Best war of current t-shirt I have ever seen.....

Discussion in 'Off-Topic' started by Albert Cannady, Feb 22, 2017.

  1. Albert Cannady

    Thread Starter New Member

    Feb 22, 2017
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  2. nsaspook

    AAC Fanatic!

    Aug 27, 2009
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    AC for power transmission/communications and DC for active devices. It was never a war, it was a rock band with two leaders before the rest of the band joined. One was a flamboyant flashy vocalist and the other was a steady drummer. As a group now they make great music.
     
  3. MaxHeadRoom

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    Jul 18, 2013
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    Ironically now the method for long distance transmission lines is to use DC!;)
    We do it here to save a lot of $$ losses $$.
    Max.
     
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  4. nsaspook

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    Now that we have efficient DC operated devices that can easily convert power formats the lack of technology that initially resulted in AC domination of long distance transmission of power is being offset but there is still a huge infrastructure of AC distribution worldwide that won't be replaced anytime soon.

    [​IMG]

    General structure of the western North America power system.
     
  5. MaxHeadRoom

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    I think that any new installations that require a long distance transmission are going to consider DC, there are incredible savings to be had, with the loss of one conductor and the much reduced losses.
    Max.
     
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  6. nsaspook

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    If you need high power long-distance bulk transfer between two points it's great but active converter stations are still more expensive than passive AC transformers so you still need to build out an intermediary AC sub-system at transfer nodes. DC is now a true complement to AC systems rather than a rival today. Using DC to decouple large AC synchronous grids (to eliminate frequency or phase angle issues) with back to back converters is also common.

    [​IMG]
     
  7. MaxHeadRoom

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    The Hydro Engineer that lives next to me is in great demand all over Canada helping set up these DC conversion stations, it is at the point they won't let him retire!.
    I could dig up the number in Megawatts it has saved in the latest line to be installed here in the next year or so.
    One of the advantages to the end user is lightening strikes are contained and no longer travel to the end user.
    Max.
     
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  8. BR-549

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    Sep 22, 2013
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    I hadn't thought about the different grid phases. A DC bus puts a quick end to that problem.

    A transformer makes an awfully simple step ladder........but look how solid state is replacing them in our modern tech power circuits.

    The solid state cost is sure to decline......the transformer might become a specialty item.
     
    Last edited: Feb 22, 2017
  9. MaxHeadRoom

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    The original conversion was done with Thyratron and Ignitron tubes, now solid state.
    Max.
     
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  10. tcmtech

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    Nov 4, 2013
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    What level of saving are you being quoted.

    The numbers I have always been told was HV AC losses were ~5 - 6% per 1000 miles VS DC at ~3.5 - 4.5%. A gain but not a huge one.

    The bigger up front savings was in the only needing two wires to carry the same power in DC as three were needed for AC being inductance and skin effect related resistive effects were reduced.

    The downside to HVDC transmission is that savings had in wire reduction was often replaced by the cost associated with the HVDC up/down conversion and related operating costs on both ends which unlike with AC systems a HVDC link is not easily made bidirectional for load sharing from end to end as in the as designed load end of the line can't be easily or cheaply reversed to feed new energy source power at that end backwards up the line to the original supply point and down converted again at that end if the load in that area so needed it.
     
  11. MaxHeadRoom

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    The report from Siemens is that the saving for the new HVDC 1,400Km 2300Mw line will offers saving between 30% to 40%.
    The Northern station will not only supply some of southern Canada but US customers also.
    The cost of the conversion equipment is recouped in a very short time.
    Max.
     
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  12. tcmtech

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    Yes. going from 6% to 3.5 % is 30% - 40% savings but in reality it's not much of a gain in overall system efficiency. Its just fudging numbers like saying a 98 % efficient transformer is 300% more efficient than a 92% efficient transformer because efficiency values were improved by a factor of 3 rather than saying a 6% improvement in losses were had. A 300% improvement sounds way more impressive than a 6% one yet they both mean the same thing. :rolleyes:

    Its the same numbers games vehicle emissions improvements claims are based on. An 80% improvement on something great but a 80% improvement on the remaining 20% isn't so much of a gain and a 80% improvement on the remaining 20% of the second 20% is very small compared to the actual original value yet by all percentages measurements they all sound like huge gains to a person who has not sat down and did the numbers. :(

    100 - (80% of 100) = 20

    20 - (80% of 20) = 4

    4 - (80% of 4) = .8

    You follow what I am saying? o_O
     
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  13. GopherT

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    Nov 23, 2012
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    In engineering speak we call this the point of deminishing returns - but thanks for the math.

    Also, you speak like engineers and business people running the utility are stupid. If there is money to be save, they will invest. If there is no money to be saved, they will find another location to spend the money. I'm sure you will fire back with various conspiracy theories and superficial examples about unprofitable projects but cash is king and grid reliability or other less obvious goals impact the cash a utility makes. I'm certain their decisions have merit.
     
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  14. Tonyr1084

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    Sep 24, 2015
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    WOW! This thread is moving the cheese on my cookies! Guess I've been out of the loop far too long.

    Now I'm wondering just how do you generate DC? I've always thought you need to generate AC then convert it to DC. Saving on line losses and reduction in the amount of copper needed - well, I'm still trying to understand all that - - - and I'm not asking for an explanation here. I'll play catch up on my own. But what of the changes and expenses needed to - not sure if this is the right way to express it - to design a DC generator?

    HEY! I'm all ears. (well, a lot of forehead too, but - - - )

    Can you make a brushless DC generator?
     
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  15. BR-549

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    A true DC generator is called a homopolar generator. Faraday Disk....etc....
     
  16. Kermit2

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    Yeah. True DC generator.

    A truly monstrous one can make enough amps to weld two giant iron asteroids together, but the one draw back they have is the low voltage. 10's of thousands of amps can be generated but getting more than 500 volts out of one has not yet been accomplished.
    Homopolar generators are not the right choice for a DC transmission station.
     
  17. MaxHeadRoom

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    It is generated in the usual way (AC) the conversion takes place either end.
    Yes, over many Km the saving in the one less line is also considerable.
    ABB were one of the first to install in the west quite a few decades ago.
    Max.
     
  18. nsaspook

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    It is much better and far cheaper to transfer electrical energy at high voltage and low current vs. low voltage and high current but it's almost impossible to engineer a AC or DC high power generator that can directly output 300,000 - 1,000,000 volts so there must be a conversion from the normal generator output of 11-33 kV. High voltage AC generators are simpler and cheaper than DC generators of the same range. With AC transmission the AC power from the generation is boosted to the needed HVAC levels by transformers. With DC transmission the AC power from the generation is boosted to the HVDC levels by converters using semiconductor technology.

    ABB replaced the original mercury arc valves (from what was then ASEA) with modern thyristors valves on the original Pacific DC Intertie.
    http://www.abb.us/cawp/seitp202/2f78c2d35da4524085256fd40063c008.aspx
    http://new.abb.com/systems/hvdc/references/the-gotland-hvdc-link

     
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  19. cmartinez

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    That explains why DC is just beginning to catch up until recent years...
     
  20. MaxHeadRoom

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    The 3 HVDC conversion stations we presently have were built in 1968.
    Presently there is a total of 5 Hydro stations with 15 Hydro generators capable of producing 5,700Mw.
    Another new one in the works.
    Max.
     
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