I think he means the inductance of the coil disregarding the core. I'm not sure if this is typically looked at for power transformers, but it's a common value to discuss for VTs to see how they will react when saturated. When the core is saturated, the reactance is virtually the same as the air-core reactance.
Air Core Reactance: REAL Constant: Usually approximately twice the leakage reactance [pu]
I am modeling a transformer inrush urrent through PSCAD. One of the ways to simulate high inrush is through changing saturation constants- The other variable is the Knee Voltge.
Probably can just use an inductor air core calculation (solenoid), and run the calc on the primary winding, since the secondary would not be linked much without the core effects.
I haven't heard anyone request this before. For inductors it's clear. This would be the point where the core's relative permeability is 1. So it's as though the core isn't there. This is really more a theoretical number since It would take so much current in an inductor that the coil would burn up straight away or come apart from short circuit forces. But in a transformer, to achieve true hard saturation requires extreme overvoltage to the point of likely turn to turn isulation failure. Even if that didn't occur, the exciting current would be extreme, just like in the inductor.
If you just want to know the short circuit impedance, then the transformer's rated impedance will probably be adequate. ie 4%Z => 1/.025 = 40 times rated amps. That's all the current a bolted fault would develop.
