Effective inductance of the primary and secondary of the transformer

[coolsummer]

For symmetrical inductor, the currents in the adjacent conductors are in the same direction, which increases the overall inductance due to the mutual coupling. While in the transformer, the currents in the adjacent conductors are in the opposite direction since they belong to different windings, will this cause the effective inductance of the primary to decrease？

 

[BigBoss]

Effective Primary Inductance will surely be changed due to Coupling Mechanism..
This is nature of the Transformers

 

[vfone]

The parallel effective inductance will decrease a bit, but still will be higher than in case with no mutual coupling.
Should be somewhere an equation which gives the exact value.

 

[coolsummer]

The parallel effective inductance will decrease a bit, but still will be higher than in case with no mutual coupling.
Should be somewhere an equation which gives the exact value.

Why doesn't the it drop dramatically since the currents are in opposite direction?

 

[FvM]

You are confusing things. The increased inductance discussed in post #1 is observed with series connection of the individual windings. In a transformer, primary inductance is measured for the primary winding with open circuit secondary winding. Respectively the secondary winding and the coupling factor doesn't affect the primary inductance at all.

 

[crutschow]

Why doesn't the it drop dramatically since the currents are in opposite direction?

There is no secondary current since the primary inductance is determined with an open secondary.
And normal load currents do not affect the primary inductance since the flux induced by the secondary current is cancelled by the induced primary current in response to the secondary current.

 

[vfone]

-- primary inductance is measured for the primary winding with open circuit secondary winding --

Maybe this is valid for series equivalent inductance with open load.
But there is no reason to measure the primary inductance of a transformer with open circuit on secondary, when in reality always will be a load.
Any simple simulator shows an increase of the parallel equivalent inductance of the primary, when both primary and secondary are mutual coupled and loaded.

 

[crutschow]

Any simple simulator shows an increase of the parallel equivalent inductance of the primary, when both primary and secondary are mutual coupled and loaded.

What is "parallel equivalent inductance"?
What the mechanism for an increase in transformer inductance with current (equation)?

 

[BigBoss]

What the mechanism for an increase in transformer inductance with current (equation)?

As you can see, the Effective Primary Inductance ( not Self Inductance ) is affected by Secondary Current.

 

[FvM]

Primary inductance is the inductance measured on the primary with open secondary, e.g. L1 in the below equivalent circuit

It's a parameter of the transformer, respectively it doesn't depend on the load.

In the popular equivalent T-circuit, the observable terminal inductance is splitted into a series (leakage inductance) and a shunt (magnetizing inductance) term. Because k is small for standard transformer (< 0.05), it doesn't affect the terminal inductance much. The situation is different for transformers with intentionally reduced magnetizing inductance or increased leakage.

Correction. k of a standard transformer is in fact >0.95 not <0.05.

 

[crutschow]

As you can see, the Effective Primary Inductance ( not Self Inductance ) is affected by Secondary Current.

I see nothing in those equations about primary inductance, only flux linkage.