Relative size and Arc Flash Hazards of 50 Hz versus 60 Hz transformers at same KVA

[GoldDigger]

For arc flash studies, to compare differences in 50Hz transformers vs. 60Hz, you only have to compare the transformer impedances.

If the 50Hz xformer and the 60Hz xformer have the same impedance (assuming same voltage and KVA), then wouldn't the arc flashes be very close to the same?

That was the assumption that I started with. And I have not seen anything to change that, although I am far from an expert on the subject. Hence the search for answers to that question also in this thread.
There will be more energy stored in the magnetized core of the 50Hz transformer since the integrated flux will be higher at the same voltage, if that has any effect. But I am guessing that the majority of the incident energy will be fed through from the primary.

 

[Sahib]

Besoeker & Golddigger:

You two provided excellent explanations. :thumbsup:

Thanks.

From your explanations, it is clear that the 50hz operation of 60hz transformer is not possible at the same KVA.

But B does not even concede no load operation of 60hz transformer at 50hz.,

To see if he is right, it is required to know various values from the B/H curve of a typical iron core of the transformer. Since there is a 20% increase in flux density for 50hz operation of 60hz transformer, the corresponding increase in magnetising current may be found from those values and so the feasibility of 50hz operation of 60hz transformer at no load may be ascertained.

My guess is that the transformer would operate close to full load in that condition.

Cheers.

 

[Besoeker]

But B does not even concede no load operation of 60hz transformer at 50hz.,
.

Nor would you if you'd actually taken on board the information I've given you in spade loads.
:roll:

 

[Sahib]

B:
Additional information for you to work out, if you are pleased to do so:

A modern transformer has typical core flux density(B) of 1.5T at field intensity (H) of 3kA-t/m

The no-load current is typically 5%.

As already noted, there is 20% increase in flux density for 50hz operation. So the flux density is 1.8T. So what is the field intensity(H) then?

 

[Besoeker]

B:
As already noted, there is 20% increase in flux density for 50hz operation.

There is a 20% increase in the Volt-time integral. You cannot conclude that this will translate into a 20% increase in flux.

 

[Besoeker]

But B does not even concede no load operation of 60hz transformer at 50hz.

Another point to add to my previous reply.
The no-load case is rge worst from the point of view of saturation. The voltage drop across X₁ and R₁ is lowest so the voltage applied to Xm will be at its greatest.

 

[Sahib]

There is a 20% increase in the Volt-time integral. You cannot conclude that this will translate into a 20% increase in flux.

Volt-time integral gives flux, 50hz Volt-time integral is greater than 60hz Volt-time integral by 20% and so is the flux. If not so practically speaking, consider it anyway as the worst case scenario.

The no-load case is rge worst from the point of view of saturation. The voltage drop across X₁ and R₁ is lowest so the voltage applied to Xm will be at its greatest.

Consider the worst case scenario.

 

[Besoeker]

Volt-time integral gives flux, 50hz Volt-time integral is greater than 60hz Volt-time integral by 20% and so is the flux.

You have ignored saturation.

 

[Sahib]

No, I did consider. In your graph above, even the portion of the magnetization curve after the knee point goes on slightly rising for steel and iron also. So for a flux density of 1.8T, there must be a corresponding value of H. But it is not shown in your graph.

 

[Sahib]

Duplicate.

 

[Besoeker]

No, I did consider.

I didn't see any reference to it in your post. Just your assertion that the flux would be 20% greater. Saturation indicates that such a linear relationship does not exist.

In your graph above, even the portion of the magnetization curve after the knee point goes on slightly rising for steel and iron also. So for a flux density of 1.8T, there must be a corresponding value of H. But it is not shown in your graph.

Can you guess why?

 

[Besoeker]

No, I did consider. In your graph above, even the portion of the magnetization curve after the knee point goes on slightly rising for steel and iron also. So for a flux density of 1.8T, there must be a corresponding value of H. But it is not shown in your graph.

TBH, this is getting a bit silly.
You have been given bucket loads of good information by myself and others.
Yet you continue to refute some of it.
Unless you can add something constructive rather than negativity, I'm done with this.
Adi?s.

 

[Sahib]

B:
Your posts indicated there would be excessive amount of current for operation of 60hz transformer at 50hz. You had no idea of how much it would be. I set out to find out how much it would be in my subsequent posts.

 

[Besoeker]

B:
Your posts indicated there would be excessive amount of current for operation of 60hz transformer at 50hz. You had no idea of how much it would be. I set out to find out how much it would be in my subsequent posts.

When you find out, post it here.

 

[mivey]

TBH, this is getting a bit silly.
You have been given bucket loads of good information by myself and others.
Yet you continue to refute some of it.
Unless you can add something constructive rather than negativity, I'm done with this.
Adi?s.

You can lead a horse to water...

 

[mivey]

Thanks, mivey for your suggestion.
I have "Electric Machines and Power Systems" by Del Toro.
Take a look at the transfomer equivalent diagram in that book.
It has also resistance and leakage reactance values for the primary.
If we use 60hz transformer on 50 hz, the voltage drop across the leakage reactance is less. If the resistance value is increased so that the total voltage drop is the same as in 60hz, the voltage applied to the ideal transformer ( after primary resistance and leakage reactance) will be same as in 60hz and so the induced voltages both in the primary and secondary windings will be same as in 60hz and so the KVA capacity.

Then why don't you try using some of the sample impedances and try a modified model like you are suggesting and see what values you get?

 

[Besoeker]

Then why don't you try using some of the sample impedances and try a modified model like you are suggesting and see what values you get?

It isn't amenable to linear calculations which is a point he didn't seem to understand and wouldn't take on board.
C'est la vie.

 

[GoldDigger]

It isn't amenable to linear calculations which is a point he didn't seem to understand and wouldn't take on board.
C'est la vie.

OK. "la vie"

 

[mivey]

It isn't amenable to linear calculations which is a point he didn't seem to understand and wouldn't take on board.
C'est la vie.

But modeling it so the core operates between the ankle and knee may provide clarity for him.

 

[mivey]

No, I did consider. In your graph above, even the portion of the magnetization curve after the knee point goes on slightly rising for steel and iron also. So for a flux density of 1.8T, there must be a corresponding value of H. But it is not shown in your graph.

So pick a value, 30-50-70 kAt/m or whatever but note that the curve is flattened out. Does that tell you anything? What does the core being saturated and the magnetic field no longer changing tell you about induced current? What does being above the knee where we can't produce sufficient back EMF to counter increased voltages tell you? Does self-destruction come to mind? Do you think it matters if there is a load applied?