What is the turns ratio?

[RabbleRabble]

I would disagree on one point. 7200V would be your V_L-L and 4157.044V would be your V_L-G. Anytime you read voltage on a WYE system, phase to phase (line to line) will be a larger number than your phase to ground (line to ground).

(V_L-L/sqrt(3)) = V_L-G

Great answer thank you. I think line to neutral voltages can be confusing.

[Izeldeen]

Transformers
A wye-delta transformer has a primary voltage of 7200 V and a secondary voltage of 360 V. What is the turns ratio?
Your Answer: 1:20

The test considered this answer wrong. The primary to secondary voltage ratio is 1 to 20. I'm sure the correct answer is 20:1, but grammatically speaking, the 1:20 answer is more correct. The following is from the noted study material:

Since there is a ratio of 1 to 4 between the turns in the primary and secondary circuits, there must be a ratio of 1 to 4 between the primary and secondary voltage and a ratio of 4 to 1 between the primary and secondary current. Please advise.

7200/1.732=4157
4157/360=11.5

[Izeldeen]

You are 100% correct on this. 7,200V (Line) WYE = 4,160V (Phase). On the Delta side Vline=Vphase. You should always use the phase voltages to get a ratio, especially when dealing with a WYE-Delta configuration. Using phase voltages your math should be 4,160V/360V = 11.55:1 Ratio not 1:11.55. Turns ration is stated with the Primary Turns First. So in this case the Primary voltage is higher so the ratio will begin with the higher number of turns.

thats right

[ranniery100]

I believe this question is wrong. On D-D system there's only Line voltage. So the answer it's a direct division between the two available voltages 7200/360 = 20:1.

On Y-D, you must divide the Line voltage on the primary to get the related phase voltage. In the secondary there's only one available voltage, which is the Phase one. So, the \TTR would be 7200/sqrt(3) / 480 = 11.55:1