I have a question regarding the phase shift produced due to an inductor. I have seen some inductor coils that have only 2-3 turns on the core. Some have only one as shown below. It is known that an AC voltage will create a phase shift between current and voltage when passed through the inductor. Now is there any realtion or threshold that states that beyond this we have phase shift of 90 between current and voltage, else we don't? Secondly, if the answer is that all the AC waves passing through the turning wires produce phase shift due to changing flux/self-induction, then if I don't have a core and I just roll a wire with AC voltage 2-3 rounds, will that create a phase shift??

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The part number of the coil used in the above is ZMCT103C. Even if these are current transformers, the primary side still has some inductance, but turns are very low. Here the AC voltage passes through the center.


2 Answers 2


If you apply an ideal sine wave voltage to an ideal inductor (air cored or not), the current lags by 90° always. The trick is using a high enough frequency so that the ideal inductor doesn't appear more like a short circuit. This is embodiled in the inductor equation: -

$$V = L\cdot\dfrac{di}{dt}$$

So, if the current is a sinewave then di/dt will imply that the resulting voltage waveform leads current by 90°.

Even if these are current transformers, the primary side still has some inductance, but turns are very low. Here the AC voltage passes through the center.

The load current defines the current flow and, the voltage developed across the single turn primary would lead the current by 90° except for one thing; current transformers use a burden resistor on the secondary that completely overrides the magnetic field in the core so, on this example, the voltage on the primary of the current transformer is largely in phase with the current flowing through it.

  • \$\begingroup\$ No I absolutely don’t mean that. I can’t see how you read that into my answer. \$\endgroup\$
    – Andy aka
    Sep 22, 2023 at 20:20
  • \$\begingroup\$ Sorry I misunderstood the answer, the inductance depends on the change of current. If the frequency is higher,higher flux changes will cause a phase shift. My question is, will it create this phase shif If I have a single wire passing through the coil as shown in the image. Secondly by higher current I meant a higher current change in time. \$\endgroup\$
    – kam1212
    Sep 22, 2023 at 20:29
  • \$\begingroup\$ No, the inductance does not depend on the change of current. I never said that either. No, flux changes won't be higher with higher frequency when the volts applied remain the same. Did you read that into my answer. If not, why are you asserting such things and proposing them to me as comments? For the rest of your comment, read the opening paragraph in my answer. \$\endgroup\$
    – Andy aka
    Sep 22, 2023 at 21:19
  • \$\begingroup\$ @kam1212 Please also take note of this: What should I do when someone answers my question. If you are still confused about something then leave a comment to request further clarification but only if you leave an upvote as a mark of appreciation even if you don't like my pointed responses in comments. \$\endgroup\$
    – Andy aka
    Sep 22, 2023 at 21:21
  • 1
    \$\begingroup\$ Because any transformer will reflect the load on the secondary back to the primary and impedance ratio it with the turns ratio squared. So, if you have a 1:1000 CT and a 10 ohm burden then, at the primary, that burden presents itself as 10 micro ohms and this will be massively smaller than the magnetization reactance (as it should be for a CT). \$\endgroup\$
    – Andy aka
    Sep 23, 2023 at 10:09

Inductors follow the equation $$V=L*di/dt$$ That shows where the 90 degree phase shift for sinusoids comes from, the voltage is proportional to the derivative of the current, or the current to the integral of the voltage. (The derivative of sine is cosine, etc.)

Every conductor has some amount of associated inductance, even a straight piece of wire (self-inductance). When winding an inductor, the inductance is proportional to the number of turns squared.

You can see a wire self-inductance calculator here.

So there is indeed some phase shift associated with any conductor, but in most cases of a straight wire it's negligible.


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