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Current in primary coil of transformer.

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New Member
Hey guys.
Mr. Gibbs has showed me the below picture:

The primary and secondary coils' voltages have no phase difference between them.
But the primary current and the primary voltage havent 90 degrees phase difference between them.
This means that the primary current doesnt equal Vp/XL1, because if it did, it would have a 90 degrees phase from Vp.

How do you calculate the current then? and why doesnt Ohm's law apply here?



New Member
The primary and secondary coils' voltages have no phase difference between them.
And they won't.

primary current doesnt equal Vp/XL1
The primary current is the secondary current reflected to the primary by the turns ratio plus the magnetizing current.


There's 90° phase shift because the load is very light do the magnetising current dominates. Because the magnetising current is purely inductive, the phase shift will be 90°. As the load is increased, the primary current will become more in phase with the secondary current.


New Member
I read more about it, and understood that by the conservation of the magnetic energy, there is also conservation of power, therefore
Ip = (Ns/Np)^2 * Vp / Zs.
I assume that Zs is the load connected to Ls, not including Ls itself, right?

So in the case of the picture, Zs=R=10Kohm, so how come there is a voltage phase between Ip and Vp?
Last edited:


Well-Known Member
Most Helpful Member
Well hello again,

Are you still interested in this or did you find the answer you were looking for?
You know now that there is a phase shift in an inductor between voltage and
current, right?
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