diesel electric

Discussion in 'Hybrid' started by whitepointer23, Oct 4, 2015.

  1. powerabout
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    powerabout Senior Member

    you can get gen and motor to run at a PF of 1?
     
  2. groper
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    groper Senior Member

    If you look at the generators in the wind turbine industry, you will routinely see generator efficiencies ( not including the wind part of it) of around 95%. So if the same alternator is driven by an engine, then it's only wasting 5% of that energy. If the electric motor is equally efficient, then the entire system should achieve around 90% give or take...
     
  3. groper
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    groper Senior Member

    Not the motor itself, it will always be inductive and always lagging. However you can put capacitors in the line which have the opposite effect and cause a leading power factor above 1. The vector sum of the 2 reactive components should cancel out to achieve proper power factor correction and the generator will see a power factor close to unity so it can deliver maximum output. The size of the capacitance can be calculated and if the load power factor varies, like with multiple motors starting stopping etc, then capacitor banks can be setup which switch more or less capacitors in and out. This happens routinely at your local substation of the utility power company so that they keep the power factor reasonable and not waste so much energy in transmission losses. With poor power factor comes higher currents for the same work. More current is more heat in conductors, transformers and ultimately the energy used to deliver us all the power ...
     
  4. powerabout
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    powerabout Senior Member

    I's like to see gen set and motor that can do that when we are talking on the same vessel
    those frequency drives to make all this DE efficient and as you say the large inductance makes me think its hard to get engine KW less 10% at the prop shaft?
    I just spent a few years on a semi sub that had tons of money in design as they built several identical and if the power factor ever got as high as .75 we thought something was wrong.
    I think the MAN data is for selling it but in reality its doesn't get there.
    Too many DE installs have been replaced with direct drive for those figures to work on small installs.
    Perhaps when you talk in many MW's it does work but under that it gets some bad press.
    The offshore vessel industry has done many and the saving is having many engines so low load gets low fuel consumption and cheaper rebuild costs in less time but all at greater build costs.
    LNG powered vessels probably dont help the case either.
     
  5. groper
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    groper Senior Member

    Well you have to clarify that - where was power factor being measured? Like I said, the motors are always inductive and always cause the lagging power factor. Did the semi subs not employ and power factor correction system? If not , then they had an idiot responsible for the electrical design... which is not unusual regardless of the budget... a capacitor bank would be connected on the line side of the installation, so there's only 1 place you can measure the PF the generator sees, and that's between the capacitors and the generator... anywhere else downstream of the distribution board you will measure the poor PF...

    You can also improve the power factor by other means besides capacitor banks. If the system is of suffiently large size, such as a ship for example, you could also employ large synchronous motors which can run at a leading power factor for power factor correction. It's power factor can be varied depending on the level of excitation and so can accommodate changes in power factor from other lagging loads... these machines are usually quite large tho, I'm not aware of any that are of a more moderate size suitable for small yachts etc
     
  6. WestVanHan
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    WestVanHan Not a Senior Member

    A few years ago Siemens sold Nordhavn on the dream of DE,but after 2 years of trying to get it to work Nordhavn gave up,sued Siemens,won,and (IIRC) settled out of court.
     
  7. groper
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    groper Senior Member

    what dream? Diesel electric ship propulsion has been going strong for decades... predominately since WW2, but even a few more examples before then.

    Modern users of the technology are everywhere, see all those azimuth thrusters on oil gas ships, cruise ships, etc? its all diesel electric... If its done right, and fit for purpose, it should see good efficiencies of around 90% net total - which is far better than hydraulic.
     
  8. Joakim
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    Joakim Senior Member

  9. FAST FRED
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    FAST FRED Senior Member

    There is a huge difference between a vessel that has varying hotel loads , propulsion loads and docking loads than a 30 ft boat with only a couple of HP required to move it along.

    Not all tech is scalable , turbines are great in large aircraft , suck in motorcycles or cars.

    A mechanical gear box with a 10hp diesel might only have 2% in mechanical losses thru the gears.
     
  10. groper
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    groper Senior Member

    Yep , a mechanical gearbox is probably more efficient. But the technology is definately scaleable into small packages. Here a link to a very high performance but tiny brushless dc motor which is 93% efficient.

    http://www.kdedirect.com/collections/xf-brushless-motors/products/kde700xf-295-g3

    You have added flexibility with DE , which may make it more appropriate depending on the SOR of any vessel.

    The point of this thread , I think, was to see if some cheap gensets could be made to work as part of DIY DE system. The point is yes it could, but if not done with some proper thought and skill, the likely result would be quite poor as the calculations showed. However if done well, then you could expect the system to deliver upto 90% efficiency. It all depends on the type of equipment used and good electrical design.
     
  11. powerabout
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    powerabout Senior Member

    So looking good on the motor side, what choices are there for the elec end on the gen set
    I guess we need to get a set up on the dyne to actually see?
     
  12. whitepointer23

    whitepointer23 Previous Member

    We already know this. I have a diesel with a hurth mechanical box. I was just putting the diesel electric question out there but as usual its turned into a what you can't do thread instead of how can it be done. The brushless motor in gropers post shows how far electrics have come in a few years in the rc model world. Maybe i just asked a stupid question .
     
  13. Joakim
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    Joakim Senior Member

    But that one still needs a gearbox and a high ratio one, since it runs around 15 000 rpm. You can find brushless DC motors as efficient running at much lower rpm, but they will be bigger and more expensive. Here are some with lower rpm: http://www.goldenmotor.com/frame-bldcmotor.htm

    Still maybe too high rpm for driving the propeller shaft directly.

    The same engine can be used for the generator and it will have about the same efficiency as a generator.
     
  14. Yobarnacle
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    Yobarnacle Senior Member

    The main advantages of diesel/electric IS efficiency and control.
    Every IC engine has an optimum rpm for power/fuel consumption.
    As a generator, the unit is designed to operate continuously at that optimum rpm.
    And redundancy is easy and relatively cheap. Multiple gensets, each capable of carrying full load.
    Gensets can also be ganged.
    If 40 kw is required, then three 20 kw gensets provides redundancy. Any pair ganged and synchronized gives you 40 kw, and a spare in the event of mechanical failure.
    And at anchor or moored, only one genset needs to be online for house loads.

    One gen set can power multiple smaller electric motors, driving multiple props.
    Electric motors, because they possess max torque at one rpm or even stalled (zero rpm), they can be instantly reversed from full ahead to full astern.
    No squalling burning clutches.
    Instant on and off.
    A burst of power, then let the vessel headreach (coast). Great low speed maneuverability.

    Unused energy from the gen set can charge batteries, run pumps ect.

    In emergency situations, stored battery power can augment the generators production, allowing flank speeds greater than is possible with generated power alone.
    Over volt a dc electric motor, it spins faster.
     

  15. groper
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    groper Senior Member

    Yes joakim I know, that little motor was to show efficiency and power density, 8kw from a motor weighing 500 grams is pretty impressive I think :) and yes as you say, if the motor can run that efficiency so can a small generator, they are the same thing in reverse...

    Does anyone know the efficiencies of small production generators like Honda 2 or similar? What about the common diesel types say upto 20kva units from the usual brands...?
     
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