Understanding Voltage Regulation in Transformers

[tim9000]

Hi,
So I have been told on here that when you eliminate the leakage flux between coils it improves Voltage regulation, I have also read online that voltage regulation is related to inductance, but could anyone elaborate on these? 'why are these so?'

[I can sort of guess something like the better the linkage inductance the more stored energy to be transferred to the secondary...maybe?]

Are there any better explenations or formulas to better illustrate the qualities that are needed for good voltage regulation in a TX? What properties necessitate good voltage regulation?P.S
On that note, what defines the power factor (more) magnetising loss, or resistive loss?

Cheers

 

[tim9000]

Hi,
So I have been told on here that when you eliminate the leakage flux between coils it improves Voltage regulation, I have also read online that voltage regulation is related to inductance, but could anyone elaborate on these? 'why are these so?'

[I can sort of guess something like the better the linkage inductance the more stored energy to be transferred to the secondary...maybe?]

Are there any better explenations or formulas to better illustrate the qualities that are needed for good voltage regulation in a TX? What properties necessitate good voltage regulation?P.S
On that note, what defines the power factor (more) magnetising loss, or resistive loss?

Cheers

From what I just found on this page, this is basically the key to my answer:
http://www.electrical4u.com/voltage-regulation-of-transformer/

 

[Jeff Rosenbury]

From what I just found on this page, this is basically the key to my answer:
http://www.electrical4u.com/voltage-regulation-of-transformer/

I think your link failed to mention that flux leakage will lead to a higher transformer impedance since this amounts to energy lost to the circuit. This impedance only affects the voltage when under load. (No load; no current; no V=IR) Thus it will cause less regulation. (Generally anyway. With phasors the answer is more complex. )

 

[tim9000]

I think your link failed to mention that flux leakage will lead to a higher transformer impedance since this amounts to energy lost to the circuit. This impedance only affects the voltage when under load. (No load; no current; no V=IR) Thus it will cause less regulation. (Generally anyway. With phasors the answer is more complex. )

H'mm, interesting. So how would the energy loss of the circuit change if the flux was perfectly coupled through the core? (if non was leaking) I'm still not 100% clear as to how inductance is having it's affect, is it anything to do with stored energy?
Thanks!

P.S: am I right in assuming that angle δ is the voltage angle between the primary and secondary coil? (If so, what causes/effects this very small angle?)

 

[Jeff Rosenbury]

Inductance is a form of stored energy. Currents generate magnetic fields. These fields build as the current builds, and they store energy. When the current tries to stop flowing, the field collapses. The field transfers its energy back into pushing a flowing current. This results in a slowing of change -- a phase shift.

In a transformer current in the primary creates that field and the field then induces current in secondary. In an ideal transformer, all the energy is coupled from the primary and used in the secondary. In a non-ideal transformer, some of the flux escapes and doesn't couple. This might instead induce eddy currents, straight inductance, copper losses, etc. These are modeled as an impedance.

If you are trying to build an electronics regulator, other factors will typically dominate. Line voltage varies by somewhere around 10%. Ripple is typically a problem, etc. There are some nice linear supplies which fix these problems, but at a cost. (Beware the dropout voltage; you will still need you equations to check that.) Switching power supplies are more efficient, but have more noise.

On the angle thing (How did you make the symbol, BTW?): No, the angle is the angle between the unloaded voltage and the loaded voltage. Notice how in the first diagram the loaded voltage is actually higher than the unloaded voltage. (This is because most of the impedance is reactive with very little resistance.) This link is more for power engineering. Such situations are counter-intuitive, but occur in power situations. I'm more of an electronics guy.

 

[tim9000]

Inductance is a form of stored energy. Currents generate magnetic fields. These fields build as the current builds, and they store energy. When the current tries to stop flowing, the field collapses. The field transfers its energy back into pushing a flowing current. This results in a slowing of change -- a phase shift.
In a transformer current in the primary creates that field and the field then induces current in secondary. In an ideal transformer, all the energy is coupled from the primary and used in the secondary. In a non-ideal transformer, some of the flux escapes and doesn't couple. This might instead induce eddy currents, straight inductance, copper losses, etc. These are modeled as an impedance.

This is where I'm rusty, because all I think of between coils is that (forgetting about leakage flux for the time being) that the flux running through the core, is the same, thus using faraday's law there is a voltage induced on the secondary coils, and a back EMF on the primary.
So what does it matter if there is energy stored in the form of inductance? (in the air through leakage, or in the core through coupling) As long as the flux is flowing between the coils, what does inductance matter? It seems irrelevant, can you explain the role?
I know in an ideal TX you would have a core with infinite permeability, thus the reluctance is zero, meaning that the inductance is infinite, but again, what does this matter? (as long as faradays law is in action)
I don't disagree with what you said, I'm just not making the connection between the operation of an inductor, and I'll give you a hypothetical:
Say you had some magic excitation source, and some magic core, where the supply of voltage just went up forever (there was a constant dΦ/dt), then there would be a constant voltage on the secondary and the magnetic field would never collaps.

If you are trying to build an electronics regulator, other factors will typically dominate. Line voltage varies by somewhere around 10%. Ripple is typically a problem, etc. There are some nice linear supplies which fix these problems, but at a cost. (Beware the dropout voltage; you will still need you equations to check that.) Switching power supplies are more efficient, but have more noise.

No, all theoretical ATM.

On the angle thing (How did you make the symbol, BTW?): No, the angle is the angle between the unloaded voltage and the loaded voltage. Notice how in the first diagram the loaded voltage is actually higher than the unloaded voltage. (This is because most of the impedance is reactive with very little resistance.) This link is more for power engineering. Such situations are counter-intuitive, but occur in power situations. I'm more of an electronics guy.

On the reply green bar there's a little sigma sign for symbols, it's in there.

H'mm ok, it's the angle between loaded and unloaded, that makes sense. So the voltage induced on the secondary should be pretty much exactly in phase with the primary excitation?

Thanks

 

[Jeff Rosenbury]

I don't know. You have reached the limits of my knowledge. I could likely work it out from fundamental principles, but laziness calls me. Now I'm going to insert some symbols because I can. με√Δ∉. Thanks for that.

Good luck.

 

[stedwards]

I don't see how flux leakage leads to poorer regulation. The mutual inductance is decreased... Did I miss something?

 

[tim9000]

I don't see how flux leakage leads to poorer regulation. The mutual inductance is decreased... Did I miss something?

Err, I'm not exactly sure what the mathematical connection to leakage flux an VR is either, I'd like to know, I assume it does, I've heard it does, but I don't get the premis that the mutual inductance is important? Or 'inductance' full stop. I was just sort of thinking inductance was a side-affect of the TX, I was thinking that it was just about the flux and faraday's law. What I want to know is, can you have a TX that has no inductance?...

 

[Jeff Rosenbury]

I don't see how flux leakage leads to poorer regulation. The mutual inductance is decreased... Did I miss something?

Flux leakage means lost energy in the transfer part. That would almost have to decrease efficiency, which would likely show up by an increased impedance (inductance in the primary?) and the resulting parasitic losses like increased eddy currents and increased copper losses. As I said, I haven't gone through the math, But energy is neither created nor destroyed, so something has to happen. Back to sleep.