Is self inductance and leakage inductance the same thing?

Question

I want to intuitively understand what they are and if they are the same thing.

Answer 1

Let's start by defining the two terms:

Self-inductance is a measure or coefficient of self-induction in a circuit, usually measured in henries. It is also the property of an electric circuit that permits self-induction.

Leakage inductance is an inductive component present in a transformer that results from the imperfect magnetic linking of one winding to another.

Here is a longer definition of leakage inductance:

Leakage inductance derives from the electrical property of an imperfectly-coupled transformer whereby each winding behaves as a self-inductance constant in series with the winding's respective ohmic resistance constant, these four winding constants also interacting with the transformer's mutual inductance constant. The winding self-inductance constant and associated leakage inductance is due to leakage flux not linking with all turns of each imperfectly-coupled winding.

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It also might help you if you first understand what inductance is:

http://www.youtube.com/watch?v=84kl_WheNtQ

Here is another which is also very helpful:

http://www.youtube.com/watch?v=NgwXkUt3XxQ

Essentially, inductance is when the energy is stored in an electromagnetic field.

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Now that you grasp inductance, let's look at self-inductance.

Self-inductance is what happens when the current can change in a coil as a result of itself. It occurs as a result of the electromagnetic field (EMF), and has a relation to the proximity and shape of the coil predicting the scope and depth of the EMF.

Here is a video explaining self-inductance:

http://www.youtube.com/watch?v=LwwSJhEfJeA

Here is another video on self-inductance:

http://www.youtube.com/watch?v=B8CPGiK59f8

Even if you don't know the math, you should be able to glean the basic concept.

In a coil, the electromagnetic fields overlap. As a result, the overlapping EMF can feed itself (to an extent), and this is called self-inductance.

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Leakage inductance, on the other hand, is a problem, not a property. Leakage inductance happens when self-inductance occurs undesirably, and by definition, leakage inductance will result in an unwanted outcome unless it is mitigated.

As a result of leakage inductance, what will happen is that the magnetic field does not follow the intended path. This will disrupt the flow of the EMF unless addressed.

Whereas self-inductance is a property of leakage inductance, leakage inductance is not a property of self-inductance.

Answer 2

This is best explained with reference to a transformer.

Self-inductance of the primary is the core magnetization inductance, measured when the secondary is open circuit. Normally this is numerically in henries (rather than milli or micro henries) for an AC power transformer. It will include the leakage inductance of the primary but as this is about 0.1% of the magnetization inductance it represents a tiny error.

A good definition of leakage inductance of the primary is that inductance that doesn't contribute to inducing a voltage on the secondary. It's impossible to measure on its own because the secondary winding also has leakage inductance and the normal measurement method is to short the secondary and measure resulting primary leakage inductance. If you look at the equivalent circuit of a transformer you will see where these inductances fit into the big picture: -

So, from left to right we have: -

• Primary leakage inductance X\$_P\$ and copper loss R\$_P\$
• Primary magnetization inductance X\$_M\$
• X\$_S\$ and R\$_S\$ are the secondary leakage inductance and copper loss.

The thing that looks like a transformer labelled N\$_P\$ and N\$_S\$ should be regarded as a perfect power converter with "turns ratio".

Answer 3

@CKCK Self-Inductance is the no load shunt current needed to energize the core that is proportional to voltage and affects B field and saturation limits that causes odd harmonics and is normally around 10% of rated current but reactive.

Leakage Inductance is the series amount that represents the amount of leakage that does not couple between the primary and secondary, which is symbolically, shown in series to attenuate source with load by this impedance divider. This is a small fraction of the core inductance and is related to coupling factor losses.

Coupling factor losses can be 5% for small power transformers <100VA and <0.1% for MVA big power units. Additional losses are resistive.