OCP coordination and transformer inrush current

[thump3r]

Good afternoon all,

I'm looking to wrap my head around overcurrent protection coordination and transformer inrush current. In the attached example, am I correct in understanding that the system may experience nuisance tripping of the 1200A breaker on the transformer's secondary side due to the inrush current point being to the right of that breaker curve?

 

[Jraef]

of the 1200A breaker on the transformer's secondary side due to the inrush current

No. Inrush in a transformer is a PRIMARY phenomenon. There is some reflection of it into the secondary side, but not significant.
The only "inrush" current significant to the secondary protection is that which is created by the LOADS on the secondary.

 

[jim dungar]

For the non hardvore techies.
A transformer sees inrush and magbetizing current on its primary windings. Current does not really flow on the secondary until the transformer has effectively started up. When power is first applied the transformer looks like an iron core inductor, once its magnetic field becomes established then it starts to produce output voltage and current. This all happens in the blink of an eye but it is part of the reason we do not take secondary loading into consideration when calculation possible inrush current values.