
What is the turns ratio?
Transformers
A wyedelta 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.

Originally Posted by
franko26
Transformers
A wyedelta 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.
Is the 7200 line or phase voltage ?

Originally Posted by
lester mcmanaway
Is the 7200 line or phase voltage ?
I copied and pasted the question at the top of the comment, your guess is as good as mine.

Originally Posted by
franko26
I copied and pasted the question at the top of the comment, your guess is as good as mine.
My guess would be line voltage then. So 7200/1.732 = 4157/360 roughly 11.55:1 would have been what I was thinking.

Originally Posted by
lester mcmanaway
My guess would be line voltage then. So 7200/1.732 = 4157/360 roughly 11.55:1 would have been what I was thinking.
i think the point i was trying to make is that the answer is 20:1, even though, grammatically, it should be 1:20 per the study guide that I included. I really hope the real test is not like this. Whats the point of having questions that will trick you, they really should be testing our knowledge. Though I think this website is excellent for getting your mind thinking in the right direction, some of the questions are questionable. There was another one: what is the fla for a single phase 115vac 1hp motor? the answer according to test guy is 16a, this is correct per nec table 430.28. remember though, the code book is only a guide. if you use the formula P=I xE or I=P/E, with P=to 746, the answer is 6.49 which is close to the 8a answer thy included. I dont believe they are going to let us use the nec on the test, so you have to figure it out mathematically.
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