Short Circuit Question (NCEES vs Complex Imaginary Test 1-#

[EEmarcus]

Is the impedance of a TX correlated to the applied voltage for the short circuit?

On Question 539 TX has 10% impedance & (100/7.2KV) and the factory short circuit test the applied KV to get rated current the answer is 10KV. (100KV * 10%)

On complex imaginary TX has 5% impedance & (12.5KV/480V) and the factory short circuit test the applied KV to get rated current is (625V) (12.5KV * 5%).

So in order to get rated current on the low-side does one assume multiply HV Rating by impedance percentage?

 

[DK PE]

Is the impedance of a TX correlated to the applied voltage for the short circuit?

On Question 539 TX has 10% impedance & (100/7.2KV) and the factory short circuit test the applied KV to get rated current the answer is 10KV. (100KV * 10%)

On complex imaginary TX has 5% impedance & (12.5KV/480V) and the factory short circuit test the applied KV to get rated current is (625V) (12.5KV * 5%).

So in order to get rated current on the low-side does one assume multiply HV Rating by impedance percentage?

The short answer is yes but if you think of it this way you can reason your way there. In an infinite source short circuit calculation, you know the short circuit current is 1/%Z... so for 5% Z, the short circuit current on secondary would be 1/0.05 = 20pu with rated voltage on primary. The SC test is usually done at rated SECONDARY current so assuming we scale back the primary voltage 20X to get secondary current of 1pu (ie rated current)... note scaling back 20X is same as multiplying by 5%. I've simplified a bit but thought this may help.

 

[pbrme]

From my experience, Short Circuits need Input