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

[mivey]

Do you think the penny has dropped?

I'm not sure the beginning step has been taken. Some mechanisms only require a little jigging, others need multiple thumps.

 

[Besoeker]

I'm not sure the beginning step has been taken.

The beginning of understanding is the acknowledgement of ignorance.

 

[Sahib]

What an entirely unreasonable and, actually, quite erroneous conclusion!
I printed out the curves, made some physical measurements to get scale and came up with a slightly lower figure of 150,000 At/m.
Within the resolution possible on A4 and the thickness of the line, the values are certainly comparable.

My great appreciation for your efforts. :thumbsup:

But, unfortunately, a more accurate method came to my mind later which would have facilitated your efforts.

It is this.

Since the relative permeability of steel core of the transformer is assumed to be unity after saturation, the ratio of change in B to the corresponding change in H should equal the permeability of air which is approximately equal to 0.000001256.

The increase in flux density due to 50 Hz operation is 0.3T and the corresponding increase in H is, say, Y. Then 0.3/Y= 0.000001256. So Y=0.3/ 0.000001256=238853.50 or say 238854. So corresponding to B=1.8T, the H=238854+3000=241854.

So the increase in H is 81 times approximately.

The no load current is 0.05 p.u

So the no-load current under 50hz operation is 0.05 x 81=4.05 times transformer rated current.

 

[Besoeker]

So the increase in H is 81 times approximately.

The no load current is 0.05 p.u

So the no-load current under 50hz operation is 0.05 x 81=4.05 times transformer rated current.

So, what do you now conclude about 50Hz operation of a transformer designed for 60Hz?

 

[Sahib]

So, what do you now conclude about 50Hz operation of a transformer designed for 60Hz?

I already concluded as

It is clear that the 50hz operation of 60hz transformer is not possible at the same KVA.

Now what do you think how much the reduction in KVA would be?

 

[Besoeker]

.......

Yet, as late as post #61, you posted this:

So no problem with no load operation of 60hz transformer on 50hz.

You even attempted to support that with calculations.

Your recent calculations very clearly demonstrate why it IS a big problem and they completely invalidate your earlier assertion.
It's something we have been telling you from year dot. And something you were extremely resistant to accept.
I'm pleased that you now seem to have seen and accepted that it is a problem.
Well done that man!
Maybe we should start billing you for knowledge/experience we are giving you.....

Now what do you think how much the reduction in KVA would be?

Something of an irrelevance. Think about what a transformer is used for.

 

[Sahib]

Yet, as late as post #61, you posted this:

So no problem with no load operation of 60hz transformer on 50hz.

You even attempted to support that with calculations.

It is stated with different operating condition ( the transformer was assumed to operate in the linear portion of the magnetization curve i.e below saturation to clarify the issue)and so is a valid assertion.

Your recent calculations very clearly demonstrate why it IS a big problem.

It was assumed that the transformer operated in the saturation region as is usual for a modern transformer.

It's something we have been telling you from year dot. And something you were extremely resistant to accept.
I'm pleased that you now seem to have seen and accepted that it is a problem.
Well done that man!
Maybe we should start billing you for knowledge/experience we are giving you.....

While I want to place my due regards for what you have done here, the vagueness in your explanation prompted me to provide more clarity by way of quantitative analysis.

Something of an irrelevance. Think about what a transformer is used for.

Another example of vagueness.

 

[GoldDigger]

I already concluded as



Now what do you think how much the reduction in KVA would be?

Well, if the problem is that the transformer willl fail under no-load conditions, how will any reduction in rated full-load capacity without a redesign help at all?

Are you asking what power handling you could get if you redesigned the transformer using the same amount of copper and iron?

 

[Besoeker]

It is stated with different operating condition ( the transformer was assumed to operate in the linear portion of the magnetization curve i.e below saturation to clarify the issue)and so is a valid assertion.

It is stated with invalid conditions for a real life transformer. You now know that.

But I think/hope you got the point. Operating a 60Hz transformer on 50Hz is not an option. Your own calculations clearly demonstrate that.
Nothing more to discuss.

 

[mivey]

Now what do you think how much the reduction in KVA would be?

What reduction? The transformer will melt down unless re-designed.

It is stated with different operating condition ( the transformer was assumed to operate in the linear portion of the magnetization curve i.e below saturation to clarify the issue)and so is a valid assertion.

Changing the operating conditions? You had some notion that we could use a 60 Hz transformer in a 50 Hz system if we reduced the load. The problem is that we have to change the design. In reality, adding load actually reduces the flux a little bit. You did not realize that operating the transformer with no load would still cause a melt-down.

While I want to place my due regards for what you have done here, the vagueness in your explanation prompted me to provide more clarity by way of quantitative analysis.

The vagueness of your discourse is the issue. You refute or attempt to debate a post and when the facts are posted you re-align your position so you can debate with a slightly different set of parameters.

Another example of vagueness.

He is trying to make you think about what you are posting. Your discourse tends to meander from one place to the next. It is like herding cats. Instead of focusing on specifics, which is hard to do with a moving target, a focus on concepts from a broader perspective sometimes helps. Sometimes.

 

[Sahib]

Well, if the problem is that the transformer willl fail under no-load conditions, how will any reduction in rated full-load capacity without a redesign help at all?

Are you asking what power handling you could get if you redesigned the transformer using the same amount of copper and iron?

What reduction? The transformer will melt down unless re-designed.

It can be done by de-rating the 60hz transformer without a redesign i.e altering the core size.
For this purpose it is only necessary to ensure that the flux density remains constant in the transformer core. So how would you achieve it?

 

[Besoeker]

It can be done by de-rating the 60hz transformer without a redesign i.e altering the core size.
For this purpose it is only necessary to ensure that the flux density remains constant in the transformer core. So how would you achieve it?

Think about the purpose of a transformer. What it is intended to do,

 

[Sahib]

Think about the purpose of a transformer. What it is intended to do,

The purpose of a transformer is to change the voltage from one level to another.

But it does not give you an excuse not to answer the question in

It can be done by de-rating the 60hz transformer without a redesign i.e altering the core size.
For this purpose it is only necessary to ensure that the flux density remains constant in the transformer core. So how would you achieve it?

 

[Besoeker]

The purpose of a transformer is to change the voltage from one level to another.

Good. You are getting there.
Now, what would you need to do to make that transformer, designed for 60Hz, to operate at the same flux density on 50Hz?

 

[Sahib]

Now, what would you need to do to make that transformer, designed for 60Hz, to operate at the same flux density on 50Hz?

That is, precisely, the question I asked you.

 

[jumper]

Good. You are getting there.
Now, what would you need to do to make that transformer, designed for 60Hz, to operate at the same flux density on 50Hz?

A flux capacitor?

Just kidding Mr.B.

A joke from a movie "Back to the future"

 

[Besoeker]

That is, precisely, the question I asked you.

I know what I would do. Or, more precisely, what I wouldn't.
Now, if you are suggesting the use of a 60Hz transformer is possible on a 50Hz supply and how that can be done then fire away with the how.

 

[Besoeker]

A flux capacitor?

Just kidding Mr.B.

A joke from a movie "Back to the future"

Appreciated Mr Jumper.
Or maybe not.
Not really my generation, you see.
So far this year I have been to two funerals of close relatives. I hope the next isn't my own but I can't rule out that possibility.

 

[Sahib]

I know what I would do. Or, more precisely, what I wouldn't.
Now, if you are suggesting the use of a 60Hz transformer is possible on a 50Hz supply and how that can be done then fire away with the how.

For the flux density to remain constant, v/f should remain constant.

So if v1 and f1 are voltage and frequency of 50hz power supply and v2 and f2 that of 60hz power supply, then the condition to be satisfied is

v1/f1=v2/f2.

Given f1=50hz and f2=60hz, then the relationship between v1and v2 is

v1=50/60(v2)=0.83*v2.

So a transformer rated at 13800/480V, 60Hz may be used at 11500/400V, 50Hz with its KVA derated by 17%.

 

[Besoeker]

For the flux density to remain constant, v/f should remain constant.

Good lad! Well done!
You have finally taken note of what I posted in #6 on the first page of this thread.

To keep the flux density the same. Flux is dependent on the volts times time. At 50Hz the volt second area for any half cycle is 20% greater than at 60Hz. So, for the same flux density, you need 20% more core.

So a transformer rated at 13800/480V, 60Hz may be used at 11500/400V, 50Hz with its KVA derated by 17%.

But not a lot of good if you wanted what the transformer was designed to give - 480V output.
To exemplify how specious your point is, you could use the transformer with 115V into give 4V out.