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Why are Power Grids so Large?

Former Community Member
Former Community Member
Why are power systems so large and interconnected? For example, what technical obstacles prevents the US eastern interconnection from being 8 isolated islands? Why not separate them by ISO/RTO? Why does every power grid in the world strive to be as large as geography allows?


Better yet why not have scattered power plants about (with redundancies of course) feeding load radially? A lot simpler and a lot less to go wrong.

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    Why did the USA power companies change from delivering D.C. electricity to consumers to supplying AC electricity to them?


    Andy B
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    Why are power systems so large and interconnected?



    Generally larger provides better economies of scale and can provide better reliability.


    Say each town had its own power station - if that power station had a fault the town would be blacked out. The only way to avoid that would be for the town to build an extra power station as a spare - so you'd need as many spare power stations as main ones - very costly. If ten towns clubbed together and interconnected their grids they need only build one extra power station instead of ten for the same effect - much cheaper. In fact if there was a bit of spare capacity on the main power stations they could probably get away without building a specific spare at all - cheaper still. Keep scaling up and the cost savings continue (if at a diminishing rate).


    There can be similar benefits for load sharing - if the territory covered is large enough that maximum load doesn't occur simultaneously across the grid - e.g. max demand the south is probably summer to cope with air conditioning, but in the north it's probably winter for heating - then one centrally located power station might be able to satisfy the peaks for both.


    The same reasoning applies on much smaller scales too - e.g. a domestic 32A socket circuit can serve a much larger floor area than two 16A circuits - especially if you think you might have to supply up to three 10A loads that might be randomly located by users.


       - Andy.
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    AJJewsbury:

    The same reasoning applies on much smaller scales too - e.g. a domestic 32A socket circuit can serve a much larger floor area than two 16A circuits - especially if you think you might have to supply up to three 10A loads that might be randomly located by users.




    I have always been a bit sceptical about the floor area argument. If a ring is good for 100 m2, then any small house needs only one socket circuit.


    Division into rooms is a better analogy. Take a 10-roomed house (5-up; 5-down). Option (1) one circuit per room (continental European practice). Each room's circuit will have to deal with that room's maximum demand. Option (2) one circuit per floor (British practice). It doesn't need to be 5 times bigger because of diversity.


    In the same way, interconnecting several power stations allows for lesser overall capacity because of diversity.

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    Sparkingchip:

    Why did the USA power companies change from delivering D.C. electricity to consumers to supplying AC electricity to them?


    Andy B




    More to the point why didn't they supply AC at 220 to 240v phase/neutral like most other countries?

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    Large and interconnected power grids not only increase reliability whilst only needing a modest level of spare capacity, but also permit of larger and more economic generating plant.

    Modern alternators are often of about 500Mw capacity, easy to connect to a large grid but too big for a single town.

    At times of low load, several large generating units can be run at efficient loadings, far better than ten towns each running plant at low load, and requiring staff.


    Also, exceptionally large loads can be connected to a large grid system, loads that be beyond the capacity of a small town system. Electric railways are a good example, with single phase loads of many Mw that are continual varying. Want of a large interconnected grid often resulted in continuation of steam locomotives when electric power would otherwise have been more suitable.

    Large electric arc furnaces are another example.
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    ProMbrooke:

     Why does every power grid in the world strive to be as large as geography allows?




    If we're talking about "as large as geography allows" Cigre have recently released a first serious attempt at an economic optimisation study of intercontinental grids.  Looking at the cost of generation in each part of the world (the renewable intermittent generation resource is particularly variable by region), daily and seasonal energy consumption, and the cost of building the interconnectors, it suggests that there would be overall cost savings from building a global grid, as well as significant reductions in CO2 as wind generation in Central Asia displaces gas turbine generation in the global energy mix.

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    GeorgeCooke:




    Sparkingchip:

    Why did the USA power companies change from delivering D.C. electricity to consumers to supplying AC electricity to them?


    Andy B




    More to the point why didn't they supply AC at 220 to 240v phase/neutral like most other countries?


     




     

    The DC requires a system such as described in the original post, AC can be distributed more efficiently removing the need for local generation.


    Andy Betteridge
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    I heard that the US authorities thought that 110 volts was safest it being a non lethal voltage or so they thought in the 1920s same as the UK authorities thought that anything over 250 was lethal. As to why they chose 60 cycles over 50 I have no clue
  • Former Community Member
    0 Former Community Member

    broadgage:

    Large and interconnected power grids not only increase reliability whilst only needing a modest level of spare capacity, but also permit of larger and more economic generating plant.

    Modern alternators are often of about 500Mw capacity, easy to connect to a large grid but too big for a single town.

    At times of low load, several large generating units can be run at efficient loadings, far better than ten towns each running plant at low load, and requiring staff.


    Also, exceptionally large loads can be connected to a large grid system, loads that be beyond the capacity of a small town system. Electric railways are a good example, with single phase loads of many Mw that are continual varying. Want of a large interconnected grid often resulted in continuation of steam locomotives when electric power would otherwise have been more suitable.

    Large electric arc furnaces are another example.







    Well, just feed more towns I think. Have 2,000 MW plants seeded around the nation. 2000/250=8. 10 turbines for redundancy. Switch a few off during seasonal periods of light load. 


    But you are right- lots of extra capacity when 50,000MW/2000- 25 stations. Even under peak load there is 12,500MWs of reserve generation capacity.
  • Former Community Member
    0 Former Community Member

    John Russell:




    ProMbrooke:

     Why does every power grid in the world strive to be as large as geography allows?




    If we're talking about "as large as geography allows" Cigre have recently released a first serious attempt at an economic optimisation study of intercontinental grids.  Looking at the cost of generation in each part of the world (the renewable intermittent generation resource is particularly variable by region), daily and seasonal energy consumption, and the cost of building the interconnectors, it suggests that there would be overall cost savings from building a global grid, as well as significant reductions in CO2 as wind generation in Central Asia displaces gas turbine generation in the global energy mix.


     








    Curve ball, what if all generation was nuclear? Or at least 80% so?

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