sizing of auto transformer for motor starts or just FLA?

[fastline]

Curious if we will run into issues sizing an autotransformer to a motor FLA or does inrush need to be considered?

As an example, we will be using a 120/240p 16/32sec. If you run the calculation pulling 240 back 13.3% to 211V, a 5kva per the Acme tables shows the calculated amperage of 71A. The transformer will be oversized a touch for the actual load BUT inrush is something that may need considered... or maybe not? Is this already sort of worked out in the design of the transformer?

 

[gar]

190107-2213 EST

fastline:

I do not understand your question.

What is the motor power rating? Voltage rating? Kind of motor? High or low inertia load? Wire size? Length of wire? Source impedance at supply breaker? Why the auto-transformer? Possibly other questions.

What do

120/240p 16/32sec

and

If you run the calculation pulling 240 back 13.3% to 211V, a 5kva per the Acme tables shows the calculated amperage of 71A.

mean?

I doubt there is any particular inrush current, but there is a large starting current. See my waveforms at the first and last posts at https://forums.mikeholt.com/showthread.php?t=174880&highlight=motor+starting+current none of these were fully loaded. But the high RPM shows a longer starting time because of inertia.

If you have a lot of source impedance, then a high inertia load will take a long starting time.