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Transformer Fault Current Calculation
Transformer Fault Current Calculation

Transformer Impedance

Transformer Impedance is measured in Percent Impedance, this is the percentage of rated primary voltage applied to the Transformer’s primary winding in order for the rated secondary Full Load Current to flow in the secondary winding (this test is preformed with the primary winding connected to a Variac or variable supply and the secondary winding shorted-out).

Transformer Impedance values may vary but typically Blakley Electrics transformers will be between 4 to 5% of primary Voltage.

For further details please contact Blakley Electrics‘ Technical department.

Impedance Voltage Vz = ( Primary Volts V x Percent Impedance Z% ) / 100

Transformer Maximum Fault Current Allowing for Loog Impedance

To calculate the Maximum Fault Current that can be achieved in a circuit fed by a transformer we refer to the below formula.

Maximum Fault Current

This formula calculates the loop impedance at the end ofa circuit fed from the secondary winding of a transformer. When calculating Fault Loop Impedance Select the Correct Transformer Type Above. Three Phase Transformers Divide the Values for Vs secondary Voltage by √3 and the VA by 3.

For Centre Tapped to Earth (C TE) transformers halve the values for Vs and VA . For RLV / 110V C TE Disconnection Times & Zs figures refer to BS 7671:2008, 411.8 Table 41.6.

Software:Transformer Fault Current Calculation – Blakley Electrics
Version:2.0
Developer:BLAKLEY Electrics
Size:110kB
Price:Free
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Transformer Fault Current Calculation

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15 Comments


  1. Kalyan
    May 22, 2021

    very cool


  2. VIJAYAPRASAD C
    Apr 15, 2020

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  3. Bui hong Diep
    Apr 15, 2020

    I like this site a lot its really good


  4. Mario Meneses
    Apr 14, 2020

    I download the calculator but don’t’ work, I can’t change the values.
    Please let me know what can I do.
    Thanks for your support


    • Rommel Dagayday
      Apr 15, 2020

      You have to click enable editing


  5. jhun damot
    May 27, 2019

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  6. Tom
    Apr 29, 2019

    There might be some problem about the 3^(1/2)


  7. TAYEB
    Apr 01, 2019

    10/10


  8. Eric
    May 13, 2018

    Very helpful – thank you


  9. B K SINGH
    Jun 28, 2017

    i like this site nice


  10. success
    Oct 20, 2014

    Keep up the good work


  11. Bassam alhaboob
    Aug 18, 2013

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  12. nedal nemer
    Jun 09, 2013

    very cool


  13. KALYAN
    Mar 21, 2013

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  14. carsona
    Sep 23, 2012

    I like this site a lot its really good.

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