Transformer Operation near Saturation 1

[sobeys81]

Hi All,

I have read this at many places that T/F has max efficiency if operated near the saturation curve but I could not find a decent explanation.

Q#1 How this improves efficiency

Q#2 How we can make a transformer operate near saturation.

I would appreciate a word.

Thanks

 

[magoo2]

This comment really relates to efficiency of material use. You can put a lot more core steel in and have it operate below the knee of the curve for normal voltage, but manufacturers choose to have the normal operating point close to the knee of the sat curve.

 

[jghrist]

#1. Depends on how you define efficiency. Transformers are designed to operate near saturation for economic efficiency because less steel is required. I'm not sure what the effect on no-load losses would be, but I'd bet that it doesn't lower the losses.

#2. You can make a transformer operate near saturation by either putting less steel in the core or operating it at a higher voltage.

 

[burnt2x]

Good point jghrist!

 

[itsmoked]

As you get up tight against saturation you are also going to get more harmonics which may cause inefficiency elsewhere.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[slavag]

Hi.
As Jghrist saied:
"You can make a transformer operate near saturation by either putting less steel in the core or operating it at a higher voltage."
And what we have after.
Low level of 2-nd harmonic( inrush current), but very long inrush current.
As Keith saied:
Lot of other harmonics, for example high level of 5-th harmonic.
For protection issue: special protection needed with option of deblocking of 87T is blocked by 2-nd harmonic in case of
internal trafo fault ( I hope, I understood me).
For operation issue.
You always need move your tap changer to high position for connect CB at the higer level of voltages.
This all, what I think about this kind of efficiency.
Regards.
Slava

 

[slavag]

Sorry.
I meant:I hope, you understand me

 

[boBK7IQ]

Another way to operate more in the saturation region is to reduce the number of turns, (increasing the volts per turn), while keeping the size of the stack the same. The reason this helps full power efficiency is because you can then use bigger wire, thus reducing copper I^2R losses.

boB

 

[edison123]

bobk71q

[COLOR=red yellow]Another way to operate more in the saturation region [/color] .

You cannot operate more in the saturation region for all the reasons already mentioned above by jghrist, itsmoked and slavag.

 

[waross]

The point on the saturation curve that a transformer operates is a design issue more than an operation issue.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

waross

huh...Would you please expand that ?

 

[waross]

I may be picking nits with the meaning of words but what I meant was:
When a designer is designing a transformer, he decides where on the saturation curve and how close to the knee he wants the transformer to operate. Once the transformer is put in service, the operators are usually responding to system parameters. The frequency will be fixed and the operators may not have control over the incoming voltage, which is what will determine the point on the curve where the transformer will operate. Even if they are able to control the voltage, for example at a generating plant rather than a substation or remote switch yard, they will be changing the voltage in response to load changes to compensate for line voltage drops. The operators will not have the luxury of deciding the saturation level that they would like to run at. The operators may respond to load conditions with voltage adjustments and the saturation level will be what it will be.
The designer will have to decide and design for the point on the curve that he wants the transformer to operate at.
This is the electric power engineering forum and so I am taking a chance and assuming that the question was concerning power transformers and their operation. (And design)
Like I said, I was nitpicking on the difference between designing a transformer and operating a transformer.
I did not intend to contradict the other excellent posts on saturation.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Hi Bill

All designers take into account the operation parameters. They understand the voltage fluctuations and design the trafo accordingly with just below the knee point of saturation. Of course, taps are also provided (whether off-load or on-load) to adjust for continuously high system voltages.

Of course, we all agree the operation in saturation points is problematic from harmonics, excessive no-load current etc.

 

[homoly]

If harmonics appear the core losses will increase and efficiency will be reduced - See Steinmetz theorem for theoretical background.

Also operating near saturation means higher flux density in core and it will greatly increase the noise level of core caused by magnetostriction. And also higher magnetizing ( no load ) current as mentioned above.

The we can speak about point of operation with maximum efficiency and this can be affected by transformer design: For example in UPS system 1+1 sharing load the transformers should have ideally maximum efficiency at 50% load, because this is the normal operation point and 100% load would appear only in the case of failure.

 

[boBK7IQ]

"bobk71q
Another way to operate more in the saturation region .

You cannot operate more in the saturation region for all the reasons already mentioned above by jghrist, itsmoked and slavag.
"

Sure you can. Saturation is not just a "Yes or No" thing with soft magnetics... The B-H curve slope just gets less steep while you are getting farther into the B-Sat region.

boB

 

[edison123]

boB - Good luck putting your theory to test in practice.

 

[boBK7IQ]

edison123 (Electrical)
17 Sep 08 22:14
boB - Good luck putting your theory to test in practice.

I have many times, and I'm sure you have too. I think that there is just a definition problem here of the word saturation. I'm merely trying to state that there is a point on the B-H curve where it "starts" to saturate and change slope, and I'm also trying to say that you can continue farther into saturation from that point (for a-while anyway).

I am getting the feeling that you are trying to say that the iron is "saturated" or "not saturated" and that's that. I am sure that for those of us that have designed many low frequency laminated steel transformers, that we all must know this, but may have a different way of understanding how someone says this. If they don't understand this, then if their transformers work, that's all that counts, or maybe they are lucky.

This is more useful for optimization of the transformer than anything else. I come from the inverter industry where efficiency and tare losses are both very important and must be optimized as much as possible.

boB

 

[boBK7IQ]

> I said:
>> I come from the inverter industry where efficiency and tare losses are both very important and must be optimized as much as possible.

I wish I could edit posts... I should also have said that in an inverter you do NOT want to operate very far into saturation, but it should be understood what you can and cannot do. One of the original questions asked how to operate more in saturation and how it affects efficiency, I think. I merely pointed out that "full power" efficiency can be optimized by operating farther into saturation. This is at the expense of no load idle power of course.

OK, that's all I meant to say I think (and hope).
boB