Transformer - the inductive resistance

In summary, adding a capacitor to a circuit with an inductor will not have an effect on the overall resistance.
  • #1
fawk3s
342
1
As I recently learned, the inductive resistance and capacitor resistance in a circuit are opposite and therefore need to be subtracted. And since transformers are basically big coils of wire, where I assume there's inductive resistance, shouldn't adding capacitors to the circuit lessen the overall resistance?

Or am I understanding this wrong?

Thanks in advance,
fawk3s
 
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  • #2
I suspect that your have misunderstood something?

In ordinary circuit analysis your have resistance, capacitance and inductance. None of them can be used to cancel the other.

The effect on the phase relationship between voltage and current is opposite for a capacitance and an inductance.

But this does not mean that you can e.g. cancel the effect of an inductor by putting in a capacitor.

The only way to cancel the impedance introduced into the circuit by a resistor, inductor or capacitor is to bypass it.
 
  • #3
According to the formula

Z = (sqrt) R^2 + (Xc-Xl)^2

where Z is the overall resistance or the impedance, R is the "wire resistance", and Xc and Xl are the resistances of the capacitor and inductor,
adding a certain capacitor to a certain inductor should lessen the overall resistance.
Say, Xc and Xl were equal. The only resistance in the circuit would be the actual wire resistance.
Or am I understanding the meaning of Z / the overall resistance wrong?

Thanks in advance,
fawk3s
 
  • #4
Why not use the proper terms?
Resistance is resistance. Reactance is reactance and Impedance is the complex result of adding the resistance and the reactance. You can't avoid complex quantities if you want to discuss what goes on in LRC circuits. Just bite the bullet and get down to it.
It may just take more than two minutes.
 
  • #5
Im sorry for using the wrong terms. English is not my native language and so I should have done some research. My mistake.

But if I understand your post correctly, you understood my question even with the wrong terms.
So the thing is, as the reactances of the capacitor and inductor come closer together, the smaller the impedance becomes. But what I cannot grasp is why isn't this used in a transformer circuit?
 
  • #6
fawk3s said:
Im sorry for using the wrong terms. English is not my native language and so I should have done some research. My mistake.

But if I understand your post correctly, you understood my question even with the wrong terms.
So the thing is, as the reactances of the capacitor and inductor come closer together, the smaller the impedance becomes. But what I cannot grasp is why isn't this used in a transformer circuit?

In a transformer circuit, you only "see" the leakage inductance, not the magnetizing inductance. The magnetizing inductance links the primary to the secondary, and transforms the secondary load impedance back to the primary side.

In transformer design, you try to keep the leakage inductance small enough so that it does not affect your circuit operation too much.
 
  • #7
fawk3s said:
According to the formula

Z = (sqrt) R^2 + (Xc-Xl)^2

where Z is the overall resistance or the impedance, R is the "wire resistance", and Xc and Xl are the resistances of the capacitor and inductor,
adding a certain capacitor to a certain inductor should lessen the overall resistance.
Say, Xc and Xl were equal. The only resistance in the circuit would be the actual wire resistance.
Or am I understanding the meaning of Z / the overall resistance wrong?

Well, the reactance of a capacitor and inductor depend differently on frequency. The reactance of a capacitor decreases with increasing frequency, while the inductor behaves oppositely.

But I guess at one particular angular frequency, i.e. w = sqrt(1/LC), you would be able to cancel the effect of the two components in series.
 
  • #8
torquil said:
Well, the reactance of a capacitor and inductor depend differently on frequency. The reactance of a capacitor decreases with increasing frequency, while the inductor behaves oppositely.

But I guess at one particular angular frequency, i.e. w = sqrt(1/LC), you would be able to cancel the effect of the two components in series.

The reactance of a capacitor is 1/wC. That gets less as the frequency increases! Vice versa for an inductor.

Also, it is common to resonate primary and secondary circuits in IF transformers. This is when they are used as filters, though.
 
  • #9
sophiecentaur said:
The reactance of a capacitor is 1/wC. That gets less as the frequency increases! Vice versa for an inductor.

That's exactly what I wrote :wink:
 
  • #10
berkeman said:
In a transformer circuit, you only "see" the leakage inductance, not the magnetizing inductance. The magnetizing inductance links the primary to the secondary, and transforms the secondary load impedance back to the primary side.

In transformer design, you try to keep the leakage inductance small enough so that it does not affect your circuit operation too much.

So basically, there would be no point to it because the design is already close-perfect. Thats what I figured, but say in a very poorly designed transformer, would there be a point in adding a capacitor to help reduce the reactance of the system when the AC going through the system is with a determined stable frequency?
 
  • #11
  • #12
torquil said:
That's exactly what I wrote :wink:

So it is. What a loony!
Sorry. Mind must have been elsewhere.
 

1. What is a transformer?

A transformer is an electrical device that is used to transfer electrical energy between two or more circuits through the use of electromagnetic induction.

2. How does a transformer work?

A transformer works by using two coils of wire, known as the primary and secondary coils, that are wrapped around a common iron core. When an alternating current is passed through the primary coil, it creates a changing magnetic field which induces a voltage in the secondary coil, resulting in the transfer of electrical energy.

3. What is the purpose of a transformer?

The purpose of a transformer is to change the voltage level of an electrical circuit. It can either step up (increase) or step down (decrease) the voltage depending on the ratio of the number of turns in the primary and secondary coils.

4. What is inductive resistance in a transformer?

Inductive resistance in a transformer refers to the opposition to the flow of current caused by the inductance of the coils. This resistance can cause power losses and affects the efficiency of the transformer.

5. What are some common applications of transformers?

Transformers are used in a variety of applications, including power distribution, voltage regulation, and electronic devices such as televisions and computers. They are also essential in the functioning of electric motors and generators.

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