why DC supply is not used or transmission

Discussion in 'General Electronics Chat' started by saraswathi.95, Jan 25, 2014.

  1. saraswathi.95

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    Apr 11, 2013
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    why do we select ac supply to travel long distances ,i,e. why don't we use dc supply as it can also pass currents in a cable.
     
  2. ericgibbs

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  3. GopherT

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  4. tcmtech

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    AC is used because it is easily changes from one voltage to another by a simple transformer system.

    That can't be done with DC on the mass usage scale.
     
  5. MaxHeadRoom

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    Where I live there are many Hydro generating stations with long distance transmission, for a few years now they have converted to DC transmission for a few reasons.
    The losses are much lower, the reduction in conductors, also lightening strikes are less troublesome as they are prevented in traveling though the system to the end user as they are prone to in AC.
    The millions in savings offset the cost of the DC switching equipment required to convert back to AC.
    Max.
     
  6. crutschow

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    High voltage DC transmission wasn't practical until the development of high voltage solid-state inverters that could convert the generator AC voltage to DC at the transmission end and then back to AC at the receiving end of the HV transmission line. The high cost of these inverters makes it feasible only for long distance lines where the lower cost of the reduced copper required and lower losses makes up for that extra expense.
     
  7. MaxHeadRoom

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    Actually the first type used Ignitron tubes before S.S./SCR's. ;)
    Max.
     
  8. bountyhunter

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    Ac allows the ability to compensate for voltage losses along the way by adjusting Xformer ratios. And as stated, allows any voltage option just be changing turns ratio.
     
  9. saraswathi.95

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    Apr 11, 2013
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    thanq,
    can you tell me if it is possible to use it,and some says it is efficient,why don't we use dc generators so that output is dc and use it for transmission.
    are there any more major difficulties in doing so,other than transformer advantage utilization.
     
  10. MrChips

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  11. inwo

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    Unless something new has been invented. Other than static machines. I believe all generators produce ac.

    Commutation gets it all moving the same direction.

    Haven't researched it, but I would think the early Edison DC system had a large AC component. (ripple)
     
  12. MaxHeadRoom

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    Actually not really, they have one in the electrical museum in my town, runs self contained with a self exited field and results in a clean DC signal.
    Max.
     
  13. inwo

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    Nov 7, 2013
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    Post a link if you find one.

    Seems like it would be really hard to do. DC with no ups and downs in amplitude. Like a steady push one way.
     
  14. MaxHeadRoom

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  15. tcmtech

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    Mostly it has to do with the high voltage DC transmissions systems running on DC voltages of 500,000 to 1 million volts. Its just not practical/possible to build a DC generator that an create that voltage.
     
  16. saraswathi.95

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    Apr 11, 2013
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    Why do some devices require ac power like tube light (why don't it work with dc)
    while some other converts the available ac into dc and then use it.
     
  17. kubeek

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    Sep 20, 2005
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    The main problem here is that it is really hard to make a rotating generator that produces high enough voltage to be useful for long distance transmission. You need hunreds of kV for it to be efficient, and the isolation in the windings just can´t stand that much easily.
     
  18. MaxHeadRoom

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    There are a few reasons, easier starting method for one, a fluorescent tube will work with DC once the arc is struck, but the brightness will vary from end to end, anode to cathode, visible on a long tube.
    Max.
     
  19. alfacliff

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    Dec 13, 2013
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    flourescent lights that use dc have inverters to produce ac. flurescent tubes require high voltage, especially when starting. the low voltage lights that use dc are like leds, and require dc to operate, usuallly provided by a smps in the base on ac.
    the main loss for ac transmission systems seems to be capacitive losses from the conductors to ground and conductor to conductor. capacitance might seem low, but figure the capacitance of a 100 mile line to ground. My son works for the local power comapny, and he has energised 365kv lines that had 600 amps flowing even before the load was connected at the destination. thats loss.
     
  20. MaxHeadRoom

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    The latest DC transmission line under way here is 1400Km at 500Kv!
    Max.
     
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