50 cycle transfomer runnning 60 cycles

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mbrooke

mbrooke

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Will operating a 50hz transformer on a 60hz line cause a higher secondary voltage or is this just a myth? Or are any other issues probable?
 
mbrooke said:
Will operating a 50hz transformer on a 60hz line cause a higher secondary voltage or is this just a myth? Or are any other issues probable?
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The voltage is related to the turns ratio, not the frequency. So if you have a 240V to 24V transformer for example, the turns ratio is 10:1 so the output will still be 24V if the input is 240. The output will be at 60Hz of course.

The problem with different frequencies is in going from a 60Hz designed transformer and using it in a 50Hz supply. It still does not change the voltage, but the EFFECT of the lower frequency applied to the 60Hz designed transformer is said to be the same as applying over voltage to it; the transformer current is higher for a given load and because the transformer will not have been designed for that added I2t heating, it over heats and fails sooner. I only mention this because I have found that this is often the reason behind that myth / misunderstanding.
 
140825-2125 EDT

No one should be propagating such nonsense. Yes it is a myth.

In a tightly coupled transformer, meaning a very high percentage of the primary magnetic flux couples to the secondary, the unloaded output voltage is very near N * the primary voltage. Where N is the secondary turns count divided by the primary turns count.

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Jraef said:
The voltage is related to the turns ratio, not the frequency. So if you have a 240V to 24V transformer for example, the turns ratio is 10:1 so the output will still be 24V if the input is 240. The output will be at 60Hz of course.

The problem with different frequencies is in going from a 60Hz designed transformer and using it in a 50Hz supply. It still does not change the voltage, but the EFFECT of the lower frequency applied to the 60Hz designed transformer is said to be the same as applying over voltage to it; the transformer current is higher for a given load and because the transformer will not have been designed for that added I2t heating, it over heats and fails sooner. I only mention this because I have found that this is often the reason behind that myth / misunderstanding.
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Good to know it is really a myth. :):cool: So basically the kva and voltage output will be the same in 60hz operation?


And in terms of short circuit currents, what do I expect?
 
140826-2235 EDT

mbrooke:

Assuming the design critera was about the same for the 50 Hz transformer as would be used for the 60 Hz design, then when the 50 Hz unit is on 60 Hz the maximum flux density will be lower. This means the magnetizing current should be less (not driven as far into saturation). I would expect the kVA rating to be about the same.

If the series internal impedance is higher (my guess is that it might be), then the short circuit current would be less. But posswibly not much difference.

The transformer will be heavier, and probably costs more.

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mbrooke said:
Will operating a 50hz transformer on a 60hz line cause a higher secondary voltage or is this just a myth? Or are any other issues probable?
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Is this a question based on curiosity of a real application?
If it is for an actual application it would be appropriate to provide the rating of the transformer in question.
You could be referring to a CPT or a power transformer. Applying a transformer at a lower frequency than its rating will result in core saturation resultng heating which also affects the secondary voltage as the core saturates. This also happens with an overvoltage condition as was previously stated.
In either case 50hz rated transformers in general will function acceptably at 60hz as stated in previous posts. But, this would be a general answer and should not to be assumed to be true in every application.
 
templdl said:
Is this a question based on curiosity of a real application?
If it is for an actual application it would be appropriate to provide the rating of the transformer in question.
You could be referring to a CPT or a power transformer. Applying a transformer at a lower frequency than its rating will result in core saturation resultng heating which also affects the secondary voltage as the core saturates. This also happens with an overvoltage condition as was previously stated.
In either case 50hz rated transformers in general will function acceptably at 60hz as stated in previous posts. But, this would be a general answer and should not to be assumed to be true in every application.
Click to expand...


75kva Dry type unit in a real scenario. My understanding is larger oil filled power transformers must be frequency specific for many reasons, however a 50hz dry type unit can be placed on 60 cycles while a 50 hz unit on 60hz must have a 20% lowered primary voltage with a reduced kva capacity.


In fact, due to the extra iron, if my calcs are correct I can squeeze out an extra 5 to 10% kva?



As for all the questions its because there is a huge surplus of left over units from an old building reno that are in excellent condition and can be reused.
 
140827-0905 EDT

mbrooke:

How do you squeeze more kVA out of a transformer? Only if you were to raise the voltage.

To a large extent a transformer rating is current limited by I^2*R losses. Also note lower frequency transformers may use thicker laminations, and when run at higher frequencies will have higher eddy current losses.

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gar said:
140827-0905 EDT

mbrooke:

How do you squeeze more kVA out of a transformer? Only if you were to raise the voltage.

To a large extent a transformer rating is current limited by I^2*R losses. Also note lower frequency transformers may use thicker laminations, and when run at higher frequencies will have higher eddy current losses.

.
Click to expand...

I could be wrong: A 50hz transformer has more iron in it compared to a 60 cycle unit. My theory is there will be less saturation (assuming primary voltage stays the same), and in turn the unit will run slightly cooler, thus allowing for a slightly higher load until the same temperature rise is met.




xformer said:
IMHO... You would also have a change in the impedance value of the transformer.
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Your onto something good. :) It would be lower, correct? Ie, a 5% Z 50hz would go to 4.5% Z 60hz?
 
mbrooke said:
I could be wrong: A 50hz transformer has more iron in it compared to a 60 cycle unit. My theory is there will be less saturation (assuming primary voltage stays the same), and in turn the unit will run slightly cooler, thus allowing for a slightly higher load until the same temperature rise is met.

Your onto something good. :) It would be lower, correct? Ie, a 5% Z 50hz would go to 4.5% Z 60hz?
Click to expand...

Huh, As the frequency goes up, the impedance of a coil goes up (ignoring iron saturation, which is not where you want to be running any transformer). Is there something I am missing here?
 
140827-2220 EDT

mbrooke:

You are correct that at 60 Hz and the same excitation voltage as at 50 Hz that the core will be driven less into saturation. Will the slight reduction in excitation current over or under compensate for changes in core loss change I don't know. This also may change with different transformer designs.

I believe the big factor is just the lower operating voltage.

On any transfotrmer you can trade off life for operation at an overloaded condition.

.
 
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