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Thread: Calculating Megawatts

  1. #1
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    Calculating Megawatts

    How many Megawatts will a 4/0 Three phase line carry 12470/7200v.According to the chart I am looking at a single 4/0 wire (acsr)will carry 340 amps. So I know on a three phase line you will have three wires of whatever size plus your neutral.How is the correct way to calculate how may megawatts any three phase line will carry according to different wire sizes?

  2. #2
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    If the 340 Amps for 4/0 ACSR is correct, use the standard calculation for 3-phase power: MW = kV(phase-phase) x Amps x 1.732/1000.

    12.47 kV x 340 x 1.732/1000 = 7.34 MW.

    Other factors such as unbalanced loading or voltage drop may affect the maximum load.

    BTW, my look up table says 4/0 ACSR rating is 480 A in a 2 ft/sec wind with a 50C rise.
    Bob Wilson

  3. #3
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    Quote Originally Posted by rcwilson View Post
    If the 340 Amps for 4/0 ACSR is correct, use the standard calculation for 3-phase power: MW = kV(phase-phase) x Amps x 1.732/1000.

    12.47 kV x 340 x 1.732/1000 = 7.34 MW.
    MVA, not MW.

  4. #4
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    Thanks for the info and formula. I had a guy try to tell me that 636 wire would just carry about 8.5 MW but I thought he must have been calculating it wrong. It should carry about 16.61 shouldn't it ?
    Thanks

  5. #5
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    Quote Originally Posted by Besoeker View Post
    MVA, not MW.
    Correct - I forgot power factor! Thanks for catching my error.


    dsmith - 636 ACSR has an typical ampacity rating of 780A in a 2ft/sec wind. That would be about 16.8 MVA at 12.47 kV.
    But the actual allowable MW loading depends on the load power factor and the length of the line, the allowable voltage drop, contingency factors etc.
    Bob Wilson

  6. #6
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    Quote Originally Posted by rcwilson View Post
    Correct - I forgot power factor! Thanks for catching my error.


    dsmith - 636 ACSR has an typical ampacity rating of 780A in a 2ft/sec wind. That would be about 16.8 MVA at 12.47 kV.
    But the actual allowable MW loading depends on the load power factor and the length of the line, the allowable voltage drop, contingency factors etc.
    Others include ambient temperature, loss limits, allowable sag, elevation, max temp. It would not be unheard of to have a summer limit of 8.5 MW due to heat sensitive things like sag constraints.
    BB+/BB=?

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