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MVA Method Load Flow Calculation

In Load Flow Calculations, the "Equivalent MVA" of equipment are:

Utility: MVAsc = Utility Fault Duty ( MVAsc )

Generator : MVAsc = 100 x MVAG / %Z = MVAG / X"d

mvasc-generator

Running Motor: MVAM = Motor HP / 1000 = Motor KW / 0.75

Starting Motor : MVAS = 6 x Motor HP / 1000 = 6 x Motor KW / 0.75

Transformer:

mvasc-transformers

Reactor & Cable:

mvasc-cable

Static Loads: MVASC = Actual MVA

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By Ver 8:48 AM

8 Responses

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  1. tiong says

    Quoted” 1. Motor MVAs are equal to the rated Equivalent MVAs.”

    I wish to confirm that Motor MVAs is the short circuit MVA please? Thank you

    August 16, 2010, 3:36 PM
  2. Ver says

    Hi Tiong,

    Motor MVAs in load flow calculation is the rated motor MVA, not the short circuit MVA

    August 16, 2010, 4:18 PM
  3. artem says

    @ 11kv bus as per mva diagram,
    upstream values mva are 67.33 (transfo. 2) and 44.94 (motor 5mva)
    downstream values mva are 8.55 (transfo. 1) and 3.94 (generator side)..
    Please help me to explain sir how did these values came. How to perform this calculation…Thank you.

    February 1, 2011, 6:39 PM
  4. Ver says

    Hi artem,

    Here is how the values were taken.

    Upstream Values:
    67.33MVA = 112.27MVA*(7.49/{7.49+5})

    44.94MVA = 112.27MVA*(5/{7.49+5})
    The sum will be:
    44.94MVA + 67.33MVA = 112.27MVA

    Downstream Values:
    8.55MVA = 12.49MVA*(76.87/{76.87+35.4})

    3.94MVA = 12.49MVA*(35.4/{76.87+35.4})

    The sum will be:
    3.94MVA + 8.55MVA = 12.49MVA

    Hope this helps.

    February 2, 2011, 4:47 AM
  5. artem says

    exactly sir ver, this helps a lot. thank you very much..mabuhay ka and god bless.

    February 2, 2011, 10:56 AM
  6. artem says

    I’m sorry sir Ver but i have additional query about the voltage dip or voltage drop upon starting the motor 150kva on the system which draws a power of 0.9 MVA..I have a result by hand calculations at 400V Bus: 77.22%, at 6.6kV: 87.72%, at 11kV: 89.28% which is a little different result on your MVA Diagram as shown that at 400V Bus: 76.7% (shown calculation), at 6.6kV Bus: 80.6%, at 11kV Bus: 90% and 33kV Bus: 96.6%.
    Please help me sir, how did you perform this calculations.. thank you..

    February 2, 2011, 1:28 PM
  7. Ver says

    Hi artem,

    I have updated the article. I hope it will be much clearer at this time.

    Thanks

    February 2, 2011, 8:25 PM
  8. artem says

    I salute you sir for sharing your knowledge and expertise, thank you very much..god bless.

    February 3, 2011, 10:36 AM



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