110109-1745 EST
To repeat some points I have made in various threads.
Instantaneously the current thru an inductor can not change.
To provide a clearer understanding of an LR circuit consider an inductance with an air core. This eliminates all problems with magnetic materials, the inductance is independent of the flux density around the coil (inductance is invariant), and there is no residual flux remnant after current is removed.
Now consider an ideal LR circuit where all resistance is external to the inductor. This is the typical way one analyzes circuits. In real life some of that resistance is physically within the coil.
Consider a series circuit with a battery, a switch, a resistor, and an inductor. Let t=0 seconds to be the time at which the switch is closed. At the instantaneous moment before the switch is closed we assume the current thru inductor is 0. This would be the case if the switch had been open for some time, and there was no other current source to the inductor.
From my statement above that one characteristic of an inductor is that the current can not instantaneously change this means that at the instant just after the switch is closed the current will still be zero. However, starting at that point, t=0, the current does start to rise. The voltage across the R and L instantaneously rises to the battery voltage, and also this is the instantaneous voltage across the ideal inductor because current is 0.
The rate of rise of current is determined by the L/R ratio. For a fixed resistance the larger L is the slower is the current rise, and vice versa. These experiments are simple to run with an oscilloscope.
There is no high inrush current with a simple LR series circuit.
Where things get complicated is when a ferromagnetic core is added to the inductor. But the addition of ferromagnetic material does not change any of my above comments.
With an inductor with a ferromagnetic core we have something that may have a varying inductance under different conditions.
Ferromagnetic materials have a saturation characteristic. This effect may have been first discovered by Edison and his employees. Summer 1879. From "Menlo Park Reminiscences" p310.
--- Upton --- He discovered that a weber turn (that is, an ampere turn) was a constant factor, a given number of which always produced the same effect magnetically. This point was practically new to the scientific world at that time.
In those days the makers of dynamos simply oversoaked their magnet circuit with current, knowing nothing about magnetic saturation. They thought that the more the current they sent through the coils, the greater the effect they would obtain. It never occurred to them that the increased current effect would be scattered in every direction but the right one.
http://en.wikipedia.org/wiki/Saturation_(magnetic)
http://www.phy6.org/Electric/-E25-Tech.htm
I did not completely read the following, but it appears to be rather good.
http://en.wikipedia.org/wiki/Transformer
Back to the inrush discussion. If the core of an inductor is left with a large residual magnetic flux, then when current is applied in the correct direction the flux level will be further increased. This will drive the core more into saturation, the inductance drops, and the current rises rapidly. In an AC circuit the voltage will reverse, and this changes the flux direction and the inductance rises. An equilibrium condition will ultimately occur. That spike of current resulting from saturation is the peak inrush. This inrush is highly variable because of random turn off times of excitation to the inductor, and the random time and thus phase of turn on.
Most transformers have very little air gap in the ferromagnetic flux path and thus the ratio of saturation peak current to steady state magnetization current can be large.
Motors have a bigger air gap and there are other factors affecting inrush current.
Looked at my Fluke 87III this afternoon. Its pulse response is listed as 1 millisecond, and regular MIN-MAX is 100 milliseconds.
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