# Transformer Saturation Question



## PEExam123 (Jan 1, 2021)

In one of the CRAM tests, there was a question on TRANSFORMER Saturation.

60 Hz Generator feeding 60 Hz Motor through a Transformer (designed for 30 Hz). The answer says "Transformer will Saturate".  Is this right ???? 

I am thinking the opposite: A high frequency (60 Hz) signal is going through the transformer (designed for 30 Hz). So it shouldn't saturate the transformer.

Please help me on this one.


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## DarkLegion PE (Jan 2, 2021)

That's correct it will  saturate because of the Voltage to Hertz ration (V/Hz). So when you have a voltage on top and the frequency is changed to something smaller, the ratio gets bigger which leads to saturation. Therefore to avoid saturation you have to decrease voltage by the same percentage the Hz was decreased (in this case 50%)


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## akyip (Jan 2, 2021)

PEExam123 said:


> In one of the CRAM tests, there was a question on TRANSFORMER Saturation.
> 
> 60 Hz Generator feeding 60 Hz Motor through a Transformer (designed for 30 Hz). The answer says "Transformer will Saturate".  Is this right ????
> 
> ...


I think the issue that PEExam123 is confused about is why the transformer's core would saturate when the transformer is rated/designed for 30 Hz.... Which I can't really explain either.

DarkLegion is correct that normally saturation will occur when the V/f ratio is too high (either the voltage is too high or frequency is too low). If the transformer was rated for 60 Hz, then yes I can see it saturating.

But since the transformer is actually rated for 30 Hz... Does it really saturate then? If 60 Hz passes through the 30 Hz transformer, then that means the transformer's rated V/f ratio (Vrated / frated) would actually be lower, implying that saturation should not happen for the 30 Hz transformer...

I'm hoping @Cram For The PE can elaborate a bit more on this.


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## DarkLegion PE (Jan 2, 2021)

akyip said:


> I think the issue that PEExam123 is confused about is why the transformer's core would saturate when the transformer is rated/designed for 30 Hz.... Which I can't really explain either.
> 
> DarkLegion is correct that normally saturation will occur when the V/f ratio is too high (either the voltage is too high or frequency is too low). If the transformer was rated for 60 Hz, then yes I can see it saturating.
> 
> ...


Wondering if I misinterpreted this then. I'm understanding it this way: If a 60Hz Voltage is passing through something rated for 30Hz the Voltage will be higher than the voltage rating for the 30Hz thus saturating the transformer.


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## akyip (Jan 2, 2021)

DarkLegion said:


> Wondering if I misinterpreted this then. I'm understanding it this way: If a 60Hz Voltage is passing through something rated for 30Hz the Voltage will be higher than the voltage rating for the 30Hz thus saturating the transformer.


Hm, not sure about that. I have the Cram for Exam volumes, so I am familiar with this question. I don't believe the question stated that the transformer is designed at a different voltage from the generator or motor. So based on that, I think the transformer's rated voltage is safely assumed to be the same as the generator's and motor's respective rated voltages on the respective sides. So that means rated voltage should be passing through the transformer, as far as the transformer is concerned.

Just my two cents. I honestly didn't even think of the original poster's question at all when I first did this problem, since I just saw 30 Hz &lt; 60 Hz means saturation...


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## Cram For The PE (Jan 2, 2021)

PEExam123 said:


> In one of the CRAM tests, there was a question on TRANSFORMER Saturation.
> 
> 60 Hz Generator feeding 60 Hz Motor through a Transformer (designed for 30 Hz). The answer says "Transformer will Saturate".  Is this right ????
> 
> ...


You are correct. I have it backwards. Typo has been fixed.


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## PEExam123 (Jan 2, 2021)

Hello Cram for The PE,

                                      "Typo has been Fixed". Does this mean you fixed the question to read " 30 Hz Generator feeding 30 Hz Motor through a Transformer (designed for 60 Hz)" ??? 

Thank You   *akyip and DarkLegion.*


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## Cram For The PE (Jan 2, 2021)

PEExam123 said:


> Hello Cram for The PE,
> 
> "Typo has been Fixed". Does this mean you fixed the question to read " 30 Hz Generator feeding 30 Hz Motor through a Transformer (designed for 60 Hz)" ???
> 
> Thank You   *akyip and DarkLegion.*


Question now states:

A [SIZE=11pt]50Hz generator is going to supply power to a 50Hz motor through a transformer designed for 60Hz. Which of the following statements is true?[/SIZE]


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## PEExam123 (Jan 2, 2021)

Great. Then in this case, the XFMR saturates.


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## Cram For The PE (Jan 2, 2021)

Yes that is correct.


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## akyip (Jan 2, 2021)

Thanks for responding, Cram!

So I guess in the original question, the 30 Hz transformer with the 60 Hz voltage doesn't saturate then (its Vrated/frated ratio is low because f actual &gt; f rated). The 30 Hz transformer would experience an under-flux instead...


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## Cram For The PE (Jan 3, 2021)

akyip said:


> Thanks for responding, Cram!
> 
> So I guess in the original question, the 30 Hz transformer with the 60 Hz voltage doesn't saturate then (its Vrated/frated ratio is low because f actual &gt; f rated). The 30 Hz transformer would experience an under-flux instead...


Yes that’s correct


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## osh1397 (Jul 18, 2021)

you wrote in the answer "As the frequency is decreased, the flux density will increase which will result in transformer core saturation. This will increase transformer losses and the heating may damage the transformer winding insulation."

This is not correct.

from the NCEES handbook P#58







For Eddy current losses I think they will not change.
For the Hysteresis losses the flux is raised to a power greater than 1, so, I think it would actually reduce.


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