# Turns Ratio of Transformers



## electricalwiz (Mar 12, 2011)

I need someone to explain the turns ratio of the following transformers
These questions are off of a practice exam

1. The turns ratio of a 480/240/120 volt single phase transformer is ?
A. 4/1 B. 3/1 C. 2/1 D. 1/1

2. The turns ration of a 480/240/120 volt delta/delta connected 3 phase transformer is ?
A. 4/1 B. 3/1 C. 2/1 D. 1/1

3. The turns ratio of a 480/208/120 volt 3 phase transformer is 
A. 2/1 B. 2.3/1 C. 4/1 D. 4/2

Answers 1. C 2. C 3. C

I understand why answer three is 4/1 but why arent answers one and two also 4/1?


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## don_resqcapt19 (Jul 18, 2010)

In one and two the seconday winding is rated at 240 volts and "center tapped" to get the 120 volts. In 3 the seconday winding is rated at 120 volts and connected in a wye to get the 208 volts.


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## tgreen (Sep 14, 2010)

Dons answer is correct. 
in question 1 and 2 the coils are 240v coils. so 480/240= 2/1 
in question 3 the 208v is achieved by measureing across 2 120v coils in a wye configureation 480/120= 4/1


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## 10492 (Jan 4, 2010)

So, it should be written:

480X240/120 single phase

If it was a 480/240X 120 single phase, (if they made such a thing) it would be 4-1?


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## tgreen (Sep 14, 2010)

i think your right and that it is written wrong. 
if it was written 480/240 x 120 then i would think that it was a duel input voltage transformer that would transform either 480 or 240 and keep the secondary at 120 respecivly


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