the optimum range Suitable for ships with high auxiliary power demand; great variation in
both propulsion and auxiliary power Electric pod propulsion is an option
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Electric Propulsion Features
All energy is generated into by 2 … 6 main diesel alternators(power plant principle). No auxiliary engines
Propeller driven by reversible electric motor. Number of motor
poles (or pole pairs) gives suitable speed reduction.
Because frequency control, fixed pitch propellers are sufficient.
Alternative converter designs:
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PWM (Pulse Width Modulation),
LCI (Load Commutated Inverter) = Synchroconverter,
Cycloconverter
All suitable for up to 20 MW propulsion motor. Technicaldifferences, selection is made case by case.
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Electric Propulsion Economic Comparison
8 … 11 % transmission loss compared with 2 % reduction gearloss => higher fuel consumption, maybe also higher installedpower
This often leads to higher ship size and building cost
When main & auxiliary engines are integrated, power reservescan be reduced. This limits the ship size and cost increase
Pentti Häkkinen /Electric propulsion and systemsWärtsilä New Professionals 3.-7.11.2008
Pod propulsion often has higher efficiency than shaftlinesolution. Propeller position is hydrodynamically optimal
Freedom in generator unit location is often important
Larger diesel engines have lower consumption, when theyoperate at optimal speed and power
Optimal speed and power: lower exhaust gas emissions
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Comparison of Torque Performance
Frequency controlled electric motor can deliver high torqueat low speed.
Fixed pitch propeller suitable for widely varying conditions.
Reversing and start from shaft standstill is easy.
Important for dredgers, icebreakers and similar.
Pentti Häkkinen /Electric propulsion and systemsWärtsilä New Professionals 3.-7.11.2008
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Comparison of Torque Performance
Torque
Constant power
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100 % Rev. speed
Diesel enginemechanical drive
in freesailing
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Comparison of Torque Performance
Short durationovertorque, 170%
for 30 seconds inicebreaker Healy
Torque
Typical performance of
frequency converter drive
Propeller curvein pollard pull
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100 % Rev. speed
Diesel enginemechanical drive
in freesailing
Ice impact torqueon propeller
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Electric Propulsion Components
Main dieselgenerator sets
Divided mainswitchboard 3.3 kV
Large electric
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Propulsion motors
bow thrusters,AC compressors
Transformer
Low voltageswitchboard 440 V
Feeding of low voltageconsumers
converters(some typesneed separatetransformers)
Some motors
need low voltageexcitation
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MS Fantasy
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MS Fantasy Engine room detail
Oil fired boiler 8ZA40S engines Lub oil purifiers Machinery auxiliaries
Stabilizers
Sea chest
Fuel oil
12ZA40S
engines
A60 firebulkhead
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WT bulkhead Evaporators Central coolers Sea water main line
pur ers
HFO day& settling
tanks
CL
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= =
•AC generation AC distribution•Synchonus Machines
System Components - Generators
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•Brushless, Excitation controlled by AVR•Unless otherwise specified:
Terminal voltage : +/- 2.5 %
Largest transient load variation : - 15 % or + 20 % of Nominal Voltage
•Some common voltage levels (Medium, Low) - (various standards IEC, IEEE, ANSI etc)
11KV 6.6KV 3.3KV 690V 450V 230V /120V
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According to rules for electric propulsion,redundancy is required.i.e. tolerance to failure against short circuit(also fire and flood could be considered)
Normally distributed in 2, 3 or 4 compartments,depending on redundancy requirements andcosts.
System Components – Switchboards
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Installed power affects normal current and shortcircuit currents. Physical limitations on handlingthermal and mechanical stresses in busbars,and swicthgear.
Various circuit breakers: air, vacuum, gas filled.Vacuum breakers may chop current and causespikes when breaking inductive load.Overvoltage protection maybe necessary.
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System Components – Propulsion Motors
Synchronous Motors(examples: Mermaid: 5 -25 MW, Azipods 5 ~ 30MW)
Permanent Magnet Synchronous Motors(example: Compact Azipod 400 kW – 5 MW, Siemens ShottelSSP)
Pentti Häkkinen /Electric propulsion and systemsWärtsilä New Professionals 3.-7.11.2008
Variable speed motors, double windings for continousoperation, cooling by air, water
Asynchronous motors are competetive below 5 MW
DC motors were popular in early days and sometimes evenconsidered today.
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System Components – Propulsion Motors
Some examples configurations
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Drives & Control
VSI (voltage source invertor) type converters (with PWM , DTC)
CSI (current source invertors) type converters (other names LCI, Synchro)
Cyclo - cycloconverters (dominant in marine applications)
others (CSI with PWM, VSI with PAM, limited application)
Pentti Häkkinen /Electric propulsion and systemsWärtsilä New Professionals 3.-7.11.2008
DC link typical for VSI and CSIconverter
Variable
Frequency,voltage AC
FixedFrequency ,Voltage AC
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System Overview - Cycloconverter
• Cycloconverter consists of 3 thyristor bridges, supplied from propulsion switch-board. Bridges are needed to feed positive and negative current into winding
• Basic arrangement for has 36 switching devices (thyristors)• More commonly a propulsion motor has 2 sets of 3-phase windings, each with
its own network of 36 devices• Cycloconverter “constructs” the output voltage wave-form from sampledportions of the supply wave-form. Both 6 pulse and 12 pulse systems possible.
Pentti Häkkinen /Electric propulsion and systemsWärtsilä New Professionals 3.-7.11.2008
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System Overview - CSI (synchro, LCI)
Thyristor controlled rectifier feeds DC link. Invertor side is fed by motor resultingin increased dimensions of motor.By controlling the switching of thyristor pairs, controlled current at variablefrequency is applied sequentially to the motor windings.
At low speeds (5-10 % of rated) EMF too low to perform natural commutation.
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MS Fantasy at KMY Helsinki Yard
When all 6main dieselgenerators
have beeninstalled,assembly ofoutfitted hull
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One of the 14 MW synchronous motors installed
sec ons can
be continued
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“sisters” MS Fantasy, MS Elation
New Modified Changed
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6 * W12V38 instead of 4 * 12ZAV40S & 2 * 8ZAL40S
[b]
2 Azipod units instead ofconventional long shaftlines, rudders, electric motors
[a] required more design work hours than [b]
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Combined Electric Gas and Steam Turbine Plant
GTS Millenium was 1st, 2 * 25 MW + 9 MW
Problems met, related to design errors
Economic balance is labile:heat for fresh water generation andgas turbine loading are decisive!
Permanent setback is fuel rice and
Waste heatrecovery
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possibly maintenance costsLM2500+ and similar gas turbinesare ‘too big’ units: seldom optimal load!
Low turbine weight allows optimal location;but ship stability needs concern
Small space demand. Air supply ducts,exhaust pipe duct smaller than in diesel electric ship
G G
G
LM2500+ LM2500+
Steam turbine
Electric plant
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GTS Millenium 2 * 25 MW + 9 MW
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General Comparison of Machinery Alternatives
Numerical example for 40.000 GRT 1400 pax. cruise liner, 2 * 7.5 MW.Electric variant has 14 extra cabins => added income 1.330.000 USD/a...loses 45.000 USD/a as diesel engine fuel, saves 41.000 as heating fuel,
saves 20.000 as machinery maintenance. Total savings 15.000 USD/a
= > Electric propulsion investment is paid back in 2.2 years!
Electricpropulsion
Gearedpropulsion
Equipment
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pcs. Cost USD pcs. Cost USD
Main engines, mounting 5 6.200.000 4 4.400.000Electric propulsion pack 1 6.700.000 - -FPP 2 750.000 - -Reduction gear, coupl. - - 2 1.400.000CPP plant - - 2 1.200.000Shaft bearings sets 2 320.000 2 40.000Aux. diesel generators - - 4 3.800.000Aux. engine auxiliaries - - 590.000Main switchboard 170.000 400.000TOTAL 14.140.000 11.830.000Difference 3.310.000
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General Comparison of Machinery Alternatives
Case: 105.000 TDW icebreaking Aframax tanker
Loa 252m, breadth 42m, draft 14.5m, trial speed 15.7 kn
Ice covered4 months /a
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82h loaded76h ballast
19h dis-charging
19hloading
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General Comparison of Machinery Alternatives
A B C D
ME 14900kW 18900kW 14070kW 16800kW
AE 4320kW 720kW 4320kW 2880kW
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General Comparison of Machinery Alternatives
A B C D
Steam cargo pumps Electric cargo pumps, nominal load 2640 kW< >11700kW fuel < > 5500kW fuel
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7RTflex58 3x6L46C 7L64 2x8L46C
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Investment Costs Comparison (1000 USD)
A B C D
MEME Aux.
Prop.plantEl. PlantCargo plntBoilers
3.190610
1.2401.250
8001.110
4.340737
8204.970
500650
3.380550
1.9701.560
5001.120
3.690660
3.0601.370
5001.130
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Hull costTotal refer.7.990 012.010 08.980 5010.460
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Annual Fuel Oil, LO and Maintenance Costs (1000 USD)
A B C D
ME fuelAE fuel
Boiler fuelLub OilMaint.OPER
1.880250
66090
1002.990
2.3800
41050
2203.060
1.890300
44050
1802.860
2.01070
44050
1802.740
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Total Annual Costs (1000 USD, 25 years, 8 % interest)
A B C D
OPERAT
CAPITALTOTAL
2.990
Ref.Ref.
3.060
360470
2.860
90-40
2.740
230-20
Here negative values indicate better performance!
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