Bahan Kuliah Minggu 13 (Electric Propulsion)

7/21/2019 Bahan Kuliah Minggu 13 (Electric Propulsion)

http://slidepdf.com/reader/full/bahan-kuliah-minggu-13-electric-propulsion 1/28

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



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:


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.



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


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



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.





Torque

Constant power


100 % Rev. speed

Diesel enginemechanical drive

in freesailing




Short durationovertorque, 170%

for 30 seconds inicebreaker Healy

Torque

Typical performance of

frequency converter drive

Propeller curvein pollard pull


100 % Rev. speed

Diesel enginemechanical drive

in freesailing

Ice impact torqueon propeller



Electric Propulsion Components

Main dieselgenerator sets

Divided mainswitchboard 3.3 kV

Large electric


Propulsion motors

bow thrusters,AC compressors

Transformer

Low voltageswitchboard 440 V

Feeding of low voltageconsumers

converters(some typesneed separatetransformers)

Some motors

need low voltageexcitation



MS Fantasy




MS Fantasy Engine room detail

Oil fired boiler 8ZA40S engines Lub oil purifiers Machinery auxiliaries

Stabilizers

Sea chest

Fuel oil

12ZA40S

engines

A60 firebulkhead


WT bulkhead Evaporators Central coolers Sea water main line

pur ers

HFO day& settling

tanks

CL



= =

•AC generation AC distribution•Synchonus Machines

System Components - Generators


•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



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


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.



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)


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.



System Components – Propulsion Motors

Some examples configurations




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)


DC link typical for VSI and CSIconverter

Variable

Frequency,voltage AC

FixedFrequency ,Voltage AC



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.




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.




MS Fantasy at KMY Helsinki Yard

When all 6main dieselgenerators

have beeninstalled,assembly ofoutfitted hull


One of the 14 MW synchronous motors installed

sec ons can

be continued



“sisters” MS Fantasy, MS Elation

New Modified Changed


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]



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


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



GTS Millenium 2 * 25 MW + 9 MW




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


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




Case: 105.000 TDW icebreaking Aframax tanker

Loa 252m, breadth 42m, draft 14.5m, trial speed 15.7 kn

Ice covered4 months /a


82h loaded76h ballast

19h dis-charging

19hloading




A B C D

ME 14900kW 18900kW 14070kW 16800kW

AE 4320kW 720kW 4320kW 2880kW





A B C D

Steam cargo pumps Electric cargo pumps, nominal load 2640 kW< >11700kW fuel < > 5500kW fuel


7RTflex58 3x6L46C 7L64 2x8L46C



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


Hull costTotal refer.7.990 012.010 08.980 5010.460



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




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!


Bahan Kuliah Minggu 13 (Electric Propulsion)

Documents

Transcript of Bahan Kuliah Minggu 13 (Electric Propulsion)