# Transformer Confusion (Simple, Help!)

1. Dec 17, 2011

### jegues

1. The problem statement, all variables and given/known data

See first figure attached.

2. Relevant equations

3. The attempt at a solution

For this question I understand parts 1) and 2) entirely and have obtained the correct answers from the solutions.

I am confused about part 3) and I think my confusion stems out from confusion related to the rated voltages of a transformer.

Please take a look at the 2nd figure attached.

In this figure, where are the rated voltages of a transformer?

Would they be at E1 and E2? Or are they V1 and V2?

Once that is sorted out I have one more confusion to figure out.

In part 3) they tell you it is at rated load. Rated load means rated current, but rated current doesn't always imply rated voltage! (Only if you have the rated power, correct?)

How is it that in the calculation for the voltage regulation they assume rated voltage of 1000V?

Thanks again!

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Last edited: Dec 17, 2011
2. Dec 17, 2011

### Staff: Mentor

It would have to be the supply and load voltages while loaded, V1 and V2.

The transformer operates on currents. It is current that pushes the magnetic core towards saturation, that's ultimately its limiting factor. Sure, voltages stress the various insulations, but otherwise don't affect the transformer action. So testing under full load would mean full rated current.

3. Dec 18, 2011

### jegues

I determined that the OCT was conducted on the LV side and the SCT was conducted on the HV side.

The only part left that I'm confused about is how they assume rated voltage across the terminals of the load.

I was told in class that rated load (which implies rated current) does not always mean rated voltage!

Is this the case?

The biggest difficulty I have is reading the questions and pulling out the information they are giving me based on rated "this", and rated "that".

4. Dec 18, 2011

### Staff: Mentor

That seems logical. Is that how you arrived at that--based on common sense? Because I suppose it would not be beyond the bounds of possibility for someone to come up with a disasterous design where this was not the case; where you really did have to apply 50% of the supply voltage in order to get the full rated current on s/c test! It would be a very inefficient transformer.
You're saying "does not always mean exactly, precisely 1000.00 volts", are you?