Current saturation of an inductor??

I need some information regarding saturation of inductor current.

1. What does it mean? What would be its behaviors?
2. What are the effects when inductor current is saturated?
3. What would cause this happens?

Regards,
goli

you'll know your inductor core is saturated if the voltage across it averages to 0V.
if you're using the inductor in a power supply, if it is saturated, the current output will just be equal to the current flowing from your source since the inductor would just be acting as a short circuit. this would translate to low efficiency.

you'll know your inductor core is saturated if the voltage across it averages to 0V

Click to expand...

The voltage across an inductor will always average to zero due to it's basic electrical properties (not considering resistive voltage drop).

Saturation is an effect of the ferromagnetic core. It doesn't occur with air coils. The core behaviour can be described with a B versus H magnetization characteriscs. Above a certain H value, B doesn't rise any more, this is the saturation induction Bsat. For a particular inductor or transformer, it correspondends to a specific voltage-time integral ∫V dt and a respective saturation current.

Visually, if you apply a constant voltage across an inductor, the current will rise linear. At saturation, the (differential) inductance drops, and the current starts to rise much faster.

P.S.: )

If you take a transformer,there is the primary putting up a magnetic field and a secondary turning the magnetic field into useful voltage. As the transformer core saturates the primary takes more current and the voltage output from the secondary is lower then you might expect.
The effect of saturation is distortion of the output (second harmonic appears). The area under the B/H curve represents loss, so at saturation the transformer gets hot.
It is caused by the magnetic field being too large for that particular core.
Frank

On a little more intuitive level, inductive reactance occurs as a change in current in the winding on a ferromagnetic core causes a change in the number of magnetic domains in the core that are aligned with the lines of magnetic flux caused by the winding. For a given core material and winding configuration, the larger the core, the greater the number of domains available to be aligned with the lines of flux and the greater the voltage*time product the core can support without saturation. At some point, however, all or most domains have been brought into alignment with the flux lines and a further increase in volt*time product cannot cause a further increase in the number of aligned domains. This is magnetic saturation of the core. Since there are no more domains available to be forced into alignment with the flux lines, inductive reactance disappears, current is no longer opposed by inductive reactance, and current abruptly spikes upward until limited by the DC resistance of the conductor in the winding and by external circuit conditions.

Saturation can occur gradually or suddenly depending upon the properties of the core material. The designer will select a core material with properties appropriate for his application. Abrupt core saturation is a desirable characteristic in, for example, timing circuits, blocking oscillators, or self-switching power inverters but very undesirable in signal transformers. Very tightly controlled, gradual saturation characteristics are required in magnetic amplifiers that were once heavily used in naval gun control applications but which are now pretty much obsolete, I believe. Magnetic amplifiers had the advantage of extreme ruggedness and immunity to voltage spikes that can wipe out semiconductor circuits.

I think it is erroneous to refer to "current saturation." It is the core that saturates. The current is simply responding to instantaneous circuit conditions. That is, when inductive reactance disappears due to core saturation, the voltage applied to the circuit is opposed only by the I*R drop of the winding and whatever external impedances are in the circuit. Since winding resistance may be very low, current can be very high unless limited by impedances external to the inductor.

Core saturation can occur by imposing too low a frequency at designed voltage OR too high a voltage at designed frequency on a transformer or by imposing too high a DC current on a choke coil.

awright

Seen in some magnetic materials, saturation is the state reached when an increase in applied external magnetizing field H cannot increase the magnetization of the material further, so the total magnetic field B levels off. It is a characteristic particularly of ferromagnetic materials, such as iron, nickel, cobalt and their alloys.

Ferromagnetic materials like iron that show saturation are composed of microscopic regions called magnetic domains that act like tiny permanent magnets that can change their direction of magnetization. Before an external magnetic field is applied to the material, the domains are oriented in random directions. Their tiny magnetic fields point in random directions and cancel each other out, so the material has no overall net magnetic field. When an external magnetizing field H is applied to the material, it penetrates the material and aligns the domains, causing their tiny magnetic fields to turn and align parallel to the external field, adding together to create a large magnetic field B which extends out from the material. This is called magnetization. The stronger the external magnetic field, the more the domains align. Saturation occurs when practically all the domains are lined up, so further increases in applied field can't cause further alignment of the domains.

Saturation limits the maximum magnetic fields achievable in ferromagnetic-core electromagnets and transformers to around 2 T, which puts a limit on the minimum size of their cores. This is one reason why high power utility transformers are so large.

In electronic circuits, transformers and inductors with ferromagnetic cores operate nonlinearly when the current through them is large enough to drive their core materials into saturation. This means that their inductance and other properties vary with changes in drive current. In linear circuits this is usually considered an unwanted departure from ideal behavior. When AC signals are applied, this nonlinearity can cause the generation of harmonics and intermodulation distortion. To prevent this, the level of signals applied to iron core inductors must be limited so they don't saturate. To lower its effects, an air gap is created in some kinds of transformer cores.

On the other hand, saturation is exploited in some electronic devices. Saturation is employed to limit current in saturable-core transformers, used in arc welding, and ferroresonant transformers which serve as voltage regulators. When the primary current exceeds a certain value, the core is pushed into its saturation region, limiting further increases in secondary current. In a more sophisticated application, saturable core inductors and magnetic amplifiers use a DC current through a separate winding to control an inductor's impedance. Varying the current in the control winding moves the operating point up and down in the saturation curve, controlling the AC current through the inductor. These are used in variable fluorescent light ballasts, and power control systems

when power inductor pass Isat, inductance drops off 10% or 20% than initial inductance.

szhighstar said:

when power inductor pass Isat, inductance drops off 10% or 20% than initial inductance.

Click to expand...

Most of the answers in this thread are simplistic because they do not account for the magnetic non-linearity of the core. In fact, what happens when the core saturates is that the current through the inductor becomes distorted. In a symmetrical case, the current becomes rich in odd harmonics, and the voltage at the fundamental (applied frequency) across the inductor tends to limit. In a lossless, high permeability core, The voltage when the core is driven well into saturation, approaches a square wave.

- - - Updated - - -

szhighstar said:

when power inductor pass Isat, inductance drops off 10% or 20% than initial inductance.

Click to expand...

Most of the answers in this thread are simplistic because they do not account for the magnetic non-linearity of the core. In fact, what happens when the core saturates is that the current through the inductor becomes distorted. In a symmetrical case, the current becomes rich in odd harmonics, and the voltage at the fundamental (applied frequency) across the inductor tends to limit. In a lossless, high permeability core, The voltage when the core is driven well into saturation, approaches a square wave.

Most of the answers in this thread are simplistic because they do not account for the magnetic non-linearity of the core.

Click to expand...

Most of the answers are considering non-linearity, I think. It may be the case that you didn't fully understand it.

If you want to contribute to the forum, you should better help others with their latest questions rather than commenting old threads.