Transformer Inrush

[sky2020]

We say the transformer inrush is 12X FLA. FLA = MVA/Sqrt(3)/kV*1000 => FLA is the FLA RMS current

So the RMS value of the inrush waveform should be 12X FLA RMS or it is the maximum of the inrush waveform (Imax) is 12X FLA RMS? I mean is the inrush current maximum or RMS?

What is the length of the inrush current in general?

 

[itsmoked]

Hate to disappoint you but inrush can reach 40X though it's more common to see 25X

Luckily it only lasts about 10ms. Usually every other half cycle with each subsequent cycle dropping about 1/3 of the first.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[prc]

Inrush current value is the peak value at the start of the current flow. The Rated current is RMS value. So, strictly you should not compare RMS to peak value. But it is how engineers are doing all these years.

12x may be applicable for distribution transformers and small power transformers; in large transformers, it may be 5-8 x only. In small control-transformers inrush may reach x20 or more.