XFRMR calculation

[Bill Watt]

(Another sample c of q question) A 10KVA XFRMR 240/120V. This XFRMR has 14.4V placed across the primary and produces rated secondary current. What is the % impedance of this XFRMR?

[neil seidner]

Bill: The formula for calculating %imp is;

%IZ= (Impedance test voltage)/(Rated voltage) X 100.

The impedance test voltage is the voltage required to produce rated current in the "short circuited" secondary. 14.4V is this voltage. The rated voltage is the rated voltage of the primary.

There is more information in "Alternating Current Fundamentals" by Duff and Herman. In chapter 13 page 415 to 417 (6th edition).

[Bill Watt]

Thanks a million Neil, I've searched for hours for that formula. I found many other related formulae, but couldn't find the right one for this particular question.

[Bill Watt]

Neil, I noticed you responded with a formula for %IZ. Does this mean that if I'm looking for %Z then I have to divide this answer by the primary current?

[neil seidner]

Bill : I did not notice this before, but after doing some research, it seems that "%Z" and "%IZ" are both used to represent the percent impedance of a transformer. I have located the formula in two different sources, one uses %Z, the other uses %IZ, in the otherwise exact same formula.