Transformer Short Circuit Calculator
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Short Circuits, also known as faults, can occur in electrical power distribution systems. When a fault occurs on the load side of a transformer, fault current, or short circuit current, flows through the transformer. Transformers are designed to withstand these fault currents, which are significantly higher than the rated current.
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It is worth noting that transformer impedance is one of the limiting factors for the short circuit current of transformer at the secondary coil. The higher the transformer impedance (% Z), the lower the ratio of fault to rated current. In other words, a Transformer with higher %Z better limits the flow of fault current.
![Capture0.JPG](https://static.wixstatic.com/media/17b446_6cbb0b9422dc4bc3aefbbd0185b4dd43~mv2.jpg/v1/fill/w_804,h_178,al_c,q_80,usm_0.66_1.00_0.01,enc_auto/Capture0_JPG.jpg)
Short Circuit Current of a Transformer is calculated using the formula as shown. Note that UL 1561 transformer has a ±10% of impedance tolerance. For high end worst case, we assume a lower transformer impedance by multiplying a 90% safety factor as shown below*.
![Capture1.png.jpg](https://static.wixstatic.com/media/17b446_447ede14075044b189a666ecd3081f73~mv2.jpg/v1/fill/w_455,h_668,al_c,q_80,usm_0.66_1.00_0.01,enc_auto/Capture1_png.jpg)
Where
IF.L. = Full Load Current (A)
TXKVA = Transformer Rating (kVA)
VL-L = Phase Voltage
Z = Transformer Impedance,
%Z = Transformer % Impedance
IS.C. = Short Circuit Current (kA)
M = Multiplier, or ratio of Short Circuit Current to Full Load Current
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To compute the short circuit current at a distance, L feet away from the first fault current, I S.C. calculated above, over a conductor of C-Values, C and of N number per phase, factor f and Multiplier M can be derived from the formulae below.
![Capture2.png.jpg](https://static.wixstatic.com/media/17b446_518c6f363c3b4707aeea0c3056480cf2~mv2.jpg/v1/fill/w_97,h_127,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/Capture2_png.jpg)
![Capture1.png](https://static.wixstatic.com/media/17b446_2c07b0f976d3441085b542dfd25acb8e~mv2.png/v1/fill/w_78,h_151,al_c,q_85,usm_0.66_1.00_0.01,blur_2,enc_auto/Capture1.png)
A downloadable Excel File for Transformer Short Circuit Current Calculation, and estimated Short Circuit Current at X2, is available below:
Transformer Short Circuit Current Calculator (Excel)
![300 x 600 px Ads hd1.jpg](https://static.wixstatic.com/media/17b446_70300bd537ed457e82fe633047bd2616~mv2.jpg/v1/fill/w_60,h_120,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/300%20x%20600%20px%20Ads%20hd1.jpg)