In the Cooper Bussmann Short Circuit Current Calculations document, for single phase, center tapped transformers they recommend a 1.5 multiplier for L-N faults. It goes onto say "The 1.5 multiplier is an approximation and will theoretically vary from 1.33 to 1.67. These figures are based on change in turns ratio between primary and secondary, infinite source available, zero feet from terminals of transformer, and 1.2 x %X and 1.5 x %R for L-N vs. L-L resistance and reactance values."
Does anybody know how they get the 1.33 and 1.67 values?
The document has an "Impedance Data for Single Phase Transformers" table with impedance multipliers. For 25-100kVA transformers, the impedance multipliers are the 1.2 x %X and 1.5 x %R (full winding), but for 167kVA to 500kVA, that changes to 2 x %X and 1.5 x %R.
Wasn't sure how the increase in the reactance multiplier impacted the 1.5 approximation...
Does anybody know how they get the 1.33 and 1.67 values?
The document has an "Impedance Data for Single Phase Transformers" table with impedance multipliers. For 25-100kVA transformers, the impedance multipliers are the 1.2 x %X and 1.5 x %R (full winding), but for 167kVA to 500kVA, that changes to 2 x %X and 1.5 x %R.
Wasn't sure how the increase in the reactance multiplier impacted the 1.5 approximation...