Short-Circuit Calculations Using Transformer and Source Impedance

Using Transformer and Source Impedance

An infinite bus short-circuit calculation can be used to determine the maximum short-circuit current on the secondary side of a transformer using only transformer nameplate data. 

This is a good (and simple) method for determining the worst-case maximum short-circuit current through the transformer since it ignores the source/utility impedance. Ignoring the source impedance means it is assumed to be zero and voltage divided by zero is infinite, hence the often-used term “infinite bus” or “infinite source.”

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To provide more accurate short-circuit calculations, the source impedance needs to be included. Let’s see how to include the effect of the actual source short-circuit current and the equivalent source impedance. 

The  equation is as :

SCAsecondary= ( FLAsecondary x 100 ) / (%Ztransformer + %Zsource)

This article has been extracted from IAEI website, the full article including a fully worked example can be found at the below link. 

Link to Full Article

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