Transformer calculations

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Eddy Current

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If i have 480V on the primary and 240V on the secondary that is a 2:1 ratio. What would i get if i had 120V on the primary? The book i am studying says 20V but wouldn't it be 60V? 120/2=60.
 
Eddy Current said:
Delmar's Standard Guide to Transformers
Click to expand...
Was this an example calculation?
I can see no explanation other than a typo to justify an answer of 20 volts.
Lowering the input voltage cannot do anything to change the voltage ratio.
But increasing the input over the design voltage can destroy the transformer as well as result in an unexpected output voltage.
 
GoldDigger said:
Was this an example calculation?
I can see no explanation other than a typo to justify an answer of 20 volts.
Lowering the input voltage cannot do anything to change the voltage ratio.
But increasing the input over the design voltage can destroy the transformer as well as result in an unexpected output voltage.
Click to expand...


Yeah an example calculation. It should be 60 right?
 
Eddy Current said:
Yeah an example calculation. It should be 60 right?
Click to expand...
That's what I get, yes.
You can work it two different ways as a double check, since mathematically they are the same:

480:240 is a factor of two, so 120:60 which is also a factor of two is correct, or
And input of 120 is one fourth of the nominal 480, so the output should be one fourth of 240, which is 60.
Yup, they match. :)
 
The KVA of the transformer would also drop to 1/4th of the Rated KVA if a 480V primary were supplied 120V.
 
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