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so i am little confused about inductance in transmission lines. the inductance can occur in transmission lines when two transmission lines(shot long or medium) comes close to each other i-e due to mutual inductance? or inductive effect can be present in single conductor due to self inductance? what is difference between both type of inductance's?

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closed as too broad by user1844, Voltage Spike, Dmitry Grigoryev, Andrew, ThreePhaseEel Feb 5 '17 at 0:40

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Two parallel wires will have both self-inductance and mutual inductance. The self inductance gives rise to an "opposing" voltage when there is a change of current: -

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

So if you try and pass a current through a wire there will be a "back emf" that opposes that current (that's the point of the negative sign). For a large value of inductance the change in current is restricted more than when the inductance is small.

Likewise, when there are two parallel wires, the change of current flow in one wire will give rise to an emf in the other wire: -

\$V=-M\dfrac{di}{dt}\$

The negative sign here implies that if the induced emf caused a current to circulate in the coupled coil, that current would create a magnetic flux that opposes the originating flux.

For two wires of self inductance L1 and L2 and sharing a coupling, M = \$k\sqrt{L_1L_2}\$

The "k" represents the coupling factor and can be 0 (no coupling) or 1 (full coupling).

You also mention transmission lines but this is where there can be confusion; it could be simply that you mean parallel wires or, it could be that you mean parallel wires in a power transmission or, you might mean a much more complex scenario where there are reflections from loads and standing waves.

I'm just dealing with the simple case of self and mutual inductance of two parallel wires.

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The inductance of the transmission line tells how much energy is stored in the magnetic field when the signal or electric power travels along that line and the current is known. More inductance => more energy in the magnetic field. This is the same as in the coils.

The mutual inductance tells, how much the magnetic fields overlap between two adjacent transmission lines. This gives some meeasure to that, how much signal or electric power jumps from one line to another. Also the interline capasitance is needed to know for exact calculation, but mutual inductance tells how much crosstalk is caused just by the overlapping magnetic fields. The mutual inductance in other words tells, how much two adjacent transmission lines act like a transformer, where the primary is one of the lines and the secondary is another line.

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  • \$\begingroup\$ @Jim Dearden a new answer \$\endgroup\$ – user287001 Jan 30 '17 at 14:04

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