Transformer Initial Inrush Current and Capacitor Fault Outrush Current

[whycliffrussell]

Transformer Inrush:

Is there a detailed standard method for calculating max transformer inrush current (initial starting inrush) during energizing a transformer? I know that the x/r is dynamic and that the inrush depends on when in time the transformer is energized relative to the residual flux residing in the core.

Capacitor Outrush:

Is there a method for calculating the max capacitor outrush current during a fault. Is is the same as the inrush current?

Inrush current = 1.2*root(2)*v(line-ground)*root(C/L)?

 

[electricpete]

In reality, trasformer magnetizing inrush current will depend heavily on core saturation (you can’t model it with linear L/R model).

Just guessing on cap current (not sure)
Cap current assuming cap terminals are shorted to ground.
I guess there is assumed some internal resistance to limit current?
Then v(t)=V0*exp(-t/RC) where we might take V0 as peak value of line to ground voltage.
i(t) = C * dv/dt = -C*V0/(RC) * V0*exp(-t/RC)
i(t) = -V0/R * V0*exp(-t/RC)

I suspect due to the high frequency nature of the transient of shorting terminals, inductance might play a role as well.

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[cuky2000]

See the enclose information

http://www.hubbellpowersystems.com/...rary/pdfs4lib/Chance-Construction/10-8901.pdf

 

[jghrist]

The peak outrush current during a fault would be determined by the same equation as in the OP except that the inductance L would be the inductance of the line between the capacitor and the fault instead of the system inductance.

 

[KVX10]

If you have access to Cooper Power System "Electrical Distribution-System Protection" Book (3rd ed.) p.104, will address this subject. (Capacitor Out-Rush Current) It does not reveal calculations, but does recommend expulsion fuse/current limiting devices to use.