OK Chris so you are looking to know what the inrush current on a MVA transformer, should be?. Is this for the purposes of fusing or cable sizing?. I personally think you are out of your depth, if you have to ask the question in the first place. Just my opinion. Cheers, Mike.
Is this for the purposes of fusing or cable sizing?.
In part,yes. The two things I love most about my work are when the lights on a big project come on for the first time and the sound of a large transformer being energized. The sound of the inrush. I want to know whats happening at that moment. Thanks all for your help and opinions.
Chris, I would like to un-reservedly apologise for the nasty reply I provided you with last night. This sort of behaviour, I'm not proud of at all. Sorry to anyone else that read my reply also, this will not be happening again.
Having read the PDF file from Brian, that top formula seems wildly familiar. With that said, is an inrush current sinusoidal? (as in a pure sine wave?). We wind our own transformers at work (PoCo) and one part of my Linemans apprenticeship was 6 months in the Transformer shop, which I only go into these days if it's too cold in the Faultsman's office!. I must ask our head Transformer guy at work how they calculate the inrush current, because we get a Post-It note tacked to the side of the tranny stating what size fusing to use, for both run and in-rush current. Bear in mind Chris, we use totally different voltages here in New Zealand, but the formula should still hold true.
Once the transformer is started there is always a residual magnetic field to control the incomming current. IE it opposes the incomming rush of current. When a transformer is energised there is no magnetic opposition to the flow of current hence the Inrush. Once the transformer has an established magnetic field the 0 crossing of the AC does not cause a complete collapse of the opposing EMF and magnetic field.
Last edited by mikesh; 06/18/0711:50 AM. Reason: spelling