
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.
Related Topics

By Tseppish in forum Electrical Testing Talk
Replies: 1
Last Post: 4 Days Ago, 02:56 PM
Tags for this Thread